RBSE Solutions for Class 12 Biology Chapter 8 Mineral Nutrition in Plants
RBSE Solutions for Class 12 Biology Chapter 8 Mineral Nutrition in Plants
Rajasthan Board RBSE Class 12 Biology Chapter 8 Mineral Nutrition in Plants
RBSE Class 12 Biology Chapter 8 Multiple Choice Questions
Question 1.
Which of the following elements are called micronutrients?
(a) Mo, Cu, Zn, Ca
(b) Mg, S, K, P
(c) Mn, Zn, Cu, Mg
(d) Mn, Mo, Cu, Zn
Answer:
(d) Mn, Mo, Cu, Zn
Question 2.
The element found in chlorophyll is?
(a) Fe
(b) Mn
(c) Mg
(d) K
Answer:
(c) Mg
Question 3.
The main function of Mo is in which of the following?
(a) Flowering
(b) Nitrogen fixation
(c) Water absorption
(d) Photosynthesis
Answer:
(b) Nitrogen fixation
Question 4.
Little leaf disease is caused by a deficiency of which element?
(a) Zn
(b) Mg
(c) B
(d) S
Answer:
(a) Zn
Question 5.
Which element is most important for transportation of carbohydrates in plants?
(a) Fe
(b) Mo
(c) B
(d) Zn
Answer:
(c) B
Question 6.
The number of essential elements for normal growth and completion of the life cycle of plants is?
(a) 105
(b) 60
(c) 27
(d) 17
Answer:
(d) 17
Question 7.
Immobile nutrient elements are –
(a) Cu, S, Fe, Mn
(b) Ca, B, Cu, S
(c) N, P, Fe, Mn
(d) P, K, Zn, Mo
Answer:
(a) Cu, S, Fe, Mn
RBSE Class 12 Biology Chapter 8 Very Short Answer Questions
Question 1.
Plants absorb nitrogen in the form of?
Answer:
Plants absorb nitrogen in the form of nitrate and nitrite and as an exception as NH4+
Question 2.
Write the name of primary macronutrients?
Answer:
Nitrogen (N), Phosphorus (P), and Potassium (K)
Question 3.
Explain the term hydroponics and Vermiculite?
Answer:
Hydroponics:
The technique of culturing plants in a nutrient solution in place of soil is called liquid culture or hydroponics. This technique is used to determine the requirement of mineral nutrients of plants.
Vermiculite:
Vermiculite is a mineral substance found in soil in nature. This is lightweight, chemically inert, heat resistant, the sterile substance having water holding capacity more than soil. This substance is heated in a furnace at 2000°F and the product is used in culturing plants. This technique is called Vermiculoponics.
Question 4.
In which form Fe and Cl are absorbed from the soil?
Answer:
He is absorbed in the form of Ferric (Fe3+) ion and chlorine are absorbed in the form of Chloride (Cl–) ion.
Question 5.
What do you understand by mineral salt absorption?
Answer:
Absorption of mineral salts from soil solution in the form of ions by the young part of the root is called mineral salt absorption. Normally mineral salt absorption takes place by use of metabolic energy. This process is called the active absorption of minerals.
RBSE Class 12 Biology Chapter 8 Short Answer Questions
Question 1.
Describe plant ash analysis.
Answer:
- This method is used to determine the presence of a relative amount of various elements in the plant.
- In this method when fresh plants are dried at 70 – 80° C in the oven for one or two days so that, all water present in the plant is driven off.
- The remaining part is weighed and the dry weight of the plant is obtained.
- The main constituents of the dry matter are the polysaccharides, lignin, proteins, fats, organic acids and some other elements.
- This dry matter is burnt in a furnace at 600° C, as a result, all organic compounds are oxidized and are driven off in the form of gases (CO2, NH3 and SO2 etc.).
- The remaining material is called plant ash and contains only mineral elements.
- The relative amount of various minerals can be determined by analysis of this ash. However, the extent of their utilization and essentiality cannot be determined by this method.
Question 2.
Describe the utility of nitrogen for plants and the symptoms caused by a deficiency of nitrogen?
Answer:
- Nitrogen is used in the synthesis of amino acids, proteins, DNA, RNA, chlorophyll and other organic compounds.
- Nitrogen regulates respiration and growth of plants.
- It is required more in actively growing cells and buds.
Deficiency Symptoms:
- Chlorosis of leaves occurs first in old leaves and later on in young leaves.
- Due to the degradation of chlorophyll, anthocyanin pigment is formed and the leaves appear pinkish in colour.
