An uprooted plant is placed horizontally on the soil surface and its roots grow downward into the soil. What is this plant response called? A) Hydrotropism B) Phototropism C) Geotropism D) Thigmotropism

What this question is testing

You are matching a plant growth response (directional growth) to the stimulus that causes it.

Identify the stimulus in the scenario

The key observation is that the roots grow downward into the soil when the plant is laid horizontally. Downward growth is a response to gravity, not light, touch, or moisture.

Match the stimulus to the correct tropism

• Geotropism (gravitropism): growth in response to gravity. Roots typically show positive geotropism (toward gravity).
• Hydrotropism: growth toward water or moisture.
• Phototropism: growth in response to light (shoots usually bend toward light).
• Thigmotropism: growth in response to touch (like tendrils wrapping around a support).

Final choice

Because the roots grow downward due to gravity, the correct answer is C) Geotropism.