CBSE Class 11 Biology Mineral Nutrition Notes

POINTS TO REMEMBER :

• Autotrophs : An organism that synthesize its required nutrients from simple and inorganic substances.

• Heterotrophs : An organism that cannot synthesize its own nutrients and depend on others.

Essential Mineral elements :

• More than sixty elements found in different plants.

• Some plant accumulates selenium, some other gold.

Criteria for Essentiality :

• Element absolutely necessary for normal growth and reproduction.

• In the absence of the element the plant can not complete their life cycle.

• Role of the element can not be replaced by any other elements.

• The element must be directly involved in the metabolism of plant.

Macronutrients : are generally present in the plants tissues in large amount (in excess of 10 mmole Kg-1 of dry matter).

Micronutrients : or trace elements are needed in very small amounts (less than 10 mmole Kg^-1 of dry matter)

Four group of essential elements :

• As components of biomolecules and forms structural elements of cells (e.g. carbon, hydrogen, oxygen and nitrogen)

• As components of energy-related chemical compounds in plants. (magnesium in chlorophyll and phosphorous in ATP)

• Element that activate or inhibit enzymes (Mg^₂+, Zn²⁺)

• Alter the osmotic potential of a cell. (K⁺)

Role of macro and micro-nutrients :

Nitrogen :

• Absorbed in the form of NO^₂- or NH₄₊

• Required by meristematic tissue and metabolically active tissue.

• Constituent of proteins, nucleic acids, vitamins and hormones.

Phosphorus :

• Absorbed in the form of H₂PO₄- or HPO^₄2-.

• Constituents of cell membrane certain proteins, all nucleic acids and required in phosphorylation reaction.

Potassium :

• Absorbed as potassium ion (K⁺)

• Required in meristematic tissues.

• Maintain cation and anion balance in cell.

• Opening and closing of stomata.

• Activation of enzyme.

• Maintenance of turgidity of cells.

Calcium :

• Absorbed in the form of calcium ions (Ca²⁺).

• Required by meristematic and differentiating tissues.

• Used in synthesis of cell wall particularly as calcium pectate in middle lamella.

• Required during formation of mitotic spindle.

• Involved in normal functioning of cell membrane.

• Activate certain enzyme.

• Important role in regulating metabolic activity.

Magnesium :

• Absorbed in the form of Mg²⁺.

• Activates enzymes of respiration, photosynthesis.

• Involved in the synthesis of DNA and RNA.

• Constituent of the ring structure of chlorophyll.

• Maintain ribosome structure.

Sulphur :

• Absorbed in the form of sulphate SO^₄2-.

• Present in two amino acids cystine and methionine

• Main constituent of several coenzyme, vitamins and ferredoxin.

Iron :

• Obtained in the form of ferric ions (Fe³⁺).

• Required in larger amount in comparison to other elements.

• Constituent of proteins involved in the transfer of electron like ferredoxin and cytochromes.

• Activates catalase enzyme.

• Essential for formation of chlorophyll.

Manganese :

• Absorbed in the form of manganous ions (Mn²⁺).

• Activates many enzymes of photosynthesis, respiration and nitrogen metabolism.

• Photolysis of water and evolution of oxygen during light reaction.

Zinc :

• Obtained in the form of Zn²⁺.

• Activates enzymes like carboxylase.

• Required in synthesis of auxin.

Cupper :

• Absorbed in the form of cupric ions (Cu²⁺).

• Essential for overall metabolism.

• Associated with enzyme involved in redox reactions. 

• Associated with enzyme involved in redox reactions.

Boron :

• Absorbed in the form of BO33- or B4O72-.

• Required in uptake and utilization of Ca2+.

• Pollen germination.

• Cell elongation.

• Cell differentiation.

• Carbohydrate translocation.

Molybdenum :

• Obtained in the form of molybdate ions (MoO22-).

• Component of enzyme like nitrogenase and nitrate reductase.

• Required in nitrogen metabolism.

Chlorine :

• Absorbed in the form of chloride anion (Cl-).

• Along with Na+ and K+ it determines the solute concentration.

• Maintain anion cation balance of the cell.

