Exam Tips: Classification

Learn the 7 hierarchy levels in order: Use "Kings Play Chess On Fine Green Silk." Examiners regularly ask for these in order, and losing sequence marks is avoidable with this mnemonic.

Species definition must include "fertile offspring": "Can interbreed" alone is incomplete. A horse and donkey can interbreed but produce infertile mules — they are still different species. Always write "can interbreed to produce fertile offspring."

Why classification changes — always link to DNA evidence: The standard mark scheme answer is that new evidence, particularly from DNA and RNA analysis, has shown that some organisms previously grouped together are not closely related, so scientists have revised the classification. Naming Woese and the three-domain system at Higher tier earns extra marks.

Binomial naming — check italics and capitalisation: In written answers, underline rather than italicise. Genus capital, species lower case. Students lose easy marks by getting capitalisation wrong: homo sapiens is wrong; Homo sapiens is correct.

Three-domain vs five-kingdom: The five-kingdom system grouped all prokaryotes together. The three-domain system separates Archaea from Bacteria based on molecular evidence. Know both systems and why the three-domain system is now preferred.