AP BIOLOGY

Detailed explanation-1: -Plants respond directly to Earth’s gravitational attraction, and also to light. Stems grow upward, or away from the center of Earth, and towards light. Roots grow downward, or towards the center of Earth, and away from light. These responses to external stimuli are called tropisms.

Detailed explanation-2: -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.

Detailed explanation-3: -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-4: -Geotropism is a type of tropism where plants show some growth in response to gravity. Roots growing downwards is an example of geotropism.

Detailed explanation-5: -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.