Human Reproduction – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

1. Humans are sexually reproducing and viviparous organisms. There are remarkable differences between the reproductive events and systems in male and female.
2. Male reproductive system includes a pair of testes, accessory ducts, glands and the external genitalia.
(i) Testes are located outside the abdominal cavity within a pouch called scrotum.
Scrotum maintains the low temperature of the testes (2-2.5°C lower than the normal body temperature) required for spermatogenesis.
(a) Each testis is oval-shape (length 4-5 cm and width 2-3 cm) and covered by a dense covering called tunica albuginea.
(b) Internally it is divided into about 250 compartments known as testicular lobules.
(c) Each lobule contains 1-3 highly coiled (structural and functional units of testis) called seminiferous tubules in which sperms are produced.
(d) Seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells.
(e) Male germ cells undergo meiotic divisions finally leading to sperm formation.
(f) Sertoli cells provide nutrition to the germ cells.
(g) Interstitial spaces are present in outside regions of seminiferous tubules which contain small blood vessels and interstitial cells or Leydig cells.
(h) Leydig cells synthesise and secrete the testicular hormones called androgens.
(ii) Male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens.
(a) The intratesticular duct system starts with tubuli recti, which are short, straight end segments of the seminiferous tubules. These tubules connect the seminiferous tubules to the highly anastomosing, cuboidal epithelium-lined channels called rete testis.
(b) From rete testis, 10-25 fine tubules arise called vasa efferentia that leave the testis and open into the epididymis.
(c) Epididymis leads to vas deferens that ascends to the abdomen and loops over the urinary bladder.
Diagrammatic sectional view of male pelvis showing reproductive system
Diagrammatic view of male reproductive system [part of testis is open to show inner details)


Urinary bladder receives a duct from the seminal vesicle to form ejaculatory duct that runs through the prostate and opens into urethra.
(e) Urethra receives the ducts of prostate gland and the bulbourethral gland (Cowper’s glands) a little ahead and runs through the penis to its external opening called urethral meatus.
(iii) The accessory glands of male reproductive system include
(a) A pair of seminal vesicles, a prostate gland and a pair of bulbourethral glands (Cowper’s glands).
(b) The secretion of all these glands is called seminal plasma.
(c) Seminal plasma contains fructose, calcium and some enzymes. It is to provide nutrition to the spermatozoa, while travelling through female reproductive tract.
(d) Seminal plasma along with sperms is called semen.
(e) Secretion of bulbourethral glands also helps in the lubrication of the penis.
(iv) External genitalia is the penis. It is made up of special erectile tissue that helps in erection of the penis. The enlarged tip of the penis is called glans penis. It is covered by a loose fold of skin called foreskin or prepuce.
3. Female reproductive system consists of a pair of ovaries, secondary sex organs, external genitalia and mammary glands.
(i) Ovaries are primary female sex organs which produce female gametes called ova and secrete the female sex hormones.
(a) These are located one on each side of the lower abdomen.
(b) It is almond-shaped, 2-4 cm in length, 1.5 cm in width.
(c) It is connected to the pelvic wall and uterus by ligaments.
(d) Each ovary is covered by a thin epithelium which encloses the ovarian stroma.
(e) Stroma is divided into two regions, i.e. peripheral cortex and inner medulla.
(ii) The female accessory ducts constitute oviducts (Fallopian tubes), uterus and vagina.
(iii) Each Fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus.

(a) The part of oviduct closer to the ovary is funnel-shaped infundibulum.
(b) The edges of infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation.
(c) Infundibulum leads to a wider part of the oviduct called ampulla.
(d) Isthmus is the last part of the oviduct, which has a narrow lumen and it joins the uterus.
(iv) Uterus or womb is a pear-shaped muscular organ. It is attached to the pelvic wall and supported by ligaments.
(a) Wall of the uterus has three layers of tissue.
(b) Perimetrium is the outermost thin membranous layer, myometrium is the middle thick layer of smooth muscles and endometrium is the innermost glandular layer which lines the uterine cavity.
(c) Uterus opens into the vagina through a narrow cervix, its cavity is called cervical canal, which along with vagina forms birth canal.
(d) Endometrium layer undergoes cyclic changes during menstrual cycle.
(e) Smooth muscles in myometrium contract during parturition to deliver the baby.
(v) Vagina is a muscular tube-like structure that opens to the outside. It receives spermatozoa during insemination and serve as birth canal.
(vi) Female external genitalia include mons pubis, labia majora, labia minora, clitoris and hymen.
(a) Mons pubis is a cushion of fatty tissue covered by skin and pubic hair.
(b) Labia majora are fleshy folds of tissue which extend down from the mons pubis and surround the vaginal opening.
(c) Labia minora are paired folds of tissue under the labia majora.
(d) Hymen is a membrane that covers the opening of vagina partially. It gets ruptured during vigorous physical activities or during the first coitus.
(e) Clitoris is a tiny finger-like structure, which lies at the upper junction of the two labia minora above the urethral opening.
(vii) Mammary glands (breasts) are paired structures that contain glandular tissue and variable amount of fat.
(a) Glandular tissue of each mammary gland is divided into 15-20 mammary lobes containing the cluster of cells called alveoli.
(b) The cells of alveoli secrete milk, which is stored in the cavities (lumen) of alveoli.
(c) Alveoli open into mammary tubules. The tubules of each lobe join to form a mammary duct.
(d) Several mammary ducts join to form a wider mammary ampulla, which is connected to lactiferous duct through which milk is sucked out.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Human Reproduction – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Reproductive Health – CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Reproductive Health Problems and Strategies:
1. Reproductive health simply refers to healthy reproductive organs with normal functions. According to the World Health Organisation (WHO), reproductive health means a total well-being in all aspects of reproduction, i.e. physical, emotional, behavioural and social.
2. The improved reproductive health of society requires following factors:
(i) Better awareness about sex-related matters.
(ii) Increased number of medically assisted deliveries and better postnatal care leading to decreased maternal and infant mortality rates.
(iii) Increased number of couples with small families.
(iv) Better detection and cure of STDs.
(v) Overall increased medical facilities for all sex-related problems.
3. Some of the measures taken for awareness of reproductive health are:
(i) The family planning programmes were initiated in India in 1951 and were periodically assessed over the past decades. The programmes were improved and covered reproduction-related areas under the popular name Reproductive and Child Healthcare (RCH) programmes. It was launched in 1997.
Major tasks of RCH programme are:
(a) Creating awareness among the people about reproduction related aspects.
(b) Providing facilities and support for building up a reproductively healthy society. Governmental and non-governmental agencies have taken various important steps to create awareness among people about reproduction-related aspects.
(ii) In schools, introducing sex education is a good step to provide right information for adolescents to discourage them from believing in myths and misconceptions about sex-related issues. Adolescents should be informed about reproductive organs, adolescence and related changes, safe and hygenic sexual practices, Sexually Transmitted Diseases (STDs), AIDS, etc.
(iii) Married couple or those in marriageable age group should be educated about available birth control options, care of pregnant mothers, postnatal care of the mother and child, importance of breast feeding, equal opportunities for the male and the female child, etc. This will lead to the formation of socially conscious healthy families of desired size.
(iv) Successful implementation of action plans like providing medical assistance and care to reproduction-related problems, pregnancy, delivery, STDs, abortions, contraception, menstrual problems, infertility, etc., needs strong support and infrastructural facilities.
(v) Statutory Ban on amniocentesis It is a prenatal diagnostic technique in which a sample of amniotic fluid is taken from the uterus of a pregnant women to detect the early development of foetus. The benefits of amniocentesis are the diagnosis of chromosomal abnormalities and developmental disorders of foetus. However, it is being misused for sex-determination of foetus that leads to female foeticides. Therefore, statutory ban on amniocentesis for sex determination keeps check on female foeticides.
4. Population explosion The tremendous increase in size and growth rate of population is called population explosion. It occurs due to increased health facilities and better living conditions.
(i) Reasons of population explosion are:
(a) Decrease death rate.
(b) Declined maternal mortality rate.
(c) Decreased infant mortality rate.
(d) Increase in number of people in reproductive age.
(ii) According to the 2001 census report, the population growth rate was around 1.7%, i.e. 17/1000/year. By this rate, our population could double in 33 years.
5. Methods to prevent population explosion are:
(i) Raising the marriageable age to 18 years for females and 21 years for males.
(ii) Couples with small families should be given sdme incentives.
(iii) Birth control is an important step to control the population growth by motivating smaller families to use contraceptive methods.
6. Contraceptive methods are ideal if they are used friendly, easily available, effective, reversible with no side effects and non-interferring with the sexual drive, desire and the sexual act.
There are several methods of birth control. These are categorised mainly as follow:
(i) Natural method of birth control involves avoiding chances of sperm and ovum meeting. It can be achieved by:
(a) Periodic abstinence in which couples avoid coitus from day 10-17 (Fertile period) of the menstrual cycle. In this period, ovulation is expected to occur and chances of fertilisation are very high. Also called as rhythm method or natural family planning.
(b) Coitus interruptus also called ‘rejected sexual intercourse’ or ‘pull-out’ method or withdrawal. In this method, the penis is withdrawn, from the vagina just before ejaculation.
(c) Lactational amenorrhea refers to the absence of menstruation during the period of lactation following parturition. Because ovulation does not occur in this period, the chances of conception are none. This method is reliable for a maximum period of six months after delivery.
(ii) Barrier methods are based on prevention of ovum and sperm from physically meeting with the help of barriers. Barriers may be chemical or mechanical.
(a) Condoms are mechanical barriers made of thin rubber or latex sheath to cover the penis in male or vagina and cervix in females which prevent meeting of sperm and ova. Condoms also provides protection sexually transmitted diseases. They are disposable and can be self inserted and thereby gives privacy to the user.
(b) Diaphragms, cervical caps and vaults are also mechanical barriers, made of rubber that are inserted into the female reproductive tract to cover cervix during coitus. They are reusable.
(c) Spermicidal creams, jellies and foams are chemical barriers, usually used along with these barriers to increase their contraceptive efficiency.
(iii) Intra Uterine Devices (IUDs) are the devices introduced in the uterus through vagina by doctors or expert nurses. These are of following types:
(a) Non-medicated IUDs, e.g. lippes loop.
(b) Copper-releasing IUDs, e.g. Cu-T, Cu-7, multiload 375.
(c) Hormone-releasing IUDs, e.g. progestasert, LNG 20.
IUDs prevent contraception in the following ways:
(a) Increase phagocytosis of sperms within the uterus.
(b) Some IUDs suppress sperm motility and fertilising ability of sperm by releasing copper ions.
(c) The hormone releasing IUDs make uterus unsuitable for implantation and make the cervix hostile to sperms.
IUDs are ideal contraceptives for females who want to delay pregnancy. It is one of most widely accepted contraception method in India.
(iv) Oral contraceptives are hormonal preparations in the form of pills.
(a) Pills are small doses of either progestogens or progesterone-estrogen combinations.
(b) Oral pills alter/inhibit ovulation and implantation and also modify the quality of cervical mucus to prevent/retard entry of sperms.
(c) Oral pills have to be taken daily for a period of 21 days starting within the first five days of menstrual cycle.
(d) Saheli an example of oral contraceptive developed by scientists at Central Drug Research Institute (CDRI) Lucknow, contains a non-steroid called centchroman. It is a once-a-week pill, with very few side effects.
(v) Replants or injections are effective for longer period, although their mode of action is similar to oral contraceptives. Progesterone alone or in combination with estrogen are used by females as injections or implants under the skin.
(vi) Emergency contraceptives included administration of progesterone or progestogen
oestrogen combinations or IUDs within 72 hours of coitus. It has been found to be very effective to avoid possible pregnancy due to rape or casual unprotected intercourse.
Both of these techniques are highly effective but poorly reversible.

Sterilisation or surgical methods are used by male/female partner as a terminal method to prevent any more pregnancies. These methods blocks the transport of gametes and prevent contraception.
(a) Vasectomy is applied in case of males. In this method, a small portion of vas deferens is removed or tied up through an incision on the scrotum.
(b) Tubectomy is applied in females, where a small part of Fallopian tubes is removed or tied up through a small incision in the abdomen or through vagina.
(7) Medical Termination of Pregnancy (MTP) or induced abortion is intentional or
voluntary termination of pregnancy before full term.
(a) The Government of India had legalised MTP in 1971 with some strict conditions to avoid its misuse. These are important to check indiscriminate and illegal female foeticides which are reported to be high in India.
(b) MTPs are done in certain cases where pregnancy can be harmful and even fatal either to the mother or the foetus or both, or duets failure of contraceptive used during coitus or rapes.
(c) MTPs are considered relatively safe during the first trimester (upto 12 weeks) of pregnancy.
(d) During second trimester, MTPs are unsafe and could be fatal too.
(e) About 45-50 million MTPs are carried out in a year all over the world. It has significant role in decreasing population though it is not meant for that purpose.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Reproductive Health – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Principles of Inheritance and Variation – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Mendel’s Laws of Inheritance:
1. Genetics is the branch of biology, which deals with inheritance and variation of characters from parents to offspring.
2. Inheritance is the process by which characters or traits are transferred from one generation to the next.
3. Variation is the degree by which progeny differs from each other and with their parents. Humans knew from as early as 8000-1000 BC, that one of the causes of variation was hidden in sexual reproduction.
4. Gregor Johann Mendel, for the first time conducted experiments to understand the pattern of inheritance of variation in living beings.
5. Mendel’s Experimental Material
(i) He conducted experiments on garden pea plant (Pisum sativum) for seven years (1856-1863) and proposed the laws of inheritance in living organisms.
(ii) He selected garden pea plant as a sample for experiment because of:
(a) Easy availability on a large scale.
(b) Many varieties are available with distinct characteristics.
(c) They are self-pollinated and can be cross-pollinated easily in case self-pollination does not occur.
(iii) Mendel selected 14 true-breeding (a breeding line which has undergone continuous self-pollination shows stable trait inheritance and expression for several generations) pea plant varieties, as pairs, which were similar except for one character with contrasting traits.
Seven contrasting characters and their traits as taken by Mendel are listed in the table given below:

6. Mendel’s Experimental Procedure
(i) He observed one trait or character at a time. For example, he crossed tall and dwarf pea plants to study the inheritance of one gene.
(ii) Mendel hybridised plants with alternate forms of a single trait (monohybrid cross). The seeds produced by these crosses were grown to develop into plants of Filial₁ progeny or F₁-generation.
(iii) He then self-pollinated the tall F₁ plants to produce plants of Filial₂ progeny or F₂-generation.
(iv) In later experiments, Mendel also crossed pea plants with two contrasting characters known as dihybrid cross.
(v) Mendel self-pollinated the F₂ plants also.

7. Mendel’s Observation in his Experiment
(i) In Frgeneration, Mendel found that all pea plants were tall and none were dwarf.
(ii) He also observed other pair of traits and found that F₁ always resembled either one of its parents and the traits of the other parent was not found in them.
(iii) In F₂-generation, he found that some of the off springs were dwarf, i.e. the character which were not seen in F₁-generation were expressed in F₂-generation.
(iv) These contrasting traits (tall/dwarf) did not show any mixing either in F₁ or in F₂-generation.
(v) Similar results were obtained with the other traits that he studied. Only one of the parental traits was expressed in F₁-generation, while at F₂-generation stage, both the traits were expressed in the ratio of 3:1.
(vi) Mendel also found identical results in dihybrid cross as in monohybrid cross.
(vii) On self-pollinating F₂ plants, he found that dwarf F₂ plants continued to generate dwarf plants in F₃ and F₄-generations.
8. Inferences of Mendel’s Experiments
(i) Mendel inferred that something was being passed down, from parents to offspring through the gamete over successive generations. He called them ‘factors’, now known as genes.
(ii) Genes are the unit of inheritance. They contain the information required to express a trait.
(iii) Genes which codes for a pair of contrasting traits are called alleles or allelomorphs, i.e. they are slightly different forms of the same gene.
(iv) Mendel also proposed that in a true breeding variety, the allelic pair of genes are identical or homozygous, TT and tt for tall or dwarf pea variety respectively.
(v) TT and tt are genotype of the plant.
(vi) Descriptive term tall and dwarf are the phenotype.
(vii) When the tall (TT) and dwarf (tt) pea plant produce gametes, the alleles of the parental pair segregate from each other and only one allele is transmittted to a gamete.
(viii) The gametes of the tall TT plants have the allele T and the dwarf tt plants have the allele t.
(ix) This segregation of alleles is a random process and, so there is a 50% chance of a gamete containing either allele, as verified by the results of crossings. After fertilisation of TT and tt traits, hybrids contain Tt and are called heterozygous.
(x) Mendel found the phenotype of Tt to be similar as TT parent in appearance, he proposed that in a pair of dissimilar factor, one dominates the other (T in this case) and hence, is called the dominant factor, while the other factor (t) is recessive.
(xi) Allele can be similar in case of homozygous TT or tt and dissimilar in case of heterozygous Tt.
(xii) In Tt plant, one character (height) is controlled by a gene hence, it is monohybrid and cross between TT and tt is called monohybrid cross.
9.

