NCERT Exemplar Class 11 Biology Solutions Mineral Nutrition
Multiple Choice Questions
1.Which one of the following roles is not characteristic of an essential element?
(a) Being a component of biomolecules.
(b) Changing the chemistry of soil.
(c) Being a structural component of energy related chemical compounds.
(d) Activation or inhibition of enzymes.
Soln.(b)
2.Which one of the following statements can best explain the term critical concentration of an essential element?
(a) Essential element concentration below which plant growth is retarded.
(b) Essential element concentration below which plant growth becomes enhanced.
(c) Essential element concentration below which plant remains in the vegetative phase.
(d) None of the above
Soln.(a): The limited concentration of essential element below which plant growth is retarded/ stunted is termed as critical concentration.
3.Deficiency symptoms of an element tend to appear first in young leaves. It indicates that the element is relatively immobile. Which one of the following elemental deficiency would- show such symptoms?
(a) Sulphur (b) Magnesium
(c) Nitrogen (d) Potassium
Soln.(a) :Th’e parts of the plants that show deficiency symptoms depend on the mobility of the element in the plant. Deficiency symptoms appear first in young leaves and young tissues for elements which are relatively immobile inside the plant e.g., Ca and S are a part of the structural component of the cell and hence are not easily released. The symptoms appear first in old leaves and tissues for those elements which are mobilised from senescing regions for supply to young tissues, e.g., N, K and Mg. .
4.Which one of the following symptoms is not due to manganese toxicity in plants?
(a) Calcium translocation in shoot apex is inhibited.
(b) Deficiency in both Iron and Nitrogen is induced.
(c) Appearance of brown spot surrounded by chlorotic veins.
(d) None of the above
Soln.(b) : The prominent symptom of manganese toxicity is the appearance of brown spot surrounded by chlorotic veins. It is important to know that manganese competes with iron and magnesium for uptake and with magnesium for binding with enzymes. Manganese also inhibits calcium translocation in shoot apex. Therefore, excess of manganese may, in fact, induce deficiencies of iron, magnesium and calcium. –
5.Reaction carried out by N2 fixing microbes include
2NH3 + 3O2 – » 2NO2 + 2H+ + 2H2O (i)
2N O 2 + O 2 – »2N O 3 (ii)
Which of the following statements about these equations is not true?
(a) Step (i) is carried out by Nitrosomonas or Nitrosococcus.
(b) Step (ii) is carried out by Nitrobacter.
(c) Both steps (i) and (ii) can be called nitrification.
(d) Bacteria carrying out these steps are usually photoautotrophs.
Soln.(d): Given reactions are of nitrification. The conversion (oxidation) of ammonia to nitrite is carried out by nitrifying bacteria Nitrosomonas and Nitrosococcus and of nitrite to nitrate by Nitrobacter and Nitrocystis. Bacteria carrying out these steps are chemoautotrophs, which are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions.
6.With regard to the biological nitrogen fixation by Rhizobium in association with soybean,
which one of the following statement/ statements does not hold true?
(a) Nitrogenase may require oxygen for its functioning.
(b) Nitrogenase is Mo-Fe protein.
(c) Leghaemoglobin is a pink coloured pigment.
(d) Nitrogenase helps to convert N2 gas into two molecules of ammonia.
Soln.(a): In roots of soybean, nodule acts as a site for N2 fixation. It contains all the necessary biochemical compounds, such as nitrogenase and leghaemoglobin. The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric N2 toNH3. This enzyme is extremely sensitive to oxygen. To protect it from oxygen, nodules contain an oxygen scavenger, called leghaemoglobin. It regulates 02 supply by creating anaerobic environment in the cell, so
7.Match the element with its associated functions/roles and choose the correct option among given below.
