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12.  Mineral Nutrition 

​Criteria for Essentiality

  1. The element is absolutely necessary for supporting normal growth and reproduction.

  2. In the absence of essential elements, plants cannot complete their life cycle or set the seeds.

  3. The essential element must be specific and is not replaceable by another element.

  4. The element must be directly involved in metabolism.

Types of Essential Elements:

  1. There are 17 essential elements in plants. Additionally, some other elements; like sodium, silicon, cobalt and selenium are required by higher plants. There are two types of essential elements, viz. macronutrients and micronutrients.

  2. Macronutrients: Elements which are present in large amounts in plant tissues are called macronutrients. They are in excess of 10 mmole per kg of dry matter. Carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium are the macronutrients.

  3. Micronutrients: Elements which are present in small amounts, i.e. less than 10 mmole per kg of dry matter are called micronutrients. Iron, manganese, copper, molybdenum, zinc, copper, boron, chlorine and nickel are the micronutrients.

Categories of Essential Elements:

  1. As components of biomolecules, e.g. carbon, hydrogen, oxygen and nitrogen. These are structural elements of cells.

  2. As components of energy-related chemical compounds, e.g. magnesium in chlorophyll and phosphorous in ATP.

  3. Elements which activate or inhibit enzymes, e.g. Mg2+ activates RUBISCO and phosphenol pyruvate carboxylase. Similarly, Zn2+ activates alcohol dehydrogenase.

  4. Elements which alter osmotic potential of a cell, e.g. potassium plays an important role in opening and closing of stomata.

Role of Macro- and Micro-nutrients:

  1. Nitrogen: Nitrogen is the mineral which is required by plants in the greatest amount. Nitrogen is mainly absorbed as NO3 –, but some amounts are also taken up as NO4+ or NH4+. Nitrogen is one of the major constituents of protein, nucleic acids, vitamins and hormones.

  2. Phosphorous: This is absorbed by plants in the form of phosphate ions; either as H2PO4 – or HPO4 –. Phosphorous is a constituent of cell membranes, some proteins, nucleic acids and nucleotides. Phosphorous is also required for all phosphorylation reactions.

  3. Potassium: Potassium is absorbed as potassium ion (K+). This is required in more quantities by the meristematic tissues. Potassium helps in maintaining an anion-cation balance in cells. Potassium is involved in protein synthesis, opening and closing of stomata, activation of enzymes and maintenance of cell turgidity.

  4. Calcium: Calcium is absorbed in the form of calcium ions (Ca2+). Calcium is required by meristematic tissues and differentiating tissues. Calcium is utilised in the synthesis of cell wall. Calcium is also required for the formation of mitotic spindle. Certain enzymes are activated by calcium.

  5. Magnesium: Magnesium is absorbed in the form of magnesium ions (Mg2+). Magnesium activates the enzymes of respiration and photosynthesis. Magnesium is involved in the synthesis of DNA and RNA. It is a constituent of the ring structure of chlorophyll. It also helps in maintaining the ribosome structure.

  6. Sulphur: Sulphur is absorbed in the form of sulphate ion (SO42 –). Sulphur is present in two amino acids; cysteine and mthionine. Sulphur is the main component of several coenzymes, vitamins and ferredoxin.

  7. Iron: Iron is absorbed in the form of ferric ions (Fe+3). Iron is the micronutrient which is required in the largest amou nt. Iron is an important component of proteins which are involved in electron transfer chain. Iron plays an important role in the formation of chlorophyll.

  8. Manganese: Manganese is absorbed in the form of manganous ions (Mn+2). Manganese activates many enzymes which are involved in photosynthesis, respiration and nitrogen metabolism. Splitting of water molecule during photosynthesis is facilitated by manganese.

  9. Zinc: Zinc is absorbed in the form of zinc ions (Zn+2). Zinc activates various enzymes; like carboxylase. Zinc is required in the synthesis of auxin.

  10. Copper: Copper is absorbed in the form of cupric ions (Cu+2). Copper is essential for overall metabolism in plants. Copper is associated with certain enzymes in redox reactions.

  11. Boron: Boron is absorbed as BO33 – or B4O72 –.Boron is required for uptake and utilization of calcium, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.

  12. Molybdenum: Molybdenum is absorbed in the form of molybdate ions (MoO22+). Molybdenum is a component of various enzymes; like nitrogenase and nitrate reductase.

  13. Chlorine: Chlorine is absorbed in the form of chloride ion. Along with Na+ and K+, chlorine helps in determining solute concentration and in anion-cation balance. Chlorine also plays an important role in splitting of water.

Deficiency Symptoms of Essential Elements

  1. There are different symptoms for deficiency of different elements. When a deficient mineral is provided to the plant, the symptoms disappear. But if the deficiency continues, it may lead to the death of the plant.

  2. Appearance of deficiency also depends on the mobility of the element in the plant. Some elements are actively mobilized in plants and are exported to young developing tissues. Deficiency of such elements first appears in the older tissues. For example; the deficiency symptoms of nitrogen, potassium and magnesium are first seen in the senescent leaves. This happens because these elements are mobilized to younger leaves.

  3. Some elements are relatively immobile in plants. These elements are not transported out of the mature organs. Deficiency of such elements first appears in younger parts of the plant, e.g. sulphur and calcium.

  4. Some deficiency symptoms in plants are; chlorosis, necrosis, stunted plant growth, premature fall of leaves and buds and inhibition of cell division.

  5. Chlorosis: Loss of chlorophyll is called chlorosis. This results in yellowing of leaves. Chlorosis is caused by the deficiency of N, K, Mg, S, Fe, Mn, Zn and Mo.

