Comprehensive active recall questions for Transport Across Cell Membranes (Unit 2- Cells) in the new AQA A Level Biology specification (from 2017) that can easily be converted to flashcards for spaced repetition.
1. Why are membranes described as fluid-mosaic?
The molecules inside the membrane can move
2. What components make up the membrane?
Cholesterol, glycolipids, glycoproteins, phospholipids, carrier proteins, channel
proteins
3. In a phospholipid, how are the heads and tails arranged, and what are their
respective properties?
Hydrophilic head- attracted to water (face outwards); hydrophobic tail- repel water
(face inwards)
4. What two molecules does the phospholipid head contain?
Phosphate ion and glycerol
5. What are the phospholipid tails made of?
Fatty acids (one saturated and the other unsaturated)
6. How is cholesterol present in the membrane?
Embedded within the membrane
7. What is the purpose of the cholesterol?
Restricts the lateral movement of the molecules
8. Describe the relationship between cholesterol and fluidity of membrane
The more cholesterol there is, the less fluid the membrane is
9. Why can cholesterol’s property be useful at high temperatures?
Membrane is less fluid at high temperature so dissolved ions cannot pass through
the gaps in the membrane
10. What is the function of a peripheral protein and give an example of one
Cell recognition; glycoprotein
11. What are two types of integral proteins?
Channel proteins and carrier proteins
12. What substances can channel proteins transport and how?
Water can flow through hollow tube so dissolved ions can be transported water-
soluble ions can diffuse
13. What substances can carrier proteins transport and how?
large, insoluble molecules (e.g. glucose or amino acids) bind to carrier protein, which
causes it to change shape, and is able to be transported to the other side of the
protein
14. What property of the membrane means that only certain molecules can pass
through?
Partially permeable
15. Which molecules can pass through and via what process?
Lipid-soluble substances and small molecules via simple diffusion
16. Which molecules cannot pass through and have to be transported via what
process?
Large molecules like glucose and polar substances like water via active transport
1. What is simple diffusion?
Net movement of molecules from an area of high concentration to an area of lower
concentration until equilibrium is reached
2. Is simple diffusion active or passive?
Passive- no ATP is required
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