10. Mendel’s law of inheritance are based on his observations on monohybrid and dihybrid crosses, he proposed three laws:
(i) Law of dominance (first law) States that characters are controlled by genes which occur in pair, when two alternate forms of a trait or character (genes or alleles) are present in an organism, only one factor (dominant) expresses itself in F₁-generation. While, the other factor (recessive) remains hidden. It explains expression of genes in a cross and 3:1 ratio obtained in the F₂-generation.
(ii) Law of segregation (second law) States that the factors or alleles of a pair segregate from each other during gamete formation, in a way that a gamete receives only one of the two factors. They do not show any blending.
(iii) Law of independent assortment (third law) It is based on inheritance of two genes, i.e. dihybrid cross which states that when two pairs of contrasting traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters. These factors randomly rearrange in the offsprings producing both parental and new combination of characters. The Punnett square can be used to understand the independent during meiosis.

11. Incomplete dominance is a phenomenon in which the F: – hybrid shows characters intermediate of the parental genes. In this process, the phenotypic ratio of F₂-generation deviates from the Mendel’s monohybrid ratio.
Example, inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp) and four O’ clock plant (Mirabilis jalapa).
In a cross between red flower (RR) and white flower plant (rr), the F₁ (Rr) was pink (in figure). When F₁ was self-pollinated, the F₂ resulted in the ratio 1: 2: L

12. Codominance is a phenomenon in which two alleles are able to express themselves independently when present together. These alleles are called codominant alleles.
The offsprings show resemblance to both the parents.
(i) A common example of codominance is ABO blood groups in humans.
(ii) The gene for blood group exist in three allelic forms I^A , I^B  and i.
(iii) I^A and I^B produce RBC surface antigens A and B, respectively, whereas ‘i’ does not produce any antigen.
(iv) IA and I^B  both are dominant alleles, whereas T is the recessive allele.
(v) In case I^A and I^B  are present together, both express equally and produce both the surface antigens A and B.

13. Multiple allelism It can also be explained by ABO blood grouping. In this case, more than two, i.e. three alleles are governing the same character. Multiple alleles can be found only when population studies are made since, an individual can have only two alleles.
14. Test cross It is a method devised by Mendel to determine the genotype of an organism. A cross is made of unknown dominant genotype with the recessive parent.
(i) For example, Fj hybrid (Tt) heterozygous of a pure tall plant (TT) and a pure dwarf plant (tt) is crossed with a pure dwarf plant.

In this example, the progeny consists of tall and dwarf plants in the ratio  1:1. Thus, monohybrid test cross ratio is 1:1.
(ii) In case of both homozygous parents, i.e. TT, the progeny obtained will have to tall plants. (Tall)

(iii) In case of dihybrid test cross, where two traits are taken, a heterozygous individual is crossed with a homozygous recessive parent.

15. Pleiotropy It is the phenomenon in which a single gene exhibits multiple phenotypic expressions. A single pleiotropic gene may produce more than one effect.
For example,
(i) Phenylketonuria, a disorder caused by mutation in the gene coding the enzyme phenylalanine hydroxylase. The affected individuals show hair and skin pigmentation and mental problems.
(ii) Starch synthesis in pea seeds is controlled by one gene with two alleles (B and b).
(a) Starch is synthesised effectively by the homozygotes, BB and hence, the starch grains are large and the seeds at maturity are round.
(b) The homozygotes, bb are less efficient in starch synthesis, hence they have small starch grains and the seeds are wrinkled.
(c) The heterozygotes, Bb produce round seeds, indicating that B is the dominant allele, but the starch grains are intermediate in size and hence, for the starch grain size, the alleles show incomplete dominance.
(d) It is an example of pleiotropy as the same gene controls two traits, i.e. seed shape and size of starch grains.
(e) Here, it is to be mentioned that dominance is not an autonomous feature of the gene or its product, but it depends on the production of a particular phenotype from the gene product.
16. Polygenic inheritance was given by Galton in 1833. In this, traits are controlled by three or more genes (multiple genes). These traits are called polygenic traits. The phenotype shows participation of each allele and is also influenced by the environment and is called quantitative inheritance as the character/phenotype can be quantified.
For example, human skin colour which is caused by a pigment melanin. The quantity of melanin is due to three pairs of polygenes (A, B and C). If it is black or very dark (AA BB CC) and white or very light (aa bb cc) individuals marry each other, the offspring shows intermediate colour often called mulatto (Aa Bb Cc). A total of eight allele combinations is possible in the gametes forming 27 distinct genotypes.
17. Complementary genes Complement the effect of each other to produce a phenotype. For example, in case of sweet pea, the flower colour is due to complementary genes. Here, one gene complements the expression of another gene.
18. Rediscovery of Mendel’s Laws
(i) Though, Mendel published his work on inheritance of characters in 1865, it remained unrecognised for several reasons till 1900. Some of them are as follow:
(a) Communication was difficult, so his work could not be widely publicised.
(b) His concept of genes as stable unit that controlled the expression of traits and of the pair of alleles which did not blend was not accepted.
(c) His approach of using mathematics to explain biological phenomenon was new and unacceptable.
(d) He could not provide any physical proof for the existence of factors.
(ii) In 1900, de Vries, Correns and Von Tschermak rediscovered Mendel’s results independently. Due to microscopy, they carefully observed cell division.
(iii) This led to discovery of chromosomes (structure in the nucleus that appeared to double and divide just before each cell division).
19. Chromosomal theory of inheritance was proposed independently by Walter Sutton and Theodore Boveri in 1902. They united the knowledge of chromosomal segregation with Mendelian principles and called it chromosomal theory of inheritance.
The main points are as follow:
(i) Gametes (sperm and egg) transmit hereditary characters from one generation to another.
(ii) Nucleus is the site of hereditary characters.
(iii) Chromosomes as well as genes are found in pairs.
(iv) The two alleles of a gene pair are located on homologous sites on the homologous chromosomes.
(u) The sperm and egg having haploid sets of chromosomes fuse to regain the diploid state.
(vi) Homologous chromosomes synapse during meiosis and get separated to pass into different cells and is the basis of segregation and independent assortment during meiosis.

20. Experimental verification of the chromosomal theory of inheritance was done by Thomas Hunt Morgan and his colleagues.
(i) Morgan selected fruit fly, Drosophila melanogaster for his experiments because:
(a) They could be grown on simple artificial medium in the laboratory.
(b) Their life cycle is only about two weeks.
(c) A single mating could produce a large number of flies.
(d) There was a clear differentiation of the sexes, i.e. male (smaller) and female (bigger).
(e) It has many types of hereditary variation that can be easily seen through low power microscopes.
(ii) Linkage and Recombination
(a) The physical association of two genes on a chromosome is called linkage.
(b) Recombination explains the generation of non-parental gene combinations.
(c) To explain the phenomena of linkage and recombination, Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex-linked, i.e. the genes are located on X-chromosome. He observed that two genes did not segregate independently of each other.
(d) He observed that the proportion of parental gene combinations were much higher than the non-parental type, when two genes in a dihybrid cross were situated on the same chromosome. Morgan concluded this as a physical association or linkage.
(e) Morgan and his group also found that even when genes were grouped on the same chromosome, some genes were very tightly linked (very low recombination), while others were loosely linked (higher recombination).
(f) Recombination of linked genes is by crossing over (exchange of corresponding parts between the chromatids of homologous chromosomes).

Linkage results of two dihybrid crosses conducted by Morgan. Cross ‘A’ shows
crossing between genes y and w. Cross ‘B1 shows crossing between genes w and m. Here, dominant wild type alleles are represented with (+) sign.
(g) Alfred Sturtevant (Morgan’s student) used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and ‘mapped’ their position on the chromosome. Genetic maps are now used as a starting point in the sequencing of whole genomes as done in case of Human Genome Sequencing Project.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Principles of Inheritance and Variation – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions are part of NCERT Exemplar Class 12 Maths. Here we have given Exemplar Problems for Class 12 Maths Chapter 2 Inverse Trigonometric Functions PDF.

NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions

NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions Solutions is given below.

Short Answer Type Questions

Long Answer Type Questions

Objective Type Questions

Fill in the Blanks Type Questions

True/False Type Questions

More Resources for Class 12 Maths

• NCERT Exemplar
• NCERT Exemplar Class 12 Maths Solutions
• Class 12 Maths NCERT Solutions
• RD Sharma Class 12 Solutions
• Class 12 Maths Important Questions

We hope the NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions help you. If you have any query regarding NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions, drop a comment below and we will get back to you at the earliest.

The post NCERT Exemplar Class 12 Maths Chapter 2 Inverse Trigonometric Functions appeared first on Learn CBSE.

Molecular Basis of Inheritance – CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The DNA and RNA World:
1. Over the years after Mendel, the nature of the genetic material was investigated, resulting in the realisation that DNA is the genetic material in majority of organisms.
2. Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) are the two types of nucleic acid found in living systems. Nucleic acids are polymers of nucleotides.
3. DNA acts as a genetic material in most organisms, whereas RNA acts as a genetic material in some viruses.
4. RNA mostly functions as messenger. RNA has other functions as adapter, structural or as a catalytic molecule.
5. Structure of Polynucleotide Chain
(i) A nucleotide has three parts, i.e. a nitrogenous base, a pentose sugar (deoxyribose in DNA and ribose in RNA) and a phosphate group.
(ii) Nitrogenous bases are purines, i.e. adenine, guanine and pyrimidines, i.e. cytosine, uracil and thymine.
(iii) Cytosine is common for both DNA and RNA and thymine is present in DNA. Uracil is present in RNA at the place of thymine.
(iv) A nitrogenous base is linked to the pentose sugar through a N-glycosidic linkage to form a nucleoside, i.e. adenosine and guanosine, etc.
(v) When a phosphate group is linked to 5′ —OH of a nucleoside through phosphodiester linkage, a corresponding nucleotide is formed.
(vi) Two nucleotides are linked through 3′ -> 5′ phosphodiester linkage to form a dinucleotide.
(vii) Several nucleotides can be joined to form a polynucleotide chain.
(viii) The backbone in a polynucleotide chain is formed due to sugar and phosphates.
(ix) The nitrogenous bases linked to sugar moiety project from the backbone.
(x) The base pairs are complementary to each other.
6. In case of RNA, every nucleotide residue has an additional—OH group present at 2-position in the ribose. Also, the uracil is found at the place of thymine (5-methyl uracil).

7. Discoveries Related to Structure of DNA
(i) Friedrich Meischer in 1869, first identified DNA as an acidic substance present in the nucleus and named it as ‘nuclein’.
(ii) James Watson and Francis Crick, proposed a very simple double helix model for the structure of DNA in 1953 based on X-ray diffraction data.
(iii) Erwin Chargaff proposed that for a double-stranded DNA, the ratios between adenine and thymine and guanine and cytosine are constant and equals to one.
8. Salient Features of Double-helix Structure of DNA
(i) DNA is a long polymer of deoxyribonucleotides. It is made up of two polynucleotide chains, where the backbone is constituted by sugar-phosphate and the bases project inside.
(ii) The two chains have anti-parallel polarity, i.e. 5′ > 3′ for one, 3′ > 5′ for another.
(iii) The bases in two strands are paired through hydrogen bond (H—bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with thymine from opposite strand and vice-versa. Guanine bonds with cytosine by three H—bonds. Due to this, purine always comes opposite to a pyrimidine. This forms a uniform distance between the two strands.
(iv) The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm and there are roughly 10 bp in each turn. Due to this, the distance between a base pair in a helix is about 0.34 nm.
(v) The plane of one base pair stacks over the other in double helix. This confers stability to the helical structure in addition to H—bonds.
9. The length of a DNA double helix is about 2.2 meters (6.6 x 10⁹ bp x 0.34 x 10^-9 m/bp)
Therefore, it needs special packaging in a cell.
(i) In prokaryotic cells (which do not have a defined nucleus), such as E.coli, DNA (being negatively charged) is held with some proteins (that have positive charges) in a region called as nucleoid. The DNA in nucleoid is organised in large loops held by proteins.
(ii) In eukaryotes, there is a set of positively charged proteins called histones that are rich in basic amino acid residues, lysines and arginines (both positive).

Histones are organised to form a unit of eight molecules called histone octamer. The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome.
(iii) A typical nucleosome contains 200 bp of DNA helix.
Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin (thread-like stained structure). Under electron microscope, the nucleosomes in chromatin can be seen as beads-on-string. This structure in chromatin is packaged to form chromatin fibres that further coils and condense to form chromosomes at metaphase stage.
(iv) The packaging of chromatin at higher level requires additional set of proteins which are collectively called Non-Histone Chromosomal (NHC) proteins.

(v) In a nucleus, some regions of chromatin are loosely packed (stains light) called euchromatin (transcriptionally active chromatin). In some regions, chromatin is densely packed (stains dark) called heterochromatin (inactive chromatin).

10. Transfonning Principle
(i) Frederick Griffith (1928) carried out a series of experiments with Streptococcus pneumoniae (bacterium causing pneumonia).
(ii) According to him, when the bacteria are grown on a culture plate, some produce smooth shiny colonies (S), while others produce rough (R) colonies.
(iii) This is because the S-strain bacteria have a mucous (polysaccharide) coat, while R-strain does not.
(iv) Mice infected with S-strain (virulent) die from pneumonia but mice infected with R-strain do not develop pneumonia.
(v) Griffith killed bacteria by heating and observed that heat-killed S-strain bacteria injected into mice did not kill them. On injecting mixture of heat-killed S and live R bacteria, the mice died. He recovered living S-bacteria from dead mice.
(vi) From this experiment, he concluded that the ‘R-strain bacteria’ had been transformed by the heat-killed S-strain bacteria. Some transforming principle transferred from heat-killed S-strain, had enabled the R-strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to transfer of the genetic material.
11. Biochemical Nature of Transforming Principle
(i) Oswald Avery, Colin MacLeod and Maclyn McCarty, worked to determine the biochemical nature of transforming principle in Griffith’s experiment.
(ii) They purified biochemicals (proteins, RNA and DNA, etc) from heat-killed S-cells and discovered that DNA alone from S-bacteria caused R-bacteria to be transformed.
(iii) They also discovered that protease (protein digesting enzyme) and RNAases (RNA-digesting enzymes) did not affect transformation.
(iv) Digestion with DNAse did inhibit transformation, indicating that DNA caused transformation.
(v) They concluded that DNA is the hereditary material. But, still all the biologists were not convinced.
12. DNA is the Genetic Material
(i) Alfred Hershey and Martha Chase (1952) gave unequivocal proof that DNA is the genetic material.
(ii) In their experiments, bacteriophages (viruses that infect bacteria) were used.
(iii) They grew some viruses on a medium that contained radioactive phosphorus and some others on sulphur containing radioactive medium.
(iv) Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. In the same way, viruses grown on radioactive sulphur contained radioactive protein, but not radioactive DNA because DNA does not contain sulphur.

(v) Radioactive phages were allowed to attach to E. coli bacteria. As the infection proceeded, viral coats were removed from the bacteria by agitating them in a blender. The virus particles were separated from the bacteria by spinning them in a centrifuge.
(vi) Bacteria which were infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria.
(vii) Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicated that the proteins did not enter the bacteria from viruses. It proved that DNA is a genetic material that is passed from virus to bacteria.
13. Properties of Genetic Material
(i) It became establised that DNA is the genetic material from the Hershey-Chase experiment.
(ii) In some viruses, RNA was also reported as genetic material, e.g. Tobacco mosaic viruses, QB bacteriophage, etc.
(iii) Characteristics of a Genetic Material
(a) It should be able to replicate.
(b) It should be chemically and structurally stable.
(c) It should provide scope for slow changes (mutation) that are required for evolution.
(d) It should be able to express itself in the form of ‘Mendelian characters’.
(iv) According to the above mentioned rules, both the nucleic acids (DNA and RNA) have the ability to direct duplications.
Stability can be explained in DNA as the two strands being complementary if separated by heating come together in appropriate conditions.
(v) The 2′ — OH group present at every nucleotide in RNA is a reactive group and makes RNA labile and easily degradable, hence it is reactive.
(vi) DNA is chemically less reactive and structurally more stable when compared to RNA. Thymine also confers additional stability to DNA. So, among the two nucleic acids, the DNA is a predominant genetic material.
(vii) Both RNA and DNA are able to mutate. Viruses having RNA genome and having shorter life span mutate and evolve faster.
(viii) DNA is dependent on RNA for protein synthesis, while RNA can directly code for it. The protein synthesising machinery has evolved around RNA. This concluded that the DNA being more stable is suitable for storage of genetic information, while for the transmission of genetic information, RNA is suitable.
14. Francis Crick proposed the central dogma in molecular biology, which states that the
genetic information flows from

15. Replication Scheme for replication of DNA termed as semiconservative DNA replication was proposed by Watson and Crick (1953). According to it,
(i) The two strands would separate and act as a template for the synthesis of new
complementary strands. .
(ii) After replication, each DNA molecule would have one parental and one newly synthesised strand.
16. Experimental proof that DNA replicates semiconservatively, comes first from E. coli and later from higher organisms, such as plants and human cells.
Matthew Meselson and Franklin Stahl performed the following experiments to prove this in 1958.
(i) E. coli was grown in a medium containing 15NH₄C1 as the only nitrogen source for many generations. 15N got incorporated into newly synthesised DNA (and other nitrogen containing compounds). This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride (CsCl) density gradient.
(ii) They then transferred the cells into a medium with normal 14NH₄Cl and took samples at various definite intervals as the cells multiplied and extracted the DNA that remained as double stranded helices. DNA samples were separated independently on CsCl gradients to measure DNA densities.
(iii) The DNA that was extracted from the culture, one generation (after 20 min) after the transfer from 15 N to 14N medium had a hybrid or intermediate density. DNA extracted from the culture after another generation (after 40 min) was composed of equal amounts of this hybrid DNA and of light DNA.
(iv) Very similar experiments were carried out by Taylor and Colleagues on Vicia faba (faba beans) using radioactive thymidine and the same results, i.e. DNA replicates semiconservatively, were obtained as in earlier experiments.

