Species

How this is marked

The paying word is 'fertile'. Saying organisms simply 'can breed' or 'produce offspring' drops the mark, because different species (like a horse and a donkey) can produce offspring, but a mule is sterile. This definition underpins the binomial system and classification questions in Paper 4.

In an exam answer

Asked why a mule is not evidence that horses and donkeys are one species: 'A mule is sterile, and members of the same species must reproduce to produce fertile offspring.'

Full topic guide: Characteristics & classification of living organisms