NCERT Solutions for Class 11th BIOLOGY
Class 11 BIOLOGY SOLUTION
Chapter 12 tMineral NUTRITION
Question 1: ‘All elements that are present in a plant need not be essential to its survival’. Comment.
Answer Plants tend to absorb different kinds of nutrients from soil. However, a nutrient is inessential for a plant if it is not involved in the plant’s physiology and metabolism. For example, plants growing near radioactive sites tend to accumulate radioactive metals. Similarly, gold and selenium get accumulated in plants growing near mining sites. However, this does not mean that radioactive metals, gold, or selenium are essential nutrients for the survival of these plants.
Answer Plants tend to absorb different kinds of nutrients from soil. However, a nutrient is inessential for a plant if it is not involved in the plant’s physiology and metabolism. For example, plants growing near radioactive sites tend to accumulate radioactive metals. Similarly, gold and selenium get accumulated in plants growing near mining sites. However, this does not mean that radioactive metals, gold, or selenium are essential nutrients for the survival of these plants.
Question 2: Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?
Answer Hydroponics is the art of growing plants in a nutrient solution in the absence of soil. Since the plant roots are exposed to a limited amount of the solution, there are chances that the concentrations of oxygen and other minerals in the plant roots would reduce. Therefore, in studies involving mineral nutrition using hydroponics, purification of water and nutrient salts is essential so as to maintain an optimum growth of the plants.
Answer Hydroponics is the art of growing plants in a nutrient solution in the absence of soil. Since the plant roots are exposed to a limited amount of the solution, there are chances that the concentrations of oxygen and other minerals in the plant roots would reduce. Therefore, in studies involving mineral nutrition using hydroponics, purification of water and nutrient salts is essential so as to maintain an optimum growth of the plants.
Question 3: Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
Answer Macronutrients: They are the nutrients required by plants in large amounts. They are present in plant tissues in amounts more than 10 mmole kg–1 of dry matter. Examples include hydrogen, oxygen, and nitrogen.
Micronutrients: They are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than 10 mmole kg– 1 of dry matter. Examples include cobalt, manganese, zinc, etc.
Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants. Sodium, silicon, cobalt and selenium are beneficial to higher plants.
Toxic elements: Micronutrients are required by plants in small quantities. An excess of these nutrients may induce toxicity in plants. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.
Essential elements: These elements are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable. They are further classified as macro and micro-nutrients.
Answer Macronutrients: They are the nutrients required by plants in large amounts. They are present in plant tissues in amounts more than 10 mmole kg–1 of dry matter. Examples include hydrogen, oxygen, and nitrogen.
Micronutrients: They are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than 10 mmole kg– 1 of dry matter. Examples include cobalt, manganese, zinc, etc.
Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants. Sodium, silicon, cobalt and selenium are beneficial to higher plants.
Toxic elements: Micronutrients are required by plants in small quantities. An excess of these nutrients may induce toxicity in plants. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.
Essential elements: These elements are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable. They are further classified as macro and micro-nutrients.
Question 4: Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.
Answer The five main deficiency symptoms arising in plants are:
• Chlorosis
• Necrosis
• Inhibition of cell division
• Delayed flowering
• Stunted plant growth
Chlorosis or loss of chlorophyll leads to the yellowing of leaves. It is caused by the deficiencies of nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc, and molybdenum. Necrosis is the death of plant tissues as a result of the deficiencies of calcium, magnesium, copper, and potassium. Inhibition of cell division is caused by the deficiencies of nitrogen, potassium, sulphur, and molybdenum. Delayed flowering is caused by the deficiencies of nitrogen, sulphur, and molybdenum. Stunted plant growth is a result of the deficiencies of copper and sulphur.
Answer The five main deficiency symptoms arising in plants are:
• Chlorosis
• Necrosis
• Inhibition of cell division
• Delayed flowering
• Stunted plant growth
Chlorosis or loss of chlorophyll leads to the yellowing of leaves. It is caused by the deficiencies of nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc, and molybdenum. Necrosis is the death of plant tissues as a result of the deficiencies of calcium, magnesium, copper, and potassium. Inhibition of cell division is caused by the deficiencies of nitrogen, potassium, sulphur, and molybdenum. Delayed flowering is caused by the deficiencies of nitrogen, sulphur, and molybdenum. Stunted plant growth is a result of the deficiencies of copper and sulphur.
