B2.1 Membranes and membrane transport
Practice exam-style IB Biology questions for Membranes and membrane transport, aligned with the syllabus and grouped by topic.
Question 1
Phospholipids form bilayers in water because they are amphipathic. What is meant by amphipathic?
A.
Being made only from carbon, hydrogen and oxygen
B.
Being soluble only in non-polar solvents
C.
Having hydrophilic and hydrophobic regions
D.
Having two identical hydrophobic fatty acid tails
Question 2
What property of a phospholipid bilayer most directly restricts the passage of Na⁺ ions?
A.
Carbohydrate chains on the cytoplasmic surface
B.
A hydrophobic core formed by hydrocarbon chains
C.
A hydrophilic surface formed by phosphate heads
D.
Covalent bonding between adjacent phospholipids
Question 3
A respiring cell has a lower oxygen concentration in its cytoplasm than outside the cell. How will oxygen enter the cell?
A.
By simple diffusion between phospholipids
B.
By active transport using ATP
C.
By osmosis through aquaporins
D.
By cotransport with sodium ions
Question 4
What distinguishes a peripheral membrane protein from a transmembrane protein?
A.
A peripheral protein contains no amino acids with hydrophilic side chains.
B.
A peripheral protein is attached to one membrane surface rather than spanning the bilayer.
C.
A peripheral protein is always covalently bonded to cholesterol.
D.
A peripheral protein forms the hydrophobic core of the membrane.
Question 5
What is the net direction of water movement by osmosis across a partially permeable membrane?
A.
From higher ATP concentration to lower ATP concentration
B.
From lower water concentration to higher water concentration
C.
From lower solute concentration to higher solute concentration
D.
From higher solute concentration to lower solute concentration
Question 6
A vesicle fuses with the plasma membrane and releases a protein hormone outside the cell. What is this process?
A.
Endocytosis
B.
Exocytosis
C.
Osmosis
D.
Facilitated diffusion
Question 7
State one feature of a phospholipid that makes it amphipathic.
[1]
Outline why phospholipids form bilayers rather than single molecular layers in water.
[1]
Question 8
An open chloride ion channel increases membrane permeability to Cl⁻. What feature of the channel allows this?
A.
ATP hydrolysis at each chloride binding site
B.
A hydrophilic pore with a size and charge environment suited to Cl⁻
C.
A hydrophobic pore lined only by fatty acid tails
D.
Covalent attachment of chloride ions to phospholipids
Question 9
What process can move particles across a membrane against their concentration gradient?
A.
Simple diffusion through the lipid bilayer
B.
Facilitated diffusion through an open channel
C.
Osmosis through aquaporins
D.
Active transport by a pump protein using ATP
Question 10
How does a higher proportion of unsaturated fatty acids affect a membrane at low temperature?
A.
It hydrolyses ATP to melt the bilayer.
B.
It decreases fluidity because straight tails pack more tightly.
C.
It prevents all movement of membrane proteins.
D.
It helps maintain fluidity because bent tails pack less tightly.
Question 11
What is the position of cholesterol in an animal cell membrane?
A.
Its hydroxyl group lies near phospholipid heads and its hydrophobic region lies among fatty acid tails.
B.
It is dissolved freely in the cytoplasm outside the membrane.
C.
It spans the membrane as a pore for water molecules.
D.
It is attached only to carbohydrate chains on the extracellular surface.
Question 12
What stimulus opens a nicotinic acetylcholine receptor?
A.
Hydrolysis of ATP by the receptor pump
B.
A decrease in membrane cholesterol concentration
C.
Direct binding of glucose to the pore
D.
Binding of acetylcholine to the receptor
Question 13
In one cycle of the sodium-potassium pump, what ion movements occur?
A.
Two Na⁺ are pumped out and three K⁺ are pumped in.
B.
Three Na⁺ are pumped out and two K⁺ are pumped in.
C.
Three Na⁺ and two K⁺ diffuse into the cell.
D.
One Na⁺ and one K⁺ are pumped out together.
Question 14
What are cell-adhesion molecules?
A.
Lipids that hydrolyse ATP to move ions across membranes
B.
Membrane proteins that bind cells to other cells or extracellular material
C.
Soluble enzymes that digest phospholipid bilayers
D.
Carbohydrates stored in vesicles for energy release
Question 15
State one type of particle that has low permeability through the hydrophobic core of a membrane.
[1]
Explain why the hydrophobic core acts as a barrier to that particle.
[1]
Question 16
Define diffusion.
[1]
Describe how carbon dioxide produced by respiration can cross the plasma membrane.
