The explain formula
An explain answer follows a cause → mechanism → effect pattern:
- State what happens (the observation or result)
- Give the biological reason (the mechanism: enzymes, concentration gradients, hormones, etc.)
- Link cause to effect (use connective words: "therefore", "this means", "because", "so")
Example: "The rate of reaction increases as temperature increases because molecules have more kinetic energy, so there are more frequent successful collisions between enzyme and substrate molecules."
Chain explanations for higher marks
Many 4–6 mark explain questions require a chain of reasoning. Each point must logically follow from the previous one:
"Exercise increases heart rate because muscles need more energy → energy is released by respiration → respiration requires more oxygen and glucose → the heart beats faster to pump blood more quickly to deliver these to the muscles."
Each arrow represents a separate marking point. Breaking the chain (skipping a step) often costs a mark.
What to avoid
Circular reasoning: "The rate increases because it goes faster": this restates the observation as the reason.
Missing the biological mechanism: "It increases because of temperature": you need to state how temperature causes the increase (kinetic energy, enzyme activity, etc.).
Vague language: "things move faster": name the molecules and the process.