Question

why do leaves fall down from the tree when they turned into yellow?

Answer 1

HELLO FRND,

The green pigment present in the leaves is used for photosynthesis.. If no green pigment ( chloroplast) the leaf cannot prepare food anymore and it dies off..so it turn yellow and fall from leaves.
Thank u..

Answer 2

Good question, well here is the answer,

No cell is immortal hence every cell die after their function is complete.

The leaves formed by the tree helps in photosynthesis, When the chrolophyll in the leaves loose its ability to actively participates in photosynthesis abscisic acid of the tree acts on the leaves.These are the enzyme from the plants that leads to senescence/death of plant tissues.

But plants have a special mechanism by which plant recognize the leaves which are going to die,hence it transport all the minerals and nutrient of the leaves to other source so as to conserve the nutrient and minerals. Thats the reason why plants turns yellow before it withers off.

Once all the nutrients are transported to other parts, the petiole (structure holding leaves to branches) weakens and falls off the branches.