AP BIOLOGY

Detailed explanation-1: -The changes in weather and daylight trigger a hormone that releases a chemical message to each leaf that it is time to prepare for winter. Over the next few weeks, abscission cells form a bumpy line at the place where the leaf stem meets the branch. And slowly, but surely, the leaf is “pushed” from the tree branch.

Detailed explanation-2: -The actual term used to describe this process of leaf drop is known as abscission. Although some parts of trees like stems and buds can handle freezing temperatures, most leaves cannot.

Detailed explanation-3: -The leaves of the deciduous trees have a tendency to lose water. But during the dry season, water is scarce. Hence, deciduous trees shed their leaves to prevent water loss.

Detailed explanation-4: -In temperate regions, cold winters pose a risk to the leaves of broadleaf trees and other perennials, and so these plants drop their leaves in a controlled fashion to reduce injuries and conserve energy.