Unit of classification is specie. It is the very lower unit of classification but we may divide living organisms on the basis of specie discrimination. We give names to organisms by using their genus and specie name. For example, Homo Sapiens is another name to man. Homo is genus and sapiens is specie. Similar species come under genus, similar gnus come under orders, similar orders come under families, similar families come under phyla and similar phyla come under main divisions.
So, specie is the smallest unit of classification and it is what we call main unit of classification. Another thing that needs to be pointed out is the characters of species must always be similar to one another but different from characters of members of other species. Similar specie members can interbreed with each other. They are unable to interbreed with members of other species. They make populations when they live together and communities when they live with other specie members. Binomial system of classification is the base of the classification of plants and animals that we have on the earth. This system is also based on the specie unit.
Hope now it must be clear to you.
So, specie is the smallest unit of classification and it is what we call main unit of classification. Another thing that needs to be pointed out is the characters of species must always be similar to one another but different from characters of members of other species. Similar specie members can interbreed with each other. They are unable to interbreed with members of other species. They make populations when they live together and communities when they live with other specie members. Binomial system of classification is the base of the classification of plants and animals that we have on the earth. This system is also based on the specie unit.
Hope now it must be clear to you.