(b) the binomial system of naming species and the advantage of such a system

The idea

The binomial system gives every species a two-part Latin name: a genus name (capitalised) followed by a species name (lower case), both italicised when printed, for example Homo sapiens or Panthera leo. The genus groups closely related species; the species epithet identifies one species within it. Because the same name is used by biologists worldwide, communication is unambiguous: a local common name such as 'robin' may refer to different birds in different countries, but Erithacus rubecula identifies one species everywhere. The system is also universal, stable and internationally agreed, so data and research can be shared and compared reliably, and names reflect evolutionary relationships through the genus grouping.

What earns the marks

• A binomial consists of two parts: the genus name and the species name.
• The genus name begins with a capital letter and the species name is lower case; both are italicised (or underlined when handwritten).
• The advantage is universal, internationally agreed naming so the same species is identified unambiguously by all biologists.
• Common names are ambiguous because one name can refer to different organisms in different regions, whereas a binomial refers to one species.
• The genus part groups together closely related species, reflecting relationships.
• Correct example: Homo sapiens; incorrect forms such as a capitalised species epithet or non-italicised print are not standard binomials.

Common mistakes and how to put them right

• Writing both parts with capital letters.

  Put it right: Only the genus is capitalised and the species epithet is lower case.

• Thinking the binomial advantage is that it describes an organism's appearance.

  Put it right: The advantage is universal, unambiguous identification and communication.

• Confusing genus and species order.

  Put it right: The genus comes first and the species second.

Exam tips

• Read each option carefully to check capitalisation and italics before choosing.
• When asked for the advantage, look for 'universal' or 'internationally agreed' wording rather than descriptive features.
• Eliminate options that use common names as if they were binomials.