A.Boron (i) Splitting of H2O to liberate O2 during photosynthesis
B.Manganese (ii) Needed for synthesis of auxins
C.Molybdenum (iii) Component of nitrogenase
D.Zinc (iv) Pollen germination
E.Iron (v) Component of ferredoxin
A-(i), B-(ii), C-(iii), D-(iv), E-(v)
A-(iv), B-(i), C-(iii), D-(ii), E-(v)
A-(iii), B-(ii), C-(iv), D-(v), E-(i)
A-(ii), B-(iii), C-(v), D-(i), E-(iv)
Soln.(b)
8.Plants can be grown in (Tick the incorrect option)
(a) soil with essential nutrients
(b) water with essential nutrients
(c) either water or soil with essential nutrients
(d) water or soil without essential nutrients
Soln. (d) : Plants need essential nutrients for growth, physiological changes and other
important activities. Soil having essential nutrients is suitable for plant growth. Plants can also be grown in water having all essential nutrients (e.y., Hydroponics, soilless culture of plants, where roots are immersed in nutrient solution without soil).
Short Answer Type Questions
1.Name a plant, which accumulate silicon.
Soln. Oryza sativa (Rice).
2.Mycorrhiza is a mutualistic association. How do the organisms involved in this association gain from each other?
Soln. Mycorrhiza is mutualistic (symbiotic) association between fungus and roots of plants. The roots provides shelter and food to the fungus and the fungus helps plant in absorption of minerals, water uptake and protection against fungus. .
3.Nitrogen fixation is shown by prokaryotes and not eukaryotes. Comment.
Soln. Prokaryotes like Rhizobium and Anabaena are capable of nitrogen fixation as they contain enzyme nitrogenase, but eukaryotes lack this enzyme.
4.Carnivorous plants like Nepenthes and Venus fly trap have nutritional adaptations. Which nutrient do they especially obtain and from where?
Soln. Niypn HIPS and Venus fly trap grow in soil that has little nitrogen. They obtain nitrogen from insect’s body. Being carnivores, these plants trap insects inside their leaves, secrete liquid to digest the insect and take nitrogen from insect’s body.
5.Think of a plant which lacks chlorophyll. From where will it obtain nutrition? Give an example of such a type of plant.
Soln. Parasitic plants lack chlorophyll. They cannot perform photosynthesis and derive their nutrition from host organism. E.g.;
Cuscuta is a parasite on hedge plant.
6.Name an insectivorous angiosperm.
Soln. Utricularia (Bladder wort)
7.A farmer adds Azotobacter culture to soil before sowing maize. Which mineral element is being replenished?
Soln. Azotobacter is a free living bacteria in the soil, which enhances the nitrogen element in the soil by process of biological nitrogen fixation.
8.What type of conditions are created by leghaemoglobin in the root nodule of a legume?
Soln. The leghaemoglobin is responsible for creating anaerobic conditions in the root nodules of the legume plant. It acts as oxygen scavenger and protects enzyme nitrogenase from oxygen and helps in proper functioning of the enzyme.
9.What is common to Nepenthes, Utricularia and Drosera with regard to mode of nutrition?
Soln. Nepenthes, Utricularia and Drosera, all are insectivorous or carnivorous plants.
10. Plants with zinc deficiency show reduced biosynthesis of________
Soln. auxin (IAA)
11 .Yellowish edges appear in leaves deficient in________
Soln. nitrogen, magnesium, potassium and iron
12 .Name the macronutrient which is a component of all organic compounds but is not obtained from soil.
Soln. Carbon
13.Name one non-symbiotic nitrogen fixing prokaryote.
Soln. Azotobacter.
14 .Rice fields produce an important green house gas. Name it.
Soln. Rice fields remain logged with excess water arid anaerobic bacteria grove on them and due to microbial activity, methane gas is released.
15.Complete the equation for reductive animation
Soln.
16.Excess of Mn in soil leads to deficiency of Ca, Mg and Fe. Justify.