17. DNA replication machinery and enzymes process of replication requires a set of catalysts (enzymes).
(i) The main enzyme is DNA-dependent DNA polymerase, since it uses a DNA template to catalyse the polymerisation of deoxynucleotides. The average rate of polymerisation by these enzymes is approximately 2000 bp/second.
(ii) These polymerases has to catalyse the reaction with high degree of accuracy because any mistake during replication would result into mutations.
DNA polymerisation is an energy demanding process, so deoxyribonucleoside triphosphates serve dual purposes, i.e. act as substrates and provide energy for polymerisation reaction.
(iv) Many additional enzymes are also required in addition to DNA-dependent DNA polymerase.
(v) (a) Replication in DNA strand occurs within a small opening of the DNA helix, known as replication fork.

(b) DNA-dependent DNA polymerases catalyse polymerisation only in one direction, i.e. 5′ -> 3. It creates additional complications at the replicating fork. Consequently, on one strand (template 3′-5′), the replication is continuous, while on the other strand (template 5′-3′), it is discontinuous. The discontinuously synthesised fragments called Okazaki fragments are later joined by DNA ligase.
18. Origin of Replication
(i) DNA polymerases cannot initiate the process of replication on their own. Also, replication does not initiate randomly at any place in DNA. So, there is a definite region in E.coli DNA where the replication originates. The region is termed as origin of replication.
(ii) Due to this requirement, a piece of DNA, if needed to be propagated during recombinant DNA procedures, requires a vector. The vectors provide the origin of replication.
19. RNA world RNA was the first genetic material. There are evidences to prove that essential life processes, such as metabolism, translation, splicing, etc., have evolved around RNA.
(i) There are some important biochemical reactions in living systems that are catalysed by RNA catalysts and not by protein enzyne.
(ii) DNA has evolved from RNA with chemical modifications that make it more stable because RNA being a catalyst was reactive and hence, unstable.
20. There are following three types of RNAs:
(i) mRNA (messenger RNA) provides the template for transcription.
(ii) tRNA (transfer RNA) brings amino acids and reads the genetic code.
(iii) rRNA (ribosomal RNA) plays structural and catalytic role during translation.
All the three RNAs are needed to synthesise a protein in a cell.
21. Traription is the process of copying genetic information from one strand of the i DNJS. into RNA. The principle of complementarity governs the process of
transcription, except the adenosine now forms base pair with uracil instead of l thymine.
(i) In transcription, only a segment of DNA is duplicated and on Iv one of the strands is . copied into RNA. Both the strands are not copied because
• If both the strands code for RNA, two different RNA me’ ^cules and two different proteins would be formed, hence complicating the genetic information transfer machinery.
• Since two RNA produced would be complementary to each other, they would form a double-stranded RNA without translation, making the process of transcription futile.
(ii) A transcription unit in DNA is defined by three regions in the DNA which are as follows:
(a) A promoter (b) The structural gene (c) A terminator
(iii) The two strands of DNA have opposite polarity and the DNA-dependent RNA polymerase also catalyse the polymerisation in only one direction that is 5′ -» 3′.
(iv) The strand that has the polarity 3′-» 5′ acts as a template and is referred to as template strand. The other strand which has the polarity (5′ -> 3′) and the sequence same as RNA (T at the place of U) is displaced during transcription. This strand is called as coding strand.
(v) The promoter and terminator flank the structural gene in a transcription unit.
(vi) The promoter is located towards 5′ end (upstream) of the structural gene.
(vii) It is the DNA sequence that provides binding site for RNA polymerase and the presence of promoter defines the template and coding strands. By switching its position with terminator, the definition of coding and template strands could be reversed.
(viii) The terminator is located towards 3f-end (downstream) of the coding strand and it usually defines the end of the process of transcription.
(ix) There are additional regulatory sequences that may be present further upstream or downstream to the promoter.
Transcription Unit and the Gene
(i) A gene can be defined as the functional unit of inheritance.
(ii) A cistron is a segment of DNA coding for a polypeptide.
(iii) The structural gene in a transcription unit could be said as monodstronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes).
(iv) The coding sequences or expressed sequences are defined as exons. Exons appear in mature or processed RNA. The exons are interrupted by introns.

(v) Introns or intervening sequences do not appear in mature or processed RNA.
(vi) Sometimes, the regulatory sequences are loosely defined as regulate 5: even
though these sequences do not code for any RNA or protein.
22. Transcription in prokaryotes occur in the following steps:
(i) A single DNA-dependent RNA polymerase catalyses the transcription of all types of RNA in bacteria.
(ii) RNA polymerase binds to promotor and initiates transcription (initiation).
(iii) It uses nucleoside triphosphates as substrate and polymerises in a template depended fashion following the rule of complementarity.
It also facilitates opening of the helix and continues elongation.
(v) Once the polymerase reaches the terminator region, the nascent RNA falls off, so also the RNA polymerase. This results in termination of transcription.
(vi) RNA polymerase is only capable of catalysing the process of elongation.
It associates transiently with initiation-factor (a) and terminator factor (b), to initiate and terminate the transcription, respectively. Thus, catalysing all the three steps.
(vii) Since, the mRNA does not require any processing to become active and also since transcription and translation take place in the same compartment, many times the translation can begin much before the mRNA is fully transcribed. As a result, transcription and translation can be coupled in bacteria.
23. Transcription in eukaryotes have additional complexities than prokaryotes.
(i) There are at least three RNA polymerases in the nucleus other than the RNA polymerase in organelles. The RNA polymerase I transcribes rRNAs (28S, 18S and 5.8S). RNA polymerase III is responsible for transcription of fRNA, 5srRNA and SnRNAs (small nuclear RNAs). RNA polymerase II transcribes precursor of mRNA, the heterogenous nuclear RNA (/mRNA).
(ii) Another complexity is that, the primary transcripts contain both the exons and the introns and are non-functional. Hence, subject to a process called splicing. In this process, introns are removed and exons are joined in a definite order.
(iii) /mRNA undergoes additional processing called as capping and tailing. In capping, an unusual nucleotide is added to the 5′-end of /mRNA. In tailing, adenylate residues
(200-300) are added at 3′-end in a template. It is the fully processed /mRNA, now called mRNA, that is transported out of the nucleus for translation process.

Significance of these complexities are:
(i) The split gene arrangements represent an ancient feature of genome.
(ii) The presence of introns is reminescent of antiquity.
(iii) The process of splicing represents the dominance of RNA world.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Molecular Basis of Inheritance – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Evolution- CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The Origin of Life and Evidences of Evolution:
1. The study of history of life forms on earth is called evolutionary biology.
2. Evolution is a process that results in heritable changes in population spread over many generations leading to diversity of organisms on earth.
3. Origin of life is considered a unique event in the history of universe.
(i) The Universe
(a) It is very old-almost 20 billion years ago. It contains huge galaxies.
(b) Galaxies contain stars and clouds of gas and dust.
(c) The origin of universe is explained by Big Bang theory.
(d) The Big Bang theory states that a huge explosion occurred, the universe expanded, temperature came down and hydrogen and helium were formed later. The galaxies were then formed due to condensation of gases under gravitation.
(ii) The earth was supposed to have been formed about 4.5 billion years back in the solar system of the milkyway galaxy.
(a) Water vapour, methane, carbon dioxide and ammonia released from molten masses covered the surface.
(b) UV rays from the sun broke up water molecule into hydrogen and oxygen and lighter hydrogen escaped.
(c) Oxygen combined with ammonia and methane to form water, carbon dioxide and others.
(d) Ozone layer formed, as it cooled, the water vapour fell as rain to fill depression and form oceans.
(e) Life appeared 500 million (about 4 billion years back) years after the formation of earth.
4. Theories of origin of life were given by different thinkers and scientists.
(i) Theory of special creation states that God created life by his divine act of creation.
(iii) Theory of panspermia/cosmozoic theory, given by early Greek thinkers states that the spores or panspermia came from outer space and developed into living forms.
(iii) Theory of spontaneous generation states that life originated from decaying and rotting matter like straw, mud, etc.
(a) Louis Pasteur rejected the theory of spontaneous generation and demonstrated that life came from pre-existing life.
(b) In his experiment, he kept killed yeast cells in pre-sterilised flask and another flask open into air. The life did not evolved in the former but new living organisms evolved in the second flask.
(iv) Theory of chemical evolution or Oparin-Haldane theory states that life originated from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution.
The conditions on the earth that favoured chemical evolution were very high temperature, volcanic storms and reducing atmosphere that contained CH₄,NH₃, water vapour, etc.
5. Miller’s experiment provided experimental evidence for chemical evolution.
(i) The experiment was carried out by SL Miller and HC Urey in 1953.
(ii) He took a closed flask containing CH₄,H₂,NH₃ and water vapour at 800°C and created electric discharge. These conditions were similar to those in primitive atmosphere.
(iii) After a week, formation of amino acids were observed. Complex molecules like sugars, nitrogen bases, pigments and fats were seen in the flask by other scientist.
(iv) Analysis of the meteorite also revealed the presence of similar compounds.
(v) Chemical evolution of life was more or less accepted.

6. Origin of First Cell
(i) First non-cellular life forms originated three million years ago.
(ii) These molecules were like RNA, protein and polysaccharides.
(iii) Cellular life form first evolved about 2000 million years ago.
(iv) These were single-celled formed in aquatic environment.
(v) This form of abiogenesis, i.e. the first form of life arose slowly through evolutionary
forces from non-living molecules It is accepted by many scientists.
7. Evidences of evolution come from
(i) Palaeontology (ii) Comparative anatomy and morphology
(iii) Biochemical/Physiology (iv) Biogeography
(v) Embryology
(i) Palaeontology is the study of fossils. The fossils are the remains of past organisms
preserved in sedimentary rocks
(a) Rocks form sediments and a cross-section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth.
(b) Different aged rock sediments contain fossils of different life forms, who died during the formation of the particular sediment,
(c) Some organisms appear similar to modern organisms. They represent extinct organisms like dinosaurs.
(d) A study of fossils in different sedimentary layers indicates the geological period in which they existed.
(e) The study showed that life forms varied over time and certain life forms are restricted to certain geological time-scale Hence, new forms of life have evolved at different times in the history of earth,
(ii) Comparative anatomy and morphological evidences show the similarities and
differences among the organisms of today and those that existed years ago.
The evidences come from comparative study of external and internal structure.
I. (a) The organs with same structural design and origin but different functions are called homologous organs. Examples are forelimbs of some animals like whales, bats and cheetah have similar anatomical structure, such as humerus, radius, ulna, carpals, metacarpals and phalanges.
(b) Homology in organ indicates common ancestry.
(c) Other examples of homology are vertebrate hearts or brains. In plants also, thorns and tendrils of Bougainvillea and Cucurbita represent homology.
(d) Homology is based on divergent evolution. The same structure developed along different directions due to adaptations to different needs. The condition is called divergent evolution.

II. (a) Organs which are anatomically different but functionally similar are called analogous organs. For example, wings of butterfly and birds.
(b) Analogy refers to a situation exactly opposite to homology.
(c) Analogous organs are a result of convergent evolution. It is the evolution in which different structures evolve for same function and hence, have similarity.
(d) Other examples of analogy are eyes of Octopus and mammals; flippers of penguins and dolphins. In plants, sweet potato (root modification) and potato (stem modification).

III. Vestigial organs like homologous organs provide evidences for organic evolution.
These are degenerate, non-functional and rudimentary organs to the possessor, while correspond to fully developed and functional organs of related organisms.
(a) There are about 90 vestigial organs in the human body. Same of them are tail bone (coccyx), wisdom teeth, nictitating membrane, vermiform appendix, etc.
(b) Some examples from other animals are hip girdles and bones of the hind limbs in some whales and certain snakes and wings of flightless birds.
Biochemical Evidences
(a) The metabolic processes in organisms are similar with same new materials and end products. For example, energy released by oxidation is stored in ATP which then powers the energy requiring process.
(b) Molecular homology is the similarity among animals at the molecular level.
For example, human DNA differs in only 1.8% of its base pairs from chimpanzee DNA and there is no difference between the two in the amino acid sequence for the protein cytochrome-c.
(iv) Biogeographical evidences The species restricted to a region develop unique features. Also, species present in far separated regions show similarity of ancestry.
This can be explained with the help of following processes:
I. Adaptive radiation is an evolutionary process in which an ancestral stock gives rise to new species adapted to new habitats and new ways of life. Examples are (0 Darwin’s finches These were small black birds, which Darwin observed in Galapagos island.
(a) He observed many varieties of finches in the same island.
(b) All varieties of finches had evolved from original seed-eating finches.
(c) There was alternation in beaks enabling some to become insectivorous and some vegetarian.


(ii) Marsupials of Australia A number of marsupials, different from each other evolved from an ancestral stock, all within the Australian island continent.
II. Parallel evolution refers to independent development of similar characters in two animal groups of common ancestry living in similar habitats of different continents. Examples are
Marsupial mammals in Australia show parallel evolution as they have evolved from placental mammals. All these closely resemble and look similar to a corresponding marsupial.
Few examples are mentioned in the table.

III. Convergent evolution is development of similar adaptive functional structures in unrelated groups of organisms. Examples are:
(i) Wings of insect, bird and bat.
(ii) Spiny anteater and scaly anteater belong to different orders of class-Mammalia. They have acquired similar adaptations for food, e.g. leg ants, termites and insects.
(v) Embryological evidences Study of comparative embryology shows common patterns of development.
(a) The principles of embryonic development were given by Von Baer.
(b) Ernst Haeckel propounded The theory of recapitulation or Biogenetic law which states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny), i.e. ontogeny recapitulates phylogeny.
(c) This means that the life history of an animal reflects its evolutionary history.
For example, during the life history, frog’s tadpole larva resembles fishes, the ancestors of amphibia.
The presence of gill clefts in all vertebrate embryos including human provides a strong evidence in support of organic evolution.
(vi) Anthropogenic evidences Excess use of herbicides, pesticides, etc has resulted in selection of resistant varieties in a lesser time scale. This is also true for microbes against which antibiotics or drugs have been used. All these evidences tell us that ‘Elvolution is a stochastic process based on chance events in nature and chance mutation in the organisms’.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Evolution- CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Human Health and Disease – CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Health, Common Diseases in Human and Immunity:
1. Health is defined as a state of complete physical, mental and social well-being.
(i) The factors which affect human health are:
(a) Genetic disorders (b) Infections (c) Lifestyle.
(ii) Balanced diet, personal hygiene and regular exercise are very important to maintain good health.
(Hi) Awareness about diseases and their effect on different body functions, vaccination against infectious diseases, proper disposal of wastes, control of vectors, maintenance of hygienic food and water resources are necessary for achieving good health.
2. Disease is a state when functioning of one or more organs or systems of the body is
adversely affected, characterised by various signs and symptoms.
Diseases can be divided broadly into the following two categories depending on the
modes of transmission
I. Infectious diseases which easily transmit from one person to another, e.g. AIDS, common cold, etc.
II. Non-infectious diseases which does not transmit from one person to another, e.g. cancer, diabetes, etc.
(i) Disease causing organisms are called pathogens, e.g. bacteria, viruses, fungi, protozoans, helminthes, etc.
(ii) The above described pathogens enter the body by direct contact, contaminated food and water, droplet infection, etc.
(iii)The pathogens multiply in body cells, interfere with normal vital activities, cause morphological and functional damage.
(iv) Infectious diseases can be divided into certain categories, based on the type of pathogen
Infectious Diseases
Bacterial Viral Protozoan Fungal Helminthic
e.g. pneumonia, e.g. common cold, e.g. amoebiasis, e.g. ringworm, e.g. ascariasis, ,
plague, typhoid, polio, etc. malaria, etc. athelete’s foot, etc. filariasis, taeniasis, etc.
diphtheria, etc

Some diseases are transmitted by vector, i.e. mosquitoes like dengue (Aedes aegypti); chikungunya (Aedes aegypti, Aedes albopictus) and malaria (.Anopheles).
3. Some of the common infectious diseases are:
I. Bacterial Diseases
(i) Typhoid is caused by bacterium (Salmonella typhi).
(a) S. typhi enters the small intestine through food and water contaminated with them and migrate to other organs through blood.
(b) Intestinal perforation and death may occur in severe cases.
(c) Widal test is a confirmation test for typhoid.
(d) Symptoms are high fever (39-40°C), weakness, stomach pain, constipation, headache and loss of appetite.
(ii) Pneumonia is caused byStreptococcus pneumoniae and Haemophilus influenzae.
(a) These bacteria infect alveoli of the lungs. The alveoli get filled with fluid causing decrease in respiratory efficiency of the lungs.
(b) Pneumonia spreads by inhaling droplets/aerosol from infected individuals or even by sharing glasses and utensils with patients.
(c) Symptoms of pneumonia are fever, chills, cough, headache, etc.
(iii) Dysentery, plague, diphtheria, etc., are some other examples of bacterial diseases.
II. Viral Disease
Common cold occurs due to a group of viruses called rhino viruses.
(a) These viruses infect the nose and respiratory passage but not the lungs.
(b) Common cold is characterised by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which generally last for 3-7 days.
(c) The infection occurs due to cough or sneezes of an infected person, either inhaled directly or transmitted through contaminated objects such as pens, books, cups, computer’s keyboard or mouse, etc.
III. Protozoan Diseases
(i) Malaria is caused by a protozoan, Plasmodium sp. (P. vivax, P. malariae and P. falciparum).
(a) P. falciparum causes most serious kind of malaria, i.e. malignant malaria which can be fatal.
(b) Female Anopheles mosquito is the vector of Plasmodium, which transfer the sporozoites (infectious form) in human body.
(c) Life cycle of Plasmodium is given in the figure.

