NEET Biology Mineral Nutrition MCQs Set 15

Answer: (d) Chlorophyll synthesis

Explanation:
1. Magnesium is the central atom of the chlorophyll molecule.
2. Calcium is the element used in cell walls and holding cells together.

Teacher's Note:
1. Mg also activates enzymes of respiration and photosynthesis.

Answer: (b) Casuarina equisetifolia

Explanation:
1. Casuarina forms actinorhizal nodules with the filamentous bacterium Frankia.
2. Cicer and Crotalaria are legumes with Rhizobium, and Cycas is a gymnosperm with cyanobacteria in coralloid roots.

Teacher's Note:
1. Frankia forms nodules in non-leguminous plants such as Alnus and Casuarina.

Answer: (a) Calcium and phosphorus

Explanation:
1. The six major elements in living organisms are C, H, N, O, Ca and P.
2. Sulphur, magnesium and sodium are present only in small proportions.

Teacher's Note:
1. This is the NCERT statement. Keep the list C, H, N, O, Ca, P in mind.

Answer: (a) Calcium

Explanation:
1. Calcium is required in large amounts and is a macronutrient.
2. Manganese, zinc and copper are micronutrients.

Teacher's Note:
1. Quantity decides the category. Ca, Mg, K, P, S, N are macronutrients.

Answer: (a) Frankia

Explanation:
1. Alnus is a non-leguminous plant that forms nodules with Frankia, a filamentous actinomycete.
2. Azorhizobium and Bradyrhizobium nodulate legumes.

Teacher's Note:
1. Frankia is a symbiotic nitrogen fixer in non-legumes.

Answer: (b) Photolysis of water during photosynthesis

Explanation:
1. Manganese activates the oxygen-evolving complex in photosystem II.
2. This complex splits water, releasing electrons, protons and oxygen.

Teacher's Note:
1. Mn and Cl are both needed for photolysis of water.

Answer: (b) Frankia

Explanation:
1. Frankia fixes nitrogen in association with roots of non-legumes such as Alnus.
2. Azotobacter is free living, Azolla is a fern, and Glomus is a mycorrhizal fungus that does not fix nitrogen.

Teacher's Note:
1. Azolla is a host fern, and the symbiotic fixer inside it is Anabaena.

Answer: (a) Molybdenum

Explanation:
1. The enzyme nitrogenase is a Mo-Fe protein.
2. It cannot function without molybdenum.

Teacher's Note:
1. Mo and Fe are the metals of nitrogenase.

Answer: (b) Magnesium

Explanation:
1. Magnesium is needed in large amounts and is a macronutrient.
2. Molybdenum, zinc and boron are micronutrients.

Teacher's Note:
1. Mg is part of chlorophyll, which explains why it is needed in larger amounts.

Answer: (b) Rhodospirillum

Explanation:
1. Rhodospirillum is a free-living photosynthetic bacterium that fixes nitrogen under anaerobic conditions.
2. Beijerinckia and Azotobacter are free-living aerobes, and Rhizobium is symbiotic.

Teacher's Note:
1. Free-living anaerobes: Rhodospirillum, Clostridium, Rhodopseudomonas.

Answer: (c) Oscillatoria

Explanation:
1. Cyanobacteria such as Oscillatoria, Anabaena and Nostoc fix nitrogen in the water of rice fields.
2. Rhizobium and Frankia are symbiotic with land plants.

Teacher's Note:
1. Blue-green algae are used as biofertilisers for paddy.

Answer: (a) A: Denitrification, B: Ammonification, C: Plants, D: Animals

Explanation:
1. Conversion of nitrate back into N₂ gas, which returns to the atmosphere, is denitrification, so A is denitrification.
2. Decomposition of dead organic matter into ammonia is ammonification, so B is ammonification.
3. Plants absorb the soil nitrates (C) and animals feed on plants (D).

Teacher's Note:
1. The nitrogen cycle runs: fixation, ammonification, nitrification, assimilation and denitrification.
2. Nitrification adds nitrate to the soil, and denitrification removes it.

