Question

What do phototropism and geotropism enable plants to do?

Answer 1

Response to a stimulus in plants is known as a tropism.

Explanation:

Tropism is a turn towards or away from a stimulus. When the movement is towards the stimulus it is called positive tropism, and when the movement is away from the stimulus it is called negative tropism.

Phototropism
The movement ( away or towards) of a plant in response to sunlight is called phototropism.

The cells on a plant that are farthest from light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light thus bending the plant towards light.

While most phototropism involves plants just growing towards the sun, some plants follow the sun throughout the day. For example the sunflower plant orients its flowers to the sun. In the morning, they point towards the rising sun. They then gradually follow me the sun throughout the day, eventually pointing west towards the setting sun.

Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.

Geotropism
Similarly, geotropism allows the plants to correctly orient themselves for growth. The root exhibits positive geotropism and grows towards the earth. The shoot exhibits negative geotropism by growing away from the earth.

Abundant evidence demonstrates that roots bend in response to gravity due to a regulated movement of the plant hormone auxin, known as the polar auxin transport. In both roots and stems auxin accumulates towards the gravity vector on the lower side. In roots this results in the inhibition of cell expansion on the lower side and the concomitant curvature of the root towards gravity. In shoots the auxin also accumulates on the lower side, however in this tissue, it increases cell expansion and results in the shoot curving up i.e. negative geotropism.

The combination of phototropism and geotropism allows plants to grow in the correct direction.