CLASS 11TH BIOLOGY CHAPTER- 12 MINERAL NUTRITION NCERT QUICK REVISION NOTES FOR NEET AND CBSE EXAM
MINERAL NUTRITION
Heterotroph: An organism that cannot synthesise its own nutrients and depend on others. Example- Bacteria, protists, members of animalia.
Biological nitrogen fixation: Conversion of atmospheric nitrogen into organic compounds by living organisms.
Nitrification: Conversion of ammonia (NH3) into nitrite and then to nitrate.
Denitrification: A process of conversion of nitrate into nitrous oxide and nitrogen gas (N₂).
Leg-hemoglobin: Pinkish pigment found in the root nodules of legumes.
It acts as oxygen scavenger and protects the nitrogenase enzyme from oxidation.
Flux: The movement of ions is called flux. Influx is inward movement of ions into the cells and efflux is the outward movement of ions.
Inhibition of cell division: Deficiency of N, K, S. and Mo. Necrosis: Death of tissues particularly leaf tissue due to deficiency of Ca, Mg, Cu, K.
Delayed Flowering: due to deficiency of N, S, Mo.
Mineral Nutrition : Plants require mineral elements for their growth and development. The utilization of various absorbed ions by a plant for growth and development is called mineral nutrition of the plant.
Hydroponics: Soil-less culture of plants, where roots are immersed in nutrient solution (without soil) is called hydroponics. The result obtained from hydroponics may be used to determine deficiency symptoms of essential elements.
ESSENTIAL ELEMENTS:
(i) Macronutnents
Macronutrients are present in plant
tissues in concentrations of more than 10 mole Kg -¹ of dry matter. C, H, O, N, PK, S, Ca, Mg
(ii) Micro-nutrients
Micro-nutrients are needed in very low amounts: less than 10 m mole Kg -¹ matter. Fe, Mn, Cu, Mo, Zn, B, Cl, Ni
In addition to the 17 essential elements, Na, Si, Co and Si are required by some higher plants.
CRITERIA FOR ESSENTIALITY:
1. The element must be necessary for supporting normal growth and reproduction.
2. Requirement must be specific and not replaceable by another element.
3. The element must be directly involved in the metabolism of the plant.
Chlorosis: Yellowing of leaves due to loss of chlorophyll. Active
Transport: Absorption occuring at the expense of metabolic energy.
Passive Transport: Absorption of minerals with concentration gradient by the process of diffusion without the expense of metabolic energy.
ROLE OF MINERALS ELEMENTS IN PLANTS (MACRO NUTRIENTS)
Nitrogen: This is the essential nutrient element required by plants in the greatest amount. It is absorbed mainly as NO3– though some are also taken up as NO2– or NH4+. Nitrogen is required by all parts of a plant, particularly the
meristematic tissues and the metabolically active cells. Nitrogen is one of the major constituents of proteins, nucleic acids, vitamins and hormones.
Phosphorus: Phosphorus is absorbed by the plants from soil in the form of phosphate ions (either as H2PO4^−or HPO4^2−). Phosphorus is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, and is required for all phosphorylation reactions.
Potassium: It is absorbed as potassium ion (K+). In plants, this is required in more abundant quantities in the meristematic tissues, buds, leaves and root tips.
Potassium helps to maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata, activation of enzymes and in the maintenance of the turgidity of cells.
Calcium: Plant absorbs calcium from the soil in the form of calcium ions (Ca2+). Calcium is required by meristematic and differentiating tissues.
During cell division it is used in the synthesis of cell wall, particularly as calcium pectate in the middle lamella. It is also needed during the formation of mitotic spindle. It accumulates in older leaves. It is involved in the normal functioning of the cell membranes. It activates certain enzymes and plays an important role in regulating metabolic activities.
Magnesium: It is absorbed by plants in the form of divalent Mg2+. It activates the enzymes of respiration, photosynthesis and are involved in the synthesis of DNA and RNA. Magnesium is a constituent of the ring structure of chlorophyll and helps to maintain the ribosome structure.
Sulphur: Plants obtain sulphur in the form of sulphate (SO4^2−). Sulphur is present in two amino acids cysteine and methionine and is the main constituent of several coenzymes, vitamins (thiamine, biotin, Coenzyme A)
and ferredoxin.
Iron: Plants obtain iron in the form of ferric ions (Fe^3+). It is required in larger amounts in comparison to other micronutrients. It is an important constituent of proteins involved in the transfer of electrons like ferredoxin
and cytochromes. It is reversibly oxidised from Fe^2+ to Fe^3+ during electron transfer. It activates catalase enzyme, and is essential for the formation of chlorophyll.
