Explain the term species which exist in our planet?

The species constitute a group of organisms which are quite alike in morphology, behavior and function. But it is not necessary that they resemble in all these features. The reason for their non resemblance is due to many factors.
There developmental stages in life cycle are quite different. It includes larva, pupa and adult. It occurs in moths and butterflies. The larvae and adults of frogs and toads do not resemble in their function and morphology. There is no similarity between a game tophyte and sporophyte stages of moss and ferns.
There occurs a sexual dimorphism. In this case the male and female sexes can be differentiated by the outward appearance. They differ in morphology, color and function. This phenomenon also occurs in plants. They are differentiated on the basis of flowers they bear. The other features of differentiation are seeds, fruits and sporophylls.