Syllabus Edition
First teaching 2023
First exams 2025
2 marksDefine the following terms:
hydrophilic
[1]
(ii)
hydrophobic
[1]
2 marksDraw a labelled diagram of a phospholipid molecule.
1 markState the name of the property of phospholipids that causes them to form bilayers when placed in water.
2 marksState the function of cholesterol in animal membranes.
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3 marksDefine the term active transport.
3 marksList three factors that affect the rate of diffusion of substances across a membrane.
1 markState the name of the process by which materials are transported from location S to location R in the diagram below.
1 markName one substance that could be transported from S to R.
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2 marksThe below diagram shows the plasma membrane of an Amoeba cell and some molecules of a small, nonpolar substance labelled substance X.
State:
The direction in which substance X would move
[1]
(ii)
The process by which substance X would move
[1]
2 marksList two possible names of substance X.
2 marksAmoeba require potassium ions to assist with detecting prey.
Outline how these ions would be transported across the membrane shown in part (a).
1 markTo feed on bacteria, Amoeba use extensions of the cell cytoplasm known as pseudopodia to engulf the bacteria.
State the name of the process used to engulf the bacteria.
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5 marksLabel structures A-E in the diagram below.
3 marksA group of students investigated the impact of different salt concentrations on the mass of celery. They entered the results into the table below.
| Concentration of salt / mol dm-3 | Initial mass / g | Final mass / g | Mass change / g | Mass change / % |
| 0.0 | 12.2 | 14.5 | + 2.3 | + 18.9 |
| 0.2 | 10.0 | 11.7 | + 1.7 | + 17.0 |
| 0.4 | 9.6 | 9.3 | - 0.3 | - 3.1 |
| 0.6 | 11.3 | 10.5 | - 0.8 | |
| 0.8 | 12.5 | 11.2 | - 1.3 | - 10.4 |
| 1.0 | 10.7 | 8.5 | - 2.2 | - 20.6 |
Calculate the percentage change in mass of the celery in a salt solution of 0.6 mol dm-3
[1]
(ii)
Estimate, with a reason, the solute concentration of the celery tissue
[2]
2 marksThe diagram below is a student's drawing of three celery cells seen under a light microscope at the end of the investigation in part (b).
Deduce, with a reason, the salt concentration in which these cells have been immersed.
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4 marksOutline the functions of membrane proteins.
2 marksThe role of cholesterol is to regulate the fluidity of the cell membrane.
Give an example of an animal cell whose cell surface membrane would need a high degree of fluidity. Explain your reasoning.
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5 marksCompare the passive transport of substances across membranes, using named examples.
2 marksThe majority of metabolites are not able to pass directly through the phospholipid bilayer and require assistance to do so.
Explain the property of membranes that causes this to be the case.
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2 marksThe concentration of sodium ions in red blood cells is lower than the concentration in blood plasma.
Suggest how this sodium ion concentration gradient is maintained.
2 marksDuring pregnancy the fetus is dependent on essential proteins which are absorbed from the mother’s blood via the placenta.
Explain how these very large molecules could be transported into the cells of the fetus.
3 marksSuggest how the composition of the membrane allows for the transport of proteins from the mother to the fetus.
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1 markIdentify the part of the fluid mosaic structure of the plasma membrane represented by the molecular diagram below.
3 marksScientists have found that wheat crops adapted to grow in winter have increased unsaturated phospholipid content.
Suggest why the presence of unsaturated phospholipids would be advantageous to these plants.
3 marksPieces of phospholipid bilayer were analysed from two different plant cell surface membranes. Sample X contained phospholipid molecules at a density of 4.2 x 106 molecules µm-2, while sample Y contained phospholipid molecules at a density of 5.5 x 106 molecules µm-2.
One sample was from a root hair cell and the other was from a cell on the outer surface of the stem.
Identify, with reasons, which cell source is likely to correspond to samples X and Y.
2 marksResearchers have discovered that an individual phospholipid molecule can exchange places with its neighbouring phospholipid molecule in a monolayer as frequently as 107 times per second. By contrast, phospholipid molecules almost never exchange places with each other from one monolayer to the other within a bilayer, referred to as a ‘flip-flop’ exchange. The ‘flip-flop’ takes place around once a month for a typical phospholipid molecule.
