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Cells and Biological Processes

Cells and Biological Processes — Free MYP4 Biology Practice Questions

1QuestionStructure and Function of EnzymesConcept Practice

2 marks~3 minCriterion B

Enzymes are named systematically according to the substrate they act upon.

Lactase → Lactose
Sucrase → Sucrose
Amylase → Starch
Protease → Protein
Lipase → Lipid

Identify the naming pattern that links each enzyme to its substrate. [1]

Deduce the substrate for the enzyme cellulase, justifying your answer using the pattern identified in part (a). [1]

Solutions

2QuestionRole of Enzymes in Digestion and RespirationConcept Practice

4 marks~6 minCriterion A

The diagram shows the pancreas releasing digestive enzymes through the pancreatic duct into the duodenum. The pancreas contains two functional regions: acinar cells, which synthesise and secrete digestive enzymes, and islets of Langerhans, which produce hormones.

Identify two digestive enzymes produced by the pancreas. [2]

Explain how pancreatic enzymes reach the duodenum after being synthesised in acinar cells. [1]

A patient has chronic pancreatitis causing progressive scarring and blockage of the pancreatic duct. Evaluate the consequences of this blockage for the digestion of macromolecules in the small intestine. [1]

Solutions

3QuestionRole of Enzymes in Digestion and RespirationConcept Practice

2 marks~3 minCriterion C

The diagram shows the active site of an amylase molecule.

Describe how amylase breaks down starch in the mouth. Use the terms active site, substrate, and enzyme-substrate complex in your answer. [1]

A student claims that amylase could also digest proteins if given enough time. Explain why this claim is incorrect, referring to the shape of the active site. [1]

Solutions

4QuestionPhotosynthesis Equation and FactorsConcept Practice

2 marks~3 minCriterion A

Chloroplasts are organelles found in the cells of photosynthetic organisms. Scientists studying crop productivity measure how efficiently chloroplasts convert light energy into stored chemical energy under varying environmental conditions.

State the organelle in a plant cell where photosynthesis occurs. [1]

Explain how the primary function of this organelle supports the energy needs of the plant. [1]

Solutions

5QuestionStructure and Function of Cell OrganellesConcept Practice

2 marks~3 minCriterion A

During an investigation into cell specialisation, students examine electron micrographs of liver cells and observe that the nucleus contains a prominent nucleolus and densely packed chromatin.

State two structural features of the nuclear envelope visible in an electron micrograph. [1]

Explain how the nucleus regulates cell activity by controlling protein synthesis. [1]

Solutions

6QuestionMicroscopy and Cell Observation TechniquesConcept Practice

2 marks~3 minCriterion D

A hospital collects cheek cell samples from patients for genetic testing. Before collection, each patient receives a document outlining how their DNA will be stored, who may access the results, and how long the data will be retained.

Identify one ethical issue that must be considered when collecting human cells for research. [1]

Explain the significance of this issue in the context of patient rights and consent. [1]

Solutions

7QuestionStructure and Function of Animal and Plant CellsConcept Practice

3 marks~5 minCriterion C

The bar chart below shows the relative number of mitochondria in three types of human cells.

Relative number of mitochondria:
Muscle cells: 1000
Skin cells: 200
Liver cells: 800

Describe the pattern shown in the data. [1]

Identify which cell type most likely requires the most energy, and link this to the data. [1]

Explain why muscle cells have the greatest number of mitochondria, referring to the role of mitochondria in cellular respiration and the specific energy demands of muscle tissue. [1]

Solutions

8QuestionIntroduction to Meiosis and Sexual ReproductionConcept Practice

2 marks~3 minCriterion B

The table below shows the diploid chromosome number and the haploid gamete chromosome number for four species.

Species	Diploid number	Gamete number
Human	46	23
Fruit fly	8	4
Dog	78	39
Pea plant	14	7

Deduce the mathematical relationship between the diploid chromosome number and the haploid gamete chromosome number, using data from two species to support your answer. [1]

A researcher studying a newly described flowering plant finds that its cells contain 58 chromosomes. Explain what happens during meiosis to produce gametes, and state the gamete chromosome number for this species. [1]

Solutions

9QuestionFunctions of Mitosis in Growth and RepaiConcept Practice

2 marks~3 minCriterion A

When a patient suffers severe burns, healthy skin is harvested from an unaffected donor site on the same patient and transplanted onto the damaged area.

