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

(a) Juvenile phase- also called vegetative phase. It is the period of growth in an organism after its birth and before it reaches reproductive maturity. This phase is of different duration in  different  organisms. 

(b)Reproductive phase- also known as maturity phaseor puberty, as reproductive structures mature during this phase. It is a period when an organism reproduces

(c)Senescent phase-This is the last phase of life span and ultimately leads to death. It is the period when an organism loses the ability to reproduce and grows old.