Question

Given below are two statements, one is labelled as Assertion (A) and the other one labelled as Reason (R).
Assertion (A): Sulphur deficiencies first appear on the younger growth in the plants.
Reason (R): Sulphur is mobile in the plants, thereby, fading the normal green colour of the young leaves.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Recall whether sulphur can move back out of older leaves.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question tests how sulphur moves inside a plant and how that movement decides where a deficiency symptom shows up first.

Step 2: Key Formula or Approach:
A mineral nutrient is called mobile if the plant can pull it out of older leaves and send it to actively growing young tissue when the soil supply runs short. Mobile nutrients such as nitrogen, phosphorus and potassium show deficiency on older leaves first, because the plant strips them from old leaves to feed new growth. Immobile nutrients such as calcium, iron and sulphur cannot be pulled back out of old leaves, so their deficiency shows up on the youngest leaves first, since those leaves get no share of what little the plant has.

Step 3: Detailed Explanation:
Assertion (A) states that sulphur deficiency first appears on younger growth. This is true, sulphur is needed to build the amino acids cysteine and methionine and, indirectly, chlorophyll, so a shortage shows up as pale yellow young leaves while the older leaves stay green.
Reason (R) claims this happens because sulphur is mobile in the plant. This is false. Sulphur actually behaves as a relatively immobile nutrient once it is built into plant compounds, so old leaves cannot release their sulphur to feed new growth. It is exactly this immobility, not mobility, that forces the deficiency to show up on the youngest leaves.
So the assertion is a correct observation, but the reason given for it states the opposite of the real mechanism.

Step 4: Final Answer:
(A) is true but (R) is false, so option 3 is correct.