External fertilization means when we gave birth to young ones outside our body, Eg. Frog . Frog lay eggs outside its body ( i.e. in water ). Now if we talk about human beings after animals then humans also gave birth to baby outside the body if there is some problem in them ,Eg. In-vitro fertilization ( test tube baby ) .
When fertilization occurs in the presence of water,known as external fertilization.For example bufo (Bufo melanostitus). Where male before emerge sparm inside the water & the female before emerge egg inside the at the time fertilization takes place.
In external fertilization fusion of sperm and egg occurs externally of the female body. External fertilization needs water to facilitate their fertilization, so it occurs in wet environments. Female and male gametes are released to the water, and male gamete is mostly mobile. This type of fertilization can be seen in lower plants. The advantage of external fertilization is that it produces a large number of offspring due to the external hazards. So survival of the embryo is comparatively lower. Amphibians and fish are examples for these types of animals
In outside treatment combination of sperm and egg happens remotely of the female body. Outer treatment needs water to encourage their preparation, so it happens in wet situations. Female and male gametes are discharged to the water, and male gamete is for the most part portable. This kind of preparation can be found in lower plants. The benefit of outside treatment is that it creates countless because of the outer risks. So survival of the developing life is nearly lower. Creatures of land and water and fish are precedents for these kinds of creatures