• The malarial parasite requires two hosts to complete its life cycle, i.e. human and mosquito.
• Plasmodium enters the human body as sporozoite, through the bite of infected female Anopheles mosquito.
• Parasites initially multiply within the liver cells and then attack the Red Blood Cells (RBCs) causing their rupture.
• Rupture of RBCs release a toxic substance called haemozoin. Haemozoin causes chill and high fever recurring every 3-4 days.
• When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development.
• The parasites multiply within them to form sporozoites that are stored in their salivary glands.
• When these mosquitoes bite a human, the sporozoites are introduced into his/her body, initiating the events mentioned above.
(d) Antimalarial drugs used for the treatment are quinine and chloroquin.
(e) Malaria can be prevented by killing mosquitoes by spraying DDT, BHC, etc., and using insect repellents, mosquito nets, etc.
(ii) Amoebiasis (amoebic dysentery) is caused by an intestinal endoparasite, Entamoeba histolytica, which is found in large intestine of humans.
(a) Carrier of pathogen is housefly. It transmits the parasite from faeces of infected person to the food, thereby contaminating them.
(b) Infection takes place mainly through the contaminated food and water.
(c) Symptoms are abdominal pain, constipation, cramps, faeces with excess mucous and blood clots.
IV. Fungal Disease
Ringworm is caused by many fungi of genera Microsporum, Trichophyton and Epidermophyton.
(i) Infection occurs through contact with an infected person or from soil and through the use of towels, clothes, combs, etc., of an infected person.
(ii) Heat and moisture help these fungi to grow in regions like skin folds as in groin or between the toes.
(Hi) Symptoms of ringworm are appearance of dry, scaly lesions on various parts of the body such as skin, nails and scalp accompanied by intense itching.
V. Helminthic Diseases
(i) Ascariasis is caused by an intestinal endoparasite of human, Ascaris lumbricoides commonly called as roundworm.
(a) Infection occurs as the eggs of parasite are excreted along with the faeces of infected person, which contaminate water, soil, plants, etc.
(b) Infection reaches to human beings through contaminated vegetables, fruits and water, etc.
(c) Symptoms of disease are abdominal pain, indigestion, muscular pain, fever, anaemia, nausea, headache and blockage of intestinal passage.
(ii) Filariasis/Elephantiasis is caused by filarial worms, Wuchereria bancrofti and Wuchereria malayi.
(a) Culex mosquito (female) is the vector.
(b) Genital organs also get affected leading to their deformation.
(c) Symptoms are inflammation of organs in which they live for many years, normally affect lymph vessels of lower limbs resulting in swelling hence, called elephantiasis.
4. Prevention measures to avoid infectious diseases are:
(i) Maintenance of personal and public hygiene is important.
(ii) Personal hygiene includes keeping the body clean, consumption of clean drinking water, food, vegetables, fruits, etc.
(iii) Public hygiene includes proper disposal of waste excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.
(iv) Eradication of vectors and destroying their breeding sites.
(v) Mosquito nets, repellants should be used.
(vi) Vaccination and immunisation programmes for diseases should be strictly followed.
(vii) Use of antibiotics and other drugs can significantly keep away infectious diseases.
5. Immunity is the capacity of an organism to resist or defend itself from the  development of a disease. It is of the following types, as shown below:

I. Innate immunity is present from birth and is inherited from the parents.
(i) It is non-specific.
(ii) It consists as following types:
(a) Physical barriers prevent entry of microorganisms in the body e.g. skin, mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts.
(b) Physiological barriers prevent microbial growth in the body, e.g. acid in the stomach, saliva in the mouth and tears from eyes.
(c) Cellular barriers phagocytose and destroy microbes. For example, some WBCs like Polymorphonuclear Leukocytes (PMNL), monocytes and natural killer cells (type of lymphocytes) in the blood as well as macrophages in tissues.
(d) Cytokine barriers are virus-infected cells, which secrete proteins called interferons. They protect non-infeeted cells from further viral infection.
II. Acquired immunity is not present from birth and develops during an individual’s life
time.
(i) It is pathogen specific and characterised by memory.
(ii) When it encounters a pathogen for the first time, it produces a response called
primaiy response, which is of low intensity.
(iii) Further encounter with same pathogen produces highly intensified secondary or
anamnestic response due to memory of the first encounter.
(iv) Immune responses are produced by two types of lymphocytes:
(a) B-lymphocytes or B-cells produce an army of proteins (in response to pathogens) called antibodies in blood.
(b) T-lymphocytes or T-cells help B-cells to produce antibodies.
(v) Types of acquired immunity:
(a) Humoral immune response or Antibody Mediated Immunity (AMI) It is mediated by antibodies present in blood and lymph.
(b) Cell-mediated immune response or Cell Mediated Immunity (CMI) It is mediated by T-lymphocytes. The graft rejection during organ transplantation, because of the ability to differentiate between self and non-self, is due to the cell-mediated immunity.
(vi) Antibodies are immunoglobulin molecules (Ig). These are of five types:

(a) Each antibody molecule has four peptide chains, i.e. two small called
light (L) chains and two longer called heavy (H) chains. Hence, an antibody is represented as H^.
(b) An antibody seems like a Y-shaped structure.
6. Acquired immunity is as following two types:

7. Vaccination and immunisation The principle is based on the property of memory of immune system.
(i) Vaccination is the process of introduction of weakened or inactivated pathogens or proteins (vaccine) into a person to provide protection against a disease.
(ii) Immunisation is a process by which the body produces antibodies against the vaccine (primary response) and develop the ability to neutralise pathogens during actual infection (secondary response), i.e. the body become immune to that antigen or infection.
(iii) Vaccine generates memory B and T-cells that recognise the pathogens on subsequent exposure and produce an intense immune response.
(iv) In case of requirement of quick immune response like tetanus infection, preformed antibodies are injected into the patient. This is called passive immunisation.
(v) Recombinant DNA technology has produced antigenic polypeptides of pathogen in bacteria or yeast. This allowed large scale production of vaccine, e.g. hepatitis-B vaccine from yeast, etc.
8. Human immune system includes (i) lymphoid organs (ii) immune cells (iii) soluble molecules like antibodies (iv) lymphoid tissues.
Lymphoid organs These are the organs where origin and/or maturation and proliferation of lymphocytes occur. They are as following two types:
(a) Primary lymphoid organs are the sites where lymphocytes differentiate and mature to become antigen-sensitive, e.g. bone marrow and thymus.
In bone marrow, all blood cells including lymphocytes are produced and B-lymphocytes mature.
Thymus is a lobed organ, located near the heart and beneath the breastbone.
It reduces as the age increases. T-lymphocytes develop and mature in thymus.
(b) Secondary lymphoid organs provide the sites where lymphocytes interact with the antigen and proliferate to become effector cells, e.g. spleen, lymph nodes, tonsils,  Peycr’s patches of small intestine and appendix.
Spleen is a large, bean-shaped organ which contains lymphocytes and phagocytes.
It acts as a filter to trap blood-borne microbes and contain a large pool of erythrocytes.
Lymph nodes are small solid structures along the lymphatic system. Their function is to trap microorganisms or other antigens that enter the lymph and tissue fluid. Mucosal Associated Lymphoid Tissue (MALT) is formed of the masses of lymphoid tissue, lining the mucosa of respiratory, digestive and urogenital tracts. About 50% of lymphoid tissue in human body is formed by MALT.
9. Allergy is a hypersensitive reaction of the immune system to certain antigens present in the environment.
(i) Allergens produce immune response in an individual, e.g. pollen grains, animal dander, dust, feathers, etc.
(ii) IgE antibodies are produced in response to allergens.
(iii) Allergy is due to chemicals like histamine and serotonin released from the mast cells.
(iv) Symptoms of allergy are sneezing, watery eyes, running nose, difficulty in breathing.
(v) Antihistamine, adrenaline and steroids are taken to reduce the symptoms of allergy.
10. Autoimmunity is an abnormal immune response in which immune system of the body starts arthritis.
rejecting its own body cell or self cells and molecules, e.g. Rheumatoid
11. AIDS or Acquired Immuno Deficiency Syndrome was first reported in 1981 in USA.
(i) The causative agent is Human Immunodeficiency Virus (HIV).
(ii) HIV belongs to the group of viruses called retrovirus. It has RNA genome enclosed in an envelope.
(iii) HIV is transmitted by
(a) Sexual contact with infected person.
(b) Transfusion of contaminated blood and blood products.
(c) Sharing infected needles.
(d) Infected mother to unborn child through placenta.
(iv) People, who are susceptible to infection are:
(a) Drug addicts, who take intravenous drug injections.
(b) Individuals who are involved with multiple sexual partners.
(c) Individuals who require repeated blood transfusion.
(d) Children born to HIV positive mother.
(v) Modes of HIV infection:
(a) Virus enters the macrophages, after entering the body of a person.
(b) RNA gets replicated to form viral DNA by enzyme reverse transcriptase.
(c) Viral DNA gets incorporated into the host cell DNA and directs the infected cells to produce virus particles.
(d) Macrophages continue to produce virus particles and thus, acts as HIV factory.
(e) These virus particles enter into helper T-lymphocytes (TH cells) in the blood, where they continue to replicate and produce viral progenies.
(f) The number of helper T-lymphocytes progressively decreases in the body of the infected person.
(g) As the number of T-cells decrease, the immunity also decreases. As a result, person cannot produce any immune response even against common bacteria like Mycobacterium, parasite like Toxoplasma, viruses and fungi.
(h) ELISA (Enzyme Linked Immuno Sorbent Assay) is a widely used diagnostic test for AIDS.
(i) Treatment with anti-retroviral drugs is only partially effective.
(vi) Preventive measures for HIV infection are:
(a) National AIDS Control Organisation (NACO) set-up in 1991 and other NGOs educate people about AIDS.
(b) Role of WHO to prevent HIV infection:
* Ensure use of disposable syringes and needles.
* Ensure keeping blood banks safe from HIV.
* Free distribution of condoms.
* Prevention of drug abuse.
* Discouraging unsafe sex and encouraging regular check-up.
12. Cancer can be defined as an uncontrolled growth or proliferation of cells without any differentiation.
(i) In our body, cell growth and differentiation is highly controlled and regulated.
(ii) The cancer cells divide repeatedly with uncontrolled cell divisions. They do not require extracellular growth factors.
(iii) Cancer cells lost the property of contact inhibition (contact with other cells inhibit the uncontrolled growth).
(iv) The repeated division of cancerous cells, form a large mass of cells called tumours.
(v) Cancer cells move from tumour to new sites through blood for forming secondary tumours. This invasion of cancer cells from one part to other parts by the body fluids is called metastasis.
(vi) Types of tumour and differences between them:
vii) Cancer causing viruses are called oncogenic viruses. They have genes called viral oncogenes.
(viii) Normal cells have genes called cellular oncogenes (c-onc.) or proto oncogenes, which are present in inactive state, but under certain conditions (like mutation) could lead to oncogenic transformation of the cells.
(ix) Carcinogens are cancer causing agents. They may be
(a) Chemicals As in cigarette smoke, benzopyrene, dyes, paints, etc.
(b) Biological Oncogenic viruses, some parasites, etc.
(c) Physical Ionising radiation like X-rays and y-rays, non-ionising radiations like UV-rays.
(x) Cancer can be detected by the following methods:
(a) Blood and bone marrow tests for increased cell counts.
(b) Biopsy and histopathological studies of the tissue.
(c) Radiography by X-rays, to detect cancer of the internal organs.
(d) Computed Tomography (CT) using X-rays, to generate a 3-D image of internal tissue.
(e) Resonance imaging involves use of non-ionising radiation and strong magnetic field to detect pathological and physiological changes in living tissue.
(f) Monoclonal antibodies against cancer-specific antigens are also used for cancer detection.
(xi) Treatment of cancer involves following methods:
(a) Surgery Tumours are removed by surgery to check further spread of cancer cells.
(b) Radiation therapy Tumour cells are irradiated by lethal doses of radiation, taking care to protect the surrounding normal cells.
(c) Chemotherapy Several chemotherapeutic drugs are used to kill cancer cells. But,their side effects like hair loss, anaemia is also reported.
Most cancers are treated by the combination of the above three.
(d) Immunotherapy Biological modifiers like a-interferons are used to activate the immune system and helps in destroying the tumour.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Human Health and Disease – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Strategies Enhancement in Food Production – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Animal Husbandry:
1. Animal husbandry is the agricultural practice of breeding and raising livestock. It deals with the care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, goat, etc. It also includes poultry farming and fisheries. More than 70% of the world’s livestock population is in India and China. Many new technologies have also been applied to achieve improvement in quality and productivity.
2. to improve quality and quantity in animal husbandry are:
I. Management of Farms and Farm Animals
(i) Dairy farm management is the management of animals for milk and its products for human consumption.
(a) It deals with processes and systems to improve quality and quantity of milk.
(b) Milk yield depends mainly on the quality of breeds in the farm.
(c) Dairy farm management processes include:
• Selection of good breeds having high yielding potential and resistance to the diseases.
• Cattle should be housed-well, should have sufficient water and should be kept in disease-free conditions.
They should be fed in a scientific manner, with good quality and quantity of fodder.
• Stringent cleanliness and hygiene ©f both the cattle and the handle  are very important, during milking, storage and transport of milk and its products.
• Regular inspection and keeping proper records of ail the activities of’dairy is also mandatory.
• Regular visits of a veterinary doctor is necessary.
(ii) Poultry farm management includes the management of poultry which i& the class of domesticated fowl (birds) used for food or for their eggs. It includes chicken, ducks, Turkey and geese.
The poultry farm management includes following processes:
(a) Selection of disease-free and suitable poultry breeds
(b) Housing should be proper and safe.
(c) Proper food and water should be provided.
(d) Health care and hygiene of poultiy Mrds is mandettery
II. Bee-keeping or apiculture is the maintenance of hives of honeybees for the large
scale production of honey and beewax. The excessive demand of honey for its nutritive value and bees wax for cosmetics, etc., led to the large scale bee-keeping practices. Bee-keeping can be practiced in any area, here there a UT sufficient bee pastures of wild shrubs, fruit orchards and cultivated crops. It is not labour-intensive.
There are several species of honeybees, but most common species reared by bee-keepers is Apis indica.
The important points for successful bee-keeping are:
(i) Knowledge of the nature and habits of bees.
(ii) Selection of suitable location for keeping the beehives.
(iii) Catching and hiving of swarms (group of bees).
(iv) Management of beehives during different seasons.
(v) Handling and collection of honey and beeswax.
(vi) Keeping beehives in crop fields such as sunflower, Bnmsiea, apple andher, during
flowering period increases pollination efficiency and improves the yield, both crop yield and honey yield.
III. Fishery is an industry, which includes catching, processing or selling of fish, shellfish and other aquatic animals like prawn, crab, lobster, edible oysfegr, etc…
(i) The common freshwater fishes are catla, rohu and common carp.
(ii) Some of the marine fishes that are eaten include Hilsa, Sardines^ Mackerel and Pomfrets.
(iii) Fisheries provides income and employment to millions of fishermen and farmers, especially in coastal states in Indian economy.
(iv) To meet the increasing demand on fisheries, different techniques like aquaculture and pisciculture are applied.
(v) Blue revolution is the movement launched to increase the production of fish and fish products. It is being implemented in the same lines as green revolution.
IV. Animal breeding is an important part of animal husbandry. It aims to increase the yield of animals and improve the desirable qualities of produce.
(i) A breed is a group of animals related by descent and similar in most characters like general appearance, features, size, configuration, etc.
(ii) Breeding can be divided as given iii the chart below:

(a) Inbreeding refers to the mating between closely related individuals within the same breed for 4-6 generations.
The strategies for inbreeding are as follow:
• Identifying superior males and females of the same breed. They are mated in pairs.
• Evaluation of progeny obtained from the above mating to identify superior males and females among them.
• A superior female, in case of cattle, is the cow or buffalo that produces more milk per lactation. A superior male is bull, which gives rise to superior progeny as compared to other males.
Effects of inbreeding are:
• It is used to evolve a pureline (inbreeding increases homozygosity).
• Harmful recessive genes are exposed by inbreeding, which are then eliminated by the selection.
• Superior genes can be accumulated by inbreeding, the undesirable genes.
• Productivity of inbreed population is increased by selection at every step.
• Continued inbreeding reduces fertility and even productivity. This is called inbreeding depression.
• In this case, selected animals of the breeding population are mated with unrelated superior animals of the same breed. This helps to restore fertility and yield.
(b) Outbreeding is the breeding of unrelated animals, either of the same breed but not having common ancestors for 4-6 generations (out-crossing) or of different breeds (cross-breeding) or even different species (interspecific hybridisation).
It can be of the following types:
• Out-crossing is the practice of mating of animals, within the same breed, but having no common ancestors on either side of their pedigree up to 4-6 generations.
– The offspring of such mating is called an out-cross.
– It is done to increase milk production, growth rate in cattle’s beef, etc.
-A single out cross helps to overcome inbreeding depression.
• Cross-breeding refers to the mating of superior males of one breed with superior females of another breed.
– It helps in accumulate desirable qualities of two breeds into progeny.
– The progeny may be used for commercial production themselves.
– A new sheep breed, Hisardale is developed in Punjab by crossing Bikaneri Ewes and Marino Rams.
• Interspecific hybridisation refers to crossing between male and female animals of two different related species.
– Progeny may combine desirable features of both the parents.
– Progeny may be of considerable economic value.
– Example of interspecific hybridisation, is a Mule obtained by crossing a male donkey with a female horse.
(c) Artificial insemination is a method of controlled breeding. The semen from selected male parent is injected into the reproductive tract of selective female parent.
Its advantages are as follow:
– Helps to overcome problems related to normal mating.
– Semen can be stored and frozen for the later use.
– The disadvantage is its fairly low success rate.
V. Multiple Ovulation Embryo Transfer (MOET) Technology is a programme for herd improvement.
(i) The method includes following steps:
(a) A cow is administered with hormones FSH-like activity, to induce follicular maturation and superovulation.
(b) The cow produces 6-8 eggs instead of one egg, normally released per cycle.
(c) A cow is now mated with an elite bull or artificially inseminated.
(d) The fertilised eggs at 8-32 celled stages are recovered non-surgically and transferred to surrogate mothers.
(e) The genetic mother can again be used for superovulation.
(ii) This technology is used for cattle, sheep, rabbits, buffaloes, mares, etc.
(iii) High milk-yielding breeds of females and high quality (lean meat with less lipid) meat-yielding bulls have been bred successfully to increase the herd size in a short time.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Strategies Enhancement in Food Production – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

NCERT Exemplar Class 12 Maths Chapter 3 Matrices are part of NCERT Exemplar Class 12 Maths. Here we have given Exemplar Problems for Class 12 Maths Chapter 3 Matrices PDF.

