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Question 1
Phospholipids placed in water can form a continuous bilayer without cellular energy input. What property of phospholipids accounts for this self-assembly?
A.
They are charged ions that repel each other into two separate layers.
B.
They are covalently joined to membrane proteins before entering water.
C.
They are amphipathic, with hydrophilic heads and hydrophobic tails.
D.
They are entirely hydrophilic, so all regions interact equally with water.
Question 2
A membrane has a phospholipid bilayer but no transport proteins. Which substance would be expected to cross the bilayer most readily by simple diffusion?
A.
A polypeptide
B.
C.
D.
Glucose
Question 3
A respiring cell uses faster than it is produced inside the cell. What explains the net movement of into the cell across the plasma membrane?
A.
Random movement produces more crossings into the cell than out of it.
B.
ATP hydrolysis in the bilayer pulls molecules into the cytoplasm.
C.
Aquaporins selectively bind and rotate to release it inside the cell.
D.
The phosphate heads actively repel from the extracellular surface.
Question 4
A membrane protein has a hydrophilic pore that opens to allow to move across the membrane down its concentration gradient. What type of transport is occurring?
A.
Osmosis through an aquaporin
B.
Active transport through a pump protein
C.
Facilitated diffusion through a channel protein
D.
Simple diffusion through phospholipid tails
Question 5
What is the usual orientation and function of carbohydrate chains attached to membrane glycoproteins and glycolipids?
A.
They lie in the hydrophobic core and increase simple diffusion of ions.
B.
They face the extracellular side and contribute to cell recognition and adhesion.
C.
They face the cytoplasm and hydrolyse ATP for active transport.
D.
They span both lipid layers and form pores for water movement.
Question 6
A vesicle inside a pancreatic cell fuses with the plasma membrane and releases digestive enzyme molecules outside the cell. What process is described?
A.
Osmosis
B.
Endocytosis
C.
Facilitated diffusion
D.
Exocytosis
Question 7
Phospholipid molecules are mixed with water and spontaneously form bilayers.
State what is meant by an amphipathic molecule.
[1]
Explain why phospholipids form a bilayer in water.
[2]
0
Question 8
Two solutions are separated by a partially permeable membrane. The membrane is permeable to water but not to the dissolved solute. Side X has a lower solute concentration than side Y. What is the net movement of water?
A.
From side Y to side X by osmosis
B.
From side X to side Y by osmosis
C.
From side X to side Y by active transport
D.
No net movement because water molecules stop moving at the membrane
Question 9
Cold-water fish often have a higher proportion of unsaturated fatty acids in membrane phospholipids than related warm-water fish. What is the advantage of this membrane composition?
A.
It increases the number of hydrogen bonds between adjacent hydrocarbon chains.
B.
It makes the bilayer impermeable to all small non-polar molecules.
C.
It raises the melting point so membranes become rigid at low temperature.
D.
It prevents close packing of fatty acid tails, helping membranes remain fluid.
Question 10
Cholesterol is present among the phospholipid tails of an animal cell membrane. What is its effect on membrane fluidity?
A.
It always increases fluidity by separating all phospholipids at every temperature.
B.
It removes the hydrophobic core by moving phospholipid heads into the centre of the bilayer.
C.
It always decreases fluidity by forming covalent bonds between fatty acid tails.
D.
It buffers fluidity by restricting phospholipid movement when warm and reducing tight packing when cold.
Question 11
Acetylcholine binds to a nicotinic acetylcholine receptor in a postsynaptic membrane. What immediate effect does this binding have on the receptor?
A.
A conformational change opens a cation channel, allowing ions such as to diffuse.
B.
The receptor detaches from the membrane and forms a secretory vesicle.
C.
ATP is hydrolysed to pump out and into the postsynaptic cell.
D.
The receptor becomes a phospholipid carrier for glucose cotransport.
Question 12
What occurs during one cycle of the sodium-potassium pump in a neuron membrane?
A.
Two ions are moved out and three ions are moved in using ATP.
B.
Three ions are moved out and two ions are moved in using ATP.
C.
Three ions and two ions diffuse in through the same open channel.
