Species are groups of organisms that

Analyze the question: It asks for the definition of a species, a basic concept in classification (taxonomy).

Explain the concept: A species is the basic unit of classification. It is a group of organisms that share similar structural and functional features and can interbreed freely to produce fertile offspring. Members of different species usually cannot interbreed, or if they do, their offspring are sterile (for example, a mule from a horse and a donkey).

Solution: check each option

• A. Different origins and always found together: Wrong. Members of a species share a common origin, and being found together has nothing to do with the definition.
• B. Common origin but cannot interbreed freely: Wrong. Members of the same species can interbreed freely. This option contradicts the definition.
• C. Similar features and can interbreed freely: Correct. It matches the standard definition: similarity plus the ability to interbreed and produce fertile offspring.
• D. Resemble each other and occupy different niches: Wrong. Members of one species generally occupy the same niche. Different niches describe different species.

Answer: C

Exam tip: Remember the key phrase "interbreed freely to produce fertile offspring". If an option says organisms cannot interbreed, it describes different species, not the same one. A quick memory aid is Species = Same kind, Successful breeding.