Soln. Excess of manganese causes deficiency of iron, magnesium and calcium. Micronutrient present in higher doses becomes toxic. Manganese toxicity is due to reduction in uptake of iron and magnesium and inhibition of calcium translocation into shoot apex.
Short Answer Type Questions
1.How is sulphur important for plants? Name the aminoacids in which it is present.
Soln. Sulphur is a macronutrient involved in chlorophyll formation, growth metabolism and nodule formation in legumes. It is present in two amino acids; methionine and cysteine. ‘
2.How are organisms like Pseudomonas and Thiobacillus of great significance in nitrogen cycle?
Soln. Pseudomonas and Thiobacillus are denitrifying bacteria which carry out denitrification in nitrogen cycle, in which under anaerobic conditions, nitrate present in soil is reduced back to nitrogen oxides, which later escapes from soil into atmosphere, and gets converted into free nitrogen. Denitrification causes acidification of soil.
3.Carefully observe the following figure.
(a) Name the technique shown in the figure and the scientist who demonstrated this
technique for the first time.
(b) Name atleast three plants for which this technique can be employed for their commercial production.
(c) What is the significance of aerating tube and feeding funnel in this setup?
Soln.(a) The figure shows hydroponics or soilless culture and it was first demonstrated by Julius Von Sachs.
(b) Tomato, seedless cucumber, lettuce.
(c) Aerating Tube – a bent tube for aeration is used in hydroponic setup. Regular aeration is required for proper growth and activities of roots.
Feeding funnel – it is used for adding nutrient solution (water + nutrients).
4.Name the most crucial enzyme found in root nodules for N2 fixation. Does it require a special pink coloured pigment for its functioning? Elaborate.
Soln. Enzyme nitrogenase present in root nodules is required for nitrogen fixation. Pink coloured pigment called leghaemoglobin is required for functioning of enzyme nitrogenase, as this pigment acts as oxygen scavenger and thus protects enzyme from oxygen, because too much oxygen inactivates the enzyme that catalyses nitrogen fixation.
5.How are the terms ‘critical concentration’ and ‘deficient’ different from each other in terms of concentration of an essential element in plants? Can you find the values of ‘critical concentration’ and ‘deficient’ for minerals – Fe and Zn.
Soln. Critfcal concentration is the limited concentration of essential element below which growth of the plant is reduced. Deficiency of element is inadequate supply of nutrient to plant resulting in visible deficiency symptoms.
For Zn. critical concentration is 0.5-1% and deficient concentration is less than 0.5% and for Fe, critical concentration is 3.5-5% and deficient concentration is less than 3.5%.
6.Carnivorous plants exhibit nutritional adaptation. Citing an example explain this fact.
Soln. Carnivorous plants fulfill their nutritional requirements by feeding on small animals, like insects or protozoans. E.g., Nepenthes, Venus fly trap, Utricularia, etc. Carnivorous, plants grow in soil deficient in nitrogen.
Pitcher plant – In pitcher plant leaves are modified into pitcher which stores the juice to lure an insect. When an insect comes to suck this juice, chemicals present in nectar dissolves the skin of the prey and the plant obtains nutrients (mainly nitrogen) from its skin.
7.A farmer adds/ supplies N, Ca, Mg and Fe regularly to his field and yet he observes that the plants show deficiency of Ca, Mg and Fe. Give a valid reason and suggest a way to help the farmer improve the growth of plants.
Soln. N, Ca, Mg and Fe are macronutrients, i.e., required in large amounts by plants for proper growth and metabolism. Inspite of supplying these elements regularly to plants, if they still show deficiency symptoms of Ca, Mg and Fe, it indicates that the soil pH is inappropriate. If pH of soil is not appropriate (very acidic or alkaline), then plant is unable to take nutrients from soil even if they are supplied regularly. E.g., too high pH leads to iron deficiency. Dryness and water logging also make if difficult for plants to take up soil nutrients. In this case as plants do not have nitrogen deficiency, it might be due to presence of nitrogen fixing bacteria in soil which make soluble nitrogenous compounds available to plants for absorption. Nutrient deficiency can be overcome by using well aged compost inspite of recently formed manure. Using good fertilisers and regulating soil pH also help in ensuring nutrient uptake.