- Rate of cell division and rate of protein synthesis is reduced and plants become stunted due to reduced growth.
Question 3.
Differentiate between active and passive absorption of minerals.
Answer:
Question 4.
Explain Chlorosis and Necrosis?
Answer:
- Chlorosis:
Due to the degradation of chlorophyll, the leaves become decolourized and become pale yellow coloured. This effect is called chlorosis. Deficiency of Mg, N, Fe, and Mn etc. result in chlorosis. - Necrosis:
Death or degradation of cells of plant tissue is called necrosis. Due to this effect, the leaves show spots, rotting, or blight symptoms. Deficiency of Ca, Mg, Cu, and K etc. causes necrosis of cells.
RBSE Class 12 Biology Chapter 8 Essay Type Questions
Question 1.
Write a short essay on mineral nutrition in plants.
Answer:
Plants obtain nutrient substances from their surrounding for their normal growth, development and completion of the life cycle. The use of these minerals in the nutrition of plants is called mineral nutrition.
Different nutrients are being listed in the flow chart given below.
Mineral nutrition in plants:
Or
Role of macro and micronutrients in plant nutrition:
- Essential elements participate in different physiological activities of plants.
- These elements play important role in, regulating the permeability of the plasma membrane, controlling osmotic pressure, electron transport system, balancing various biochemical reactions with the help of enzymes, storage of reserve food material in storage organs, buffer actions, etc.
- A brief account of availability, uses and effect of deficiency and excess of essential elements on the plants is given below.
Carbon, Hydrogen and Oxygen:
- These are non-mineral essential elements which are absorbed by plants from atmosphere and soil in the form of CO2, O2 and H2O.
- These are constituents of all organic compounds such as carbohydrates, fats, proteins, etc.
- About 90 – 95% of the dry weight of most higher plants consists of C, H and Oxygen. Normally plants do not suffer from the deficiency of these elements.
Nitrogen:
- The amount of nitrogen in the air is about 78% by volume.
- Plants absorb nitrogen from the soil in the form of NO2, NO3 and as an exception as NH4.
- It is the main component of amino acids, proteins, nucleic acids, vitamins and phytohormones.
- Nitrogen is especially required in meristematic cells, buds and other metabolically active cells.
- Chemical fertilizer urea is the main source of nitrogen.
Deficiency Symptoms:
- Deficiency of nitrogen results into chlorosis, first in old leaves followed by young leaves. Due to the degradation of
- chlorophyll leaves begin to appear pinkish due to anthocyanin effect.
- Plants show stunting due to a reduced rate of respiration and protein synthesis.
Phosphorus:
- Phosphorus is absorbed from soil in the form of soluble inorganic phosphate ions either as H2PO–4 or HPO2−4.
- It is transported in a plant in inorganic form but it is found in the plant in the form of organic compounds. Normally it’s an amount in plants is 0.2 to 0.8% of the dry weight of the plant and is next to nitrogen among the mineral nutrients derived from the soil.
- It is the main constituent of DNA, RNA, Phospholipids, NAD, NADP, ATP, ADP, etc.
- It plays a significant role in oxidation-reduction reactions, respiration, photosynthesis and fatty acid synthesis.
- It is also required in all phosphorylation reactions.
- It is founded in high amount in meristematic regions.
Deficiency Symptoms:
- Plants show stunted growth and leaves become dark green in colour.
- Leaves and stem show anthocyanin pigmentation.
- Acute deficiency results into formation of necrotic areas in leaves and fruits.
- Leaves become deformed and may fall early.
- The activity of cambium is suppressed.
- Fruiting may be inhibited.
Calcium:
- Calcium is found in the form of calcite and dolomite ore in soil insufficient amount.
- It is absorbed from soil in the form of calcium ions (Ca++).
- It is an important component of middle lamella where it is found as calcium pectate.
- It is also needed during the formation of the mitotic spindle.
- Hence is required by meristematic and differentiating cells.
- It provides elasticity to the cell wall.
- Calcium plays an important role in the binding of nucleic acids with proteins and formation of chromosomes.
- It also plays an important role in the transportation of carbohydrates and amino acids.
Deficiency Symptoms:
- Cell walls lose their elasticity and become rigid.
- Cellular differentiation is adversely affected.
- Young leaves become distorted and the leaf tip bends downwards. This is called hooked leaf symptom.
- Chlorosis occurs along the margins of young leaves.
- A premature drop of flowers takes place.
Potassium(K):
- It is found in soil insoluble and exchangeable form.
- It is absorbed in the form of potassium ion (K+).
