Distinguish between the terms 'species' and 'genus' in biological classification.

IB DP Biology Standard Level (2023 syllabus) — A3.1 Diversity of organisms · Distinguish · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A species is a group of organisms that can interbreed and produce fertile offspring, whereas a genus is a broader grouping that contains one or more related species.
Members of the same genus share a more recent common ancestry and are more closely related to each other than to members of other genera.
In binomial nomenclature the genus name is the first part of the scientific name (capitalised), and organisms of the same species share both the genus and the specific epithet.
All individuals of a given species belong to exactly one genus, but a single genus may contain multiple species, making the genus a less precise, broader category than species.

Examiner tips

Use the definition of species first, then explain the broader nature of a genus.
Mention the binomial nomenclature rule to show understanding of naming conventions.
Show the relationship of common ancestry to justify why a genus groups related species.

Common mistakes

Confusing the order of the genus and species in the scientific name.
Saying a species can contain multiple genera, which is incorrect.
Using plural forms incorrectly, e.g., "species are" instead of "species is".

Mark scheme (4 marks)

A species is a group of organisms that can interbreed (and produce fertile offspring), whereas a genus is a broader grouping containing one or more related species.
Members of the same genus share more recent common ancestry / are more closely related to each other than to members of other genera.
In binomial nomenclature the genus name is the first part of the scientific name (written with a capital letter), and organisms of the same species share both the genus and specific epithet.
All individuals of a given species can be placed in exactly one genus, but a single genus may contain multiple species (so genus is a less precise / broader category than species).

Key terms in this question

species · genus