▶️ Answer/Explanation
Gravitropism is the growth response of a plant to gravity. Shoots typically exhibit negative gravitropism, meaning they grow away from the gravitational pull. In the diagrams, option A shows the shoot growing upward, directly opposite to the direction of gravity, which is a clear negative gravitropic response. Option B shows positive gravitropism (toward gravity), C shows no clear directional growth relative to gravity, and D shows growth partially aligned with gravity. Therefore, the correct choice is A.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Tropic responses are growth movements toward or away from a stimulus. Gravitropism (or geotropism) involves gravity; plant roots show positive gravitropism because they grow towards the pull of gravity to anchor the plant and find water. Phototropism involves light; plant shoots show positive phototropism as they grow towards a light source to maximize photosynthesis. Therefore, statement $2$ is correct for roots, and statement $4$ is correct for shoots. Statements $1$ and $3$ describe negative tropisms that do not typically apply to these specific plant organs.
✅ Answer: (D)
▶️ Answer/Explanation
Gravitropism (or geotropism) is a growth response to gravity mediated by the distribution of auxins. When a seedling is horizontal, auxins accumulate on the lower side of both the root and the shoot. In the shoot, a high concentration of auxin stimulates cell elongation, causing the lower side to grow faster and the shoot to curve upward (negative gravitropism). Conversely, in the root, a high concentration of auxin inhibits cell elongation. This causes the upper side of the root to grow faster than the lower side, resulting in the root curving downward (positive gravitropism). Therefore, diagram C correctly illustrates the shoot growing away from gravity and the root growing toward it.
✅ Answer: (C)
✅ Answer: (C)