D.
One glucose molecule is moved in with two ions down a sodium gradient.
Question 13
A plasma membrane separates the cytoplasm from an external aqueous solution containing oxygen, glucose and sodium ions.
Identify the molecule listed that can cross the lipid bilayer most readily by simple diffusion.
[1]
Explain why sodium ions have low permeability through the lipid bilayer.
[2]
State one property, other than charge, that affects permeability by simple diffusion.
[1]
0
Question 14
Membrane proteins vary in how they are associated with the phospholipid bilayer.
Outline one structural feature of an integral membrane protein.
[1]
Distinguish between the locations of integral and peripheral membrane proteins.
[2]
0
Question 15
The diagram shows a membrane-bound vesicle moving to the plasma membrane in a secretory cell.
Identify the process shown.
[1]
Explain how membrane fluidity allows this process to occur.
[2]
State one example of a substance released from cells by this process.
[1]
0
Question 16
Artificial liposomes were made from purified phospholipids without membrane proteins. The permeability of the liposome membrane to different substances was measured under the same concentration gradient.
Describe the relationship between the properties of the substances and their permeability through the lipid bilayer.
[2]
Explain why sodium ions and glucose do not cross the liposome membrane rapidly.
[2]
0
Question 17
Membrane proteins from animal cells were treated with different solutions. The percentage of each protein released from the membrane fraction was measured.
| Protein | No treatment / % released | High-salt solution / % released | Alkaline solution / % released | Detergent / % released |
|---|---|---|---|---|
| P | 5 | 84 | 88 | 90 |
| Q | 4 | 8 | 7 | 92 |
| R | 3 | 5 | 6 | 94 |
Identify the protein most likely to be peripheral. Give a reason for your answer.
[2]
Explain why detergent is required to release a transmembrane protein from the membrane.
[2]
0
Question 18
A sodium-dependent glucose cotransporter moves glucose into an intestinal epithelial cell even when glucose concentration is higher inside the cell than in the lumen. ATP is not hydrolysed by the cotransporter. Why is this still classified as active transport?
A.
The cotransporter forms an open pore through which glucose diffuses freely in both directions.
B.
Glucose crosses the hydrophobic core directly because it is a small non-polar molecule.
C.
The process is active because water moves by osmosis into the epithelial cell.
D.
The glucose movement depends on a gradient maintained by ATP-driven sodium-potassium pumps.
Question 19
Plant root hair cells contain aquaporins in their plasma membranes. The diagram shows a root hair cell placed in a solution with a higher solute concentration than the cytoplasm.
Define osmosis.
[1]
Explain why water moves out of the cell in this situation.
[2]
Suggest the effect of aquaporins on the rate of this water movement.
[1]
0
Question 20
Cells use both channel proteins and pump proteins to transport substances across membranes.
State the usual energy source used by pump proteins for active transport.
[1]
Distinguish between transport through an open channel protein and transport by a pump protein.
[2]
Outline how channel proteins contribute to selective permeability.
[1]
0
Question 21
The fluid mosaic model represents the structure of biological membranes.
Draw and label a two-dimensional representation of the fluid mosaic model of a plasma membrane.
[4]
0
Question 22
The table compares the fatty acid composition of membrane phospholipids in related fish species living at different habitat temperatures.
| Fish species | Habitat temperature / °C | Unsaturated fatty acids / % | Saturated fatty acids / % |
|---|---|---|---|
| Species A | 2 | 78 | 22 |
| Species B | 8 | 69 | 31 |
| Species C | 15 | 54 | 46 |
| Species D | 22 | 41 | 59 |
Identify the relationship between habitat temperature and the percentage of unsaturated fatty acids.
[1]
Explain how a higher proportion of unsaturated fatty acids helps maintain membrane fluidity in cold water.
[2]
Suggest why a membrane with many saturated fatty acids may be advantageous at higher habitat temperatures.
[1]
0
Question 23
Cholesterol is present in the plasma membranes of animal cells.
State the position of cholesterol molecules in the phospholipid bilayer.
[1]
Explain why cholesterol is described as a modulator of membrane fluidity.
