The process in which the male and female gametes fuse together to form a new individual is called sexual reproduction. Let us have a brief account of the human reproductive organs and their role in reproduction.Reproductive OrgansThe male reproductive organs comprise of a pair of testes, sperm ducts, and a *****. The sperms are produced by the testes. The sperms are very small in size with a head, a middle piece, and a tail.The female reproductive organs comprise of a pair of ovaries, oviducts, and the uterus. The eggs (ova) are produced by the ovaries. The development of the baby takes place in the uterus. A mature egg is released into the oviduct every month.FertilizationThe semen contains millions of sperms. A single sperm fuses with the ova during fertilization. The nuclei of the egg and the sperm fuse together to form a single nucleus. Thus, a zygote is formed. Fertilization is of two types:Internal FertilizationThe fertilization that takes place inside the body of the female is known as internal fertilization. For eg., humans, cows, dogs, etc. This method is more prevalent in terrestrial animals. However, some aquatic animals also adopt this method. This may take place by direct introduction of sperms by the male in the female reproductive tract, or the male deposits the sperms in the environment which is picked up by the female and deposited in her reproductive tract.They are three ways by which offsprings are produced by internal fertilization:Oviparity– The fertilized eggs are laid outside the body of the female where they receive nourishment from the yolk.Ovoviviparity– The fertilized eggs are retained in the female’s body where they receive nourishment from the yolk. The eggs are laid right before they are hatched.Viviparity– The offsprings are born directly instead of hatching from the eggs. They receive nutrition from the mother. This can be seen in mammals.External FertilizationThe fertilization that takes place outside the body of the female is called external fertilization. For eg., frogs, fish. Most fertilization takes place during the process of spawning. The environmental signals such as water temperature trigger spawning.Embryo DevelopmentThe zygote divides repeatedly to form a ball of cells. This ball of cells is known as the embryo. These cells differentiate into respective tissues and organs. The embryo gets implanted in the wall of the uterus. This process is known as implantation.