• Essential for photolysis of water during light reaction of photosynthesis.

Deficiency symptoms of essential elements :

• Critical concentration: the concentration of the essential element below which plant growth is retarded.

• The element is said to be deficient when present below the critical concentration.

• For the elements that are actively mobilized within the plant that show the deficiency symptoms in the older tissues. (nitrogen, potassium and magnesium)

• The deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs.(sulphur and calcium)

• Deficiency symptom includes chlorosis, necrosis, and stunted growth, premature fall of leaves and buds, and inhibition of cell division.

• Chlorosis: is the loss of chlorophyll.

• Necrosis: death of cells and tissues.

Toxicity of Micronutrients :

• Micronutrient required in low amount.

• Moderate decrease causes the deficiency symptoms.

• Moderate increase causes toxicity.

• Any mineral ion concentration in tissues that reduces the dry weight of the tissues by 10 percent is considered toxic.

Nitrogen cycle :

• Nitrogen fixation: conversion of molecular nitrogen into ammonia.

• Biological nitrogen fixation: Conversion of atmospheric into organic compounds by living organisms.

• Ammonification: decomposition of organic nitrogen of dead plants and animals into ammonia is called Ammonification. (Nitromonasbacteria)

• Nitrification. Ammonia oxidized into nitrite by NitrosomonasandNitrococcus bacteria. The nitrite further oxidized to nitrate with the help of Nitrobacter. These steps are called nitrification.

• Assimilation:

o Nitrates absorbed by plant from soil and transported to the leaves.

o In the leaves nitrates reduced to form ammonia that finally forms the amine group of amino acids.

• Denitrification: Nitrate in the soil is also reduced to molecular nitrogen. This process is carried by bacteria likePseudomonas and Thiobacillus.

Biological nitrogen fixation :

• Reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation.

• The enzyme nitrogenase which catalyses the process are present in prokaryotes, called nitrogen fixer.

• Nitrogen fixing microbes could be free-living or symbiotic.

• Free-living nitrogen fixing aerobic microbes are Azotobacter and Beijernickia.

• Free-living nitrogen fixing anaerobic microbes are Rhodospirilium.

• A number of cyanobacteria like Anabaena and Nostoc are free-living nitrogen fixer.

Symbiotic nitrogen fixation :

• Best example of symbiotic nitrogen fixation is observed in legume-Rhizobium bacteria.

• Rhizobium form root nodules in leguminous plants.

• Frankia also produces nitrogen-fixing nodules on the roots of non-leguminous plants (e.g. Alnus).

• Both Rhizobium and Frankia are free living in soil, but as symbiont, can fix atmospheric nitrogen.

• The root nodules contain pink coloured pigment contains a protein called leg-haemoglobin.

Nodule formation :

• Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant.

• Rhizobia multiply and colonize the surroundings of roots and get attached to the epidermal and root hair cells.

• An infection thread is produced carrying the bacteria into the cortex of root.

• Bacteria released from the thread into the cells which differentiated into special nitrogen fixing cells.

• Nodule develops vascular connection for exchange of nutrients.

• The nodule contains an enzyme called nitrogenase.

• Nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia.

• Nitrogenase is highly sensitive to molecular oxygen; it requires anaerobic condition.

• Nodule contains a special protein called leg-haemoglobin.

• Leg-haemoglobin acts as oxygen scavenger and provides anaerobic condition to the bacteria inside the nodules; protect the enzyme nitrogenase from oxidation.

• Ammonia synthesis by nitrogenase is energetically expensive process; 8 ATP required synthesizing each molecule of NH3.

Fate of ammonia :

• At physiological pH, the ammonia is protonated to form NH4+.

• Most of plant assimilated nitrate and ammonium ions.

• Reductive amination: the ammonia reacts with α-ketoglutaric acid and forms Glutamic acid.

• Transamination: it involves the transfer of amino group from one amino acid to the keto group of a keto acid.

• Glutamic acid is the main amino acid from which by the process of transamination other amino acids are synthesized.

• Two important amides – asparagines and glutamine found in the protein of plant.

• They are formed from two amino acids namely aspartic acid and Glutamic acid respectively.

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