When a seedling is placed horizontally in the dark, its primary root curves downwards toward gravity. What directional growth response does this demonstrate?
Answer and explanation
Correct answer: B. positive geotropism
- Step 1: Growth in the direction of the gravitational pull is positive geotropism. Step 2. Root statocytes detect gravity; auxins accumulate on the lower side of the root, where high auxin inhibits cell elongation, causing downward curvature. Answer: positive geotropism (gravitropism). Why not the others: Shoots show negative geotropism (growing upwards against gravity); phototropism requires light; hydrotropism is response to water.
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