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GCSE Biology · key term
A membrane that allows some substances to pass through but prevents others from doing so.
Used by AQA, Edexcel and OCR
Specification 4.1.3.2, 4.1.3.3, 4.5.3.3 · Paper 1, Paper 2
A membrane that allows some substances, including water, to pass through but prevents others from passing through.
Revise: OsmosisOsmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane. Water moves both ways, but its net movement is towards the more concentrated solution.
In comparisons, state that osmosis concerns only water and requires a partially permeable membrane. Diffusion and active transport can move other substances.
When explaining osmosis, state the direction of water movement, refer to a partially permeable membrane and link excessive gain or loss of water to inefficient cell function.
When explaining urea removal, link the facts in a chain: the dialysis fluid contains no urea, so a concentration gradient exists and urea diffuses across the partially permeable membrane from the blood into the fluid.
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A membrane that allows some substances, such as water molecules, to pass through but prevents others from crossing freely.
A membrane that allows some small dissolved substances and water to pass through but prevents blood cells and large proteins from crossing.
Specification 1.15, 7.21B · Paper 1, Paper 2
Revise: Transport in CellsOsmosis is a special case involving water. It is the net movement of water molecules through a partially permeable membrane, from a dilute solution to a more concentrated solution. A dilute solution has a high concentration of water molecules; adding more dissolved substance lowers the concentration of water molecules.
A barrier that allows some substances to pass through but prevents others from passing through.
Specification B2.1a, B2.2f, B3.3f, PAG 8 · Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Revise: Transport in cellsOsmosis is a special case involving water. It is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
A membrane that allows some substances, including water, to pass through but restricts others.
A membrane that lets some substances, including water, pass through but restricts others.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A membrane that allows some substances through but prevents others from passing through.
A membrane that allows some substances, including water, to pass through more readily than others.