  6. Necrosis: Death of tissue; particularly leaf tissue; is called necrosis. Necrosis is caused by the deficiency of Ca, Mg, Cu and K.

  7. Deficiency of N, K, S and Mo causes stunted growth because of inhibition of cell division. Deficiency of N, S and Mo delays flowering.

Toxicity of Micronutrients
  1. If a mineral ion concentration in tissues reaches to a level that it reduces the dry weight of tissues by about 10%, the mineral then becomes toxic. It is difficult to identify the symptoms of toxicity. Sometimes, excess of an element may inhibit the uptake of another element. For example; the symptom of manganese toxicity is the appearance of brown spots surrounded by chlorotic veins. Manganese competes with iron and magnesium for uptake. Manganese also inhibits calcium translocation in shoot apex. Hence, excess of manganese results in deficiency of iron, magnesium and calcium. So, the apparent symptoms of manganese toxicity are in fact the deficiency symptoms of iron, magnesium and calcium.

MECHANISM OF ABSORPTION OF ELEMENTS

  1. Absorption of minerals takes place in two main phases. In the first phase, passive absorption takes place through apoplast pathway. In the second phase, absorption takes place through symplast pathway. The first phase involves passive transport (facilitated diffusion), while the second phase involves active transport. After that, minerals are transported through xylem.

NITROGEN CYCLE

  1. Nitrogen is available in limited amount in soil. Plants have to compete with microbes for this form of nitrogen. Hence, nitrogen is a limiting nutrient for plants.

  2. Lightning and ultraviolet radiations provide energy to convert gaseous nitrogen into oxides of nitrogen (NO, NO2 and N2O). Atmospheric nitrogen oxides also come from industrial combustions, forest fires, automobile exhausts and power stations.

  3. Decomposition of organic nitrogen of dead plants and animals leads to the formation of ammonia. This process is called ammonificaiton. Most of this ammonia is converted into nitrate by soil bacteria, while some of the ammonia vaporizes and re-enters the atmosphere.

  4. Conversion of ammonia into nitrate; by soil bacteria takes place in following steps:

  5. Biological Nitrogen Fixation (BNF):

    1. In this process, the atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. This can be shown by following equation:

N2 + 6H+ + 6e− → 2NH3

  1. This process is coupled with the hydrolysis of 16 equivalents of ATP. This is also accompanied by the co-formation of one molecule of H2.

  2. In free-living diazotrophs, the nitrogenase-generated ammonium is assimilated into glutamate through the glutamine synthetase or glutamate synthase pathway. Many nitrogen-fixing organisms exist only in anaerobic conditions; because the enzymes responsible for nitrogenase action are highly susceptible to destruction by oxygen.

Symbiotic Biological Fixation of Nitrogen
  1. The plants of the legume family (Fabaceae) are the major contributors towards nitrogen fixation. The root nodules of these plants harbor the Rhizobium bacteria. These bacteria produce nitrogen compounds which help the plant to grow properly. When the plant dies, the fixed nitrogen is released into the soil. Thus nitrogen becomes available for other plants.
     

REVISION NOTES

 

CLASS 11 BIOLOGY

UNIT I – DIVERSITY IN THE LIVING WORLD

Chapter 1 – The Living World 

Chapter 2 – Biological Classification 

Chapter 3 – Plant Kingdom 

Chapter 4 – Animal Kingdom 

UNIT II – STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS

Chapter 5 – Morphology of Flowering Plants 

Chapter 6 – Anatomy of Flowering Plants 

Chapter 7 – Structural Organisation in Animals 

UNIT III – CELL : STRUCTURE AND FUNCTIONS

 

Chapter 8 – Cell: The Unit of Life 

Chapter 9 – Bio-Molecules 

Chapter 10 – Cell Cycle and Cell Division 

UNIT IV – PLANT PHYSIOLOGY 

Chapter 11 – Transport in Plants 

Chapter 12 – Mineral Nutrition 

Chapter 13 – Photosynthesis in higher plants 

Chapter 14 – Respiration in Plants 

Chapter 15 – Plant Growth and Development 

UNIT V – HUMAN PHYSIOLOGY 

Chapter 16 – Digestion And Absorption 

Chapter 17 – Breathing and Exchange of Gases 

Chapter 18 – Body fluids and circulation 

Chapter 19 – Excretory Products and their Elimination 

Chapter 20 – Locomotion and Movement 

Chapter 21 – Neural Control and Coordination 

Chapter 22 – Chemical Coordination and Integration 

CLASS 12 BIOLOGY

Unit-VI Reproduction
  

Chapter 1 : Reproduction in Organisms 

Chapter 2 : Sexual Reproduction in Flowering Plants 

Chapter 3 : Human Reproduction 

Chapter 4 : Reproductive Health 

Unit-VII Genetics and Evolution

Chapter 5 : Principles of Inheritance and Variation 

Chapter 6 : Molecular Basis of Inheritance 

Chapter 7 : Evolution 

Unit-VIII Biology and Human Welfare

Chapter 8 : Human Health and Disease 

Chapter 9 : Strategies for Enhancement in Food Production 

Chapter 10 : Microbes in Human Welfare 

Unit-IX Biotechnology  

Chapter 11 : Biotechnology Principles and Processes 

Chapter 12 : Biotechnology and its Applications 

Unit-X Ecology and Environment 

Chapter 13 : Organisms and Populations 

Chapter 14 : Ecosystem 

Chapter 15 : Biodiversity and Conservation 

Chapter 16 : Environmental Issues 

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