Explain how mitosis enables the transplanted skin to restore the damaged tissue. [1]

Identify one limitation that reduces the effectiveness of skin graft treatment in patients with extensive burns. [1]

Solutions

10QuestionActive Transport and Energy RequirementConcept Practice

2 marks~3 minCriterion A

The diagram below shows a cross-section of a cell membrane. Structure X is a membrane protein associated with an ATP molecule.

Identify structure X. [1]

Explain how structure X uses ATP to move substances across the membrane. [1]

Solutions

11QuestionStem Cells in Regenerative MedicineConcept Practice

2 marks~3 minCriterion B

The table below shows the relationship between stem cell type and differentiation potential.

Stem cell type — Number of cell types produced
Totipotent — All cell types in the body, plus extraembryonic tissues
Pluripotent — All cell types in the body
Multipotent — Only a limited range of cell types (e.g., blood cells)

Identify the pattern between stem cell type and the number of different cell types produced. [1]

Deduce the number of different cell types a unipotent stem cell can produce. [1]

Solutions

12QuestionTypes of Stem Cells (Embryonic, Adult, Induced Pluripotent)Concept Practice

2 marks~3 minCriterion A

The diagram shows three types of stem cells: embryonic stem cells (ESC), adult stem cells (ASC), and induced pluripotent stem cells (iPSC). Each type differs in origin and differentiation potential.

State which type of stem cell is naturally pluripotent. [1]

Explain why iPSCs are considered pluripotent yet are distinct from ESCs in terms of their origin. [1]

Solutions

13QuestionEthical Considerations in Stem Cell ResearchConcept Practice

2 marks~3 minCriterion D

Parkinson's disease progressively destroys dopamine-producing neurons in the brain, causing tremors and loss of motor control. Researchers are investigating whether embryonic stem cells — harvested from human embryos at the blastocyst stage — could be used to replace these lost neurons.

Identify one ethical issue specific to the use of embryonic stem cells in this treatment. [1]

Identify one real-world benefit that embryonic stem cell therapy could offer to a patient with Parkinson's disease. [1]

Solutions

14QuestionFactors Affecting Enzyme ActivityAssessment Practice

4 marks~6 minCriterion A

A student investigates enzyme activity across a range of pH values. The graph shows activity curves for two enzymes, X and Y, found in different regions of the human digestive system.

Deduce the pH at which enzyme Y shows maximum activity. [1]

Explain how the activity of enzyme X changes as pH increases from 2 to 7, referring to enzyme structure. [2]

Evaluate which enzyme is more likely to function in the stomach, using data from the graph to justify your answer. [1]

Solutions

15QuestionStructure and Function of EnzymesAssessment Practice

6 marks~9 minCriterion D

HMG-CoA reductase catalyses a key step in cholesterol synthesis. Statins are drugs whose molecular shape closely resembles the enzyme's natural substrate, HMG-CoA. A patient with elevated blood cholesterol is prescribed a statin. After several months, the patient reports muscle pain and elevated liver enzymes. The diagram shows the active site of HMG-CoA reductase with a statin molecule bound.

Explain how the molecular structure of statins allows them to act as competitive inhibitors of HMG-CoA reductase. Use the diagram in your answer. [2]

Discuss the ethical considerations a physician must weigh when deciding whether to continue statin therapy for this patient. [2]

Evaluate the effectiveness of competitive inhibition as a long-term strategy for managing elevated cholesterol, considering how the body may respond to sustained enzyme inhibition. [2]

Solutions

16QuestionRole of Enzymes in Digestion and RespirationAssessment Practice

4 marks~6 minCriterion C

Amylase is an enzyme that catalyses the breakdown of starch during digestion. Both starch and cellulose are polysaccharides built from glucose monomers, yet amylase cannot catalyse the breakdown of cellulose.

State what is meant by the "active site" of an enzyme and describe how the lock-and-key model explains enzyme specificity. [1]

Explain why the structural difference between starch and cellulose prevents cellulose from entering the active site of amylase. [2]

A student claims: "Because both starch and cellulose are made of glucose, any enzyme that digests starch should also digest cellulose." Evaluate this claim using your knowledge of enzyme structure and substrate specificity. [1]

Solutions

17QuestionDenaturation and pH/Temperature EffectsAssessment Practice

4 marks~6 minCriterion D

A student investigates the activity of pepsin (optimum pH 2) and trypsin (optimum pH 8) across a range of pH levels. The diagram shows the activity curves of both enzymes.

