Geotropism is a plant's response to:

Correct option is C

(c) Gravitational force

Explanation:

Geotropism (also called gravitropism) is the movement or growth of a plant in response to gravity. Roots show positive geotropism as they grow downward into the soil, while stems show negative geotropism as they grow upwards against gravity. This phenomenon helps plants stabilize and efficiently absorb water and nutrients from the soil.

Key Points:

• Positive geotropism – Roots grow downward, toward gravity.
• Negative geotropism – Shoots grow upward, against gravity.
• Auxin hormone regulates geotropic responses.
• Helps in anchoring the plant and efficient water absorption.
• Other types of tropism: Phototropism (light), Thigmotropism (touch).

Analysis of Other Options:

• (a) Nutrients – Incorrect; nutrient availability influences growth but does not cause directional movement.
• (b) Soil moisture – Incorrect; response to moisture is called hydrotropism.
• (d) Sunlight – Incorrect; response to light is called phototropism.

Additional Information:

• Charles Darwin first studied geotropism in plants.
• Statoliths (starch-filled organelles) help detect gravity.
• Shoots bend towards light due to auxin accumulation on the shaded side.