- Potassium is not a component of any biochemical compound and is not a structural element.
- It plays an important role in four biochemical reactions viz cation neutralization, transport across the membrane, enzyme activation and osmotic potential regulation.
- The best function of potassium is in regulating the opening of stomata.
- It also plays an important role in photosynthesis and normal growth of seeds and fruits.
Deficiency Symptoms:
- The first symptom of deficiency of potassium is marginal chlorosis.
- The leaves become mottle due to chlorosis.
- Shortening of internodes results in stunted growth and bushy appearance of plants. Necrotic spots appear on the margins of more mature leaves.
- Disease resistance of plants decreases.
- Rate of protein synthesis decreases.
Magnesium:
- Magnesium is found in soil as magnesium carbonate (MgCO3) and is absorbed as magnesium ion (Mg++).
- It is an important component of chlorophyll pigment.
- This element activates the enzymes of respiration, protein synthesis and photosynthesis. It helps in joining the two subunits of ribosomes.
- It is also involved in the synthesis of DNA and RNA.
- It is found in abundant amount in oilseeds as it plays an important role in the formation of oil seeds.
Deficiency symptoms:
- Magnesium deficiency causes extensive interveinal chlorosis.
- Leaves show reddish and yellow and orange spots due to the predominance of anthocyanin pigments.
- There is a decline in photosynthesis.
- In acute cases leaves become nearly white.
Sulphur (S):
- This is absorbed from soil in the form of sulphate ion (SO++4). Besides this sulphur dioxide (SO2) present as an environmental pollutant may also be absorbed by plants.
- It is helpful in the synthesis of amino acids such as cysteine, methionine, etc. needed in protein synthesis.
- It is also found in vitamin B and coenzyme-A.
- It is an important component of protoplasm.
- In the roots of plants of pea family growing in sulphur rich soil, the nodules are better developed.
- The characteristic pungent odour of cruciferous plants, & onion and garlic is due to sulphur-rich volatile oils.
Deficiency symptoms:
- Leaves show chlorosis.
- Shortage of sulphur-containing amino acids occurs.
- Plants become stunted and fail to form fruits.
- Plants become stiff and woody due to the formation of more of thick-walled tissue such as sclerenchyma and xylem.
Iron (Fe):
- Plants absorb iron from the soil in the form of ferric ions (Fe+++).
- It plays an important role in cell division, respiration and different steps of the electron transport system.
- It is an important constituent of cytochrome and ferredoxin and acts as an activator of aconitase, catalase, peroxidase and some Krebs cycle enzymes.
- It is helpful in chlorophyll synthesis but is not a part of chlorophyll molecules.
- It is found as fixed protein (Phytopheritin) in leaves and in the chromatin network of the nucleus.
- In metabolic reactions, it participates as Fe++ (Ferrous).
Deficiency symptoms:
- Young leaves show extensive chlorosis and may become white or yellow-white. The derailment of reactions of photosynthesis, respiration and protein synthesis occurs.
- Cell division activity is inhibited.
- Plant growth becomes slow.
Manganese:
- It is found in soil normally in the form of manganese dioxide (MnO2) and plants absorb it in the form of Mn++ ion.
- Manganese acts as an activator of several enzymes related to respiration, photosynthesis, and nitrogen metabolism reactions.
- It plays an important role in the synthesis of chlorophyll and the development of chloroplasts.
- The best-defined function of Mn is photolysis of water and evolution of O2.
Deficiency symptoms:
- Young, as well as old leaves, show chlorosis.
- Limited development of roots. Its deficiency causes specific plant diseases.
Example:
- Marsh spot of pea
- Grey speck of oats
Boron (B):
- Boron is absorbed from soil in the form of borate ions (BO3−3, B4O2−7).
- It reacts with calcium present in the soil to form calcium borate which cannot be absorbed by roots.
- Because of this, the availability of boron is low in calcium-rich soils.
- Boron plays an important role in the translocation of carbohydrates, cell division, nitrogen metabolism, pollen germination and functioning of the plasma membrane.
Deficiency symptoms:
- The leaves become thick and dark green in colour due to deficiency of boron.
- Storage tissue and fleshy parts become disorganized.
- The number of flowers is reduced. Flowers become sterile due to an effect on pollen germination.
- Death of growing points results in dwarfing.
Zinc (Zn):
- This element is absorbed from soil in the form of zinc ions (Zn++).
- Zinc is required for the synthesis of growth hormone indole acetic acid. (IAA).
- It also controls the absorption of phosphorus.
- Zinc is a component of several types of enzymes especially carboxylases.