5.If a plant shows a symptom which could develop due to deficiency of more than one nutrient, how would you find out experimentally, the real deficient mineral element?
Soln.Deficiency symptoms are first studied by means of pot and culture experiments. Rapidly growing plants which develop characteristic symptoms are used in culture experiments. They are called test (= indicator) plants. They are then grown in soil under test in small pots. The results are compared to know the deficiency elements. Similar tests are performed with selected crops.
Soln.Deficiency symptoms are first studied by means of pot and culture experiments. Rapidly growing plants which develop characteristic symptoms are used in culture experiments. They are called test (= indicator) plants. They are then grown in soil under test in small pots. The results are compared to know the deficiency elements. Similar tests are performed with selected crops.
6.Why is it that in certain plants deficiency symptoms appear first in younger parts of the plant while in other they do so in mature organs?
Soln. The parts of the plants that show the deficiency symptoms depend on the mobility of the element in the plant. For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues. For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves. In older leaves,biomolecules containing these elements are broken down, making these elements available for mobilising to younger leaves. 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, for example, elements like sulphur and calcium are a part of the structural component of the cell and hence are not easily released.
Soln. The parts of the plants that show the deficiency symptoms depend on the mobility of the element in the plant. For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues. For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves. In older leaves,biomolecules containing these elements are broken down, making these elements available for mobilising to younger leaves. 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, for example, elements like sulphur and calcium are a part of the structural component of the cell and hence are not easily released.
7.How are the minerals absorbed by the plants?
Soln. Plants absorb their mineral salt supply from the soil through the roots from the zones of elongation and root hair. The minerals are absorbed as ions which are accumulated by the plants against their concentration in the soil. Plant shows two phases in mineral absorption – initial and metabolic. In the initial phase there is a rapid uptake of ions into outer or free space of the cells (apoplast) that comprises of intercellular spaces and cell walls. Ions absorbed in free space are freely exchangeable, e.g., replacement of unlabelled K+ ions with labelled K+ ions. In the metabolic phase the ions pass into inner space comprising of cytoplasm and vacuole. In the inner space the ions are not freely exchangeable with those of external medium. Entry of ions into outer space is passive absorption as no energy is required for it. Absorption of ions into inner space requires metabolic energy. It is, therefore, an active absorption. Movement of ions into cells is called influx while movement of ions out of the cells is called efflux.
Soln. Plants absorb their mineral salt supply from the soil through the roots from the zones of elongation and root hair. The minerals are absorbed as ions which are accumulated by the plants against their concentration in the soil. Plant shows two phases in mineral absorption – initial and metabolic. In the initial phase there is a rapid uptake of ions into outer or free space of the cells (apoplast) that comprises of intercellular spaces and cell walls. Ions absorbed in free space are freely exchangeable, e.g., replacement of unlabelled K+ ions with labelled K+ ions. In the metabolic phase the ions pass into inner space comprising of cytoplasm and vacuole. In the inner space the ions are not freely exchangeable with those of external medium. Entry of ions into outer space is passive absorption as no energy is required for it. Absorption of ions into inner space requires metabolic energy. It is, therefore, an active absorption. Movement of ions into cells is called influx while movement of ions out of the cells is called efflux.
8.What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobiuml What is their role inN2fixation?
Soln.The conditions necessary for nitrogen fixation by Rhizobium are :
(i) Presence of enzyme nitrogenase.
(ii)A protective mechanism for the enzyme nitrogenase against O2
(iii)A non-heme iron protein-ferrodoxin as an electron carrier.
(iv)The hydrogen donating system (viz, pyruvate, hydrogen, sucrose, glucoseetc).
(v) A constant supply of ATP.
(vi)Presence of thiamine pyrophosphate (TPP), coenzyme-A, inorganic phosphate and Mg++ as co-factors.
(vii)Presence of cobalt and molybdenum,
(viii) A carbon compound for trapping
released ammonia.
In the process of biological nitrogen fixation by free living and symbiotic nitrogen fixers, the dinitrogen molecule is reduced step by step to ammonia (NH3) by the addition of pairs of hydrogen atoms. The pyruvic acid mainly serves as an electron donor but in some cases hydrogen, sucrose, glucose, etc., have also been shown to operate. In leguminous plants, the glucose-6-phosphate molecule probably acts as a substrate for donating hydrogen. The overall process occurs in presence of enzyme nitrogenase, which is active in anaerobic condition. The enzyme nitrogenase consists of two sub-units – a non-heme iron protein (or dinitrogen reductase) and an iron molybdenum protein (Mo-Fe protein or dinitrogenase).