NCERT Exemplar Class 12 Maths Chapter 3 Matrices

NCERT Exemplar Class 12 Maths Chapter 3 Matrices Solutions is given below.

Short Answer Type Questions

Long Answer Type Questions

Objective Type Questions

Fill In the Blanks Type Questions

True/False Type Questions
82. A matrix denotes a number.
Sol. False
A matrix is an ordered rectangular array of numbers of functions.
83. Matrices of any order can be added.
Sol. False
Two matrices are added, if they are of the same order.
84. Two matrices are equal if they have same number of rows and same number of columns.
Sol. False
If two matrices have same number of rows and same number of columns, we cannot say two matrices are equal as their corresponding elements may be different.
85. Matrices of different order cannot be subtracted.
Sol. True
Two matrices of same order can be subtracted
86. Matrix addition is associative as well as commutative.
Sol. True
Matrix addition is associative as well as commutative i.e.,
(A + B) + C = A + (B + C) and A + B = B + A, where A, B and C are matrices of same order.
87. Matrix multiplication is commutative.
Sol. False
If AB is defined, it is not necessary that BA is defined.
Also if AB and BA are defined, it not”necessary that they have same order. Further if AB and BA are defined and have same order, it is not necessary their corresponding elements are equal.
So, in general AB^BA
88. A square matrix where every element is unity is called an identity matrix.
Sol. False
Since, in an identity matrix, the diagonal elements are one and rest are all zero.
89. If A and B are two square matrices of the same order, then A + B = B + A.
Sol. True
Since, matrix addition is commutative i.e., A + B = B +A, where A and B are two square matrices.
90. If A and B are two matrices of the same order, then A-B = B-A.
Sol. False
A-B = -(B-A)
Thus A-B≠B-A
However when A – B = B – A
A-B = 0 or A =B

92. Transpose of a column matrix is a column matrix. False
Sol.Transpose of a column matrix is a row matrix.
93. If A and B are two square matrices of the same order, then AB = BA. False
Sol.For two square matrices of same order it is not always true that AB = BA.

More Resources for Class 12 Maths

• NCERT Exemplar
• NCERT Exemplar Class 12 Maths Solutions
• Class 12 Maths NCERT Solutions
• RD Sharma Class 12 Solutions
• Class 12 Maths Important Questions

We hope the NCERT Exemplar Class 12 Maths Chapter 3 Matrices help you. If you have any query regarding NCERT Exemplar Class 12 Maths Chapter 3 Matrices, drop a comment below and we will get back to you at the earliest.

The post NCERT Exemplar Class 12 Maths Chapter 3 Matrices appeared first on Learn CBSE.

Microbes in Human Welfare- CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Microbes in Household Products, Industrial Products and in Sewage Treatment:
1. Microbes are the major components of biological systems on the earth. They are present everywhere, i.e. in soil, water, air, inside our bodies and those of other animals and plants. They can also be found deep inside the geysers (thermal vents), deep in soil, under the layer of snow and in highly acidic environments.
(i) Microbes are so minute that they cannot be seen by naked eyes.
(ii) Various types of microbes are Protozoa, bacteria, fungi, virus, viroids and prions.
2. Microbes in household products The common products obtained by the use of microbes are curd, dough, toddy, cheese, etc.
(i) Curd is formed by adding bacteria such as Lactobacillus and others, commonly called as Lactic Acid Bacteria (LAB) in milk.
(a) A small amount of curd is added to the fresh milk as starter, which contain millions of LAB.
(b) LAB at suitable temperature multiply and convert milk into curd, which also improves nutritional quality by increasing vitamin-B₁₂ .
(c) During growth, LAB produce acids that coagulate and partially digest the milk proteins.
(d) LAB also checks disease causing microbes in the stomach.
(ii) Dough is formed by fermentation caused by bacteria.
(a) Dough used to make bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).
(b) Carbon dioxide released during the process of fermentation gives the fluffy appearance to dough.
(c) Dough is also used to make foods like idli, dosa, in addition to different types of breads.
(iii) Toddy is a traditional drink of Southern India. It is made by fermentation of sap
from palm trees by bacteria. A number of other drinks and food are also made by fermentation.
(iv) Cheese is made by partial degradation of milk using different microbes.
(a) Swiss cheese is made by a bacterium Propionibacterium shermanii. The large holes in this cheese are due to production of a large amount of C02 by the bacterium.
(b) Roquefort cheese is made by ripening with the fungi, Penicillium roqueforti to obtain a specific flavour.
(v) Microbes are also used to ferment fish, soybean and bamboo shoots to make food.
3. Microbes in industrial products have immense importance. The main industrial products obtained from microbes are fermented beverages, antibiotics, organic acids, alcohol, enzymes and bioactive molecules, etc. Production of these products on industrial scale needs growing microbes in very large vessels called fermentors.
(i) Fermented beverages are wine, beer, whisky, brandy and rum.
(a) These are obtained by fermenting malted cereals and fruit juices with Saccharomyces cerevisiae or brewer’s yeast to produce ethanol.
(b) Variety of alcoholic drink depend on the type of raw material used and the type of processing.
(c) Wine and beer are produced without distillation.
(d) Whisky, brandy and rum are produced by the distillation of the fermented broth.
(ii) Antibiotics (anti – against and bio – life) are chemical substances, which are
produced by some microbes and can kill or retard the growth of other (disease causing) microbes.
(a) Penicillin was the first antibiotic discovered by Alexander Fleming.
(b) Fleming discovered penicillin, while working on Staphylococcus bacteria. He observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found out that it was due to a chemical produced by the mould. He named it penicillin after the mould Penicillium notatum.
(c) Ernst Chain and Howard Florey discovered full potential of this antibiotic.
(d) Penicillin was extensively used during World War II. Fleming, Chain and Florey were awarded Nobel Prize in 1945 for this discovery.
(e) Antibiotics are used to cure deadly diseases such as plague, whooping cough, diphtheria and leprosy.
(iii) Organic acids are produced by the microbial metabolic action. Important ones are:
(a) Citric acid – Aspergillus niger (fungi)
(b) Acetic acid – Acetobacter aceti (bacteria)
(c) Butyric acid – Clostridium butylicum (bacteria)
(d) Lactic acid – Lactobacillus (bacteria)
(iv) Ethanol is produced by yeast (Saccharomyces cerevisiae) on commercial scale.
(v) Enzymes used in various fields are also produced by microbes as given below:
(a) Lipase used in detergent formulations and helps in removing oily stains from the laundry.
(b) Pectinase and protease used for clarifying bottled juices.
(c) Streptokinase produced by Streptococcus and modified by genetic engineering is used as a ‘Clot buster’ for removing clots from blood vessels of patients, who have undergone myocardial infarction leading to heart attack.
(vi) Bioactive molecules produced by microbes are:
(a) Cyclosporin-A produced by Trichodermapolysporum (fungus). It is used as immuno¬suppressive agent in organ-transplant patients.
(b) Statins produced by Monascus purpureus (yeast), is used as blood cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.
4. Microbes in sewage treatment play major role:
(i) Sewage is the municipal wastewater containing mainly human excreta. It contains
large quantity of organic matter and pathogenic microbes. Therefore, before
discharging into natural bodies, sewage needs to be made less polluting.
(ii) Sewage treatment is carried out in Sewage Treatment Plants (STPs) in following steps:
A. Primary treatment of sewage is:
(a) This step involves physical removal of large and small particles from sewage through filtration and sedimentation.
(b) Floating debris is removed by sequential filtration by passing through wire mesh screens.
(c) After this, the grit (soil and small pebbles) is removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant forms the primary effluent.
(d) The effluent is taken for secondary treatment.
B. Secondary treatment (biological treatment) of sewage is done on primary effluent.
(a) Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.
(b) This allows vigorous growth of useful aerobic microbes into floes (masses of bacteria associated with fungal filaments to form mesh-like structures).
(c) These microbes consume major part of organic matter in the effluent, while growing. This reduces the Biochemical Oxygen Demand (BOD) of the effluent.
(d) When BOD of sewage gets reduced, it is passed into settling tank.
(e) The bacterial floes settle in tank and the sediment is called activated sludge.
(f) A small amount of activated sludge is pumped back into the aeration tank to serve as inoculum.
(g) The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
(h) In sludge digesters, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this process, bacteria produce a mixture of gases, such as methane, hydrogen sulphide and the carbon dioxide, which form biogas (can be used as source of energy).
(i) The effluent from secondary treatment is generally released into natural water bodies.
(iii) Biochemical Oxygen Demand (BOD) refers to the amount of the oxygen that would be consumed if all the organic matter in one litre of water is oxidised by bacteria.
(a) BOD measures the rate of uptake of oxygen by the microbes in a sample of water. Indirectly, it measures the organic matter present in the water.
(b) More BOD of waste water indicates more polluting potential.
(iv) Due to the increasing urbanisation, sewage is being produced in larger quantities. So, the untreated sewage is often discharged directly into rivers leading to their pollution and increase in water borne diseases.
(v) The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan to save the major rivers of our country from pollution.
Under these plans, it is proposed to build a large number of sewage treatment plants so that only treated sewage can be discharged in the rivers.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Microbes in Human Welfare- CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Biotechnology: Principles and Processes – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Principles of Biotechnology and Tools of Recombination DNA Technology:
1. Biotechnology can be defined as the use of microorganisms, plants or animal cells or their components to produce products and processes useful to humans. According to the European Federation of Biotechnology (EFB), biotechnology is the integration of natural science and organisms, cells, parts thereof and molecular analogues for products and services. The term ‘Biotechnology’ was coined by Karl Ereky in 1919.
2. Principles of biotechnology are based on the concept of the following techniques:
(i) Genetic engineering is the technique to alter the chemistry of genetic material (DNA/RNA), to introduce these into another organisms and thus, change the phenotype of the host organism.
(ii) Adequate maintenance of sterile conditions to support growth of only the desired microbes/eukaryotic cells in large quantities for the manufacture of biotechnological products like antibiotics, vaccines, enzymes, etc.
3. The techniques of genetic engineering include the following:
(i) Creation of recombinant DNA by combining desired genes.
(ii) Gene transfer.
(iii) Maintenance of DNA in host and gene cloning.
The basic steps in genetic engineering can be summarised as:
(i) Identification of DNA with desirable genes.
(ii) Introduction of the identified DNA into the host.
(iii) Maintenance of introduced DNA in the host hrtd transfer of the DNA to its progeny.
4. Construction of First Artificial Recombinant DNA
(i) It was achieved by linking a gene encoding antibiotic resistance with a native plasmid (an autonomously replicating circular extrachromosomal DNA) of Salmonella typhimurium.
(ii) Stanley Cohen and Herbert Boyer accomplished this in 1972.
(iii) They isolated the antibiotic resistance gene by cutting out a piece of DNA from a plasmid.
(iv) The cutting of DNA at specific locations was carried out by molecular scissors, i.e. restriction enzymes.
(v) The cut piece of DNA was then linked to the plasmid DNA with the enzyme DNA ligase. The plasmid DNA acts as vectors to transfer the piece of DNA attached to it.
(vi) When this DNA is transferred into E. coli, it could replicate using the new host’s DNA polymerase enzyme and make multiple copies.
(vii) This ability to multiply copies of antibiotic resistance gene in E. coli was called cloning of antibiotic resistance gene in E. coli.
5. Tools of recombinant DNA technology are as follow:
(i) Restriction enzymes    (ii) Polymerase enzymes
(iii) Ligases                         (iv) Vectors
(v) Competent host organism.
6. Restriction enzymes or ‘molecular scissors’ are used for cutting DNA.
(i) Two enzymes from E. coli that were responsible for restricting the growth of bacteriophage were isolated in 1963, one of them added methyl group to DNA and the other cut DNA into segments. The later was called restriction endonuclease.
(ii) The first restriction endonuclease Hind II was isolated by Smith Wilcox and Kelley (1968). They found that it always cut DNA molecules at a particular point by recognising a specific sequence of six base pairs known as recognition sequence.
(iii) Besides Hind II, more than 900 restriction enzymes have been isolated now, from over 230 strains of bacteria, each of which recognise different recognition sequences.
(iv) Naming of Restriction Enzymes
(a) The first letter is derived from the genus name and the next two letters from the species name of the prokaryotic cell from which enzymes are extracted.
(b) The Roman numbers after name show the order in which the enzymes were isolated from the bacterial strain.
For example, Eco RI comes from Escherichia coli RY13 and Eco RII comes from E. coli R 245, etc.
(v) Restriction enzymes belong to a class of enzymes called nucleases.
Nucleases are of two types:
Exonucleases They remove nucleotides from the ends.
Endonucleases They cut at specific positions within the DNA.
(a) Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA.
(b) Palindrome in DNA is a. sequence of base pairs that reads same on the two strands when orientation of reading is kept same.
For example, the following sequences reads the same on the two strands in 5′ -> 3′ direction as well as 3′ -> 5′ direction.
5′ — GAATTC — 3′
3′ — CTTAAG — 5′
(vi) Mechanism of Action of Restriction Enzymes

(a) Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands.
(b) This leaves single stranded portions at the ends.
(c) There are overhanging stretches called sticky ends on each strands as given in above figure. These are named so, because they form hydrogen bonds with their complementary cut counterparts.
(d) The stickiness of the ends facilitates the action of the enzyme DNA ligase.
(e) Restriction endonucleases are used in genetic engineering to form recombinant molecules of DNA, which are composed of DNA from different sources/genomes.
(f) These sticky ends are complementary to each other when cut by same restriction enzyme, therefore can be joined together (end-to-end) using DNA ligases.
7. Separation and Isolation of DNA Fragments
(i) The cutting of DNA by restriction’endonucleases results in the fragments of DNA.
(ii) The technique, which separates DNA fragments based on their size is called gel electrophoresis.
(iii) DNA fragments are negatively charged molecules. They can be separated by forcing them to move towards the anode under an electric field through a medium/matrix.
(iv) The most common medium used is agarose, a natural polymer extracted from sea weeds.
(v) The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. The smaller the fragment size, the farther it moves.

(vi) The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation.
(vii) The DNA fragments can be seen as bright orange coloured bands. These separated bands are cut out from the agarose gel and extracted from the gel piece. This is called elution.
(viii) The purified DNA fragments can be used in constructing recombinant DNA by joining them with cloning vectors.
8. Cloning vectors are the DNA molecules that can carry a foreign DNA segment into the host cell.
(i) The vectors used in recombinant DNA technology can be:
(a) Plasmids Autonomously replicating circular extra-chromosomal DNA.
(b) Bacteriophages Viruses infecting bacteria.
(c) Cosmids Hybrid vectors derived from plasmids which contain cos site of X phage.
(ii) Copy number can be defined as the number of copies of vectors present in a cell.
(iii) Bacteriophages have high number per cell, so their copy number is also high in genome.
(iv) Plasmids have only one or two copies per cell.
(v) Copy number can vary from 1-100 or more than 100 copies per cell.
(vi) If an alien piece of DNA is linked with bacteriophage or plasmid DNA, its number can be multiplied equal to the copy number of the plasmid or bacteriophage.
(vii) Features Required to Facilitate Cloning into Vector
(a) Origin of replication (Ori)     (b) Selectable marker
(c) Cloning sites                             (d) Vectors for cloning genes in plants and animals.
(a) Origin of replication (Ori) is a sequence from where replication starts.
• Any piece of DNA when linked to this sequence can be made to replicate within the host cells.
The sequence is also responsible for controlling the copy number of the linked DNA.
(ii) Selectable marker helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
• Transformation is a process through which a piece of DNA is introduced in a host bacterium.
• The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc, are some useful selectable markers for E. coli.

