Define
(a) Juvenile phase,
(b) Reproductive phase,
(c) Senescent phase.

Explanation

(a) Juvenile phase:
It is the period of growth in an individual organism after its birth and before it reaches reproductive maturity.
(b) Reproductive phase:
It is the period when an individual organism reproduces sexually.
(c) Senescent phase:
It is the period when an organism grows old and loses the ability to reproduce.