Transport across membranes requires students to distinguish three mechanisms clearly, calculate percentage changes correctly, and explain osmosis results in extended writing.

The Topic Mastery Sheet compares all three transport mechanisms in a reference table, gives a step-by-step guide to the percentage change calculation with an explicit note about sign convention, and includes a full Level of Response framework for the osmosis extended writing question. The error box covers the mark penalty that applies to a missing symbol in the percentage change answer - a well-documented source of mark loss in Edexcel marking.

The Student Exam Practice Sheet (20 marks) covers: MCQ, active transport explanation, a three-test-tube osmosis data set (including calculation using official Edexcel mark scheme values), a mechanism comparison task, and a full 6-mark Level of Response question with rubric.

The Teacher Answer Key provides complete LoR indicative content at all three levels and flags the specific calculation penalty referenced in the official mark scheme.

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