Problem 1: Describing instead of explaining
The most common error is answering "what happens" without stating "why it happens." Examiners report that students frequently describe a process accurately but fail to give the biological reason. "The rate increases" (description) is not the same as "The rate increases because higher temperature gives molecules more kinetic energy, so there are more frequent successful collisions" (explanation).
Problem 2: Circular reasoning
"The rate increases because it goes faster." This restates the observation as the reason. The examiner is looking for a biological mechanism: enzyme activity, concentration gradients, hormone action, etc. The reason must be different from the observation.
Problem 3: Broken cause-effect chains
Many 4–6 mark explain questions require a chain of reasoning where each point logically follows from the last. Missing one link in the chain breaks the argument and costs marks. Example chain: exercise → muscles need more energy → more respiration → more O₂ needed → heart beats faster to deliver more O₂. Missing the "more respiration" step breaks the link between exercise and oxygen demand.
Problem 4: Vague language
Examiners specifically penalise vague words: "it", "things", "stuff", "goes up", "gets bigger." Replace with precise biological terms: "insulin", "glucose concentration", "rate of diffusion increases because the concentration gradient is steeper."