Suggest a reason for this difference in molecular behaviour.
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2 marksDetergents are amphipathic molecules.
Suggest why scientists use detergents to study the structure of membranes.
2 marksDiffusion can be studied using Visking tubing. Students set up an investigation in which equal volumes of the following solutions were placed into separate pieces of Visking tubing:
The Visking tubing, containing the solutions, were placed in distilled water and maintained at a constant temperature of 23 °C. The volume and mass of the bags were measured at 5 minute intervals for 160 minutes.
The data recorded is shown below.
Calculate the rate of increase in mass and in volume for the visking tubing containing glucose solution during the first 30 minutes.
3 marksCompare and contrast the change in mass for the Visking tubing in each solution.
2 marksExplain why the volume of both sets of Visking tubing increases over time.
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7 marksDraw a labelled diagram to show the structure of the fluid mosaic model. Your drawing should label proteins with four named membrane protein functions.
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Phospholipids are described as amphipathic molecules.
Explain what this means.
Liposomes are spherical vesicles surrounded by a phospholipid bilayer. They can be used in a range of applications, such as the delivery of mRNA vaccines to specific areas of the body.
Sketch a small section of the structure of a liposome, indicating its exterior, interior and the hydrophobic and hydrophilic regions.
Describe the properties that allow some molecules to diffuse rapidly across cell membranes.
The diagram below shows a typical epithelial cell from the lining of the airways. The stickiness of mucus in the airways is controlled by CFTR chloride ion channels.
When there is too little water in the mucus the CFTR channel opens, allowing Cl- ions to move into the mucus. When active, the CFTR channel also inhibits the activity of sodium channels and limits movement of Na+ ions into the cells. The resulting high concentration of salt in the mucus draws water out of the cells, making the mucus less sticky.
Cystic fibrosis is a genetic disorder characterised by a build-up of thick, sticky mucus that damages the function of the airways and digestive system. People with class I cystic fibrosis have inherited two faulty versions of the gene that codes for CFTR, resulting in non-functioning CFTR channels.
Suggest how a lack of functioning CFTR channel impacts the movement of Na+ and Cl- ions across epithelial cells.
[3]
Explain why the mucus of cystic fibrosis sufferers is thick and sticky.
[1]
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As part of an investigation cubes of potato were placed in a solution containing sodium ions. The concentration of oxygen in air bubbled through the solution was changed and the rates of respiration and uptake of sodium ions were measured. The results are shown in the table below.
| Concentration of oxygen / % | Rate of respiration / arbitrary units | Rate of uptake of sodium ions / arbitrary units |
| 3.8 | 43 | 54 |
| 15.6 | 56 | 76 |
| 24.7 | 62 | 87 |
| 32.9 | 89 | 90 |
Describe the relationship between oxygen concentration, rate of respiration and rate of uptake of sodium ions.
Suggest reasons for the relationship between oxygen concentration, rate of respiration and rate of uptake of sodium ions described in part (a).
Give two similarities between the processes by which inorganic ions and water molecules enter cells.
Distinguish between the passive and active movement of molecules across cell membranes.
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Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.
Group Y: plants had a substance that inhibited respiration added to the solution
Group Z: plants did not have the respiratory inhibitor added to the solution
The scientists calculated the total mass of magnesium ions absorbed by the plants every 5 minutes. Their results are shown in the graph below:
Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z.
Using the graph in part (a), calculate the rate of uptake of magnesium ions for group Y plants after 40 minutes. Give suitable units.
Consider the graph in part (a). Explain the results of the investigation.
State two differences between the processes of facilitated diffusion and active transport.
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Draw an annotated diagram of the cell membrane based on the fluid mosaic model, including all the relevant structures.
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Amoebas (singular amoeba) are free-living, single-celled eukaryotes that live in freshwater ponds and lakes. They carry out osmoregulation using an organelle called a contractile vacuole, shown in the image below.
Explain why amoebas need to carry out osmoregulation.
A contractile vacuole can expand to take on water, and is able to fuse with the cell-surface membrane.
Suggest how a contractile vacuole aids osmoregulation in amoebas.
Describe what would happen to an amoeba cell placed into saltwater.
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