• Ligation of alien DNA is carried out at a restriction site present in one of the twoantibiotic resistance genes. Example is ligating a foreign DNA at the Bam HI site of tetracycline resistance gene in the vector pBR322.
-» The recombinant plasmids will lose tetracycline resistance due to insertion of foreign DNA. But, it still can be selected out from non-recombinant ones by plating the transformants on ampicillin containing medium.
-» The transformants growing on ampicillin containing medium are then transferred on a medium containing tetracycline.
-» The recombinants will grow in ampicillin containing medium but not on that containing tetracycline.
The non-recombinants will grow on the medium containing both the antibiotics.
In this example, one antibiotic resistance gene helps in selecting the transformants whereas, the other antibiotic resistance gene gets ‘inactivated due to insertion’ of alien DNA and helps in selection of recombinants.
* Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure, so alternative selectable markers are developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.
-» In this method, a recombinant DNA is inserted within the coding sequence of an enzyme J3-galactosidase.
-» This results into inactivation of the enzyme, P-galactosidase (insertional inactivation).
-> The bacterial colonies whose plasmids do not have an insert, produce blue colour, but others do not produce any colour, when grown on a chromogenic substrate.
(c) Cloning sites are required to link the alien DNA with the vector.
• The vector requires very few or single recognition sites for the commonly used restriction enzymes.
• The presence of more than one recognition sites within the vector will generate several fragments leading to complication in gene cloning.
(d) Vectors for cloning genes in plants and animals are many which are used to clone genes in plants and animals.
• In plants, the Tumour inducing (Ti) plasmid of Agrobacterium tumefaciens is used as a cloning vector.
-» Agrobacterium tumefaciens is a pathogen of several dicot plants.
-» It delivers a piece of DNA known as T-DNA in the Ti plasmid which 1 transforms normal plant cells into tumour cells to produce chemicals
required by pathogens.
• Retrovirus, adenovirus, papillomavirus are also now used as cloning vectors in animals because of their ability to transform normal cells into cancerous cells.
9. Competent host organism (for transformation with recombinant DNA) is required because DNA being a hydrophilic molecule, cannot pass through cell membranes, Hence, the bacteria should be made competent to accept the DNA molecules,
(i) Competency is the ability of a cell to take up foreign DNA.
(ii) Methods to make a cell competent are as follow.
(a) Chemical method In this method, the cell is treated with a specific concentration of | a divalent cation such as calcium to increase pore size in cell wall.
The cells are then incubated with recombinant DNA on ice, followed by placing them briefly at 42°C and then putting it back on ice. This is called heat shock treatment.
• This enables the bacteria to take up the recombinant DNA.
(b) Physical methods In this method, a recombinant DNA is directly injected into the nucleus of an animal cell by microinjection method.
• In plants, cells are bombarded with high velocity microparticles of gold or tungsten coated with DNA called as biolistics or gene gun method.
(c) Disarmed pathogen vectors when allowed to infect the cell, transfer the recombinant
DNA into the host.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Biotechnology: Principles and Processes – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Biotechnology and Its Applications- CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Biotechnological Applications in Agriculture and Medicine:
1. Biotechnology essentially deals with industrial scale production of biopharmaceuticals and biologicals. The applications of biotechnology include therapeutics, diagnostics, genetically modified crops for agriculture, processed food, bioremediation, waste treatment and energy production.
2. Biotechnology have the following three critical research areas:
(i) To provide the best catalyst in the form of improved organism, usually a microbe or pure enzyme.
(ii) To create optimal conditions through engineering for a catalyst to act.
(iii) Downstream processing technologies to purify the protein/organic compound.
3. Biotechnological Applications in Agriculture
(i) Biotechnology applications in agriculture involve following three options:
(a) Agrochemical based agriculture.
(b) Organic agriculture.
(c) Genetically engineered crop-based agriculture.
(ii) Green revolution increased food production due to the use of:
(a) Improved crop varieties.
(b) Agrochemicals (fertilisers and pesticides).
(c) Better management practices.
(iii) Genetically Modified Organisms (GMOs) are plants, animals, bacteria and fungi whose genes have been altered by manipulation.
(iv) Genetic modification in plants have lead to following:
(a) Crops became more tolerant to abiotic stresses, such as cold, drought, salt, heat, etc.
(b) Dependence on chemical pesticides reduced, i.e. pest resistant crops.
(c) Post harvest losses reduced.
(d) Efficiency of mineral usage increased in plants (preventing loss of soil fertility).
(e) Nutritional value of food is enhanced, e.g. vitamin-A enriched rice.
(f) Tailor made plants are created by using GM plants to supply alternative resources to industries, in the form of starches, fuels and pharmaceuticals.
(v) Some of the applications of biotechnology in agriculture are the production of pest resistant plants, which decrease the amount of pesticide used.
Bt toxin is produced by a bacterium and expressed in plants to provide resistance to insects, in effect created a biopesticide, e.g. Bt cotton, Bt corn, golden rice, tomato, potato and soybean, etc.
(a) Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Bt is short form,).
(b) This bacterium produces proteins that kill certain insects such as lepidopterans (tobacco, budworm and armyworm), coleopterans (beetles) and dipterans (flies and mosquitoes).
(c) B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.
(d) Bt toxin protein exist as inactive protoxins, but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut, which solublise the crystals.
(e) The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis leading to death of an insect.
(f) Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into several crop plants as cotton.
(g) Most Bt toxins are insect-group specific. The toxin is coded by a gene named cry, e.g. the proteins encoded by the genes cry IAc and cry IIAb control the cotton bollworms and cry IAb controls corn borer.
(vi) Pest resistant plants are developed by using biotechnological processes.
(a) A nematode Meloidogyne incognita infects the roots of tobacco plants, which reduces the production of tobacco.
(b) RNA interference (RNAi) process is used for cellular defence. It involves silencing of a specific mRNA due to a complementary dsRNA. It occurs in all eukaryotic organisms as a method of cellular defense.
(c) dsRNA binds and prevents translation of the mRNA (silencing).
(d) The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
(e) Agrobacterium vectors are used to introduce nematode-specific genes into the host plant. It produces both sense and anti-sense RNA in the host cells.
(f) These two RNAs are complementary to each other and forms a double stranded RNA (dsRNA) that initiate RNAi and hence, silence the specific mRNA of the nematode.
(g) The parasite cannot survive in transgenic host, expressing specific interfering RNA. The transgenic plant thus, gets itself protected from the parasite.
4. Biotechnological applications in medicine have made immense impact in the area of healthcare by enabling the mass production of safe and more effective therapeutic drugs.
(a) The recombinant therapeutics do not induce unwanted immunological responses as in case of similar products isolated from non-human sources.
(b) Currently, about 30 recombinant therapeutics have been approved for human use over the world. In India, 12 of these are presently being marketed.
I. Genetically engineered insulin leads to sufficient availability of insulin for the management of adult-onset diabetes.
(a) Insulin used for diabetes was earlier extracted from the pancreas of slaughtered cattle and pigs. This caused allergy or other reactions in some patients.
(b) Insulin consists of two short polypeptide chains, i.e. chain-A and B, linked together by disulphide bridges.
Maturation of proinsulin into insulin (simplified)
(c) In mammals, insulin is synthesised as a prohormone (needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C-peptide.

(d) C-peptide is not present in the mature insulin $nd is removed during maturationinto insulin. Thus, the main challenge for the production of insulin using rDNA techniques was getting insulin assembled into a mature form.
(e) Eli Lilly an American company in 1983, prepared two DNA sequences corresponding to A and B-chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains. Chains-A and B were produced separately, extracted and combined by creating disulphide bonds to form human insulin.
II. Production of vaccines through genetic engineering such vaccines are called recombinant vaccines also called ‘subunit vaccines’ or ‘second generation vaccines’, e.g hepatitis-B. These are of two types:
(a) Protein vaccines use of specific protein produced by rDNA in vaccine.
(b) DNA vaccines use of genetically engineered DNA to be injected as vaccine to produce an immunological response.
Hepatitis vaccine contains the viral envelope protein, hepatitis-B surface antigen (HB8 Ag). This gene is isolated from yeast vectors.
Some protein coding genes isolated from pathogens are also incorporated and expressed in plants produce antigens and are also called edible vaccines.
III. Gene therapy is a collection of methods that allows correction of gene defects, diagnosed in a child or embryo.
(a) Genes are inserted into a person’s cells and tissues to treat a disease.
(b) Correction of a genetic defect involves delivery of a normal gene into the individual or embryo to take over the function and compensate for the non-functional gene.
(c) First gene therapy was given to a four year old girl with Adenosine Deaminase (ADA) deficiency by M Blease and WF Andresco in 1990s.
• ADA is caused due to the deletion of the gene for adenosine deaminase.
• In some children, ADA deficiency can be cured by bone marrow transplantation and enzyme replacement therapy, but they are not completely curable.
(d) Steps involved are as follows:
• In first step of gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
• A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient.
• As these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes.
• If the gene isolated from bone marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.
• Some other’diseases that can be treated by gene therapy are haemophilia, cystic fibrosis, Parkinson’s disease, etc.
IV. Molecular diagnosis helps to solve the problem of early diagnosis and treatment of diseases.
(a) Using conventional methods of diagnosis (serum and urine analysis), early detection of diseases is not possible.
(b) To overcome this problem, some molecular diagnosis techniques were developed that provide early detection of diseases. These are as follows:
• Polymerase Chain Reaction (PCR) helps in early detection of diseases or pathogens by the amplification of their nucleic acid.
Low concentration of pathogens (bacteria, viruses, etc) in the blood does not allow its detection.
PCR can amplify nucleic acids of such pathogens even when their concentration is very low.
PCR technique can be used for detecting HIV in suspected AIDS patients, genetic mutation in suspected cancer patients and in identifying genetic disorders.
• Recombinant DNA technology is a modern molecular diagnostic technique. It is done in the following steps:
A single stranded DNA or RNA tagged with a radioactive molecule called probe, is allowed to hybridise to its complementary DNA in a clone of cells.
The cells are then detected by autoradiography.
The clone having mutated gene will not appear on the photographic film, because the probe will not have complementarity with the mutated gene.
• Enzyme Linked Immuno Sorbent Assay (ELISA) is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc) or by detecting the antibodies synthesised against the pathogen.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Biotechnology and Its Applications- CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Ecosystem – CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Ecosystem—Structure and Function,- Productivity and Decomposition:
1. An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. The word ‘Ecosystem’ was coined by Sir AG Tansley (1935).
2. The size of an ecosystem varies greatly from a small pond to a large forest or a sea.
3. Ecosystem can be grouped into two main categories:
(i) Terrestrial ecosystem Forest, grassland, desert, etc.
(ii) Aquatic ecosystem Pond, lake, river, wetland, estuary, etc.
4. Crop fields and an aquarium are considered as man-made ecosystems.
5. Structure and Function of Ecosystem
(i) Each ecosystem consists of biotic (autotrophs, herbivores and carnivores) and abiotic components and their interactions with each other results in a physical structure, that is characteristic for each type of ecosystem.
(ii) Identification and enumeration of plant and animal species of an ecosystem gives its specific composition.
(iiii) Vertical distribution of different species occupying different levels is called stratification. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.
(iv) Major functional components of an ecosystem are:
(a) Productivity (b) Decomposition
(c) Energy flow (d) Nutrient cycling
(v) Let us understand these components in a pond ecosystem:
(a) A pond is a shallow water body in which all the above mentioned basic structural and functional components are present.
(b) Abiotic components are water with all the dissolved inorganic and organic materials and soil deposited at the bottom.
(c) Autotrophic components are phytoplanktons, some algae and the floating, submerged and marginal plants found at the edges.
(d) Consumers are zooplanktons, which are free swimming and bottom dwellers.
(e) Decomposers are the fungi, bacteria and flagellates found abundantly in the bottom.
(f) Functioning of pond ecosystem occurs in following steps:
* Autotrophs convert inorganic material into organic material with the help of solar energy.
* Heterotrophs consume autotrophs.
* Decomposers decompose dead organic materials and mineralise it to release them back for reuse by the autotrophs.
* The above events are repeated again and again.
Unidirectional movement of energy occur towards the higher trophic levels and lost in the form of heat to the environment.
6. Productivity is the rate of biomass production. It is expressed in g^-2 yr^-1 or (kcal m^-2) yr^-1.
(i) The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis is called primary production.
(ii) The primary productivity can be divided into:
(a) Gross Primary Productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration.
(b) Net Primary Productivity (NPP) is gross primary productivity minus respiratory losses (R).
NPP = GPP – R
NPP is the available biomass for the consumption to heterotrophs, i.e. herbivores and decomposers.
(iii) Secondary productivity is defined as the rate of formation of new organic matter by . consumers.
(iv) Primary productivity of an ecosystem depends on:
(a) Plant species inhabiting a particular area.
(b) Availability of nutrients.
(c) Photosynthetic capacity of plants.
(d) Variety of environmental factors.
(v) Annual net primary productivity of the whole biosphere is about 170 billion tons (dry weight) of organic matter. Of this, despite of occupying about 70% of the surface of earth, the productivity of the oceans are only 55 billion tons.
7. Decomposition is the process in which decomposers breakdown complex organic matter into inorganic substances like carbon dioxide, water and nutrients.
(i) The raw materials called detritus are dead plant remains such as leaves, barks, flowers and dead remains of animals, including faecal matter.
(ii) Process of decomposition occurs in the following steps:
(a) Fragmentation is the breakdown of detritus into smaller particles by detritivores, e.g. earthworm.
(b) Leaching is the process by which water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
(c) Catabolism is the process of degradation of detritus into simple inorganic substances by bacterial and fungal enzymes.
(d) Humification is the process of accumulation of a dark coloured amorphous substance called humus. It is highly resistant to microbial action, undergoes decomposition at an extremely slow rate and serves as a reservoir of nutrients.
(e) Mineralisation is the process by which humus is further degraded by some microbes to release inorganic substances.

Leaves partially consumed by decomposers such as fungi and bacteria.
They begin to lose form and become litter.
Diagrammatic representation of decomposition cycle in a terrestrial ecosystem
(iii) Decomposition rate depends on
(a) Oxygen availability
(b) Chemical composition of detritus
(c) Climatic factors
(d) Temperature and soil moisture
(iv) Decomposition rate is slower, if detritus is rich in lignin and chitin. It is quicker, if detritus is rich in nitrogen and water soluble substances like sugars.
(v) Warm and moist environment speeds up decomposition, whereas low temperature and anaerobiosis inhibits decomposition and causes the formation of organic materials.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Ecosystem – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

Organisms and Populations- CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Organisms and Its Environment:
1. Ecology is the branch of biology, which studies the interactions among organisms and their physical (abiotic) environment.
2. The subject ecology is basically concerned with four levels of biological organisation.
These are given below:
(i) Organism Living component of the environment at individual level and is basic unit of ecological hierarchy.
(ii) Population The sum total of all individuals of a species in a specific geographical area.
(iii) Communities Assemblage of all the populations of different species present in an area that interact among themselves.
(iv) Biome It is a large unit, which consists of a major vegetation type, associated fauna in a particular climatic zone. Tropical rainforest, deciduous forest, sea coast, deserts, etc., are the major biomes of India.
Note: Other important terms used in ecology are:
Ecosystem Represents, the organisms and their environment in a particular area.
Habitat It refers to a specific place or locality delimited by a combination of factors, physical features and barriers where a community dwells.
Niche The ecological niche of an organism represents the physical space occupied by it, the resources it utilises and its functional role in the ecological system.
Biosphere The surface of earth with all life forms, i.e. union of all ecosystems. It is a highly ordered system.
3. Environment Ecology at organism level deals with how different organisms are adapted to their environment in terms of their survival and reproduction.
(0 Different biomes are formed due to: .
(a) annual variations in the intensity and duration of temperature.
(b) annual variations in precipitation.
The major biomes of the world are desert, grassland, rainforest and tundra.

