What causes the appearance of the leaves to change?

Leaves change as they grow and develop. Young leaves are easy to distinguish from old ones. Cells accumulate various substances in the process of life, the vacuole in old cells occupies most of the internal space, and over time, a protective wax forms on the surface of the leaf. Leaves change their color before falling off. All due to the fact that the plant gets rid of accumulated harmful substances and removes them into the leaves. After falling off, they are processed by various worms and bacteria, and these substances can already be absorbed by the plant again.