The Fe-protein component reacts with ATP and reduces Mo-Fe protein which then converts N2to ammonia. The ammonia is either directly taken by host or is converted to nitrates with the help of nitrifying bacteria (e.g., Nitrosomonas).
Soln.The conditions necessary for nitrogen fixation by Rhizobium are :
(i) Presence of enzyme nitrogenase.
(ii)A protective mechanism for the enzyme nitrogenase against O2
(iii)A non-heme iron protein-ferrodoxin as an electron carrier.
(iv)The hydrogen donating system (viz, pyruvate, hydrogen, sucrose, glucoseetc).
(v) A constant supply of ATP.
(vi)Presence of thiamine pyrophosphate (TPP), coenzyme-A, inorganic phosphate and Mg++ as co-factors.
(vii)Presence of cobalt and molybdenum,
(viii) A carbon compound for trapping
released ammonia.
In the process of biological nitrogen fixation by free living and symbiotic nitrogen fixers, the dinitrogen molecule is reduced step by step to ammonia (NH3) by the addition of pairs of hydrogen atoms. The pyruvic acid mainly serves as an electron donor but in some cases hydrogen, sucrose, glucose, etc., have also been shown to operate. In leguminous plants, the glucose-6-phosphate molecule probably acts as a substrate for donating hydrogen. The overall process occurs in presence of enzyme nitrogenase, which is active in anaerobic condition. The enzyme nitrogenase consists of two sub-units – a non-heme iron protein (or dinitrogen reductase) and an iron molybdenum protein (Mo-Fe protein or dinitrogenase).
The Fe-protein component reacts with ATP and reduces Mo-Fe protein which then converts N2to ammonia. The ammonia is either directly taken by host or is converted to nitrates with the help of nitrifying bacteria (e.g., Nitrosomonas).
Question 9: What are the steps involved in formation of a root nodule?
Answer Multiple interactions are involved in the formation of root nodules. The Rhizobium bacteria divide and form colonies. These get attached to the root hairs and epidermal cells. The root hairs get curled and are invaded by the bacteria. This invasion is followed by the formation of an infection thread that carries the bacteria into the cortex of the root. The bacteria get modified into rod-shaped bacteroides. As a result, the cells in the cortex and pericycle undergo division, leading to the formation of root nodules. The nodules finally get connected with the vascular tissues of the roots for nutrient exchange increases in region C.
Answer Multiple interactions are involved in the formation of root nodules. The Rhizobium bacteria divide and form colonies. These get attached to the root hairs and epidermal cells. The root hairs get curled and are invaded by the bacteria. This invasion is followed by the formation of an infection thread that carries the bacteria into the cortex of the root. The bacteria get modified into rod-shaped bacteroides. As a result, the cells in the cortex and pericycle undergo division, leading to the formation of root nodules. The nodules finally get connected with the vascular tissues of the roots for nutrient exchange increases in region C.
Question 10: Which of the following statements are true? If false, correct them:
(a) Boron deficiency leads to stout axis.
(b) Every mineral element that is present in a cell is needed by the cell.
(c) Nitrogen as a nutrient element, is highly immobile in the plants.
(d) It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.
Answer (a) True
(b) All the mineral elements present in a cell are not needed by the cell. For example, plants growing near radioactive mining sites tend to accumulate large amounts of radioactive compounds. These compounds are not essential for the plants.
(c) Nitrogen as a nutrient element is highly mobile in plants. It can be mobilised from the old and mature parts of a plant to its younger parts.
(d) True
(a) Boron deficiency leads to stout axis.
(b) Every mineral element that is present in a cell is needed by the cell.
(c) Nitrogen as a nutrient element, is highly immobile in the plants.
(d) It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.
Answer (a) True
(b) All the mineral elements present in a cell are not needed by the cell. For example, plants growing near radioactive mining sites tend to accumulate large amounts of radioactive compounds. These compounds are not essential for the plants.
(c) Nitrogen as a nutrient element is highly mobile in plants. It can be mobilised from the old and mature parts of a plant to its younger parts.
(d) True
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