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Cortical cells.

Ureides a soya bean plant transport nitrogen.

Amides are transported along with water through xylem. 

1.  Nitrification is the process by which ammonia is converted first into nitrites and then into nitrates.

2.  Nitrosococcus and Nitrosomonas convert ammonia into nitrite

3.  Nitrobacter converts nitrite into nitrate proteins that function as selective pores for movement of ions.

Nitrification refers to the phenomenon of conversion of ammonia into NO₂^- (nitrite) and then into NO₃^- (nitrates). 

Two nitrifying bacteria are : 

(i) Nitrosomoras : It converts ammonía (NH₃) into nitrites (NO₂^-). 

2NH₃ + 3O₂ → 2H+ 2H₂O + 2NO₂^- 

(ii) Nitrobucter : It converts nitrites into nitrates. 

2NO₂^- + O₂ → 2NO₃

Tomato, Lettuce.

Hydroponics is the technique of growing plants with their roots immersed in nutrient solution without soil. 

Application: It is used to grow many crops under artificial conditions for economic purposes.

(i) Pseudomonas, (ii) Thiobacillus.

Deficiency symptoms are externally visible pathological conditions which are produced due to absence or deficiency of some essential nutritive substances. 

Importance : Deficiency symptoms in relation to particular elements helps the farmer and the farm scientist to recognise the same when they are present in the field or area.

Deficiency which is caused by critical elements (NPK).

The criteria for essentiality of an element are given below: 

• The element must be absolutely necessary for supporting normal growth and reproduction. In the absence of the element the plants do not complete their life cycle or set the seeds.
• The requirement of the element must be specific and not replaceable by another element. In other words, deficiency of any one element cannot be met by supplying some other element.
• The element must be directly involved in, the metabolism of the plant.

Interveinal chlorosis, formation of short and slender stalk and inhibition of chlorophyll formation.

Essential component of amino acids like cystine, cysteine and methionine, constituent of coenzyme A, Vitamins like biotin and thiamine, constituent of proteins and ferredoxin plants utilise sulphur as sulphate (SO₄- ) ions.

Potassium (K) plays a key role in maintaining osmotic potential of the cell. The absorption of water, movement of stomata and turgidity are due to osmotic potential.

Molybdenum (Mo) is essential for nitrogenase enzyme during reduction of atmospheric nitrogen into ammonia.

Chlorosis, necrosis, delayed flowering, retarded growth and whip tail disease of cauliflower.

Translocation of carbohydrates, uptake and utilisation of Ca⁺⁺ , pollen germination, nitrogen metabolism, fat metabolism, cell elongation and differentiation. It is absorbed as borate BO^3- ions.

(a) True

(b) False

All the mineral elements present in a cell are not needed by the cell, e.g. plants growing near radioactive mining sites tend to accumulate large amounts of radioactive compounds which are not essential.

(c) False

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) Aluminium toxicity causes the appearance of brown spots in the leaves.

It is a system where roots are suspended in air and nutrients are sprayed over the roots by a motor driven rotor.

Anabaena has symbiotic association with Azolla.

Chlorosis refers to the yellowing of leaves due to loss of chlorophyll. Deficiency of nitrogen, sulphur, magnesium and iron can cause this.

• Flux refers to the movement of ions.
• Influx means movement of ions into the cells. 
• Efflux refers to movement of ions out of the cells.

Manganese competes with iron and magnesium for uptake.

• It also competes with magnesium for binding with enzymes.
• It inhibits the translocation of calcium to shoot apex.

• It determines the anion – cation balance in plant cells
• It is involved in the opening and closing of stomata 
• It maintains the osmotic balance and turgidity of cells.

Plants need potassium because it helps in the maintenance of cell turgidity, opening and closing of stomata, cation - anion balance, activation of enzymes, essential for photosynthesis, respiration, protein synthesis and in membrane permeability. Magnesium is required for chlorophyll formation, growth, metabolism and nodule formation in legumes.

(c) obligate stem parasite

(b) Loranthus grows on fig and mango trees

(b) mycorrhizal association

(c) Symbiosis

The higher plants do not have the association of bacteria or fungi, which are able to fix atmospheric nitrogen.

(b) triple covalent bond

(b) deficiency of zinc

(c) A – (iii); B – (i); C – (iv); D – (ii)

(d) A – (iii); B – (iv); C – (i); D – (ii)

(a) to prevent water lodging

Correct Answer is : (c) protein

(a)  True

(b) Out of all the mineral elements, only 17 are considered as essential elements.

(c)  Nitrogen is highly mobile in plants.

(d)  True

Asymbiotically − Azotobacter, Bacillus polymyxa 

Symbiotically − Rhizobium, Anabaena.

(i) Nitrifying Bacteria − Nitrosomonas. 