[1]
Question 17
The diagram shows three membrane proteins labelled X, Y and Z.
Identify the label that represents a transmembrane protein.
[1]
Distinguish between integral and peripheral membrane proteins.
[1]
Question 18
State where carbohydrate chains of membrane glycoproteins and glycolipids are located.
[1]
Outline two functions of these carbohydrate chains.
[1]
Question 19
Define endocytosis.
[1]
Distinguish endocytosis from exocytosis.
[1]
Question 20
Define a cell-adhesion molecule.
[1]
Outline how CAMs help form tissues.
[1]
Question 21
The graph shows relative permeability of an artificial phospholipid bilayer to four substances.
Identify the substance with the highest relative permeability.
[1]
Describe the relationship between hydrophobicity and permeability shown in the graph.
[1]
Explain why Na⁺ has low permeability through the bilayer.
[1]
Question 22
A membrane molecule has a lipid part embedded in the bilayer and a carbohydrate chain projecting from the extracellular surface. What is the molecule?
A.
Glycoprotein
B.
Aquaporin
C.
Peripheral protein
D.
Glycolipid
Question 23
Why is sodium-dependent glucose cotransport described as indirect active transport?
A.
The cotransporter hydrolyses ATP at the glucose-binding site.
B.
ATP maintains the Na⁺ gradient, which then drives glucose uptake.
C.
Glucose diffuses through the lipid bilayer without a protein.
D.
Na⁺ and glucose move in opposite directions through the same protein.
Question 24
A channel in a neuron opens when membrane potential changes and allows K⁺ to diffuse out of the cell. What type of channel is it?
A.
Sodium-dependent glucose cotransporter
B.
Voltage-gated potassium channel
C.
Sodium-potassium pump
D.
Neurotransmitter-gated sodium channel
Question 25
Define osmosis.
[1]
Explain osmosis in terms of random movement of water, solute concentration and membrane permeability.
[1]
Question 26
State the role of a channel protein in facilitated diffusion.
[1]
Compare facilitated diffusion through a channel with active transport by a pump.
[1]
Question 27
The diagram space is for a two-dimensional representation of the fluid mosaic model.
Draw and label a phospholipid bilayer, indicating hydrophilic and hydrophobic regions.
[1]
Add and label one integral protein and one peripheral protein.
[1]
Question 28
State how a double bond affects the shape of an unsaturated fatty acid tail.
[1]
Explain why cold-water fish often have a high proportion of unsaturated fatty acids in membrane lipids.
[1]
Question 29
State the position of cholesterol in an animal cell membrane.
[1]
Explain why cholesterol is described as a modulator of membrane fluidity.
[1]
Question 30
The diagram shows a neuron membrane containing gated ion channels.
State the stimulus that opens voltage-gated ion channels.
[1]
Outline the action of a neurotransmitter-gated nicotinic acetylcholine receptor.
[1]
Question 31
State why the sodium-potassium pump is an exchange transporter.
[1]
Explain how the sodium-potassium pump contributes to membrane potential in neurons.
[1]
Question 32
Potato cylinders were placed in sucrose solutions of different concentrations. The table shows the percentage change in mass after 40 minutes.
| Sucrose concentration / mol dm⁻³ | Change in mass after 40 min / % |
|---|---|
| 0.00 | +16.4 |
| 0.10 | +10.7 |
| 0.20 | +5.2 |
| 0.30 | +0.4 |
| 0.40 | −4.8 |
| 0.50 | −10.6 |
| 0.60 | −15.9 |
State the sucrose concentration at which there is the smallest change in mass.
[1]
Describe the trend in percentage change in mass as sucrose concentration increases.
[1]
Explain the mass change in the most concentrated sucrose solution.
[1]
Suggest one variable that should be controlled in this investigation.
[1]
Question 33
The graph shows ion movement across a membrane before and after a specific ion channel opens.
State the time period in which the ion channel is open.
[1]
Describe the change in ion movement when the channel opens.
[1]
Explain why ion movement through the channel is an example of facilitated diffusion.
[1]
Question 34
Cells were engineered to express different amounts of aquaporin. Water uptake was measured after transfer to a dilute solution.
Identify the treatment with the greatest rate of water uptake.
[1]
Describe the relationship between aquaporin expression and water uptake.
[1]
Explain why aquaporins increase water uptake.
[1]
Suggest why ion concentrations inside the cell do not necessarily change at the same rate as water uptake.
