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NCERT Class 11 Biology Chapter 12 Mineral Nutrition
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Mineral Nutrition
Chapter: 12
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. ‘All elements that are present in a plant need not be essential to its survival’. Comment.
Ans. Plants absorb different nutrients from soil but element is inessential for a plant if it is not involved in the plant’s physiology and metabolism e.g. gold and selenium get accumulated in plants growing near mining sites while gold, or selenium are not essential nu- trients for the survival of these plants.
Q.2. Why is purification of water and nutrient salts so important in stud-ies involving mineral nutrition us- ing hydroponics?
Ans. Hydroponics is method of growing plants with their roots immersed in nutrient solution without soil. It is used to grow multiple crops in artifi-cial conditions for commercial usage. It is also useful in studying deficiency symptom of a particular element by eliminating it in nutrient solution.
Q.3. Explain with examples: macronu-trients, micronutrients, beneficial nutrients, toxic elements and es-sential elements.
Ans. Macronutrients-
(i) They are essential elements needed by plants in large amounts in excess of 10 mmole/kg of dry matter.
(ii) It includes Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous, Sulphur, Potassium, Calcium and Magnesium.
Micronutrients or trace elements-
(i) They are essential elements need- ed by plants in small amounts less than 10 mmole / kg of dry matter.
(ii) These include Iron, Molybdenum, Manganese, Chlorine, Copper, Zinc, Boron, and Nickel.
Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants e.g. Sodi. um, silicon, cobalt, selenium. Toxic elements: Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 per cent is considered toxic e.g. manganese toxicity.
Essential elements is defined as:
(A) Element must be absolutely neces-sary for normal growth and develop-ment.
(B) Life cycle of plant will not be com-plete in their absence.
(C) Requirement of element is specific and not replaceable.
(D) Element are directly involved in plant metabolism.
(E) Essential elements are divided into macronutrients and micronutrients.
Q.4. Name at least five different def-ciency symptoms in plants. Describe them and correlate them with the concerned mineral def-ciency.
Ans. The five main deficiency symptoms arising in plants are:
(a) Chlorosis:
(i) It is loss of chlorophyll leading to yellowish in leaves.
(ii) Caused by the deficiency of N, Mg, K, Fe.
(b) Necrosis:
(i) It is death of tissues.
(ii) It is due to the deficiency of Ca, Mg, Cu, K.
Whiptail disease is degeneration of lamina. It is caused by the deficiency of molybdenum.
Little leaf Disease has small leaves caused by the deficiency of zinc.
Stunted plant growth is a result of the deficiencies of copper and sulphur.
Q.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?
Ans. Hydroponics is method of growing plants with their roots immersed in nutrient solution without soil. It is used to grow multiple crops in artificial conditions for commercial usage. It is also useful in studying deficiency symptom of a particular element by eliminating it in nutrient solution.
Q.6. Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?
Ans. Deficiency symptoms appear in the parts of a plant depending on the mo-bility of element in plant.
Elements that are actively mobilized within the plants and exported to young tissues e.g. Nitrogen, Potassium and Magnesium show the deficiency symptoms first in the older tissues. Elements which are immobile and not transported out of mature organs e.g. Calcium show the deficiency symp- toms first in the young tissues.
Q.7. How are the minerals absorbed by the plants?
Ans. The absorption of soil nutrients by the roots of plants occurs in two main phases – apoplast and symplast.
Q.8. What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobium. What is their role in N2-fixation?
Ans. Rhizobium is unable to fix nitrogen as free living aerobe in soil. It develops ability to fix nitrogen only as a sym-biont with legumes roots when it becomes anaerobic.
1. The nodule has enzyme nitrogenase and leghemoglobin.
2. Enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of nitrogen to ammonia.
3. Enzyme nitrogenase is highly sen-sitive to the molecular oxygen and requires anaerobic conditions.
4. Ammonia synthesis by nitrogenase requires 8 ATP for each NH3 produced. ATP required is obtained from the respiration of the host cells.
N₂ + 8H⁺ + 16 ATP == 2 NH₃ + H₂ +16 ADP.
5. Leghemoglobin is oxygen scavenger and protects nitrogenase from oxygen.
Q.9. What are the steps involved in for-mation of a root nodule?
Ans. Nodule formation between Rhizobium and roots of the host plant shows fol-lowing stages –
Rhizobia multiply and get attached to root hair cells.
Infection of root hairs causes it to curl and formation of infection thread enclosing the bacteria. Infection thread carries the bacteria into the cortex of the root.
Bacteria get modified to form rod shaped bacteroids.
Infected cortical and pericycle cells divide to form the nodule in the root. The nodule thus formed establishes a direct vascular connection with the host for exchange of nutrients.