Long Answer Type Questions
1.It is observed that deficiency of a particular element showed its symptoms initially in older leaves and then in younger leaves.
(a) Does it indicate that the element is actively mobilised or relatively immobile?
(b) Name two elements which are highly mobile and two which are relatively immobile.
How is the aspect of mobility of elements important to horticulture and agriculture?
Soln.(a) For elements that are actively mobile, deficiency symptoms tend to appear first in older leaves and tissues and then in younger leaves. Deficiency symptoms of mobile elements are first visible in the senescent leaves. In the older leaves, biomolecules containing these elements are broken down making these elements available for mobilising to younger leaves. For immobile elements, deficiency symptoms first appear in young leaves. It means in the given plant deficiency symptoms are of actively mobilised element.
(b) Flighly mobile elements – Nitrogen and magnesium
Immobile elements – Sulphur and calcium
(c) Deficiency symptoms vary from element to element, eg: chlorosis is due to deficiency of N, Mg, Fe etc. and necrosis is due to deficiency of Ca, Mg, Cu, etc. Symptoms of deficiency of mobile elements are more pronounced in older leaves and symptoms of deficiency of relatively immobile element appear first in younger leaves. This information can be utilised by horticulturist and agriculturist to get a broad idea of the deficiency elements in plants and will apply corrective measures by supplying the deficient nutrient.
2. We find that Rhizobium forms nodules on the roots of leguminous plants. Also Frankia another microbe forms nitrogen fixing nodules on the roots of non-leguminous plant Alnus.
(a) Can we artificially induce the property of nitrogen fixation in a plant – leguminous or non-leguminous?
(b) What kind of relationship is observed between mycorrhiza and pine trees?
(c) Is it necessary for a microbe to be in close association with a plant to provide mineral nutrition? Explain with the help of one example.
Soln.(a) The gene responsible for nitrogen fixation in plants is nitrogen fixing gene (nif gene). Ability of nitrogen fixation can be artificially induced in leguminous and non-
leguminous plants by genetic engineering which involves transformation of nif genes from bacteria into plant by using Ti plasmid from Agrobacterium tumefaciens.
(b) Mycorrhiza is symbiotic association of,fungal hyphae with roots of higher plants. In mutual beneficial relationship, both the members are incapable of living separately. Mycorrhiza in Pinus is ectotrophic (external) association.
(c) It is necessary for microbe to be in close association with plant to provide nutrition because they develop the ability to fix nitrogen only as symbiont, when they become anaerobic. E.g., N2 fixing bacteria are unable to fix nitrogen by themselves. Roots of a legume secrete chemical attractants (flavonoids and betaines). Bacteria collect over the root hair, release nod factors that cause curling of root hair around the bacteria, degradation of cell wall and formation of an infection thread enclosing the bacteria. Infection thread grows alongwith multiplication of bacteria. The infected cortical cells dedifferentiate and start dividing. It produces swellings or nodules. The infected cells enlarge. Bacteria stop dividing and form bacteriods. Symbiotic nitrogen fixation requires cooperation of nod genes of legume, nod, nif and fix gene clusters of bacteria.
3.What are essential elements for plants? Give the criteria of essentiality. How are minerals classified depending upon the amount in which they are needed by the plants?
Soln. An essential element is the one which has a specific structural or physiological role and without which plants cannot complete their life cycle.
Criteria to know essentiality of an element:
(i) It is indispensable for the growth of plants.
(ii)The element is directly involved in the metabolism of plants. It becomes a component of either a structural or functional molecule. The element may additionally have a corrective effect on mineral balance and other soil conditions.
(iii)A plant is unable to complete its vegetative or reproductive phase in the absence of the element.
