Question

why do leaves fall down from trees when they turn yellow??

Answer 1

when the tree is about to drop its leaves, it stops making new chlorophyll. As the old chlorophyll is broken down, the green fades. Other pigments are left in theleaves. Of course in Santa Barbara, not all plants lose their leaves in the Fall.

Answer 2

Plants leaves,fruits fall off these are called RAPHIDES
These are unwanted,waste material of a plant
All the unnecesary things are stored in leaves and fruits and fall off.

leaves usually turn yellow because of chlorophyll
These create new chlorophyll.!