AP BIOLOGY

Detailed explanation-1: -The roots grown downward in the direction of gravity, which is positive gravitropism, and the shoot grows upward away from gravity, which is negative gravitropism. The reason plants know which way to grow in response to gravity is due to amyloplasts in the plants.

Detailed explanation-2: -In higher plants, stems and roots show negative and positive gravitropism, respectively.

Detailed explanation-3: -For instance, the roots of the plants grow towards the gravitational field whereas the stem grows away from the gravitational field. The downward growth of roots is an example of a positive gravitropism whereas the upward growth of roots is an example of negative gravitropism.

Detailed explanation-4: -Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull (i.e., downward) and stems grow in the opposite direction (i.e., upwards).

Detailed explanation-5: -Plant stem grows upward opposite to the force of gravity. Hence, it exhibits negative geotropism.