lesson
Water moves through a partially permeable membrane
1 · Learn
Osmosis is the net movement of water through a partially permeable membrane from a more dilute solution towards a more concentrated solution under the usual school model. The membrane allows some substances through more readily than others.
Particles still move both ways; 'net' describes the overall difference. Do not describe osmosis as all solute particles moving through any barrier.
2 · Worked example
A model cell containing a more concentrated solution than its surroundings can gain water by osmosis, if the membrane permits water movement.
3 · Your turn
Which substance's net movement is being described by osmosis in this model?
Check your answer
Water.
4 · Apply your learning
Interpret supplied mass-change data and distinguish percentage change from raw mass change; any tissue practical needs supervision.
Adult guidance and safety
Use supplied data and approved diagrams. Laboratory work requires qualified supervision, suitable equipment and a risk assessment. No independent chemical, electrical, heating, radiation or biological-culture experiments. Human biology is general education, not personal diagnosis or treatment.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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