How do plants exhibit gravitropism?

Plants exhibit gravitropism by growing towards or away from the force of gravity, guided by their internal auxin distribution.

Gravitropism, also known as geotropism, is a biological process that directs the growth of plants in response to gravity. This phenomenon is primarily observed in the roots and shoots of plants. Roots exhibit positive gravitropism, meaning they grow in the direction of gravitational pull, while shoots exhibit negative gravitropism, growing against the direction of gravity.

The mechanism behind gravitropism involves the plant hormone auxin. Auxin is produced in the shoot tips and root caps and is responsible for cell elongation. When a plant is positioned upright, auxin is evenly distributed throughout the plant. However, when a plant is tilted, gravity causes auxin to accumulate on the lower side. In the shoots, this increased concentration of auxin stimulates cell elongation on the lower side, causing the shoot to curve upwards. In the roots, the higher concentration of auxin inhibits cell elongation on the lower side, causing the root to curve downwards.

The plant's ability to sense gravity is believed to be due to statoliths, dense organelles that settle to the lower side of the cell under the influence of gravity. These statoliths are thought to trigger the redistribution of auxin, leading to differential growth and the bending of the plant in response to gravity.

In summary, gravitropism is a vital mechanism that allows plants to orient themselves and grow in a direction optimal for their survival. It is a complex process involving the plant hormone auxin and the plant's ability to sense gravity through statoliths.