Why do plants use gravity?

Gravity perception is important to plants because they need to send their roots downwards towards water and nutrients and their shoots upwards towards light. Plants are known to detect gravity using statelets, which are small starch-filled packets that settle at the bottom of gravity-sensing cells

Explanation:

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i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.