[2]
0
Question 24
Gated ion channels in neuron membranes open or close in response to specific stimuli.
State the stimulus that opens or closes voltage-gated ion channels.
[1]
Explain why diffuses into a neuron when voltage-gated sodium channels open during a nerve impulse.
[2]
Outline how a nicotinic acetylcholine receptor is gated.
[1]
0
Question 25
The sodium-potassium pump is an exchange transporter in the plasma membrane of neurons.
State the numbers and directions of ions moved by one cycle of the sodium-potassium pump.
[2]
Explain how sodium-potassium pumps contribute to membrane potentials in neurons.
[2]
0
Question 26
Plant protoplasts were placed in a dilute sucrose solution. One group was treated with a chemical that blocks aquaporins. The change in protoplast volume was recorded.
State the direction of net water movement in the untreated protoplasts during the first minutes of the experiment.
[1]
Compare the rate of osmosis in untreated and aquaporin-blocked protoplasts.
[2]
Explain the increase in volume of the protoplasts in terms of osmosis.
[2]
0
Question 27
Membrane vesicles containing one type of ion channel were placed in solutions containing either or . Ion movement across the vesicle membrane was measured when the channels were open.
Identify one piece of evidence from the graph that the channel is selective.
[1]
Explain why movement of through the open channel is facilitated diffusion.
[2]
Suggest the effect on flux if a molecule blocked the pore of the channel.
[1]
0
Question 28
Root epidermal cells were incubated in a solution where the external nitrate concentration was lower than the internal nitrate concentration. Nitrate uptake was measured under different treatments.
Using the data, state two reasons why nitrate uptake is active transport.
[2]
Explain how a pump protein could move nitrate across the membrane in these cells.
[2]
0
Question 29
Cultured epithelial cells were treated with enzymes that remove specific surface components. Binding of a fluorescent lectin to the cell surface and adhesion between cells were then measured.
| Enzyme treatment | Fluorescent lectin binding / % of control | Cell adhesion / % of control |
|---|---|---|
| Control | 100 | 100 |
| Protease | 96 | 68 |
| Lipase | 94 | 82 |
| Glycosidase | 14 | 24 |
State the side of the plasma membrane on which the carbohydrate chains of glycoproteins and glycolipids are located.
[1]
Using the data, explain why carbohydrate-containing membrane molecules are involved in cell adhesion.
[2]
Suggest why protease and lipase treatments do not have identical effects on adhesion.
[1]
0
Question 30
Membrane lipids were extracted from two related fish species. Species C lives in cold coastal water and species W lives in warmer water. The fatty acid composition and membrane transition temperature were analysed.
Describe the relationship between the percentage of unsaturated fatty acids and membrane transition temperature.
[2]
Explain how the fatty acid composition shown is an adaptation to cold water.
[2]
0
Question 31
A secretory cell line was engineered so that secretory vesicles fluoresce when they fuse with the plasma membrane. Cells were kept at different temperatures before stimulation of secretion.
Identify the membrane transport process shown by the annotated sequence.
[1]
Using the data, explain why membrane fluidity is required for this process.
[2]
Suggest one consequence for a secretory cell if vesicle fusion were inhibited.
[1]
0
Question 32
Two populations of cultured cells were engineered to express different cell-adhesion molecules (CAMs) on their plasma membranes. Cell aggregation was measured after mixing the populations with or without antibodies against the CAMs.
Identify the evidence that CAMs are involved in cell-cell adhesion.
[1]
Explain how the structure and location of CAMs allow them to form cell-cell junctions.
[2]
Evaluate the effect of adding an antibody against CAM-A on tissue formation in this model.
[1]
0
Question 33
Epithelial cells in the small intestine absorb glucose and are joined to neighbouring epithelial cells in an organized tissue.
Explain how a sodium-dependent glucose cotransporter can move glucose into the epithelial cell against its concentration gradient.
[2]
State the role of sodium-potassium pumps in this indirect active transport system.
[1]
Outline the role of cell-adhesion molecules in forming tissues.
[1]
0
Question 34
Liposomes were made with phospholipids only or with phospholipids and cholesterol. Membrane fluidity was measured over a range of temperatures.
