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Answer: 3. gravitropism
The movement of plants in response to stimuli is called as tropism. Plants respond to different stimuli like light (phototropism), water present in the soil (hydrotropism), gravity (gravitropism) and touch (thigmotropism).
Gravitropism refers the growth and movement of plant parts with respect to the force of gravity exerted by earth. The roots shows positive gravitational tropism because they are growing towards earth gravity. The shoots or stems shows negative gravitational tropism because they are moving or growing against the gravity.