Deficiency symptoms:
- Deficiency of zinc causes littering of leaves.
- Leaves become distorted and small in size.
- Discoloured necrotic spots appear on leaves.
- Phloem tissue shows malformation (poorly formed).
- Little leaf disease is the main symptom of zinc deficiency.
Copper (Cu):
- It is absorbed from soil by roots in the form of divalent cupric ions (Cu++) or monovalent cuprous ions (Cu+).
- Copper acts as an electron carrier in oxidation-reduction reactions.
- It is a component of plastocyanin and cytochrome oxidase which acts as an electron carrier in photosynthesis.
Deficiency symptoms:
- Wilting and curling of leaves occurs.
- The leaf tip shows chlorosis and becomes discoloured.
- In Citrus deficiency of copper causes dieback disease of a leaf.
Molybdenum (Mo):
- This element is absorbed in the form of molybdenum oxide (MoO2).
- This is required for nitrogen fixation in leguminous plants.
- Molybdenum ions are part of enzyme nitrogenase and nitrate reductase which are involved in nitrogen fixation.
Deficiency Symptoms:
- Mottling of leaves is a characteristic symptom of molybdenum deficiency.
- Chlorosis of leaves and poor flower setting is observed. In cauliflower, the leaves become distorted and subsequently die. This is called whiptail disease and is caused due to molybdenum deficiency.
Chlorine (Cl):
- Chlorine is absorbed from soil in the form of chloride ions (Cl–).
- This element is not a component of any biochemical substance.
- It plays an important role in carbohydrate metabolism and in balancing anion-cation concentration in the cell.
- It is helpful in the photolysis of water leading to the evolution of oxygen.
Deficiency symptoms:
- Leaves show variegated chlorosis followed by necrosis.
- Fruit formation is reduced and the size of fruit is also reduced.
Nickel (Ni):
- Dalton (1988) included nickel as essential element.
- It is found in soil in sufficient amount and is absorbed in the form of nickel ions (Ni++). Nickel is neither a component of any biochemical compound nor its function and deficiency are properly understood.
- It is an essential part of the enzyme urease. It is probably helpful in the transportation of nitrogenous compounds.
Deficiency symptoms:
- Plants show chlorosis and formation of necrotic tissue in leaves.
- Plants growing in soil normally do not suffer a deficiency of nickel because it is required in very minute quantity.
Note: It is important to note that deficiency symptoms of mobile elements first appear in old leaves whereas the deficiency symptoms of immobile elements first appear in young leaves. - Deficiency symptoms due to deficiency of Ca and B appear in terminal buds.
- Deficiency symptoms first appear in old leaves due to deficiency of mobile elements such as N, P, K, Mg, Zn, Mo.
- Deficiency symptoms first appear in young leaves due to deficiency of immobile elements such as Cu, S, Fe, Mn.
Question 2.
Write names of essential elements of plants and write their function, availability, form in which absorbed and deficiency symptoms of any four.
Answer:
The elements which have been found to occur in all plants and are necessarily required for the normal growth, development and reproduction of plants are called essential elements. The total number of elements essential for plants is seventeen (17). These are C, H, O, P, K, Ca, Mg, S, B, Cu, Fe, CI, Mo, Mn, Zn and Ni.
Role of macro and micronutrients in plant nutrition:
- Essential elements participate in different physiological activities of plants.
- These elements play important role in, regulating the permeability of the plasma membrane, controlling osmotic pressure, electron transport system, balancing various biochemical reactions with the help of enzymes, storage of reserve food material in storage organs, buffer actions, etc.
- A brief account of availability, uses and effect of deficiency and excess of essential elements on the plants is given below.
Carbon, Hydrogen and Oxygen:
- These are non-mineral essential elements which are absorbed by plants from atmosphere and soil in the form of CO2, O2 and H2O.
- These are constituents of all organic compounds such as carbohydrates, fats, proteins, etc.
- About 90 – 95% of the dry weight of most higher plants consists of C, H and Oxygen. Normally plants do not suffer from a deficiency of these elements.
Nitrogen:
- The amount of nitrogen in the air is about 78% by volume.
- Plants absorb nitrogen from the soil in the form of NO2, NO3 and as an exception as NH4.
- It is the main component of amino acids, proteins, nucleic acids, vitamins and phytohormones.
- Nitrogen is especially required in meristematic cells, buds and other metabolically active cells.
- Chemical fertilizer urea is the main source of nitrogen.
