Transport across cell membranesAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Transport across cell membranes topic test

Total 54 marks

Name

Class

Date

1
Eukaryotic cells contain many membranes: the cell-surface membrane and the membranes around organelles such as mitochondria. A biochemist analyses the cell-surface membrane of a nerve cell and finds phospholipids, cholesterol, channel proteins and glycoproteins.
(a)
Which statement about the glycoproteins in the cell-surface membrane is correct?
[1 mark]
AThey form the hydrophobic core of the membrane.
BThey act as receptors and recognition sites on the outer surface of the membrane.
CThey carry ions across the membrane using energy from ATP.
DThey restrict the movement of phospholipids within the membrane.
(b)
Which statement describes the role of cholesterol in the membrane?
[1 mark]
AIt forms channels for ions to pass through.
BIt makes the membrane fully rigid so that no molecules can move.
CIt binds to antigens on the outside of the cell.
DIt restricts the movement of phospholipids and other molecules in the membrane.
(c)
Explain why the structure of the membrane is described as a fluid mosaic.
[2 marks]
Total for question 1: 4 marks
2
Oestrogen is a steroid hormone that passes straight into its target cells. Potassium ions, in contrast, can only enter the same cells through specific protein channels in the cell-surface membrane.
(a)
Which statement best explains why oestrogen can cross the cell-surface membrane without a protein?
[1 mark]
AIt is lipid-soluble, so it dissolves in and passes through the hydrophobic interior of the phospholipid bilayer.
BIt is positively charged, so it is attracted to the phosphate heads of the bilayer.
CIt is actively transported using ATP.
DIt is too large to pass through the channel proteins and so goes between them.
(b)
Which statement about the channel proteins for potassium ions is correct?
[1 mark]
AThey change shape using energy from ATP to move potassium ions against their concentration gradient.
BThey allow any ion that is small enough to pass through.
CThey are specific and allow potassium ions to move down their electrochemical gradient through a hydrophilic pore.
DThey are found only in the membranes of organelles.
(c)
State two ways in which a cell could increase the rate of diffusion of potassium ions across its cell-surface membrane, other than by increasing the concentration gradient.
[2 marks]
Total for question 2: 4 marks
3
Epidermal cells from a rhubarb stalk have a water potential of −800 kPa. A student places a piece of the epidermis in a sodium chloride solution with a water potential of −1200 kPa. After ten minutes the cell-surface membrane has pulled away from the cell wall.
(a)
Explain why the cell-surface membrane pulled away from the cell wall.
[3 marks]
(b)
The epidermis is then transferred to pure water. Explain why the cells do not burst.
[4 marks]
Total for question 3: 7 marks
4
A researcher incubated cultured gut-lining cells in a solution containing 2 mmol dm⁻³ of the sugar galactose. After one hour the concentration of galactose inside the cells was 14 mmol dm⁻³. The researcher then added a poison that stops mitochondria producing ATP. Over the next 30 minutes the concentration of galactose inside the cells fell to 2 mmol dm⁻³.
(a)
Explain these results.
[6 marks]
(b)
Galactose is absorbed by cells lining the ileum by co-transport with sodium ions. Explain how the poison would stop this co-transport even though the co-transporter protein does not use ATP directly.
[6 marks]
Total for question 4: 12 marks
5
Two adjacent plant cells are in contact. Cell X has a water potential of −450 kPa and cell Y has a water potential of −620 kPa.
(a)
In which direction is there net movement of water between the two cells, and why?
[1 mark]
AFrom Y to X, because Y has the lower water potential.
BFrom Y to X, because X has the more negative water potential.
CFrom X to Y, because X has the higher water potential.
DThere is no net movement, because both water potentials are negative.
(b)
Which change would decrease the water potential of cell X?
[1 mark]
ADissolving more solute in its cell sap.
BAbsorbing water from its surroundings.
CMoving it into a solution of higher water potential.
DRemoving solutes from its cytoplasm.
(c)
Explain why water moves between the cells by osmosis and not by active transport.
[2 marks]
Total for question 5: 4 marks
6
A student cut discs from the leaf of a red cabbage, rinsed them, and placed one disc in each of six test tubes containing the same volume of distilled water. The tubes were kept at 20, 30, 40, 50, 60 and 70 °C for ten minutes. She then used a colorimeter to measure the absorbance of the water in each tube, which depends on the amount of red pigment that has leaked out of the cells. Absorbance rose sharply above 50 °C.
(a)
Which is the dependent variable in this investigation?
[1 mark]
AThe temperature of the water.
BThe volume of distilled water in each tube.
CThe time the discs were left in the tubes.
DThe absorbance of the water.
(b)
Which best explains the increase in absorbance above 50 °C?
[1 mark]
APhospholipids pack more tightly together, squeezing pigment out.
BMembrane proteins are denatured and the phospholipids move more, so the membrane becomes more permeable.
CThe cells make more pigment at higher temperatures.
DWater enters the cells by osmosis and bursts the cell walls.
(c)
Explain why the pigment cannot leave the cells at 20 °C.
[2 marks]
Total for question 6: 4 marks
7
Two types of cell, P and Q, absorb the same nutrient by facilitated diffusion through carrier proteins. The two types have the same number of carrier proteins per μm² of membrane. Cell P has a folded cell-surface membrane with a surface area of 450 μm². Cell Q has a smooth membrane with a surface area of 150 μm².
(a)
At a low external concentration, each μm² of membrane transports 4.0 × 10² molecules of the nutrient per second. Calculate the rate of uptake for each cell and explain the difference.
[3 marks]
(b)
At very high external concentrations the rate of uptake by cell P stops increasing. Explain why, and state how cell P could increase its rate of uptake further.
[4 marks]
Total for question 7: 7 marks
8
In cystic fibrosis, the gene for a chloride channel protein in the cell-surface membranes of airway epithelial cells is mutated, so the channel is faulty or absent. In healthy cells, chloride ions pass out of the cells through these channels into the mucus lining the airway.
(a)
Explain how a faulty channel protein leads to thicker, stickier mucus.
[6 marks]
(b)
A researcher tests a drug that helps faulty channel proteins reach the cell-surface membrane. She measures the rate of chloride secretion from cultured airway cells, using three cultures for each type. Cells with the faulty channel and no drug secreted chloride at a mean rate of 0.4 units. The same cells with the drug secreted 2.1 units, and cultures of healthy cells secreted 4.0 units. Evaluate the evidence that the drug restores normal function.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).