(iv)The element cannot be replaced by any other element.
(v) The absence or deficiency of the element produces disorders. These disorders are a direct result of the lack or deficiency of the element.
(vi)The element alone can correct the disorders produced by its absence or deficiency.
Essential elements are differentiated into two categories, macroelements and microelements depending on the amount in which they are needed by plants.
Macroelements (Macronutrients) : They are those essential elements which are present in easily detectable quantities, 1-10 mg per gram of dry matter. Macroelements are usually involved in the synthesis of organic molecules and development of osmotic potential. They are nine in number- C, H, O, N, P, K, S, Mg and Ca.
Microelements (Micronutrients) : They are those essential elements which are required by plants in small amounts, less than 1.0 mg/ gm of dry matter. Microelements are mostly involved in the functioning of enzymes, as cofactors or metal activators. They are eight in number — Fe, Zn, Mn, B, Cu, Mo, Cl and Ni.
4.With the help of examples describe the classification of essential elements based on the function they perform.
Soln. Based on the diverse functions of essential elements, these are categorised into four categories given below :
(i)Constituents of biomolecules: These are the essential components of biomolecules. Hence, known as the structural elements of cells, e.g., carbon, hydrogen, oxygen and nitrogen.
Carbon, oxygen and hydrogen are known to be the components of all the organic substances. While, nitrogen acts as the constituent of all amino acids, proteins, nucleic acids, vitamins and cytokinins.
(ii)Energy related chemical compounds: Some elements also function in providing energy to the cell, e.g., phosphorus is a component of ATP which functions as an energy currency of all the living systems, while magnesium is a component of chlorophyll, which is involved in the conversion of light energy into chemical energy.
(iii)Enzymes showing catalytic effects : Many of the essential elements are required in the form of cofactors by enzymes. They function as the activator or inhibitor of enzymes, e.g., Mg2+ acts as an activator of several enzymes in both photosynthesis (e.g., Ribulose biphosphate (RuBP) carboxylase, phosphoenol pyruvate (PEP) carboxylase) and respiration (e.g., hexokinase and phosphofructokinase). While Zn2+ acts as an activator of alcohol dehydrogenase and Mo of nitrogenase during the course of fixation of nitrogen. •
(iv)Elements altering osmotic potential: Some of the essential elements also alter the osmotic potential. Most of the osmotic potential of cell is due to inorganic salts. Potassium plays an important role in the opening and closing of stomata.
5.We know that plants require nutrients. If we supply these in excess, will it be beneficial to the plants? If yes, how/ If no, why?
Soln. nil Nutrient supply in excess amount is not beneficial to plant because in higher doses, micronutrients become toxic. Any tissue concentration which reduces dry weight of tissue by 10% is called toxic concentration. Critical toxic concentration is different for different micronutrients as well as different plants. For example Mn2+ is toxic beyond 600 pg g_1 for soyabean and beyond 5300 pg g 1 for sunflower. Toxic effects may be due to direct excess of the micronutrient or its interference in the absorption and functioning of other nutrient. E.g: Manganese toxicity (brown spots surrounded by chlorotic veins) is due to
(i) Reduction in uptake of iron and magnesium.
(ii)Inhibition of binding of magnesium to specific enzymes,
(iii) Inhibition of calcium translocation into shoot apex. Therefore, excess of manganese causes deficiency of iron, magnesium and calcium. The toxicity symptoms of Mn are actually combined deficiency symptoms of Fe, Mg and Ca.
6.Trace the events starting from the coming in contact of Rhizobium to a leguminous root till nodule formation. Add a note on importance of leghaemoglobin.
Soln. The process of formation of nodules is a series of multiple interactions that takes place between Rhizobium bacterium and the root system of legume plant (host).
During the process, bacteria initially grow in soil near the roots of higher plants. They are unable to fix nitrogen there, but after coming in contact with the roots of leguminous plants, they interact chemically and enter into roots through root hair.
