AP BIOLOGY

Detailed explanation-1: -The reason plants know which way to grow in response to gravity is due to amyloplasts in the plants. Amyloplasts (also known as statoliths ) are specialized plastids that contain starch granules and settle downward in response to gravity. Amyloplasts are found in shoots and in specialized cells of the root cap.

Detailed explanation-2: -Graviperception by plant roots is believed to occur via the sedimentation of amyloplasts in columella cells of the root cap. This physical stimulus results in an accumulation of calcium on the lower side of the cap, which in turn induces gravicurvature.

Detailed explanation-3: -The general response to gravity in plants is well known: roots respond positively, growing down, into the soil, and stems respond negatively, growing upward, to reach the sunlight.

Detailed explanation-4: -In plants, the general response to gravity is well known: their roots respond positively, growing down, into the soil, and their stems respond negatively, growing upward, to reach the sunlight.