yes they turn yellow and fall, and that's because of :

1) Temperatures fall, so the leaves cant support it.
2) and Shorter days and less sunlight (the leaves need sun to stay green and alive)

The leaves die because they are not getting photoplasm (green stuff that is made from sunlight to feed the plant) so they stop getting colour and are gradually browning and dying, they turn the red/yellow/orange beccause they are on their way to brown. they fall because they are not getting food (photoplasm) and they are dying so they cannot hold onto the tree.
Yeah THATS RIGHT im smart xD but no really i learned that in grade 6...
like LE DUH!!! lmao

anyway good luck with watever u needed that for... oh yea and go to school

leaves turn yellow in autumn because of the hot weather in summer; the higt tempreture and ihe lack of water can affect the leaves so they fall in the ground

so many reasons, but thy cant get sufficient food n those days, thy cant make their food due to weather at tht time.. its a natural process which lets thm have new leaves in spring :P