Deficiency Symptoms:
- Deficiency of nitrogen results into chlorosis, first in old leaves followed by young leaves. Due to the degradation of chlorophyll leaves begin to appear pinkish due to anthocyanin effect.
- Plants show stunting due to a reduced rate of respiration and protein synthesis.
Phosphorus:
- Phosphorus is absorbed from soil in the form of soluble inorganic phosphate ions either as H2PO–4 or HPO2−4.
- It is transported in a plant in inorganic form but it is found in the plant in the form of organic compounds. Normally it’s an amount in plants is 0.2 to 0.8% of the dry weight of the plant and is next to nitrogen among the mineral nutrients derived from the soil.
- It is the main constituent of DNA, RNA, Phospholipids, NAD, NADP, ATP, ADP, etc.
- It plays a significant role in oxidation-reduction reactions, respiration, photosynthesis and fatty acid synthesis.
- It is also required in all phosphorylation reactions.
- It is founded in high amount in meristematic regions.
Deficiency Symptoms:
- Plants show stunted growth and leaves become dark green in colour.
- Leaves and stem show anthocyanin pigmentation.
- Acute deficiency results into formation of necrotic areas in leaves and fruits.
- Leaves become deformed and may fall early.
- The activity of cambium is suppressed.
- Fruiting may be inhibited.
Calcium:
- Calcium is found in the form of calcite and dolomite ore in soil insufficient amount.
- It is absorbed from soil in the form of calcium ions (Ca++).
- It is an important component of middle lamella where it is found as calcium pectate.
- It is also needed during the formation of the mitotic spindle.
- Hence is required by meristematic and differentiating cells.
- It provides elasticity to the cell wall.
- Calcium plays an important role in the binding of nucleic acids with proteins and formation of chromosomes.
- It also plays an important role in the transportation of carbohydrates and amino acids.
Deficiency Symptoms:
- Cell walls lose their elasticity and become rigid.
- Cellular differentiation is adversely affected.
- Young leaves become distorted and the leaf tip bends downwards. This is called hooked leaf symptom.
- Chlorosis occurs along the margins of young leaves.
- A premature drop of flowers takes place.
Potassium(K):
- It is found in soil insoluble and exchangeable form.
- It is absorbed in the form of potassium ion (K+).
- Potassium is not a component of any biochemical compound and is not a structural element.
- It plays an important role in four biochemical reactions viz cation neutralization, transport across the membrane, enzyme activation and osmotic potential regulation.
- The best function of potassium is in regulating the opening of stomata.
- It also plays an important role in photosynthesis and normal growth of seeds and fruits.
Deficiency Symptoms:
- The first symptom of deficiency of potassium is marginal chlorosis.
- The leaves become mottle due to chlorosis.
- Shortening of internodes results in stunted growth and bushy appearance of plants. Necrotic spots appear on the margins of more mature leaves.
- Disease resistance of plants decreases.
- Rate of protein synthesis decreases.
Magnesium:
- Magnesium is found in soil as magnesium carbonate (MgCO3) and is absorbed as magnesium ion (Mg++).
- It is an important component of chlorophyll pigment.
- This element activates the enzymes of respiration, protein synthesis and photosynthesis. It helps in joining the two subunits of ribosomes.
- It is also involved in the synthesis of DNA and RNA.
- It is found in abundant amount in oilseeds as it plays an important role in the formation of oil seeds.
Deficiency symptoms:
- Magnesium deficiency causes extensive interveinal chlorosis.
- Leaves show reddish and yellow and orange spots due to the predominance of anthocyanin pigments.
- There is a decline in photosynthesis.
- In acute cases leaves become nearly white.
Sulphur (S):
- This is absorbed from soil in the form of sulphate ion (SO++4). Besides this sulphur dioxide (SO2) present as an environmental pollutant may also be absorbed by plants.
- It is helpful in the synthesis of amino acids such as cysteine, methionine, etc. needed in protein synthesis.
- It is also found in vitamin B and coenzyme-A.
- It is an important component of protoplasm.
- In the roots of plants of pea family growing in sulphur rich soil, the nodules are better developed.
- The characteristic pungent odour of cruciferous plants, & onion and garlic is due to sulphur-rich volatile oils.
Deficiency symptoms:
- Leaves show chlorosis.
- Shortage of sulphur-containing amino acids occurs.
- Plants become stunted and fail to form fruits.
- Plants become stiff and woody due to the formation of more of thick-walled tissue such as sclerenchyma and xylem.
Iron (Fe):
- Plants absorb iron from the soil in the form of ferric ions (Fe+++).
- It plays an important role in cell division, respiration and different steps of the electron transport system.