Identify which enzyme functions most effectively in the small intestine (pH ≈ 8). [1]

Explain why pepsin and trypsin have different optimum pH values, referring to the role of amino acid R-groups in maintaining active site shape. [2]

Evaluate the consequences for protein digestion if pepsin were secreted into the small intestine rather than the stomach. [1]

Solutions

18QuestionFactors Affecting Enzyme ActivityAssessment Practice

4 marks~6 minCriterion A

A student investigates the effect of a metal-ion cofactor on enzyme activity. In the presence of the cofactor

\text{Zn}^{2+}

, the enzyme catalyses its reaction efficiently. When

\text{Zn}^{2+}

is removed by adding a chelating agent, the reaction rate falls sharply. The student proposes that the cofactor is essential for maintaining the functional shape of the active site.

State the difference between a cofactor and a coenzyme. [1]

Explain how

\text{Zn}^{2+}

enables the enzyme to catalyse its reaction effectively. [1]

Analyse how the removal of

\text{Zn}^{2+}

affects the active site and, using this, account for the sharp fall in reaction rate observed by the student. [2]

Solutions

19QuestionAerobic vs Anaerobic RespirationAssessment Practice

4 marks~6 minCriterion A

The diagram below shows glycolysis occurring inside a cell. Use it to answer the questions that follow.

Identify the location within the cell where glycolysis takes place. [1]

Explain how glucose is transformed during glycolysis, including the net ATP yield. [2]

Analyse why glycolysis is considered the universal first stage of both aerobic and anaerobic respiration, referring to the fate of pyruvate and the role of oxygen availability. [1]

Solutions

20QuestionPhotosynthesis Equation and FactorsAssessment Practice

3 marks~5 minCriterion A

A research team measures CO₂ uptake in a tomato plant at constant temperature (25 °C) and constant CO₂ concentration (0.04%), varying only light intensity. The graph shows that CO₂ uptake rises steeply at low light intensities, then levels off into a plateau at high light intensities.

Describe the trend shown in the graph. [1]

Explain why CO₂ uptake increases as light intensity rises from zero to the plateau. [1]

Analyse why the rate plateaus at high light intensities, even though light continues to increase. [1]

Solutions

21QuestionLeaf Structure and Adaptations for PhotosynthesisAssessment Practice

6 marks~9 minCriterion D

A student collects leaves from the same species growing in two locations: a sunny open field and a shady forest understory. She examines cross-sections under a microscope and records the following data.

Palisade mesophyll layers	sun leaf 3	shade leaf 1
Chloroplasts per palisade cell	sun leaf 45	shade leaf 18
Leaf thickness (mm)	sun leaf 0.25	shade leaf 0.12

Describe the relationship between light exposure and the three structural features shown in the data. [2]

Deduce the leaf structure you would expect in a plant growing in an extremely dim understory, where light levels are far lower than in the shady forest. Use the data to support your deduction. [2]

Analyse how the difference in palisade layer number between sun and shade leaves represents a trade-off between maximising photosynthesis and minimising resource investment. [2]

Solutions

22QuestionAerobic vs Anaerobic RespirationAssessment Practice

6 marks~9 minCriterion D

A fitness coach tells amateur runners that staying below the anaerobic threshold "builds aerobic base without toxic lactate buildup." The coach sells a heart-rate wristband that vibrates when heart rate approaches this threshold, warning runners to slow down. Sports scientists now understand that lactate plays a more complex metabolic role than this claim suggests.

Explain why describing lactate as a "toxic waste product" is scientifically inaccurate, referring to its metabolic fate under aerobic conditions. [2]

Explain how

H^+

ion accumulation, rather than lactate itself, contributes to muscle fatigue during intense exercise. [2]

Evaluate the coach's professional responsibility in promoting this training method and wristband to amateur athletes who lack the scientific background to critically assess the claims. [2]

Solutions

23QuestionAerobic vs Anaerobic RespirationAssessment Practice

4 marks~6 minCriterion A

Yeast cells were placed in a sealed container with glucose solution. As respiration proceeded, the oxygen inside was gradually consumed.