Manganese: It is absorbed in the form of manganous ions (Mn^2+). It activates many enzymes involved in photosynthesis, respiration and nitrogen metabolism. The best defined function of manganese is in the splitting of water to liberate oxygen during photosynthesis.
Zinc: Plants obtain zinc as Zn^2+ ions. It activates various enzymes, especially carboxylases. It is also needed in the synthesis of auxin.
Copper: It is absorbed as cupric ions (Cu2^+). It is essential for the overall metabolism in plants. Like iron, it is associated with certain enzymes involved in redox reactions and is reversibly oxidised from Cu^+ to Cu2^+.
Boron : It is absorbed as BO3^3− or B4O7^2-. Boron is required for uptake and utilisation of Ca^2+, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.
Molybdenum: Plants obtain it in the form of molybdate ions ( MoO2^2+). It is a component of several enzymes, including nitrogenase and nitrate reductase both of which participate in nitrogen metabolism.
Chlorine: It is absorbed in the form of chloride anion (Cl–). Along with Na+ and K+, it helps in determining the solute concentration and the anion-cation balance in cells. It is essential for the water-splitting reaction in photosynthesis, a reaction that leads to oxygen evolution.
Critical Concentration: The concentration of the essential element below which plant growth is retarted. The element is said to be deficient when present below the critical concentration.
Deficiency symptoms: Chlorosis, stunted growth, premature fall of leaves and buds and inhibition of cell division.
Toxicity of micronutrient: Any mineral ion concentration in tissues that reduces the dry weight of tissues by 10% is considered toxic. Toxicity of one element may lead to deficiency of other element since the former may inhibit the uptake of latter., e.g., Mn competes with Fe, Mg for uptake and also inhibits Ca translocation to shoot apex. Therefore Mn toxicity symptoms are actually same as deficiency symptoms of Fe, Mg and Ca.
ROLE OF MICROBES IN NITROGEN CYCLE:
¶ Rhizobium, Azotobacter, Rhodospirillum; Fix atmospheric nitrogen.
¶ Nitrosomonas and/or Nitrococcus: Conversion of ammonia to nitrite.
¶ Nitrobacter: Conversion of nitrite into nitrate.
¶ Pseudomonas and Thiobacillus: reduce nitrate into nitrogen.
NITROGEN CYCLE:
¶ Nitrogen fixation: The process of conversion of Nitrogen (N₂) into ammonia (NH4).
¶ Ammonification: The process of decomposition of organic nitrogen of plants and animals (proteins) into ammonia.
¶ Dead Plants and Animals change into ammonia by Ammonifying Bacteria
Nitrification: The ammonia Ammonifying Bacteria NH3
so formed may volatilise and re-enter the atmosphere, or some of the ammonia may be converted into nitrate by soil bacteria.
Biological Nitrogen Fixation: Reduction of nitrogen to ammonia by living organisms. Certain prokaryotes are able to fix nitrogen because of presence of 'nitrogenase' enzyme in them.
NITROGEN FIXING MICROBES MAY BE:
(a) Free living
(i) Aerobic-Azotobacter
(ii) Anaerobic-Rhodospirillum
(b) Cyanobacteria-Nastoc, Anabaena
(c) Symbiotic
(i) With leguminous plants-Rhizobium
(ii) With non-leguminous plants - Frankia
Enzyme nitrogenase: The enzyme nitrogenase is Mo-Fe protein and catalysis the conversion of atmospheric nitrogen to ammonia (First stable product of nitrogen fixation)
Leg-hemoglobin: A pink colour pigment, similar to hemoglobin of vertebrates and functions as an oxygen scavenger and protects nitrogenase from oxygen.
N₂ + 8e +8H 16ATP dinitrogenase 2NH, +H₂ + 16ADP + 16 Pi
STEPS OF NODULE FORMATION:
(a) Rhizobium bacteria present in soil contract a susceptible root hair.
(b) Infection of the root hair cause it to curve and deformed due to chemical secretion.
(c) An infection thread is produced carrying the bacteria into the cortex of the root.
(d) The bacteria get modified into rod-shaped bacteria and cause inner cortical and pericycle cells to divide plant produce cytokinin and auxin to stimulate cell division and enlarge to form nodules.
(e) Division and growth of cortical and pericycle cells lead to nodule formation.
MECHANISMS OF N₂ FIXATION
It require 3 components.
(a) A strong reducing agent like FADH₂, NADPH₂.
(b) Nitrogenase enzyme.
(c) ATP (as energy service).
STEPS
(a) Formation of Diamide
(b) Formation of Hydrazine (N₂H₁)
(c) Formation of Ammonia,
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