(ii) Nitrifying Bacteria − Nitrobacter

Leghemoglobin. It is an oxygen scavenger, which protects the enzyme nitrogenase.

Development of root nodules happens in following steps: 

a. Rhizobium bacteria contact a susceptible root hair and divides near it. 

b. Successful infection of the root hair results in curling of the root hair.

c. The infected thread carries the bacteria to the inner cortex. The bacteria get modified into rodshaped bacteroids and cause inner cortical and pericycle cells to divide. Division and growth of cortical and pericycle cells lead to nodule formation. 

d. A mature nodule is complete with vascular tissues. The vascular tissues of the nodule are continuous with those of the root.

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

Heterotroph : An organism that cannot synthesise its own nutrients and depend on others.

Death of cells and tissues is called Necrosis. 

Plants require mineral elements for their growth and development. The utilization of various absorbed ions by a plant for growth and development is called mineral nutrition of the plant.

Conversion of atmospheric into organic compounds by living organisms is called Biological nitrogen fixation. 

Minerals get depleted in the soil due to several reasons : 

(i) Overcropping which withdraws minerals from the top layers of the soil. 

(ii) Use of high yielding varieties which require higher quantity of mineral nutrients. 

(iii) Non-rotation of crops causing deficiency of minerals at a particular level in the soil. 

(iv) Leaching or washing down of minerals along with gravitational water. 

(v) Precipitation of minerals due to change in soil pH.

 Restoration of Mineral Fertility : It is done through two methods, natural and artificial. 

(i) Natural replenishment : In soil under natural vegetation, mineral fertility is restored naturally through : 

(a) Recovery of minerals from decomposition of fallen leaves, twigs, dead roots, dead animals and animal excreta. 

(b) Slow process of weathering of bed rocks. 

(c) Burrowing habit of some animals like earthworms which bring sub-soil over the surface of top soil. 

(d) Biological nitrogen fixation. 

(ii) Artificial replenishment: It is carried out by human efforts : 

(a) Addition of farmyard manure. Manure contains humus. Humus form colloidal particles in soil for increased hydration, crumb structure, aeration, loosening the soil, slow release of minerals and organic substances that stimulate plant growth. 

(b) Green manuring. 

(c) Crop rotation or sowing of alternate crops successively in the same field. It helps in maintaining nitrogen fertility of the soil. 

(d) Addition of fertilizers.

(i) Rhizobium is nitrogen fixing bacterial symbiont of legumes, Rhizobia increase in number and attach with epidermis of roots. Root hairs curls and bacteria invade it. An infection thread is formed carrying the bacteria into the cortex of root. 

(ii) Nodule formation starts in cortex of root. Bacteria is released from the thread into the cells which leads to formation of specialized nitrogen fixing cells. 

(iii) Nodules establish direct vascular connection with host for exchange of nutrients. 

(iv) Nodule contain all necessary biochemical components like enzyme nitrogenase and leghaemoglobin. 

(v) Enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen into ammonia. 

(vi) The reaction is as follows : 

N₂ + 8e- + 8H+ + 16ATP → 2NH₃ + H₂ + 16ADP +16Pi

There are four steps in the nitrogen cycle namely, nitrogen fixation, ammonification, nitrification and denitrification. 

(i) Nitrogen fixation 

(a) During this step, the atmospheric free nitrogen is converted into those nitrogen compounds which can be absorbed by plants. 

(b) The fixation may be biological and carried out by free living bacteria, (e.g., Azotobacter, Clostridium) or cyanobacteria or bacterium in symbiotic association (e.g., Rhizobiun). 

(c) The fixation can also occur by physical processes in the atmosphere. 

(d) Ammonium compounds are formed as a result of this process. 

(ii) Ammonification 

(a) When the dead/waste parts of plants and animals are decomposed, ammonia is formed. 

(b) It is carried out by certain fungi and certain bacteria. 

(c) The process of formation of ammonia from organic nitrogenous wastes, is called ammonification. 

(iii) Nitrification 

(a) The process of conversion of ammonia into nitrites and then into nitrates is called nitrification.

(b) The first step, i.e., conversion of ammonia to nitrite is carried out by bacteria like Nitrosomonas and Nitrococcus. 

(c) The second step, i.e., conversion of nitrites to nitrates is done by Nitrobacter. 

2NH₃ + 3O₂ → 2NO₂ ^- + 2H⁺ + 2H₂O 

2NO₂^- + O₂ → 2NO₃ ^- 

(d) The nitrates are absorbed and metabolised by plants. 

(iv) Denitrification 

(a) The process by which the fixed forms of nitrogen, i.e., nitrites and nitrates, are converted back into free nitrogen, is called denitrification. 

(b) It is carried out by Pseudomonas like bacterium. 

(c) This nitrogen again enters the nitrogen cycle.