(ii) Regional and local variations within each biome lead to the formation of a wide variety of habitats.
(iii) Life on earth exists in favourable habitats as well as in extreme and harsh habitats like scorching Rajasthan desert, rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs and stinking compost pits and even in our intestine.
(iv) The biotic components of a habitat are pathogens, parasites, predators and competitors of the organism with which they interact constantly.
(v) The key abiotic elements that lead to variations in habitats are:
(a) Temperature    (b) Water
(c) Light                  (d) Soil.
4. Major abiotic factors are:
(i) Temperature is the major abiotic factor, which is most ecologically relevant.
(a) There is seasonal variation in average temperature of land.
(b) It decreases progressively from the equator to the poles and from plain areas to the mountains.
(c) The range of temperature varies from sub-zero levels in polar areas to >50°C at high altitude in tropical deserts during summer.
(d) The temperature affects the kinetics of body enzymes and thus, the basal metabolism and other physiological functions of the organism.
(e) Based on tolerance of temperature range, organisms can be divided as:
Euiythennal These can tolerate a wide range of temperature.
Stenothermal These can tolerate a narrow range of temperature.
(ii) Water is the next major important factor without which life cannot exist.
(a) The productivity and distribution of plants in an environment depends on amount of water available.
(b) For aquatic organisms, the quality (chemical composition and pH) of water is important.
(c) Salinity refers to salt concentration (measured in parts per thousand) of water. Salt concentration is less than 5 in land water, 30-35 in sea and more than 100 in some hyper saline lagoons.
(d) Based on tolerance of range of salinity, organisms can be grouped as:
Euryhaline Organisms, which can tolerate a narrow range of salinity.
Stenohaline Organisms, which can tolerate a narrow range of salinity.
(e) Many freshwater animals cannot live for long in seawater and vice versa because of the osmotic problems they would face.
(iii) Light is an essential factor for the process of photosynthesis performed by autotrophs.
(a) Oxygen is released during photosynthesis.
(b) Many small plants like herbs and shrubs can perform photosynthesis under very low light conditions because they are overshadowed by tall, canopied trees.
(c) Most of the plants also depend on sunlight to meet their photoperiodic requirement for flowering.
(d) Light is also important for many animals as they use the diurnal and seasonal variations in light intensity and difration (photoperiod) as cues for timing their foraging, migratory and reproductive activities.
(e) The UV component of solar radiation is harmful to many organisms. All the colour components of the visible spectrum are not available for marine plants living at different depths of the ocean.
(iv) Soil The nature and properties of soil vary from place to place. It depends on climate, weathering process and whether soil is transported or sedimentary and how its development occurred.
(a) The soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils.
(b) The characteristics like pH, mineral composition and topography determine the vegetation of an area.
(c) This in turn dictates the type of animals supported.
5. Responses to abiotic factors determines how organisms can cope or manage with stressful conditions of the habitat.
(i) During the course of millions of years of their existence, many species would have evolved a relatively constant internal (within the body) environment that permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the overall fitness of the species.
(ii) The organisms should try to maintain the constancy of its internal environment,
i. e. homeostasis, despite of varying external environmental conditions that tend to upset its homeostasis.
(iii) Human beings can maintain their homeostasis by using artificial means
(air conditioner in summer and heater in winter).
(iv) Ways by which other organisms can cope up with environmental changes are given below:
Regulate
(a) Some organisms maintain homeostasis by physiological and sometimes behavioural means.
(b) All birds and mammals and few lower vertebrates and invertebrates are capable of thermoregulation and osmoregulation.
(c) In mammals, during summer, sweating occurs profusely and the evaporation brings down temperature of the body.
(d) In mammals, during winter, shivering occurs which is a kind of exercise that produces heat and raises the body temperature.
(e) Plants, on the other hand, do not have such mechanisms to maintain their internal temperature.
Conform
(a) About 99% of animals and almost all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature.
(b) In aquatic organisms, the osmotic concentration of the body fluids change with that of the osmotic concentration of the ambient water. These animals and plants are called conformers.
(c) Thermoregulation is energetically expensive for many organisms. This is specially true for small animals like shrews and humming birds.
Heat loss or gain is a function of surface area. Since, smal^animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; they have to expend much energy to generate body heat through metabolism. This is the reason that very small animals are rarely found in polar regions.
(d) It can be concluded that during the course of evolution, some species have evolved the ability to regulate but only over a limited range of environmental conditions, beyond which they simply conform.
Migrate
It is the temporary movement from a stressful habitat to a more hospitable area and
return, when the stressful period is over.
(a) Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas.
(b) Every winter the famous Keolado National Park in Bharatpur (Rajasthan) hosts, thousands of migratory birds coming from Siberia and other extremely cold Northern regions every winter.
Suspend
(a) Under unfavourable conditions bacteria, fungi and lower plants slow down their metabolic rate and forms a thick-walled spore to overcome stressful conditions. These spores germinate under onset of suitable environment.
(b) In higher plants, seeds and some other reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(c) Some animals, which fail to migrate might avoid the stress by escaping in time. For example, Bear undergoes hibernation during winter.
(d) Some snails and fish undergo aestivation to avoid summer related problems.
(e) During unfavourable conditions, many zooplanktons in lakes and ponds enter diapause (a stage of suspended development).

6. Adaptation is any attribute of an organism, i.e. morphological, physiological or behavioural, that enables the organism to survive and reproduce in its habitat. Many adaptations have evolved over a long evolutionary time and are genetically fixed.
Some examples of adaptations are:
(i) Adaptations in kangaroo rat
(a) The kangaroo rat in North American deserts is capable of meeting all its water requirements by internal oxidation of fat (water is a byproduct) in the absence of water.
(b) It can concentrate its urine, so that minimal volume of water is used to expel excretory products.
(ii) Adaptations in desert plants
(a) Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpiration.
(b) They have special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time.
(c) Some desert plants like Opuntia, have no leaves. They are reduced to spines and photosynthesis occurs in flattened stems.
(iii) Adaptations in mammals
(a) Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. This is called Allen’s rule.
(b) In polar seas, aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.
(iv) Adaptations at high altitudes in humans
(a) At high altitude places like Rohtang Pass near Manali (> 3500 m) and Mansarovar, in China occupied Tibet, people suffer from altitude sickness.
(b) Its symptoms are nausea, fatigue and heart palpitations.
(c) This is because at low atmospheric pressure of high altitudes, body does not get enough oxygen.
(d) The relief occurs gradually due to acclimatisation.
(e) The body cope up with this low oxygen stress by
• Increasing red blood cells production.
• Decreasing the binding affinity of haemoglobin.
• Increasing the breathing rate.
(v) Adaptations in desert lizards (Behavioural response)
(a) They absorb heat from the sun when their body temperature drops below the comfort zone.
(b) They move into shade when the ambient temperature starts increasing.
(c) Some species burrow into the soil and escape from the above ground heat.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Organisms and Populations- CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

NCERT Exemplar Class 12 Maths Chapter 4 Determinants are part of NCERT Exemplar Class 12 Maths. Here we have given Exemplar Problems for Class 12 Maths Chapter 4 Determinants PDF.

NCERT Exemplar Class 12 Maths Chapter 4 Determinants

NCERT Exemplar Class 12 Maths Chapter 4 Determinants Solutions is given below.

Short Answer Type Questions
Direction for Exercises 1 to 6: Using the properties of determinants,

Long Answer Type Questions

Objective Type Questions

Fill In the Blanks Type Questions

True/False Type Questions

More Resources for Class 12 Maths

• NCERT Exemplar
• NCERT Exemplar Class 12 Maths Solutions
• Class 12 Maths NCERT Solutions
• RD Sharma Class 12 Solutions
• Class 12 Maths Important Questions

We hope the NCERT Exemplar Class 12 Maths Chapter 4 Determinants help you. If you have any query regarding NCERT Exemplar Class 12 Maths Chapter 4 Determinants, drop a comment below and we will get back to you at the earliest.

The post NCERT Exemplar Class 12 Maths Chapter 4 Determinants appeared first on Learn CBSE.

Biodiversity and Conservation – CBSE Notes for Class 12 Biology

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

Biodiversity:
1. Biodiversity can be defined as the occurrence of different types of genes, gene pools, species, habitats and ecosystem in a given region.
(i) The term biodiversity was given by a socio biologist Edward Wilson to describe the combined diversity at all the levels of biological organisation.
(ii) There are more than 20,000 species of ants, 3,00,000 species of beetles, 28,000 species of fishes and nearly 20,000 species of orchids.
(iii) Biodiversity can be divided into following three levels:
(a) Genetic diversity is the diversity at the genetic level.
• It enables a population to adapt to its environment.
• India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
Example, Genetic variation in the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces.
(b) Species diversity is diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
(c) Ecological diversity is the diversity at ecosystem level. For example, India with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows has a greater ecosystem diversity.
2. Global species diversity means total species present on the earth.
(i) According to IUCN (2004) the total number of plant and animal species is slightly more than 1.5 million.
(ii) For many taxonomic groups, species inventories are more complete in temperate than in tropical countries.
(iii) A more conservative and scientifically sound estimate by Robert May, places the global species diversity at about 7 million.
(iv) More than 70% of all the species recorded are animals, while plants comprise no more than 22% of the total.
(v) Among animals, insects are most species rich-taxonomic group, making about 70% of the total. It means, out of every 10 animals, 7 are insects on the earth.
3. Biodiversity in India
(i) Although India has only 2.4% of the world’s land area, its share of the global species diversity is 8.1%. This makes India one of the 12 megadiversity countries of the world.
(ii) About 45,000 species of plants and twice as many of animals have been recorded from India.

(iii) According to May’s global estimates, only 22% of the total species have been recorded so far. If this proportion.is applied to India’s diversity figures, there may be probably more than 1,00,000 plant species and more than 3,00,000 animal species yet to be discovered and described.
4. Patterns of biodiversity indicate that the biodiversity is not uniform throughout the world because it is affected by:
(i) Latitudinal gradients demonstrates the decrease in species diversity as we move away from the equator towards the poles.
(a) Tropics (latitudinal range of 23.5°N to 23.5°S) harbour more species than temperate or polar areas.
(b) Example, Colombia located near the equator has around 1,400 species of birds, while New York at 41°N has 105 species and greenland at 71°N has only 56 species.
(c) Studies indicate that the tropical areas have more biodiversity.
For example,
• India with much of its land area in the tropical latitudes, has more than 1,200 species of birds.
• A tropical forest in equator has up to 10 times as many species of vascular plants as a forest of equal area in a temperate region like the midwest of USA.
• Tropical Amazonian rainforest in South America has the greatest biodiversity on earth. It homes 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals, 427 of amphibians, 378 of reptiles and of more than 1,25,000 invertebrates.
• Scientists estimate that in these rainforests, there might be at least 2 million insect species waiting to be discovered and named.
(d) Reasons for Greater Biodiversity in Tropics
• Speciation is generally a function of time. The temperate regions were subjected to frequent glaciation in the past, but the tropics have remained undisturbed and hence, had evolved more species diversity.
• Tropical environments, unlike temperates are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
• More solar energy is available in tropics, which contributes to higher productivity, this in turn might contribute indirectly to greater diversity.
(ii) Species-Area Relationships
(a) Alexander Von Humboldt, a German naturalist and geographer observed that within a region, species richness increased with increasing explored area, but up to a limit.
(b) In fact, the relation between species richness and area for a wide variety of taxa (like angiosperm plants, birds, bats and freshwater fishes) turn out to be rectangular hyperbola.

(c) On a logarithmic scale, the relationship is a straight line as given in the following equation
log S = log C + Z log A where, S = Species richness, A=Area
C = Y-intercept, Z = Slope of the line (regression coefficient)
(d) The value of Z lies in the range of 0.1-0.2 regardless of taxonomic group or the region.
(e) If we analyse the species-area relationship among very large areas like the entire continents, the slope of the line will be much steeper, i.e. Z values in the range of 0.6-1.2. For example, for fruit eating birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.
5. Importance of Species Diversity to the Ecosystem
(i) According to ecologists, communities with more species tend to be more stable than those with less species.
(ii) Attributes of a stable community are
(a) It should not show too much variation in productivity from year to year.
(b) It must be either resistant or resilient to occasional disturbances (natural or man made).
(c) It must be resistant to invasions by alien species.
(iii) David Tilman’s longterm experiments on ecosystem found that plots with more species showed less year-to-year variation in total biomass. He also showed that increased diversity contributed to higher productivity.
(iv) It is not clear how species richness contributes to the well-being of an ecosystem. But, it is enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the survival of the human race on this planet.
(v) Paul Ehrlich through his rivet popper hypothesis tried to explain the importance of biodiversity for the survival of species.
(a) The hypothesis assumes the ecosystem to be an airplane and the species to be the rivets joining all parts together.
(b) If every passenger pops a rivet to take home (resulting in species extinction), it may not affect the flight safety initially (proper ecosystem functioning) but with time as more and more rivets are removed, the plane becomes dangerously weak.
(c) Loss of rivet on the wings (key species that drives major ecosystem functions) is a more serious threat to flight safety than loss of a few rivets on the seats or windows of the plane.
6. Loss of biodiversity is caused by the over population, urbanisation and industrialisation.
(i) The colonisation of tropical Pacific Islands by humans have led to the extinction of more than 2,000 species of native birds.
(ii) The IUCN Red list (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
(iii) Some latest examples of recent extinctions are dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger.
(iv) The last twenty years alone have witnessed the disappearance of 27 species.
(v) Presently, 12% of bird species, 23% of all mammal species, 32% of all amphibian species and 31% of all gymnosperm species in the world face the threat of extinction.
(vi) Careful analysis of records shows that amphibians appear to be more vulnerable to extinction.
(vii) The grim scenario of extinctions is the fact that more than 15,500 species world wide are facing the threat of extinction.
Results of Loss of Biodiversity in a Region
(a) Decline in plant production.
(b) Lowered resistance to environmental perturbations, such as drought.
(c) Increased variability in certain ecosystem processes such as plant productivity, water use, pest and disease cycles.
Causes of Biodiversity Losses
These are mainly four as given below. They are also named as The Evil Quartet.
(i) Habitat Loss and Fragmentation
(a) The main cause of extinction of species is the destruction of their habitat
(b) Examples,
• Tropical rainforests once covering more than 14% of the land surface, now cover only 6% of land area.
• Amazon rainforest (called lungs of the planet) is being cut and cleared for the cultivation of soybeans and for conversion to grasslands for raising beef cattle.
(c) When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to their population decline.
(d) The degradation of many habitats by pollution also threatens the survival of many species, many have extincted in last 500 years.
(ii) Over-exploitation of natural resources by humans results in degradation and extinction of the resources. For example, Steller’s sea cow, passenger pigeon and many marine fishes have extincted in last 500 years.
(iii) Alien (exotic) Species Invasions
When alien (exotic) species are introduced unintentionally or deliberately, some become invasive and cause harmful impact resulting in extinction of the indigenous species. Examples,
(a) Nile perch a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of cichlid fish in the lake.
(b) Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and pose threat to native species.
(c) The recent example is of the African cat fish (Clarias gariepinus) introduced for aquaculture purpose, is posing a threat to the indigenous cat fishes of Indian rivers.
(iv) Co-extinctions When a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct. For example, if the host species becomes extinct, all those parasites exclusively found on it will also become extinct. In plant pollinator mutualism, extinction of one results in the extinction of the other.

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

The post Biodiversity and Conservation – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability are part of NCERT Exemplar Class 12 Maths. Here we have given Exemplar Problems for Class 12 Maths Chapter 5 Continuity and Differentiability PDF.

NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability

NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability Solutions is given below.

Short Answer Type Questions

Long Answer Type Questions

Objective Type Questions

Fill In the Blanks Type Questions

True/False Type Questions

More Resources for Class 12 Maths

• NCERT Exemplar
• NCERT Exemplar Class 12 Maths Solutions
• Class 12 Maths NCERT Solutions
• RD Sharma Class 12 Solutions
• Class 12 Maths Important Questions

We hope the NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability help you. If you have any query regarding NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability, drop a comment below and we will get back to you at the earliest.

The post NCERT Exemplar Class 12 Maths Chapter 5 Continuity and Differentiability appeared first on Learn CBSE.

Environmental Issues – CBSE Notes for Class 12 Biology

​NCERT SolutionsMathsPhysicsChemistryBiologyScience​

Pollution, Solid and Radioactive Wastes:
1. Pollution is an undesirable change’in the physical, chemical and biological characteristics of air, water, land and soil.
(i) Pollutants are agents that cause undesirable change in the environment.
(ii) The Government of India has passed the Environment Protection Act, 1986 to protect and improve the quality of our environment (air, water and soil).
2. Air pollution occurs due to undesirable change in the physical, chemical and biological characteristics of air that exerts harmful effects on human beings.
(i) Causes of Air Pollution
(a) Smoke stacks from thermal power plants, forest fires, volcanic eruptions, etc.
(b) Garbage decomposition also releases unwanted gases in the air.
(c) Excessive use of fossil fuels by automobiles and industries release particulate and air pollutants.
(d) Use of leaded petrol.
(ii) Types of Air Pollutants

(iii) Harmful Effects of Air Pollution on Health
(a) Carbon monoxide (CO) causes giddiness, headache, cardiovascular malfunction, asphyxia, etc.
(b) Hydrogen sulphide (H₂S) causes nausea, eye and throat irritation.
(c) Sulphur dioxide (SO₂) causes respiratory tract diseases like asthma, bronchitis, cancer, emphysema, etc.
(d) Fine particulates released by industries cause breathing and respiratory problems, inflammation and damage to the lungs.
(e) In plants reduced growth and yield and premature death occurs.
(iv) Control Methods of Air Pollution
There are several methods used for controlling air pollution in India.
These are:
(a) Electrostatic Precipitator (ESP) is an electrical device to remove particulate matter present in the exhaust of thermal power plant.

• About 99% of particulate matter can be removed by ESP.
• It has electrode wires and a stage of collecting plates.
• Electrode wires are provided with an electric current of several thousand volts, which produces a corona that releases electrons.
Discharged corona Negatively charged wire
• These electrons get attach to the dust Electrostatic precipitator
particles and give them negative
charge within a small fraction of a second.
• Collecting plates are grounded that attract the charged dust particles.
• The velocity of air between the plates must be low enough to allow the dust to fall.
(b) Scrubber is used to remove harmful gases like sulphur dioxide from industrial
exhaust.

