This free quiz has 20 multiple choice questions on cell membranes and transport, all taken from Cambridge International (CIE) A Level Biology exam papers. It marks itself, so you get your score as soon as you finish.
What the quiz covers (Cambridge 9700 topic 4: Cell membranes and transport)
The fluid mosaic model: phospholipids, cholesterol, glycoproteins, glycolipids, channel proteins and carrier proteins
How temperature and solvents affect membrane permeability, for example in beetroot experiments
Diffusion and facilitated diffusion, and which substances need transport proteins
Osmosis and water potential, including the effects on red blood cells and plant cells
Active transport, endocytosis and exocytosis, and which processes use ATP
Surface area to volume ratio and diffusion distance, including calculations with cubes, cylinders and agar blocks
How to use it
For the calculation questions, write out the surface area and volume separately before you work out the ratio, and check your units. For osmosis questions, compare water potentials, not concentrations, and decide which way water will move before you look at the options.
Where students lose marks (from Cambridge examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Water potential, not concentration: Explaining osmosis using 'water concentration' or a 'concentration gradient', or writing that water moves from a 'high water potential gradient' to a 'low water potential gradient'. Examiners did not credit these.
✔ Gains credit: water moves by osmosis across the partially permeable membrane, from a higher (less negative) water potential to a lower (more negative) water potential, down a water potential gradient.
Carrier proteins do both jobs: Stating that carrier proteins carry out active transport while channel proteins carry out facilitated diffusion. This was not credited, because carrier proteins are also used in facilitated diffusion.
✔ Gains credit: carrier proteins are used for both active transport and facilitated diffusion. Channel proteins are used only for facilitated diffusion and provide a hydrophilic, water-filled pore.
'Too large' is not the reason: Saying glucose needs a transport protein because it is 'too large', or calling ions 'polar molecules'. Ions are charged, and size alone does not explain why the bilayer stops them.
✔ Gains credit: ions are charged and glucose is polar (water soluble), so neither can pass through the hydrophobic core of the phospholipid bilayer. Transport proteins give a hydrophilic pathway across the membrane.
Cholesterol regulates fluidity: Writing that cholesterol simply 'increases' or 'controls' fluidity, referring to 'cell fluidity', or saying it provides energy. A change in fluidity only gained credit when it was linked to temperature.
✔ Gains credit: cholesterol regulates the fluidity of the membrane, increasing fluidity at low temperatures and reducing it at high temperatures, and gives the membrane mechanical stability.
Bulk transport is not active transport: Describing endocytosis or exocytosis as active transport, or saying a vesicle fuses with 'the membrane'. Active transport uses carrier proteins, and 'the membrane' could mean a membrane inside the cell.
✔ Gains credit: exocytosis is bulk transport. Vesicles move along microtubules and fuse with the cell surface membrane, releasing their contents. It is an active process that requires ATP.
Surface area needs volume: Stating only that a feature gives 'a large surface area', without linking it to volume or explaining that more cell surface membrane means more room for transport proteins.
✔ Gains credit: the feature increases the surface area to volume ratio, giving more cell surface membrane and so more space for carrier proteins and pumps, which increases the rate of uptake.
Receptors bind signalling molecules: Describing cell surface receptors as 'detecting' a signalling molecule, or saying the signalling molecule is taken into the target cell by endocytosis before it binds to a receptor inside.
✔ Gains credit: the signalling molecule binds to a receptor (a glycoprotein or glycolipid) on the cell surface membrane of the target cell, because its shape is complementary to the receptor.
Keep practising
Go on to the CIE Lipids and Phospholipids quiz, the CIE Transport in Plants quiz or the CIE Cell Structure quiz, or browse all our CIE A Level Biology quizzes. If membranes still feel shaky, book a one-to-one lesson and we can work through Cambridge exam questions together.