Define the following 4 terms in the text box below:
(sperm, fertilization, testoterone, semen)

Sperm cells are male gametes that are produced in the male reproductive organs gonads of humans and other animals. They are involved in sexual mode of reproduction.

Fertilization is a process of combination of male and female gametes i.e. sperm and ovum to produce a fertilized zygote that develops new individual.

Testosterone is the main sex hormone produced by testicles, it regulates different processes, not only fertility but also red blood cell production, fat distribution and muscle mass too. It is basically involved in the maturing of male sexual characteristics.

Semen is the liquid in males that contains sperms secreted by gonads, also called male reproductive fluid or seminal fluid.