- It is an important constituent of cytochrome and ferredoxin and acts as an activator of aconitase, catalase, peroxidase and some Krebs cycle enzymes.
- It is helpful in chlorophyll synthesis but is not a part of chlorophyll molecules.
- It is found as fixed protein (Phytopheritin) in leaves and in the chromatin network of the nucleus.
- In metabolic reactions, it participates as (Fe++).
Deficiency symptoms:
- Young leaves show extensive chlorosis and may become white or yellow-white. The derailment of reactions of photosynthesis, respiration and protein synthesis occurs.
- Cell division activity is inhibited.
- Plant growth becomes slow.
Manganese:
- It is found in soil normally in the form of manganese dioxide (MnO2) and plants absorb it in the form of Mn+ ion.
- Manganese acts as an activator of several enzymes related to respiration, photosynthesis, and nitrogen metabolism reactions.
- It plays an important role in the synthesis of chlorophyll and the development of chloroplasts.
- The best-defined function of Mn is photolysis of water and evolution of (O2)
Deficiency symptoms:
- Young, as well as old leaves, show chlorosis.
- Limited development of roots. Its deficiency causes specific plant diseases.
Example:
- Marsh spot of pea
- Grey speck of oats
Boron (B):
- Boron is absorbed from soil in the form of borate ions (BO3−3, B4O2−7).
- It reacts with calcium present in the soil to form calcium borate which cannot be absorbed by roots.
- Because of this, the availability of boron is low in calcium-rich soils.
- Boron plays an important role in the translocation of carbohydrates, cell division, nitrogen metabolism, pollen germination and functioning of the plasma membrane.
Deficiency symptoms:
- The leaves become thick and dark green in colour due to deficiency of boron.
- Storage tissue and fleshy parts become disorganized.
- The number of flowers is reduced. Flowers become sterile due to an effect on pollen germination.
- Death of growing points results in dwarfing.
Zinc (Zn):
- This element is absorbed from soil in the form of zinc ions (Zn++).
- Zinc is required for the synthesis of growth hormone indole acetic acid. (IAA).
- It also controls the absorption of phosphorus.
- Zinc is a component of several types of enzymes especially carboxylases.
Deficiency symptoms:
- Deficiency of zinc causes littering of leaves.
- Leaves become distorted and small in size.
- Discoloured necrotic spots appear on leaves.
- Phloem tissue shows malformation (poorly formed).
- Little leaf disease is the main symptom of zinc deficiency.
Copper (Cu):
- It is absorbed from soil by roots in the form of divalent cupric ions (Cu++) or monovalent cuprous ions (Cu+).
- Copper acts as an electron carrier in oxidation-reduction reactions.
- It is a component of plastocyanin and cytochrome oxidase which acts as an electron carrier in photosynthesis.
Deficiency symptoms:
- Wilting and curling of leaves occurs.
- The leaf tip shows chlorosis and becomes discoloured.
- In Citrus deficiency of copper causes dieback disease of the leaf.
Molybdenum (Mo):
- This element is absorbed in the form of molybdenum oxide (MoO2).
- This is required for nitrogen fixation in leguminous plants.
- Molybdenum ions are part of enzyme nitrogenase and nitrate reductase which are involved in nitrogen fixation.
Deficiency Symptoms:
- Mottling of leaves is a characteristic symptom of molybdenum deficiency.
Chlorosis of leaves and poor flower setting is observed. In cauliflower, the leaves become distorted and subsequently die. - This is called whiptail disease and is caused due to molybdenum deficiency.
Chlorine (Cl):
- Chlorine is absorbed from soil in the form of chloride ions (Cl–).
- This element is not a component of any biochemical substance.
- It plays an important role in carbohydrate metabolism and in balancing anion-cation concentration in the cell.
- It is helpful in the photolysis of water leading to the evolution of oxygen.
Deficiency symptoms:
- Leaves show variegated chlorosis followed by necrosis.
- Fruit formation is reduced and the size of fruit is also reduced.
Nickel (Ni):
- Dalton (1988) included nickel as essential element.
- It is found in soil in sufficient amount and is absorbed in the form of nickel ions (Ni++). Nickel is neither a component of any biochemical compound nor its function and deficiency are properly understood.
- It is an essential part of the enzyme urease. It is probably helpful in the transportation of nitrogenous compounds.
Deficiency symptoms:
- Plants show chlorosis and formation of necrotic tissue in leaves.
- Plants growing in soil normally do not suffer a deficiency of nickel because it is required in very minute quantity.
