Why do leaves turn brown and red in autumn?

Question

Why do leaves turn brown and red in autumn?

Answer 1

Best explanation I found because I couldn't think of a way to put it myself without going too techy...

Leaves are nature's food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis. That means "putting together with light." A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their green color.

As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter.

During winter, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green chlorophyll.

The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.

Yes it's American but it serves the purpose!

Answer 2

Plants are really cold-blooded organisms and slow down in the cold. They don't want to waste water in the winter so they cut off the main water-loss organs, the leaves.

While they're getting rid of their leaves anyway, they very sensibly take all the good stuff out and fill them up with the plant equivalent of c**p.  

Answer 3

Without going into too much deph, the tree draws out all the useful substances from the leaves - to store it at its centre, so it can survive the winter months.

It makes sense for a tree to loose its leaves then to regrow them, as its less energy spent in total.

Answer 4

Because the tree is going into hibernation for the winter it stops producing water and food to the leaves.. the changing colour of the leaves is a sign that they are struggeling and so fall off.. the tree then goes asleep for the winter..