[1]
Question 35
Membrane lipid composition was measured in two related fish species living at different water temperatures.
| Species | Habitat temperature / °C | Saturated fatty acids / % | Unsaturated fatty acids / % |
|---|---|---|---|
| Species A | 4 | 28 | 72 |
| Species B | 24 | 55 | 45 |
Identify the species with the higher proportion of unsaturated fatty acids.
[1]
Describe the relationship between habitat temperature and unsaturated fatty acid percentage.
[1]
Explain the adaptive value of this lipid composition.
[1]
Question 36
State where sodium-dependent glucose cotransport is important in humans.
[1]
Explain how glucose can enter an epithelial cell against its concentration gradient by indirect active transport.
[1]
Question 37
A mutation reduces the fluidity of secretory vesicle membranes in a pancreatic cell.
State the process by which digestive enzymes are normally released from this cell.
[1]
Suggest why reduced vesicle membrane fluidity could reduce enzyme secretion.
[1]
Question 38
Researchers compared adhesion between animal cells with normal membrane glycoproteins and cells treated with an enzyme that removes extracellular carbohydrate chains.
| Treatment | Mean adhesion index / AU | SD / AU |
|---|---|---|
| Normal cells | 0.82 | 0.06 |
| Enzyme-treated cells | 0.47 | 0.05 |
State which treatment shows lower cell adhesion.
[1]
Calculate the difference in mean adhesion index between the two treatments.
[1]
Suggest why removal of extracellular carbohydrate chains affects cell adhesion.
[1]
Question 39
Artificial animal-cell membranes were made with different cholesterol contents. Leakage of a polar dye was measured at low, moderate and high temperatures.
State the temperature at which membranes without cholesterol show the greatest dye leakage.
[1]
Compare the effect of cholesterol on dye leakage at high and low temperatures.
[1]
Evaluate the statement: “Cholesterol simply reduces membrane fluidity.”
[1]
Question 40
Secretory cells were incubated with a compound that decreases membrane fluidity. The release of a labelled protein was measured over time.
Describe the effect of the compound on protein release.
[1]
Identify the membrane transport process responsible for release of the labelled protein.
[1]
Suggest why decreasing membrane fluidity affects this process.
[1]
Question 41
Outline how amphipathic lipids form a bilayer in water.
[1]
Explain how the structure of the lipid bilayer allows membranes to act as barriers while still permitting some simple diffusion.
[1]
Question 42
Define osmosis and state one role of aquaporins.
[1]
Explain water movement across membranes in cells placed in solutions of different solute concentration.
[1]
Question 43
Distinguish between endocytosis and exocytosis.
[1]
Explain why membrane fluidity is essential for vesicle formation, movement of membrane material and secretion.
[1]
Question 44
The graph shows membrane potential of a neuron and the relative opening of voltage-gated Na⁺ and K⁺ channels during a nerve impulse.
Identify which channel type opens first.
[1]
Describe the change in membrane potential when Na⁺ channels open.
[1]
Explain the direction of Na⁺ movement through open Na⁺ channels.
[1]
Suggest why delayed opening of K⁺ channels helps restore the membrane potential.
[1]
Question 45
Glucose uptake into epithelial cells was measured under four conditions: normal medium, medium without Na⁺, medium with a sodium-potassium pump inhibitor, and medium with extra ATP but no Na⁺.
Identify the condition with the lowest glucose uptake.
[1]
Compare glucose uptake in normal medium and medium with a sodium-potassium pump inhibitor.
[1]
Explain why removing extracellular Na⁺ affects glucose uptake.
[1]
Evaluate whether adding ATP directly to the medium should restore uptake when extracellular Na⁺ is absent.
[1]
Question 46
Outline how channel proteins make membranes selectively permeable.
[1]
Compare and contrast facilitated diffusion through channel proteins with active transport by pump proteins.
[1]
Question 47
State two components that should be included in a two-dimensional drawing of the fluid mosaic model.
[1]
Discuss how components of the fluid mosaic membrane contribute to transport, recognition and adhesion.
[1]
Question 48
Outline how saturated and unsaturated fatty acids differ in structure and effect on packing.
[1]
Evaluate how fatty acid composition and cholesterol help membranes function over a range of temperatures.
[1]
Question 49
Outline sodium-dependent glucose cotransport in an epithelial cell.
[1]
Evaluate the importance of membrane transport proteins and cell-adhesion molecules in epithelial tissue function.
[1]
Question 50
Outline the action of voltage-gated Na⁺ and K⁺ channels in neurons.
[1]
Discuss how gated ion channels and sodium-potassium pumps together allow rapid changes in membrane potential.
[1]
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