Note: It is important to note that deficiency symptoms of mobile elements first appear in old leaves whereas the deficiency symptoms of immobile elements first appear in young leaves. - Deficiency symptoms due to deficiency of Ca and B appear in terminal buds.
- Deficiency symptoms first appear in old leaves due to deficiency of mobile elements such as N, P, K, Mg, Zn, Mo.
- Deficiency symptoms first appear in young leaves due to deficiency of immobile elements such as Cu, S, Fe, Mn.
Question 3.
Write a detailed account of the mechanism of mineral salt absorption.
Answer:
Plants absorb mineral salt from the soil in the form of cations and anions through different methods. The mechanism of mineral absorption can be understood under the following heads.
(1) Passive absorption
- Mass flow hypothesis
- Ion exchange theory
- Donnan equilibrium theory
(2) Active absorption
- Carrier concept
- Ion pump or cytochrome pump concept
- Electrochemical gradient hypothesis
(1) Passive absorption:
According to this theory, mineral elements enter the cell from the soil solution along their electrochemical potential gradient i.e. from their higher concentration to the place of their lower concentration without any expenditure of energy of the cell. Three theories have been put forwarded in support of passive absorption of minerals.
1. Mass flow hypothesis:
According to this theory, under the influence of transpiration pull, mineral ions are also absorbed along with the stream of water. Mass flow, also called as the bulk flow is the unidirectional movement of molecules or ions through the root along with a stream of water due to the suction force created by transpiration pull. An increase in the rate of transpiration results in to increase in the rate of passive absorption.
2. Ion Exchange theory:
Exchange of cations and anions in between the external solution (soil solution) and the surface of the root is called ion exchange. This hypothesis assumes that exchange of cations and anions takes place by ions of similar charge i.e. K+ of the external solution can exchange with H+ on the surface of the membrane and similarly the anion can also exchange with free hydroxyl ion.
3. Donnan equilibrium theory:
- This theory was proposed by Donnan (1927).
- According to this theory, there are some fixed ions in the cell which cannot pass out of the cell membrane. These are called stable ions, whereas both anions and cations can enter the membrane from outside.
- Normally there is an equilibrium of ions between external and the internal solution. This theory assumes that a cell has a concentration of fixed ions to which its membrane is impermeable. An equal number of anions and cations from the external solution will diffuse across the membrane until it reaches the state of equilibrium.
- This theory explains the accumulation of anions against a concentration gradient without the participation of metabolic energy.
Note: It is assumed that at least a part of the total salt uptake may result from passive absorption and it may account for salt accumulation within the plant tissue. The rate of mineral salt absorption is too rapid and cannot be explained by passive absorption which requires metabolic energy.
(2) Active absorption:
According to this theory, mineral elements move against the concentration gradient or the electrochemical potential and metabolic energy of the cell is used in the process. This process requires ATP molecules. This absorption is called active absorption. Following theories have been put forwarded in support of this theory.
1. Carrier Concept:
- This theory was proposed by Van Den Honert (1937).
- According to this concept, the part of the cell or tissue in which ions are absorbed by the use of metabolic energy is called inner space and the area outside this is called outer space.
- The boundary or barrier (cell membrane or plasma membrane and tonoplast) between inner and outer space is impermeable to the movement of free ions.
- According to Honert (1937), protein molecule present at the surface of membrane acts as a carrier and combines on outer space with a specific ion in the soil solution, transports it across the membrane and releases it in the inner space.
- The process can be explained with the help of following steps.
- Carrier + ATP (Activation of Carrier)
- Activated carrier + Ion – Carrier ion complex.
- Carrier ion complex – Carrier + Ion
2. Ion Pump or Cytochrome Pump Theory:
- This theory was proposed by Lundegardh and Burstroem (1933).
- According to this theory, there is a direct relationship between the rate of respiration and the absorption of anions.
- Anions are transported from the outer surface of membranes to the inner surface by cytochromes.
- To balance the electrochemical potential, the cations move from the outer surface to the inner surface of the membrane.
- This theory assumes that anions are taken up by expenditure of energy whereas movement of cations is passive.
3. Electrochemical gradient hypothesis:
- This hypothesis has been proposed by Peter Mitchel (1968).
- According to this hypothesis, anions are transported across the membrane due to electrochemical potential developed on the outer and inner face of the membrane.
- In this process, the ATPase enzyme plays an important role.
- The essential elements of plants have been divided into two groups.
Macronutrient elements
Micronutrient elements.
- The essential elements of plants have been divided into two groups.