The exhaust is passed through a spray of water or lime.
• Water dissolves the gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.
* Drawbacks Recently, the dangers of particulate matter that are very small and cannot be removed by these precipitators has been found. According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) if inhaled can cause breathing and respiratory problems, irritation, damage to lungs and premature deaths.
(c) Catalytic convertors are fitted into automobiles for
reducing emission of poisonous gases like NO₂ and CO.
• They are made of expensive metals like platinum, palladium and rhodium as catalysts.
• When exhaust passes through the catalytic convertor, nitric oxide splits into nitrogen and oxygen; carbon monoxide is oxidised into carbon dioxide and unburnt hydrocarbons get burnt completely into CO₂ and H₂O.
• Unleaded petrol should be used in motor vehicles fitted with catalytic convertor as leaded petrol inactivates the catalyst.
(i) A Case Study— Control of Air Pollution in Delhi
(a) Delhi leads the country in high levels of air pollution due to large numbers of vehicles. In 1990s, Delhi ranked fourth among the 41 most polluted cities of the world.
(b) As per directives of Supreme Court, all buses of Delhi were converted to run on Compressed Natural Gas (CNG) by the end of 2002.
(c) Benefits of CNG over diesel/petrol
* Burns most efficiently and leaves no unburnt remains.
– Cheaper than diesel/petrol.
* Cannot be siphoned off by thieves and adulterated like petrol or diesel.
(d) Other ways to reduce vehicular pollution
* Phasing out of old vehicles.
* Use of unleaded petrol.
* Use of low-sulphur petrol and diesel.
* Application of stringent pollution-level norms for vehicles.
* Use of catalytic convertors in vehicles.
(vi) Auto Fuel Policy of Government of India
(a) Euro II norms stipulate that sulphur be controlled at 350 parts per million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42% of the concerned fuel.
(b) According to it, all automobiles have to meet the Euro III emission specification in eleven Indian cities by 1 April, 2005.
(c) The same eleven cities have to meet the Euro IV norms by 1 April, 2010.
(d) The rest of the country will have Euro III emission norm compliant automobiles and fuels by 2010.
(e) By all these efforts, a substantial fall in CO₂ and SO₂ level has been found in Delhi between 1997 and 2005.
3. Noise pollution is undesirable high level of sound. In India, the Air (Prevention and Control of Pollution) Act came into force in 1881, but was amended in 1987 to includes noise as art air pollutant.
Noise measurement Sound is expressed in decibels (dB). A sound of over 115 dB is very harmful for ears. Prolonged exposure to noise level above 80 dB leads to perma nent hearing loss.
(i) Causes are
(a) Use of loudspeakers and music systems. (b) Jet planes and rockets take-off.
(c) Industrial, factory noises, etc.
(ii) Harmful effects are sleeplessness, stress, increased heartbeat, breathing problems, damage to ear drums and impaired hearing ability.
(iii) Control Methods
(a) By applying sound-absorbent materials or by muffling noise in industrial units.
(b) Delimitation of horn-free zones around hospitals and schools.
(c) Strict laws for permissible sound levels of crackers and loudspeakers should be followed.
(d) Loudspeakers should be played up to a fixed time only.
4. Water pollution is any undesirable change in the physical, chemical or biological properties of water that may affect the human beings and aquatic species.
(ii) The Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.
(ii) Sources of Water Pollution
(a) Domestic sewage includes everything that comes from residential area to common public sewage system. A mere 0.1% impurities make domestic sewage unfit for human use.
Composition of domestic sewage
* Suspended solids, e.g. sand, silt and clay.
* Colloidal material, e.g. faecal matter, bacteria, cloth and paper fibres.
* Dissolved materials, e.g. nutrients (nitrate, ammonia, phosphate, sodium and calcium).
* It mainly contains biodegradable organic wastes, which are readily decomposed with the help of decomposers.
(b) Industrial wastes are released by petroleum, paper manufacturing, metal • It contains heavy metals like mercury and many organic compounds.
(iii) Effects of Water Pollution

(a) Biological magnification can be defined as the increase in concentration of toxicants at successive trophic levels.
• Mercury and DDT are well known for biological magnification.
• Toxic materials cannot be metabolised or excreted. Therefore, they get accumulated in an organism and pass on to higher trophic levels.
• DDT accumulates in birds and disturbs calcium metabolism, which results in thinning of egg shell. This results in decline of bird population.
(b) Eutrophication can be defined as the natural ageing of a lake by nutrient enrichment of its water.
Process of Eutrophication
• Water in young lake is cold and clear to support life.
• Gradually with time, it gets enriched with nutrients as nitrogen and phosphorus by streams draining in it.
• Due to this, aquatic life (plants and animals) flourish in lake.
• Organic remains deposit at the bottom of the lake and with time, water becomes warmer.
Eventually, floating plants develop in the lake, finally converting it into land. This accelerated ageing of lakes due to sewage, agricultural and industrial wastes is called cultural or accelerated eutrophication.
(c) Biochemical Oxygen Demand (BOD) is the amount of oxygen required for microbial breakdown of biodegradable organic matter. It is higher in polluted water and lesser in clean water.

(d) Algal bloom is excessive growth of planktonic (free-floating) algae in aquatic bodies.
• In domestic sewage, nutrients like nitrogen and phosphorus favours the growth of algal bloom.
• It causes fish mortality and deterioration of water quality.
Example, Excessive growth of water hyacinth (Eichhornia crassipes). It is the most problematic aquatic weed, also called Terror of Bengal.
It grows abundantly in eutrophic water bodies and imbalances water ecosystem.
(vi) A Case Study— Integrated Wastewater Management
(a) Wastewater including sewage can be treated in an integrated manner by utilising a mix of artificial and natural processes.
• One such example is town of Areata situated along Northern coast of California. An integrated wastewater treatment process was developed with the help of biologists from Humboldt State University in this town.
• The cleaning occurs in two steps:
— The conventional sedimention, filtrating and chlorine treatment is carried out.
The treated water still contain lots of heavy metals and other toxic pollutants.
– In second step, algae, fungi and bacteria are grown in marsh land through which water flowed. These life forms neutralise, absorb and assimilate the pollutants and purify the water naturally.
The marshes also constitute a sanctuary, with a high level of biodiversity.
(b) Ecosan toilets have been developed in areas of Kerala and Sri Lanka for ecological sanitation. The advantages of ecological sanitation are:
• A practical, hygienic and efficient method of disposal.
• Cost effective approach.
• Human excreta can be recycled into natural fertiliser to reduce need of chemical fertiliser.
5. Solid wastes refer to everything that goes out in trash. The various types are:
(i) Municipal solid wastes contain wastes from homes, offices, schools, hospitals, etc., that are collected and disposed by the municipality, which generally consists of paper, leather, textile, rubber and glass, metals and plastic, etc.
(ii) Industrial wastes contain wastes like scraps, fly ash, etc., generated by industries.
(Hi) Hospital wastes contain disinfectants and other harmful chemicals generated by
hospitals.
(iv) Electronic wastes (e-wastes) are the damaged electronic goods and irreparable computers.
(a) Methods of Solid Waste Disposal
There are various methods of solid waste disposal. Some of them are:
• Open burning involves burning of municipal waste in open dumps but the unburnt piled waste serves as breeding ground for rats and flies.
• Sanitary landfills are areas where wastes are dumped in a depression or trench after compaction and covered with dirt. The problem is seepage of chemicals from these landfills can pollute underground water resources.
• Rag-pickers and kabadiwallas collect and separate out wastes into reusable or recyclable categories.
• Natural breakdown involves dumping biodegradable materials into deep pits for natural degradation.
• Incineration is a method of hospital waste disposal.
• E-Wastes
– E-wastes are buried in landfills or in ~inerated.
– About half of the e-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.
– Developed countries have specifically built facilities for recycling of e-wastes.
– Recycling is only solution available for treating e-waste but caution should be taken to carry out process environment friendly.
(b) A Case Study — Remedy for Plastic Waste
• A plastic sack manufacturer, Ahmad Khan from Bengaluru realised that plastic waste was a real problem.
His company developed a fine powder, called polyblend of recycled modified plastic.
• This mixture is mixed with the bitumen and used to lay roads.
• It enhanced the bitumen’s water repellant properties and helped to increase road life by a factor of three.
• Using this technique, by the year 2002, more than 40 kms of road in Bengaluru has already been laid.
6. Soil pollution is any undesirable change in soil profile affecting its productivity.
(i) Green revolution led to manifold increase in crop production by the use of inorganic fertilisers and pesticides.
(ii) Pesticides, herbicides, fungicides, etc., are being increasingly used afterwards which resulted in so’l pollution.
(iii) Causes of Soil Pollution
(a) Chemical seepage from industries.
(b) Excessive use of inorganic fertilisers, pesticides, etc.
(iv) Harmful Effects of Soil Pollution
(a) Non-target organisms are killed in the soil.
(b) Soil becomes unfertile.
(c) Pesticides can result in biomagnification.
(vi) Control Methods
(a) Strict ways should be adopted by the industries and other sources for waste disposal.
(b) Use of organic farming It is a cyclical, zero-waste method, where waste products from one process are cycled in as nutrients for other processes, allowing maximum utilisation of resources and increasing the efficiency of production.
(ini) A Case Study— Organic Fanning
(a) Ramesh Chandra Dagar, a farmer in Sonipat (Haryana) included bee-keeping, dairy management, water harvesting, composting and agriculture in a chain of processes.
(b) This chain supports each other and allow an extremely economical and sustainable venture.
(c) Chemical fertilisers are not required as cattle excreta is used as manure.
(d) Crop waste is used for making compost, which is used as natural fertiliser or to generate natural gas, which is used for satisfying energy needs of farm.
(e) To spread information and help the practice of integrated organic farming. Dagar has created the Haryana Kisan Welfare club, with current membership of
5000 farmers.
7. Radioactive wastes include nuclear waste, which is given off as radiation.
(i) Nuclear energy was initially considered as a non-polluting way for generating electricity initially.
(ii) Later, two serious inherent problems were realised. The first is accidental leakages as occurred in the Three Mile Island and Chernobyl, which proved that radioactive wastes are most potent pollutants. The second is safe disposal of radioactive wastes.
(iii) Harmful Effects
(a) Radiations causes mutation at a very high rate.
(b) At high doses, nuclear radiations are lethal.
(c) At low doses, these cause disorders and diseases like cancer.
(iv) Disposal method of radioactive wastes involve pretreatment and storage in shielded containers and then burying at about 500m deep below the earth’s surface. However, this method of disposal is getting opposition from public.

CBSE NotesCBSE Notes BiologyNCERT Solutions Biology

The post Environmental Issues – CBSE Notes for Class 12 Biology appeared first on Learn CBSE.

The Solid State Class 12 Notes Chemistry Chapter 1

1. Solids are substances which have fixed shape
and volume. 1’hey are characterised by rigidity, incompressibility, slow diffusion and mechanical strength. They are classified as:
(a) Crystalline solids
(b) Amorphous solids .
2. The crystalline solids are further classified as:
(a) Metallic solids
(b) Ionic solids
(c) Covalent solids
(d) Molecular solids
3. A regular three dimensional arrangement of points in space is called a space lattice or crystal lattice. There are only 14 three-dimensional lattices known as Bravais lattices. The basic difference between the 14 Bravais lattices are the angles between the faces and the relative proportion of the sides.
4. A unit cell is the smallest unit of the crystal which when repeated again and again gives the crystal of the given substance.
5. There are three types of unit cells based on the cube. These are:
(a) Primitive or simple cube which has one constituent at each comer.
(b) Body-centred cube in which one constituent at the centre of the cube as well as one at each comer.
(c) Face-centred cube in which there is one constituent at the centre of each face as well as one at each comer.
6. A pure metal in the solid crystalline state is composed of atoms that are identical in shape and size. The identical spheres can be packed in a number of ways.
7. The number of nearest neighbours of an atom, ion or a molecule is called its coordination number.
8. In the hcp and ccp structures, about 74 percent of the available space is occupied by the spheres. In bcc arrangement, about 68 percent of the available space is filled up. In simple cubic structures, about 52.4 percent of the available space is occupied by the spheres.
9. The density of the unit cell,

10. Any departure from perfectly ordered arrangement of atoms or ions in crystals is called imperfection or defects. These are of two types:
(a) Point defects (b) Line defects
11. Schottky defects occurs when a pair of ions of opposite charge, i.e., cations and anions are missing from the ideal lattice. The presence of a large number of schottky defects lowers the density of a crystal, e.g., AgBr.
12. The atoms or ions which occupy the normally vacant interstitial sites in a crystal are known as interstitials. It results in increase in density of crystal.
13. Frenkel defects is a combination of schottky defects and interstitials. It occurs when an ion leaves its position in the lattice and occupies an interstitial site leaving a gap in the crystal.
14. Non-stoichiometric defects are a large number of inorganic solids in which the ratio of the number of atoms of one kind to the number of atoms of the other kind does not correspond to the ideal whole number ratio. Such compounds are called non-stoichiometric compounds.
15. When there is an excess of metal ions in non- stoichiometric compounds, the crystal lattice has vacant anion sites. These sites are occupied by electrons. Hie anion sites occupied by electrons are called F-centres.
16. Based on their electrical conductivity, solids are classified as:
(a) Conductors
(b) Insulators
(c) Semi conductors
17. Pure substances that show conducting behaviour like that of silicon and germanium are called intrinsic semiconductors.
18. When solid substances are placed in a magnetic field, they do not show the same behaviour. Depending on their response to magnetic field, the substances are classified as:
(a) Diamagnetic substances:
(i) These substances are weakly repelled by a magnetic field.
(ii) The electrons are paired.
(b) Paramagnetic substances:
(i) These substances are weakly attracted by the magnetic field.
(ii) These substances have permanent magnetic dipoles due to die presence of atoms, molecules or ions containing unpaired electrons.
19. Substances having unpaired electrons are classified as:

Class 12 Chemistry Notes

The post The Solid State Class 12 Notes Chemistry Chapter 1 appeared first on Learn CBSE.

Solutions Class 12 Notes Chemistry Chapter 2

1. A solution is a homogeneous mixture of two or 9.
more chemically non-reacting substances.
The components of a solution generally cannot be separated by filtration, settling or centrifuging.
2. A solution may be classified as solid, liquid or a gaseous solution.
3. Solubility is defined as the amount of solute in a saturated solution per 100g of a solvent.
4. The solubility of a gas in a liquid depends upon
(a) the nature of the gas and the nature of the liquid,
(b) the temperature of the system, and
(c) the pressure of the gas.
5. The effect of pressure on the solubility of a gas in a liquid is governed by Henry’s Law. It states that the solubility of a gas in a liquid at a given temperature in directly proportional to the partial pressure of the gas Mathematically, P = KHX where P is the partial pressure of the gas; and X is the mole fraction of the gas in the solution and KH is Henry’s Law constant.
6. The vapour pressure of a liquid is the pressure exerted by its vapour when it is in dynamic equilibrium with its liquid, in a closed container.
7. According to Raoults Law, the vapour pressure of a solution containing a non-volatile solute is directly proportional to the mole fraction of the solvent ( X_A). The proportionality constant being the vapour pressure of the pure solvent, i.e., P× X_A or P = P° X_A.
8. A solution which obeys Raoult’s Law at all concentrations and temperatures is known as an ideal solution.
9. Characteristics of an ideal solution:
(a) ∆_sol V = 0, i.e., there is no change in volume when an ideal solution is formed.
(b) ∆_sol H= 0; i.e., heat is neither evolved nor absorbed during the formation of an ideal solution.
10. (a) The solution shows positive deviation from Raoult’s Law if its vapour pressure is higher than that predicted by Raoult’s Law.
(b) The solution shows negative deviation if its vapour pressure is lower than that predicted by Raoult’s Law.
11. Colligative properties of solutions are those properties which depend only upon the number of solute particles in the solution and not on their nature. Such properties are
(a) Relative lowering in vapour pressure,
(b) Elevation of boiling point,
(c) Depression of freezing point and
(d) Osmotic pressure.
12.

Thus, according to Raoult’s Law, the relative lowering of vapour pressure of a solution is equal to the mole fraction of the solute.
13. For a dilute solution, the elevation in boiling point is found to be proportional to the molality of the

where ∆T_b is the elevation in boiling point, ‘m’ is the molality and K_b is the Molal elevation constant
14. The depression in freezing point (∆T_f) is proportional to the molality of the solution.

where K_f is molal depression constant (freezing point depression constant).
15. The spontaneous flow of solvent molecules from a dilute solution into a concentrated solution when the two are separated by a perfect sernipermeable membrane is called osmosis.
16. Osmotic pressure (π) is the pressure which must be applied to the solution side (more concentrated solution) to just prevent the passage of pure solvent into it through a sernipermeable membrane.
Mathematically, π = CRT= n_B/V- RT
where n is the osmotic pressure of the solution,
C is the concentration of solution
n_B is the number of moles of solute,
V is the volume of the solution in litres,
R is the gas constant, and T is the temperature on the Kelvin scale.
17. Isotonic solutions are those solutions which have the same osmotic pressure. Also they have same molar concentration.
For isotonic solutions, π₁ = π₂ Also, C₁ = C₂
18. Van’t Hoff factor, ‘ i’ is used to express the extent of association or dissociation of solutes in solution. It is die ratio of the normal and observed molar masses of the solute, i. e.,

19. In case of association, observed molar mass being more than the normal, the factor ‘T has a value less than one. But in case of dissociation, the van’t Hoff factor is more than one because the observed molar mass has a less value.
20. In case of solutes which do not undergo any association or dissociation in a solvent, the Vant Hoff factor, ‘i’, will be equal to one because the observed and normal molar masses will be same.
21. Inclusion of van’t Hoff factor, ‘F, modifies the equations for colligative properties as follows:

Class 12 Chemistry Notes

HSSLive Chemistry

The post Solutions Class 12 Notes Chemistry Chapter 2 appeared first on Learn CBSE.