Question

The deficiency symptoms of an essential element tend to appear first in young leaves, indicating that the element is relatively immobile. Such symptoms would be shown by which one of the following elemental deficiencies?

• A. Sulphur
• B. Iron
• C. Nitrogen
• D. Potassium

Hint:

Immobile nutrients cannot be withdrawn from old leaves, so their deficiency shows up in young leaves first.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept.
Whether a nutrient deficiency shows up first in old leaves or young leaves depends on how mobile that nutrient is inside the plant. Mobile nutrients can be pulled out of old leaves and sent to young growing tissue, so old leaves show symptoms first. Immobile nutrients cannot move out of mature tissue, so young leaves suffer first since they get no fresh supply.

Step 2: Key Fact.
Nitrogen and Potassium are both highly mobile. When short, the plant moves them out of older leaves to feed new growth, so old leaves show yellowing first. Iron, on the other hand, is a classic example of an immobile nutrient, it does not move out of mature leaf tissue once deposited, so the young, newly forming leaves show symptoms, typically interveinal chlorosis with the veins staying green.

Step 3: Detailed Explanation.
Sulphur deficiency can also cause some yellowing, but the standard textbook case of young-leaf-first symptoms is iron deficiency, since iron is needed continuously for chlorophyll synthesis in new leaves and cannot be recycled from older ones. So Nitrogen and Potassium are ruled out for being mobile, and between Sulphur and Iron, Iron is the classic example used for this exact symptom pattern.

Step 4: Final Answer.
Iron deficiency shows up first in young leaves because iron is relatively immobile in the plant. \[ \boxed{\text{Iron}} \]