State the position of cholesterol in the membrane, using the inset diagram.
[1]
Analyse the effect of cholesterol on membrane fluidity at low and high temperatures.
[3]
0
Question 35
Intestinal epithelial cells absorb glucose using sodium-dependent glucose cotransporters in the apical membrane. Sodium-potassium pumps are located mainly in the basal membrane. Glucose uptake was measured under different conditions.
| Treatment | Extracellular Na+ / mM | Cytosolic Na+ / mM | Glucose uptake / % of control |
|---|---|---|---|
| Control | 145 | 10 | 100 |
| Pump inhibited | 145 | 40 | 35 |
State the direction in which the sodium-potassium pump moves sodium and potassium ions.
[1]
Using the data, explain why inhibition of the sodium-potassium pump reduces glucose uptake.
[2]
Explain why sodium-dependent glucose uptake is described as indirect active transport.
[2]
0
Question 36
An artificial membrane was made from purified phospholipids and placed between two aqueous solutions. Small non-polar molecules crossed the membrane readily, but glucose and sodium ions did not cross unless transport proteins were added.
I.
Explain why phospholipids form a bilayer in water.
[2]
II.
State one property of the membrane core that allows it to act as a barrier.
[1]
Explain why can cross the membrane by simple diffusion but cannot.
[2]
Discuss why adding channel proteins makes a membrane selectively permeable rather than simply more permeable to all substances.
[2]
0
Question 37
A membrane fraction from liver cells was treated with a mild salt solution and then with a detergent that disrupts the lipid bilayer. Some proteins were released by the salt solution, while others were released only after detergent treatment.
I.
Identify the type of membrane protein most likely to be released by mild salt treatment.
[1]
II.
Give one reason for your answer to part (i).
[1]
Compare the locations of integral and peripheral proteins in membranes.
[2]
Discuss how the structure and orientation of membrane proteins contribute to membrane function.
[3]
0
Question 38
Epithelial cells lining the intestine have carbohydrate-containing molecules on the extracellular side of the plasma membrane. These molecules are involved in recognition by immune cells and in attachment between neighbouring epithelial cells.
I.
State the difference in composition between a glycoprotein and a glycolipid.
[1]
II.
State where the carbohydrate chains of these molecules are located in a plasma membrane.
[1]
Explain how glycoproteins and glycolipids can contribute to cell recognition.
[2]
Discuss how the fluid mosaic model accounts for both the barrier and interaction functions of the intestinal cell membrane.
[3]
0
Question 39
A neuron was stimulated while the conductance of voltage-gated sodium and potassium channels was recorded. Conductance is a measure of how readily ions pass through open channels.
Identify the ion channel mainly responsible for the initial depolarization shown in the graph. Give a reason.
[2]
Explain how the later increase in potassium conductance contributes to repolarization.
[2]
nicotinic acetylcholine receptor is a neurotransmitter-gated cation channel. Predict the immediate effect of acetylcholine binding to this receptor.
[1]
0
Question 40
Root hair cells of two plant varieties were placed in sucrose solutions of different concentration. Variety A expresses many aquaporins in the plasma membrane; variety B expresses few aquaporins.
I.
Define osmosis in the context of these root hair cells.
[1]
II.
Explain why no net change in volume occurs at one sucrose concentration.
[2]
Explain why variety A changes volume faster than variety B when placed in a concentrated sucrose solution.
[2]
Evaluate the claim that aquaporins remove the need for osmosis to be explained by random movement of water molecules.
[3]
0
Question 41
A freshwater alga maintains a high internal concentration of potassium ions compared with the surrounding water. Its plasma membrane contains potassium channels and ATP-driven potassium pump proteins.
I.
Distinguish between facilitated diffusion through a potassium channel and active transport by a potassium pump.
[2]
II.
State why potassium ions cannot cross the lipid bilayer rapidly without a transport protein.
[1]
Explain how the alga can maintain an internal potassium concentration higher than that of the surrounding water.
[2]
Discuss the consequences for the alga if ATP production is inhibited while potassium channels remain open.
