Question

The functions of zinc are:

(A) It is involved in the synthesis of indole acetic acid, metabolism of gibberellic acid and synthesis of RNA.

(B) It is a constituent of enzymes such as carbonic anhydrase (CA), alcoholic dehydrogenase and superoxide dismutase (SOD).

(C) Because of its preferential binding to sulphydryl group, Zn plays an important role in the stabilization and structural orientation of the membrane proteins.

(D) It influences translocation and transportation of P in plants. Under Zn-deficiency, poor translocation of P occurs, resulting in P-deficiency.

Choose the correct answer from the options given below:

• A. (A), (B) and (D) only
• B. (A), (C) and (D) only
• C. (A), (B) and (C) only
• D. (B), (C) and (D) only

Hint:

Recall which way the zinc-phosphorus relationship actually runs: zinc deficiency raises P uptake, it does not cause P deficiency.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We are given four statements, A to D, about the functions of zinc in plants, and we need to find which combination of statements is factually correct.

Step 2: Key Formula or Approach:
Zinc has several well documented roles in plants: it is needed for the synthesis of tryptophan, the precursor of the auxin indole acetic acid, and it supports RNA synthesis and ribosome stability; it is a structural component of several enzymes, including carbonic anhydrase, alcohol dehydrogenase and superoxide dismutase; and it binds preferentially to sulphydryl, that is thiol, groups in membrane proteins, helping keep cell membranes stable. A separate, well known agronomic fact is that zinc deficiency actually increases, not decreases, the uptake and translocation of phosphorus to the shoot, which can push P to toxic levels and worsen the zinc deficiency further, a phenomenon usually called phosphorus induced zinc deficiency.

Step 3: Detailed Explanation:
Statement A describes zinc's role in auxin synthesis and RNA synthesis, both of which are accepted zinc functions, so statement A can be taken as correct.
Statement B lists carbonic anhydrase, alcohol dehydrogenase and superoxide dismutase as zinc containing enzymes, which is a textbook accurate list of zinc metalloenzymes, so statement B is correct.
Statement C describes zinc binding to sulphydryl groups to stabilize membrane protein structure, which is also an accepted and well documented function of zinc in maintaining membrane integrity, so statement C is correct.
Statement D claims that zinc deficiency causes poor translocation of phosphorus, leading to phosphorus deficiency. This is the reverse of the established relationship: zinc deficient plants typically show increased, not reduced, uptake and translocation of phosphorus to the shoot, often causing phosphorus to accumulate to toxic levels rather than causing a phosphorus deficiency, so statement D is factually wrong.
Since A, B and C hold up against known plant nutrition facts and D contradicts the accepted zinc-phosphorus relationship, the correct combination excludes D.

Step 4: Final Answer:
The correct combination of statements is (A), (B) and (C) only.