Identify the two waste products of anaerobic respiration in yeast. [2]

A student bubbles the gas produced through limewater and observes it turning cloudy. Deduce which product this test detects and explain what the result indicates about the yeast's metabolic activity. [1]

Analyse why yeast switches from aerobic to anaerobic respiration as oxygen is depleted in the sealed container, referring to the electron transport chain and NAD⁺ regeneration. [1]

Solutions

24QuestionLeaf Structure and Adaptations for PhotosynthesisAssessment Practice

4 marks~6 minCriterion C

The diagram shows cross-sections of two leaves: one adapted to shade and one adapted to full sunlight.

Identify one structural difference between the shade-adapted leaf and the sun-adapted leaf as shown in the diagram. [1]

Explain how a higher concentration of chlorophyll in shade-adapted leaves allows them to maintain photosynthesis under low light intensity. [2]

A student claims that a thicker palisade layer in sun-adapted leaves is an advantage only when light is the limiting factor. Evaluate this claim. [1]

Solutions

25QuestionPhotosynthesis Equation and FactorsAssessment Practice

7 marks~11 minCriterion C

A student investigates how light intensity and carbon dioxide (CO2) concentration affect the rate of photosynthesis in Elodea canadensis. Oxygen bubbles released per minute are counted at light intensities from 0 to 10 000 lux, at two CO2 concentrations: low (0.03%) and high (0.15%). The graph shows both curves. At high CO2, the recorded values include 38 bubbles/min at 8 000 lux and 35 bubbles/min at 9 000 lux. The low CO2 curve plateaus at approximately 20 bubbles/min beyond 5 000 lux; the high CO2 curve reaches 40 bubbles/min at 10 000 lux.

A student proposes the hypothesis: "Light intensity is the only limiting factor for photosynthesis in aquatic plants."

Identify the anomalous data point in the high CO2 curve and suggest one possible reason for it. [2]

Explain which factor limits the rate of photosynthesis at 2 000 lux for each CO2 concentration, using data from the graph to support your answer. [2]

Evaluate the student's hypothesis using evidence from both curves. In your answer, discuss the role of light intensity and CO2 concentration as limiting factors and reach a justified conclusion about whether the hypothesis is supported. [3]

Solutions

26QuestionSpecialized Cells and Their AdaptationsAssessment Practice

6 marks~9 minCriterion A

The diagram below shows four specialised human cells labelled A–D: a sperm cell, a red blood cell, a nerve cell (neuron), and a ciliated epithelial cell.

Identify each cell type (A–D) shown in the diagram. [2]

State one structural adaptation specific to each cell type and describe how that structure differs from a generalised (unspecialised) human cell. [2]

Analyse how the structural adaptations you identified in (b) enable each cell to perform its function more effectively than an unspecialised cell could. [2]

Solutions

27QuestionUsing Light Microscopes and Staining TechniquesAssessment Practice

4 marks~6 minCriterion B

A student examines an onion epidermal peel using a compound light microscope. The diagram shows three circular fields of view — A, B, and C — of the same specimen captured through the ×4, ×10, and ×40 objective lenses respectively. Field A contains approximately 20 cells; Field B contains approximately 8 cells; Field C shows a single cell in detail.

Identify which field of view shows the highest magnification. [1]

Explain the relationship between magnification and the number of cells visible in the field of view, using evidence from the three fields. [1]

Justify why a student must always begin with the lowest-power objective lens when initially locating a specimen, referring to both the field of view and the working distance. [2]

Solutions

28QuestionSurface Area to Volume Ratio in CellsAssessment Practice

4 marks~6 minCriterion B

The diagram shows three spherical cells of increasing radius:

r = 1\ \mu\text{m}

r = 2\ \mu\text{m}

, and

r = 4\ \mu\text{m}

. Surface area is given by

SA = 4\pi r^2

and volume by

V = \dfrac{4}{3}\pi r^3

State what happens to the SA:V ratio as cell radius increases. [1]

Explain how the change in SA:V ratio affects the ability of oxygen to meet the metabolic demands of a growing cell. [2]

Analyse why cells divide rather than continue growing indefinitely, using the SA:V ratio and the consequences for cellular function in your response. [1]

Solutions

29QuestionSpecialized Cells and Their AdaptationsAssessment Practice

2 marks~3 minCriterion D

Goblet cells lining the airways secrete mucus that traps pathogens and debris. In cystic fibrosis (CF), a mutation in the CFTR gene causes goblet cells to produce abnormally thick, sticky mucus that obstructs airways and promotes chronic infection.

