NEET Biology Mineral Nutrition MCQs Set 11

Answer: (b) Mo

Explanation:
1. Molybdenum is a component of nitrogenase and of nitrate reductase.
2. Both enzymes are central to nitrogen fixation and nitrate assimilation.

Teacher's Note:
1. Nitrogenase is a Mo-Fe protein. Without Mo, plants cannot reduce nitrate to nitrite properly and symbiotic fixation fails.

Answer: (b) K

Explanation:
1. Potassium is the most abundant free (mineral) cation in cells, and it helps in osmotic regulation, stomatal movement and enzyme activation.
2. P and Fe are mostly bound in biomolecules.

Teacher's Note:
1. K⁺ accumulates in guard cells during stomatal opening. It maintains the anion-cation balance and the turgidity of cells.

Answer: (b) NO₃⁻

Explanation:
1. Most plants absorb nitrogen mainly as nitrate ions.
2. Some NH₄⁺ and a little NO₂⁻ is also taken up.
3. Plants cannot use N₂ directly, since only some prokaryotes can fix it.

Teacher's Note:
1. In leaves nitrate is reduced to ammonia by nitrate reductase and nitrite reductase. This ammonia is then used in the synthesis of amino acids.

Answer: (b) Zn

Explanation:
1. Khaira disease of rice is due to zinc deficiency.
2. Zinc is also needed for the synthesis of auxin (IAA).

Teacher's Note:
1. Zinc deficiency gives brown spots on rice leaves (Khaira) and little leaf in other plants. It activates carboxylases and alcohol dehydrogenase.

Answer: (d) Ca

Explanation:
1. Mn, Mo and Cu are micronutrients needed in very small amounts.
2. Ca is required in larger amounts, so it is a macronutrient.

Teacher's Note:
1. Remember the micronutrients: Fe, Mn, Cu, Zn, B, Mo, Cl, Ni. All the rest of the essential elements are macronutrients.

Answer: (b) Carbon

Explanation:
1. Of the elements listed, carbon is the most abundant, making up about 45% of the dry weight of a plant.
2. Iron and manganese are micronutrients and nitrogen is only about 1 to 2%.

Teacher's Note:
1. Carbon, oxygen and hydrogen form more than 90% of dry weight, since the plant body is made of carbohydrates and other organic compounds.

Answer: (c) Pb, I, Na

Explanation:
1. The essential elements are C, H, O, N, P, K, S, Ca, Mg, Fe, Mn, Cu, Zn, B, Mo, Cl and Ni.
2. Options 1, 2 and 4 contain only essential elements.
3. Pb, I and Na are not essential for normal growth, although Na is beneficial for some plants.

Teacher's Note:
1. Seventeen elements are essential. Beneficial elements such as Na, Si, Se and Co are needed only by some plants and do not meet the criteria of essentiality.

Answer: (b) Mg

Explanation:
1. Mg is the central metal atom of the chlorophyll ring.
2. On burning chlorophyll, the Mg is left behind in the ash.

Teacher's Note:
1. The porphyrin ring of chlorophyll has Mg at the centre, while the haem ring has Fe.

Answer: (b) Fe, Mg and light

Explanation:
1. Magnesium is the central atom in the porphyrin ring of chlorophyll.
2. Iron is needed for chlorophyll synthesis, though it is not a part of the molecule. Light is also required for chlorophyll formation.

Teacher's Note:
1. Mg is a constituent of chlorophyll, while Fe is essential for its synthesis. Deficiency of either one causes chlorosis.

Answer: (c) Cu

Explanation:
1. Copper deficiency causes die back of citrus and reclamation disease of cereals.
2. Cu is a constituent of plastocyanin and is needed for several redox enzymes.

Teacher's Note:
1. Cu deficiency shows as die back of shoots in citrus. Mo deficiency causes whiptail, B deficiency causes brown heart and Zn deficiency causes little leaf.

Answer: (a) N, P, K

Explanation:
1. Nitrogen, phosphorus and potassium are the elements most often limiting in soils.
2. Farmers therefore add them as NPK fertilisers.

Teacher's Note:
1. These three are called critical nutrients because crops remove large amounts of them from the soil.

Answer: (b) Cu and Zn

Explanation:
1. Reclamation disease (of cereals and legumes in newly reclaimed soils) is due to Cu deficiency.
2. Little leaf is due to Zn deficiency, because Zn is needed for auxin synthesis.

Teacher's Note:
1. Zn is needed for auxin (IAA) synthesis, so shortage gives small leaves and short internodes (rosette). Cu deficiency leads to die back and reclamation disease.

Answer: (a) B

Explanation:
1. Boron deficiency causes brown heart of beet and turnip, stout axis and poor fruit and seed formation.
2. It is the only micronutrient not linked with enzyme activation.

Teacher's Note:
1. Boron is needed for calcium uptake and utilisation, pollen germination, cell elongation and sugar transport.

Answer: (d) All

Explanation:
1. Cysteine, cystine and methionine all contain sulphur.
2. Sulphur is also present in coenzyme A, thiamine, biotin and ferredoxin.

Teacher's Note:
1. Sulphur is absorbed as sulphate (SO₄²⁻). The disulphide bridge between two cysteines in proteins gives cystine.

Answer: (c) Mn

Explanation:
1. Macronutrients are needed above 10 mmol per kg dry matter: C, H, O, N, P, K, S, Ca and Mg.
2. Mn is needed in a lower concentration, so it is a micronutrient.

Teacher's Note:
1. Micronutrients (trace elements): Fe, Mn, Cu, Zn, B, Mo, Cl and Ni. Mg and Ca are macronutrients even though they are metals.