There is an enormous variety of life on Earth. To date, scientists have catalogued more than 1.3 million species of plants, animals, fungi and bacteria. But many species have yet to be
identified. In fact, scientists estimate that the true number of species on our planet may be
as high as 8.7 million.
A species is the smallest unit of biological classification. With the exception of some plant
species that are able to reproduce individually, most organisms of a single species can only
reproduce with other members of the same species. Over many generations, all of the
species alive today developed unique traits to help them survive. These differences help
scientists distinguish between species.
Based on the passage, a species is a(n)