[3]
0
Question 42
Researchers tested three substances for movement across pure lipid vesicles and across vesicles containing specific transport proteins. Substance X is small and non-polar, substance Y is large and polar, and substance Z is a chloride ion.
| Substance | Pure lipid vesicle / a.u. | Vesicle with transport proteins / a.u. |
|---|---|---|
| X | 98 | 96 |
| Y | 3 | 70 |
| Z | 1 | 85 |
I.
Predict which substance would cross a pure lipid vesicle most readily.
[1]
II.
Explain your prediction in part (i).
[1]
Explain why substance Z requires a membrane protein for rapid movement across the vesicle membrane.
[2]
Evaluate the statement: "A selectively permeable membrane is just a membrane with very small pores."
[2]
0
Question 43
Membrane lipids were extracted from three closely related fish species living at different average water temperatures. The proportion of unsaturated fatty acid tails in their phospholipids and a measure of membrane fluidity were determined at a common test temperature.
I.
Describe the relationship shown between fatty acid unsaturation and membrane fluidity.
[1]
II.
Explain why unsaturated fatty acid tails have this effect on fluidity.
[2]
Compare the expected membrane composition of cold-water and warm-water fish.
[2]
Evaluate whether the graph alone proves that habitat temperature caused the differences in membrane composition.
[3]
0
Question 44
Animal cells were grown with normal cholesterol content or with reduced cholesterol content. Membrane fluidity was measured at low, moderate and high temperatures.
I.
Describe the position of cholesterol molecules in an animal cell membrane.
[1]
II.
Explain why this position is related to cholesterol structure.
[2]
Explain how cholesterol affects membrane fluidity at low and high temperatures.
[2]
Discuss why it is inaccurate to state that cholesterol simply increases membrane fluidity.
[2]
0
Question 45
A secretory pancreatic cell packages digestive enzymes into vesicles. The vesicles move to the plasma membrane and release their contents into a duct. The same cell can also take up large extracellular protein complexes by vesicle formation.
I.
Identify the process by which digestive enzymes are released from the cell.
[1]
II.
Describe the membrane events that occur during this process.
[2]
Explain how membrane fluidity allows both vesicle formation and vesicle fusion.
[3]
Discuss why vesicle transport is necessary for secretion of digestive enzymes rather than simple diffusion through the lipid bilayer.
[2]
0
Question 46
A toxin inhibits sodium-potassium pumps in neurons but does not directly block ion channels. After exposure to the toxin, neurons gradually lose the ability to generate normal action potentials.
I.
Describe one cycle of the sodium-potassium pump.
[2]
II.
State why the sodium-potassium pump is classified as active transport.
[1]
Explain how sodium-potassium pumps help generate membrane potentials in neurons.
[2]
Evaluate why the toxin affects action potentials even though it does not directly block gated ion channels.
[2]
0
Question 47
The membrane of a motor neuron contains voltage-gated sodium and potassium channels. The membrane of a muscle fibre at a neuromuscular junction contains nicotinic acetylcholine receptors.
I.
State the stimulus that opens a voltage-gated ion channel.
[1]
II.
State the stimulus that opens a nicotinic acetylcholine receptor.
[1]
III.
State the type of transport that occurs through these channels when they are open.
[1]
Compare how sodium and potassium channels contribute to changes in membrane potential during a nerve impulse.
[3]
Discuss how channel selectivity and gating allow rapid but controlled signalling at the neuromuscular junction.
[2]
0
Question 48
Cells lining the small intestine absorb glucose from the gut lumen. Their lumen-facing membrane contains sodium-dependent glucose cotransporters. Their opposite membrane contains sodium-potassium pumps. Adjacent intestinal cells are joined by cell-adhesion molecules.
I.
State what is meant by a sodium-dependent glucose cotransporter.
[1]
II.
Explain why glucose uptake by this mechanism is described as indirect active transport.
[2]
Explain why the locations of the cotransporter and sodium-potassium pump on opposite sides of the epithelial cell are important for glucose absorption.
[3]
Discuss how cell-adhesion molecules contribute to the function of intestinal epithelial tissue.
[2]
0
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