Replacement of damaged and worn-out cells in an organism can happen as a result of ?

Cell Division /reproduction

Explanation:

In typical organisms, in order to replace worn out cells it is necessary to produce more cells. Therefore it is very essential for an organism to carry out cell division through mitosis in order to produce identical cells that are similar to parent cells. Mitosis plays a very important role in the regeneration and replacement of worn-out and damaged tissues or cells. Mitosis helps in producing  identical copies of cells thereby helping in repairing the damaged tissue or replacing the worn-out cells.

littering streams           is the answer

a. to encourage apoptosis