AP BIOLOGY

Detailed explanation-1: -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. Plants’ growth response to gravity is known as gravitropism; the growth response to light is phototropism.

Detailed explanation-2: -Gravitropisms. Phototropism is a response to the stimulus of light, whereas gravitropism (also called geotropism) is a response to the stimulus of gravity . When the stem grows against the force of gravity (upwards), this is known as a negative gravitropism.

Detailed explanation-3: -The correct option is C-ve geotropism. “Geo” means earth and “tropism” means movement. The movement towards the earth, due to gravity is called positive (+ve) geotropism like roots; and movement away from the earth is called negative (-ve) geotropism.

Detailed explanation-4: -Gravity affects the ecology and evolution of every living organism. 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-5: -Plant shoots show negative geotropism and grow away from the force of gravity. This ensures that plants grow upwards and means that more light is absorbed for photosynthesis. Roots show positive geotropism and grow towards the force of gravity.