The process of nodule formation is as follows:
(i) Rhizobium multiply and colonise itself to the surrounding of the roots of host plant where it gets physically attached to the epidermal root hair cells.
(ii) After attachment, the root hair get curled up at the tip due to which bacteria invade the root hair.
(iii) The enzymes from the bacteria degrade the parts of root hair cell wall which produces a thread-like structure called infection thread.
(iv) The bacteria invade the infection thread and reaches upto the inner cortex of the root.
(v) The bacteria after reaching cortex (mainly tetraploid cell) stimulate the initiation of formation of nodule.
(vi) Bacteria enlarge in size and become bacteroid (rod-shaped) thus, leaving the infection thread and enter the cells, i.e., inner cortical and pericycle cells to divide.
(vii) This growth and division of pericycle and cortical cells leads to the formation of a knob-like structure called mature root nodule.
(viii) The nodule, thus formed after division is finally responsible for the direct vascular connection with the host for the exchange of nutrients.
Leghaemoglobin is pink coloured pigment similar to haemoglobin of humans. It acts as oxygen scavenger and protects the enzyme nitrogenase, required for N2 fixation from oxygen. Excess oxygen inactivates the enzyme nitrogenase. Leghaemoglobin creates anaerobic conditions as nitrogenase cannot function in aerobic conditions.
7.Give the biochemical events occurring in the root nodule of a pulse plant. What is the end product? What is its fate?
Soln. Nitrogen fixation in root nodules occurs directly within the bacteroids. The host plant provides bacteroids with carbohydrates, which they oxidise and from which they obtain energy. These carbohydrates are first formed in leaves during photosynthesis and then are translocated through phloem to the root nodules. Sucrose is the most abundant carbohydrate translocated, at least in legumes. Some of the electrons and ATP obtained during oxidation by the bacteroids are used to reduceN2 to NH4+ .
The overall chemical reaction for nitrogen fixation (reduction) is
N2 + 8,electrons + 16 MgATP + 16 H2O – »
2 NH3 +H2+ 16 MgADP + 16 Pi + 8 H+
The process requires both a source of electrons and protons and numerous ATP molecules. The original source of electrons and protons is carbohydrate translocated from the leaves (and then respired by the bacteria). Respiration of carbohydrate in bacteroids leads to reduction of NAD+ to NADH+ or of NADP+ to NADPH.
Fate of Ammonia : Nitrogen assimilation results in the formation of ammonia which is further used for the synthesis of amino acids. Most of the plants can assimilate both nitrate and ammonium ions (NH4) (the ammonium ions are formed by the protonation of ammonia at physiological pH). Ammonium ions are toxic to plants and cannot accumulate in them.
Thus, these NH4 are used in the synthesis of amino acids in plants by following two methods:
(i) Reductive amination: During this process, the ammonia reacts with a-ketoglutaric acid (organic acid) and forms an amino acids, i.e., glutamic acid,
(ii) Transamination : It is the transfer of amino group (—NH2) of one amino acid to keto group (C = O) of another keto acid. The enzyme responsible for this is transaminase or aminotransferase. Glutamic acid is the main amino acid involved in the synthesis of other amino acids through transamination. Glutamic acid is mainly responsible for making the transfer of amino group to keto group
possible.
8.Hydroponics have been shown to be a successful technique for growing of plants. Yet most of the crops are still grown on land. Why?
Soln. Hydroponics is a solution culture used
for raising many plants in soilless medium.
Various disadvantages of this technique are:
(i) There is need for continuous root aeration for proper plant growth.
(ii)Solution needs to be replaced every few days to achieve maximum growth.
(iii)Certain ions are absorbed more rapidly than others causing undesirable pH changes.
(iv)This technique is very expensive. The setting and handling of hydroponics require much more investment than soil based production.
(v) Some methods of hydroponic production might spread water borne diseases.
(vi)It is not used by traditional farmers due to lack of knowledge.
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