Exam Focus

Exam Focus

DNA and the genome are tested in almost every AQA Biology Paper 2 and Edexcel 1BI0/1 (Paper 1). The most common question formats are:

• 1-mark recall: "What is a gene?" or "State the bases that pair together in DNA." Know definitions precisely.
• 2-mark explain: "Explain how the base sequence of DNA determines the structure of a protein." Always mention amino acid sequence and protein shape.
• Application questions: Given a DNA base sequence, identify the complementary strand using A-T and C-G pairing rules.
• 6-mark extended response: "Describe how a protein is made from DNA" — very high frequency. Structure your answer in two clearly labelled stages: transcription (nucleus: DNA unzips → mRNA made → leaves through nuclear pores) and translation (ribosome: codons read → tRNA brings amino acids → peptide bonds form → protein folds). Missing the location of either step costs marks.
• 4-mark explain: "Explain how a mutation could affect an organism." Chain your answer: base change → different codon → different amino acid → different protein shape → loss of function. Award yourself one mark per link in the chain.

Edexcel 1BI0 style: Edexcel Paper 1 (1BI0/1) frequently opens DNA/genome questions with a stimulus — for example, a passage about a genetic study, a data table of DNA base percentages, or a photo of an electrophoresis gel. Read the stimulus carefully before answering. The command word "Suggest" appears when Edexcel expects you to apply your knowledge to an unfamiliar context. 6-mark extended responses require you to use BOTH the stimulus information AND your own knowledge — answers using only one source cannot reach the top band.

Key command words: "State" (give without explanation), "Describe" (list features), "Explain" (give reasons). For base pairing questions, always write both pairs: A-T and C-G. For protein synthesis questions, always state WHERE each stage happens.