An interbreeding group of animals or plants that are reproductively isolated from all other such groups.

• A. Species
• B. Cladistics
• C. Cladogram
• D. Biological species concept

Answer: (A)

The main idea is identifying the unit defined by reproductive isolation. A group of organisms that actually or potentially interbreed and is reproductively isolated from all other such groups is called a species. The phrase describes that unit—the species—as the basic building block of biodiversity. The Biological Species Concept is the framework that explains why such units exist, defining a species in terms of reproductive isolation, but the question is asking for the label of the unit itself, which is species. Cladistics and cladograms deal with evolutionary relationships based on shared traits, not reproductive boundaries, so they aren’t the right fit here.