Answer: (c) Nitrogenase is insensitive to oxygen

Explanation:
1. Nitrogenase is highly sensitive to oxygen and gets inactivated by it.
2. Leghaemoglobin removes oxygen from the nodule, keeping conditions anaerobic for the enzyme, so the other statements are correct.

Teacher's Note:
1. Leghaemoglobin is an oxygen scavenger like haemoglobin and gives nodules a pink colour.

Answer: (b) Cycas

Explanation:
1. Cycas has coralloid roots that contain the cyanobacterium Anabaena, which is autotrophic and fixes nitrogen.
2. Alnus has Frankia and Cicer and Pisum have Rhizobium, which are heterotrophic.

Teacher's Note:
1. Cyanobacteria are the autotrophic nitrogen fixers.

Answer: (b) Calcium

Explanation:
1. Calcium is part of the cell wall (calcium pectate) and is immobile once deposited.
2. Phosphorus, potassium and sulphur move easily to young parts.

Teacher's Note:
1. Deficiency of immobile elements such as Ca, Fe and B appears first in young leaves.

Answer: (c) Rhizobium

Explanation:
1. Soyabean is a legume that forms root nodules with Rhizobium.
2. Rhizobium culture is therefore used as its biofertiliser.

Teacher's Note:
1. Azotobacter and Azospirillum suit cereals, and Nostoc suits paddy.

Answer: (a) Oxidise ammonia to nitrates

Explanation:
1. Nitrosomonas and Nitrococcus oxidise ammonia to nitrite, and Nitrobacter oxidises nitrite to nitrate.
2. Conversion of free nitrogen is fixation, of proteins to ammonia is ammonification and of nitrate to nitrogen is denitrification.

Teacher's Note:
1. Nitrification is an oxidation process carried out by chemoautotrophs.

Answer: (b) Oxygen removal

Explanation:
1. Leghaemoglobin binds free oxygen and keeps the nodule interior low in oxygen.
2. This protects nitrogenase from oxygen damage.

Teacher's Note:
1. Leghaemoglobin is made partly by the host plant and partly by the bacterium.

Answer: (d) Cadmium

Explanation:
1. Phosphorus, iron and manganese are essential elements.
2. Cadmium is not required by plants and is toxic at higher levels.

Teacher's Note:
1. Essential elements are those without which the plant cannot complete its life cycle.

Answer: (b) Manganese

Explanation:
1. Manganese is part of the water-splitting complex of photosystem II.
2. Boron, zinc and copper do not take part directly in photolysis.

Teacher's Note:
1. Chloride ions are also needed for this reaction.

Answer: (c) Photolysis of water

Explanation:
1. Manganese helps in splitting of water to release oxygen in the light reaction.
2. It is not directly involved in the dark reaction or in water uptake.

Teacher's Note:
1. Link Mn with the oxygen-evolving complex.

Answer: (a) Phosphorus is a constituent of cell membranes, certain nucleic acids and all proteins

Explanation:
1. Phosphorus is present in phospholipids and nucleic acids but not in all proteins, which are made of amino acids that lack phosphorus.
2. The other three statements are correct.

Teacher's Note:
1. Proteins contain C, H, O, N and often S, but phosphorus is only in phosphoproteins.

Answer: (c) High input of energy

Explanation:
1. Nitrogenase reduces N₂ to NH₃ and uses a large amount of ATP for it.
2. It needs Mo and Fe, not Mn, and it is inhibited by oxygen radicals.

Teacher's Note:
1. About 16 ATP are used for each molecule of nitrogen fixed.

Answer: (c) Ammonia

Explanation:
1. Nitrogenase reduces N₂ directly to ammonia.
2. Ammonia is then converted into amino acids such as glutamate.

Teacher's Note:
1. N₂ to NH₃ is the first stable product.

Answer: (a) Senescent leaves

Explanation:
1. Nitrogen and potassium are mobile elements and move from older to younger parts.
2. So the older, senescent leaves show the symptoms first.

Teacher's Note:
1. Immobile elements show symptoms in young tissues, mobile elements in old tissues.