A shoot grows towards the direction of light. These statements compare shoot cells on the side in the light with cells on the side in the shade.
- Cells on the side in the light have more auxin.
- Cells on the side in the shade have more auxin.
- Cells on the side in the light elongate more.
- Cells on the side in the shade elongate more.
Which statements explain why the shoot grows towards the light?
A) 1 and 3
B) 1 and 4
C) 2 and 3
D) 2 and 4
▶️ Answer/Explanation
Ans: D
In phototropism, auxin accumulates on the shaded side (Statement 2) due to light-induced redistribution. This higher auxin concentration promotes cell elongation on the shaded side (Statement 4), causing the shoot to bend towards the light.
Statements 1 and 3 are incorrect because auxin is lower on the light side, and cells there elongate less. Thus, the correct combination explaining phototropism is D (2 and 4).
The diagram shows the shoot and root of a seedling, responding to gravity.
Which row shows where the auxin accumulates and the effect of this in the shoot?
▶️ Answer/Explanation
Ans: B
In shoots, auxin accumulates on the lower side in response to gravity. Here, auxin promotes cell elongation, causing the shoot to bend upward (negative gravitropism).
Row B correctly identifies this: auxin in the lower side leads to faster growth. Options A and D misplace auxin accumulation, while C describes root response (auxin inhibits growth).
Thus, B is the correct answer.