- C, H, and O are called non-mineral essential elements. Normally soil is deficient in Nitrogen (N), Phosphorus (P) and Potassium (K). Hence these elements are called critical elements.
- In order to fulfil the deficiency of these critical elements, farmers supplement the soil with ammonium sulphate, ammonium nitrates and superphosphates etc. as chemical fertilizer.
- Dalton et.al. (1988) included nickel (Ni) in the category of essential elements.
- Mn+2 and Cl– ions are required in the photolysis of water during photosynthesis. Degradation of chlorophyll pigment is called chlorosis.
- The mechanism of mineral absorption has been explained on the basis of active absorption and passive absorption. In passive absorption, energy is not required whereas inactive absorption, metabolic energy is necessarily required.
Question 4.
Write an essay on Macronutrients.
Answer:
Macronutrients:
Such essential elements which are found in a plant in the range of 1.0 to 10.0 mg per gram of dry weight of plant are called macronutrients or mega nutrients.
These are further divided into two categories.
- Primary macronutrients – Nitrogen, Phosphorus and Potassium are also called as critical elements and soils normally show a deficiency of these elements.
- Secondary macronutrients – Calcium, Magnesium, and Sulphur are secondary macronutrients.
Essential elements:
- Green plants synthesize carbohydrate by photosynthesis using CO2 absorbed from atmosphere and water absorbed from the soil.
- Plants require several inorganic mineral elements and these are derived from soil or atmosphere.
- Out of 105 elements found on earth, about 60 elements have been found present in plants, but all these are not essential for plants.
- Various studies have revealed that for normal growth of a plant, seventeen (17) elements are necessary. These are called essential elements.
- Many non-essential elements present beyond a certain limit may be toxic to plants.
A criterion for determining the essentiality of 17 essential elements:
- These elements are necessarily required for normal growth, development and reproduction of plants.
- The function of the essential elements should be specific and its deficiency can be fulfilled only by this element and not by any other element.
- The element must be directly involved in the metabolism of the plant.
- A specific symptom must appear in the plant due to deficiency of a specific element and the symptom must disappear by a supply of that element.
Macronutrients:
Elements which are found in the plant in an amount from 1.0 to 10.0 mg per gm of the dry weight of the plant are called macronutrients. These are nine in number – C, H, O, N, P, K, S, Mg, and Ca. Among this N, P and K are considered as primary macronutrients and also called as critical elements whereas Ca, Mg and S are considered as secondary macronutrients.
Question 5.
Write an essay on micronutrients.
Answer:
Micronutrients:
Such essential elements which are found less than 1.0 mg per gram of dry weight of plant are called micronutrients. Although these are found in low amount, they play an important role in plant metabolism. These are also called trace elements. These are eight in number.
Example: B, Cu, Cl, Mn, Mo, Zn, Fe and Ni.
Micronutrients:
Elements which are found in plants in an amount less than 1.0 mg per gm of dry weight are called minor or micronutrients. Although required in very small amount, they play a significant role in plant metabolism. These are also called trace elements. These are nine in number – B, Cu, Cl, Mn, Mo, Ni, Zn, and Fe.
- Besides the above 17 elements, some other elements have also been found beneficial in higher plants. These are called beneficial or functional elements. Eg: Na, Si, Co and So.
- Essential elements are also classified on the basis of their function or role in plant nutrition.
These categories are:- Structural elements:
The essential elements which are constituents of biochemicals are called structural elements. Example: e, h, o, n. - Energy-related elements:
Such essential elements are useful in energy-related biochemical reactions in the plant. Example: Phosphorous in ATP and Mg in chlorophyll. - Enzyme activators:
These essential elements act as activator or inhibitors of different enzymes. Example: Mn, Zn, Mo. Mg, Etc.
- Structural elements:
Note: Some essential elements regulate the osmotic activity of plant cells. Example K, Cl, etc. Potassium plays a significant role in stomatal movement (opening and closing of stomata).
- The 17 essential elements are generally referred to as mineral nutrients, but the source of four of these elements is atmosphere and water and not the soil. Some scientists consider these elements as non-mineral elements. Example Carbon, Hydrogen, Oxygen and Nitrogen.
- Although nitrogen is a major component of atmosphere higher plants cannot derive it directly from the atmosphere.
As nitrogen is obtained by plants in the form of nitrate or nitrite through the soil, it is categorized among mineral elements. - Hence out of 17 essential elements only C, H, and O are non-mineral elements and remaining 14 elements (N, P, K, S, Mg, Cu, Zn, Mo, Cl, Ni) are mineral elements.
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