This free quiz has 10 real AQA A-level Biology exam questions on transport across cell membranes (27 marks, about 35 minutes). It marks itself: the table question is marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.2.3)
the phospholipid bilayer, and why lipids and steroid hormones cross it easily
matching examples to the ways substances cross membranes
similarities between diffusion and osmosis
water potential and osmosis in the ileum
explaining the shape of a graph of monosaccharide uptake
how cells lining the ileum absorb glucose against a concentration gradient
active transport, co-transport and osmosis in pear cell vacuoles (4 marks)
naming and describing five ways substances move into cells (5 marks)
How to use it
Write each written answer in full before you open the mark scheme. Say water potential, never water concentration, and always give the direction water moves by osmosis. For each transport process, name the protein involved and say whether ATP is used.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Why phospholipids form a bilayer. Most students named the bilayer, but only about 30% explained it in terms of water. Common errors were calling the phosphate heads hydrophobic and the fatty acid tails hydrophilic, or writing ‘a lipid layer’ instead of a phospholipid bilayer.
✔ Gains credit: phospholipids form a bilayer because the hydrophilic phosphate heads are attracted to water on both sides of the membrane, while the hydrophobic fatty acid tails point away from water.
Heat damages membranes. A common mistake was saying high temperatures denature enzymes and slow a reaction. Others wrote about damage to cell walls, or to ‘the cells’ in general, rather than the cell-surface membrane.
✔ Gains credit: higher temperatures denature membrane proteins and increase the fluidity of the phospholipids, so the cell-surface membrane becomes more permeable and more pigment is released.
Down a gradient, without ATP. Movement ‘along’ or ‘across’ a gradient, or ‘from a high gradient to a low gradient’, gained no marks. Saying passive processes need ‘no energy’ was rejected, and many wrongly called facilitated diffusion active or said it uses ATP.
✔ Gains credit: passive processes move substances down a gradient (from high to low concentration, or from high to low water potential) and don't use energy from ATP or respiration.
Active transport and ATP. Students often left out carrier proteins or wrongly said channel proteins are used. Many wrote that ATP hydrolysis ‘produces’ or ‘makes’ energy, which was rejected.
✔ Gains credit: ATP hydrolase hydrolyses ATP to ADP and Pi, releasing energy that moves ions against a concentration gradient through a carrier protein.
Carriers become saturated. When an uptake curve levelled off, the commonest mistake was blaming loss of the concentration gradient. A significant minority wrote about enzyme active sites instead of carrier proteins.
✔ Gains credit: when the rate levels off, all the carrier or channel proteins are in use (saturated), so they limit the rate; more carrier proteins in the membrane means faster transport.
Water potential, not concentration. Many answers were at GCSE level and talked about water ‘concentration’ instead of water potential, or confused high and low water potential. Others left out the word osmosis, or wrote ‘water moves out’ without saying from where to where.
✔ Gains credit: the solution has a lower (more negative) water potential than the cells, so water moves out of the cells into the solution by osmosis.
Microvilli, not villi. Many students confused microvilli with villi, describing them as having ‘thin walls’ or being ‘one cell thick’. Others said microvilli increase surface area without linking it to faster transport.
✔ Gains credit: microvilli are folds of the cell-surface membrane that increase the surface area for more channel and carrier proteins, so absorption is faster.
Keep practising
The other AQA 3.2 self-marking quizzes: Cell structure · Mitosis · Immune system
Topic 3.1 quizzes start with carbohydrates
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.