Mineral Nutrition Exercise Solutions | KalviGavani

| Feature | Macronutrients | Micronutrients | |---|---|---| | Required amount | > 10 mmol/kg dry weight | < 10 mmol/kg dry weight | | Examples | C, H, O, N, P, K, Ca, Mg, S | Fe, Mn, Zn, Cu, B, Mo, Cl, Ni | | Role | Structural and metabolic | Catalytic (enzyme activators/co-factors) | | Deficiency impact | Severe (major metabolic disruption) | Moderate (specific enzyme disruption) |

Hydroponics is the technique of growing plants in a nutrient solution (water containing dissolved mineral nutrients) without soil. Uses: 1. Studying mineral requirements of plants (by removing one element at a time) 2. Identifying essential elements and their deficiency symptoms 3. Commercial crop production (lettuce, tomatoes, herbs) 4. Growing plants in areas with poor soil

Biological nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by living organisms using the enzyme nitrogenase. Symbiotic N₂ fixers: Rhizobium (in legume root nodules), Frankia (in non-legume root nodules) Free-living N₂ fixers: Azotobacter (aerobic), Clostridium (anaerobic), Nostoc, Anabaena (cyanobacteria) Reaction: N₂ + 8H⁺ + 8e⁻ + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pi

Leghaemoglobin is a pink-red pigment found in the root nodules of leguminous plants. Its functions: 1. It acts as an oxygen scavenger — binds to O₂ and maintains a low O₂ concentration 2. Protects nitrogenase enzyme from O₂ (nitrogenase is O₂-sensitive and gets inactivated) 3. Provides an anaerobic environment for nitrogen fixation while still supplying O₂ for respiration of bacteroids

The nitrogen cycle is the continuous cycling of nitrogen between the atmosphere, soil, and living organisms. It involves the following steps: 1. Nitrogen Fixation (N₂ → NH₃/NH₄⁺): - Conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) or ammonium ions (NH₄⁺) - Biological N₂ fixation: By Rhizobium (symbiotic, in legume root nodules), Azotobacter, Clostridium, Nostoc, Anabaena (free-living) - Industrial N₂ fixation: Haber process (N₂ + 3H₂ → 2NH₃ at high temperature and pressure) - Atmospheric N₂ fixation: Lightning converts N₂ to NOₓ, which dissolves in rain 2. Nitrification (NH₄⁺ → NO₂⁻ → NO₃⁻): - Oxidation of ammonia to nitrate by nitrifying bacteria - Step 1: NH₄⁺ → NO₂⁻ (nitrite) by Nitrosomonas - Step 2: NO₂⁻ → NO₃⁻ (nitrate) by Nitrobacter - Nitrates are the form in which plants absorb nitrogen from the soil 3. Assimilation: - Plants absorb nitrates (NO₃⁻) or ammonium ions (NH₄⁺) from the soil - Convert them into amino acids, proteins, nucleic acids, and other nitrogen-containing compounds - Animals obtain nitrogen by eating plants 4. Ammonification (Organic N → NH₄⁺): - Decomposition of organic nitrogen (dead organisms, waste) into ammonium ions - Carried out by decomposers (bacteria and fungi) - Also called mineralisation 5. Denitrification (NO₃⁻ → N₂): - Conversion of nitrates back into atmospheric nitrogen gas - Carried out by Pseudomonas denitrificans under anaerobic conditions - Returns nitrogen to the atmosphere, completing the cycle

MACRONUTRIENTS: 1. Nitrogen (N): - Functions: Component of amino acids, proteins, nucleic acids, chlorophyll, ATP, co-enzymes - Deficiency: Chlorosis (yellowing of OLDER leaves first — N is mobile), stunted growth, delayed flowering, smaller leaves 2. Phosphorus (P): - Functions: Component of ATP, nucleic acids (DNA, RNA), phospholipids; root development; energy transfer - Deficiency: Poor root growth, purple/reddish discolouration of leaves, delayed maturity, reduced seed formation 3. Potassium (K): - Functions: Stomatal opening/closing, enzyme activation, osmotic regulation, protein synthesis - Deficiency: Marginal necrosis (scorched leaf edges), weak stems, chlorosis, reduced growth 4. Calcium (Ca): - Functions: Cell wall formation (calcium pectate in middle lamella), membrane integrity, cell division, signal transduction - Deficiency: Stunted root growth, curling of leaf tips, blossom end rot in fruits, meristem death 5. Magnesium (Mg): - Functions: Central atom of chlorophyll, enzyme activator (RuBisCO, phosphatases), phosphate transfer - Deficiency: Interveinal chlorosis in OLDER leaves (Mg is mobile), purple/reddish discolouration 6. Sulphur (S): - Functions: Component of amino acids (cysteine, methionine), co-enzyme A, vitamins (biotin, thiamine) - Deficiency: Chlorosis in YOUNGER leaves (S is immobile), similar to N deficiency but in new growth MICRONUTRIENTS: 7. Iron (Fe): - Functions: Chlorophyll synthesis, electron transport (cytochromes, ferredoxin), component of catalase - Deficiency: Interveinal chlorosis in YOUNG leaves (Fe is immobile) 8. Manganese (Mn): - Functions: Enzyme activator (photosynthesis, respiration), component of oxygen-evolving complex of Photosystem II - Deficiency: Interveinal chlorosis, grey spots on leaves 9. Zinc (Zn): - Functions: Auxin synthesis, enzyme activator (carbonic anhydrase, alcohol dehydrogenase) - Deficiency: Little leaf disease, rosette formation, stunted growth 10. Boron (B): - Functions: Pollen germination, pollen tube growth, cell wall formation, sugar transport - Deficiency: Death of growing tip, brown rot in beet, heart rot in sugar beet, poor fruit development

Biological nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by living organisms using the enzyme nitrogenase. The Nitrogenase Reaction: N₂ + 8H⁺ + 8e⁻ + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pi - Nitrogenase is an O₂-sensitive enzyme (inactivated by oxygen) - Requires 16 ATP molecules per N₂ molecule fixed (very energy-intensive) - Requires reducing equivalents (8e⁻) Types of Nitrogen-Fixing Organisms: 1. Symbiotic N₂ Fixers: - Rhizobium: Forms root nodules on leguminous plants (pea, bean, clover, soybean) - Frankia: Forms root nodules on non-leguminous plants (Alnus, Casuarina) - The bacterium provides fixed nitrogen (NH₃) to the plant - The plant provides organic carbon (sugars) and a protected environment to the bacterium - This is a mutualistic (symbiotic) relationship 2. Free-Living (Asymbiotic) N₂ Fixers: - Azotobacter: Aerobic, found in soil - Clostridium: Anaerobic, found in soil - Nostoc, Anabaena: Cyanobacteria (blue-green algae), found in water and soil - Beijerinckia: Tropical soil bacterium Root Nodule Formation in Legumes: 1. Rhizobium bacteria in the soil recognise specific flavonoids secreted by legume roots 2. Bacteria attach to root hairs and secrete Nod factors 3. Root hairs curl and form an infection thread 4. Bacteria enter the root cortex through the infection thread 5. Cortical cells divide to form the root nodule 6. Bacteria differentiate into bacteroids (nitrogen-fixing form) 7. Leghaemoglobin (pink pigment) protects nitrogenase from O₂ Role of Leghaemoglobin: - Pink-red pigment found in root nodules - Binds to O₂ (oxygen scavenger) - Maintains low O₂ concentration to protect nitrogenase (which is O₂-sensitive) - Provides O₂ for bacteroid respiration at a controlled rate - Analogous to haemoglobin in blood (contains iron)