Common Mistakes and Misconceptions

Every year, examiners' reports highlight the same recurring errors that cost students marks. This lesson identifies the most common mistakes and misconceptions in Edexcel A-Level Biology and explains how to avoid them. Correcting these errors can make a significant difference to your grade.

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Osmosis Misconceptions

Mistake 1: Describing Water Movement Incorrectly

Wrong: 'Water moves from a high concentration to a low concentration.'

Correct: 'Water moves by osmosis from a region of higher water potential to a region of lower water potential (more negative water potential) across a partially permeable membrane.'

Incorrect Term	Correct Term
'Concentration of water'	Water potential
'Semi-permeable membrane'	Partially permeable membrane (Edexcel preference)
'Water moves to dilute the solution'	Water moves down a water potential gradient

Exam Tip: Always use the term water potential (symbol: Ψ, psi). Pure water has a water potential of zero, and dissolved solutes make water potential more negative. Water always moves from less negative (higher) to more negative (lower) water potential.

Mistake 2: Confusing Turgid and Plasmolysed