Describe one way that understanding goblet cell adaptation in CF has led to a real-world medical application. [1]

Discuss one ethical issue raised by genetic screening for cystic fibrosis, considering more than one perspective. [1]

Solutions

30QuestionSurface Area to Volume Ratio in CellsAssessment Practice

4 marks~6 minCriterion C

Two cuboid model cells are shown in the diagram. Cell A has dimensions

1\ \text{cm} \times 1\ \text{cm} \times 1\ \text{cm}

. Cell B has dimensions

3\ \text{cm} \times 3\ \text{cm} \times 3\ \text{cm}

. Both cells have identical membrane permeability.

Calculate the surface area to volume ratio for each cell. [2]

Explain why Cell A experiences a faster rate of nutrient uptake by diffusion than Cell B. [1]

A student claims that simply increasing membrane permeability in Cell B would make its diffusion rate equivalent to that of Cell A. Evaluate this claim. [1]

Solutions

31QuestionComparison of Mitosis and MeiosisAssessment Practice

4 marks~6 minCriterion A

The diagram below shows a cell during a specific stage of cell division.

Deduce which stage of cell division — metaphase of mitosis, metaphase I of meiosis, or metaphase II of meiosis — is depicted. Justify your answer using the arrangement of chromosomes shown. [2]

Explain how the alignment of chromosomes at the equatorial plate during this stage ensures that each resulting daughter cell receives the correct chromosome number. [2]

Solutions

32QuestionFunctions of Mitosis in Growth and RepaiAssessment Practice

5 marks~8 minCriterion C

In a study of liver regeneration, rats underwent surgical removal of 70% of their liver (partial hepatectomy). Liver tissue samples were collected at 0, 12, 24, and 48 hours post-surgery, and the mitotic index (percentage of cells undergoing mitosis) was recorded.

Time (hours)	0	12	24	48
Mitotic index (%)	0.2	1.5	4.8	2.1

Describe the trend in mitotic index between 0 and 48 hours post-surgery, referring to specific values. [2]

Explain how the data between 0 and 24 hours relates to the role of mitosis in liver repair. [1]

Evaluate whether the data supports the hypothesis that hepatocyte mitosis peaks at 24 hours post-hepatectomy, including an explanation of what the mitotic index at 48 hours suggests about the regenerative process. [2]

Solutions

33QuestionFunctions of Mitosis in Growth and RepaiAssessment Practice

8 marks~12 minCriterion D

A biomedical company has developed a mitogen therapy to accelerate liver regeneration in patients with cirrhosis. Clinical trials report a 3% risk of uncontrolled cell division leading to tumour formation. Large-scale mitogen production relies on industrial bioreactors, generating significant energy demands and chemical waste. Access to the therapy is currently limited to high-income countries due to cost.

Explain how mitogen therapy uses mitosis to replace damaged liver tissue. [2]

Discuss two societal benefits this therapy offers compared with conventional liver transplantation. [2]

Analyse the environmental consequences of large-scale mitogen production, considering both energy consumption and chemical waste. [2]

Evaluate the ethical challenges of applying a single risk-benefit model — based on a 3% average cancer risk — to genetically and demographically diverse patient populations. [2]

Solutions

34QuestionCell Cycle and MitosisAssessment Practice

4 marks~6 minCriterion C

The diagram shows a cell in late telophase, with two forming nuclei visible and the cell beginning cytokinesis.

State two events that occur during telophase. [2]

Explain how cytokinesis differs structurally between animal and plant cells. [1]

Evaluate the significance of cytokinesis occurring as a process distinct from mitosis, referring to what would happen if nuclear division were not followed by cytoplasmic division. [1]

Solutions

35QuestionComparison of Mitosis and MeiosisAssessment Practice

6 marks~9 minCriterion D

A couple with a family history of cystic fibrosis — an autosomal recessive disorder caused by mutations in the CFTR gene — undergoes IVF combined with preimplantation genetic diagnosis (PGD). Fertilised eggs develop through repeated mitotic divisions. At the 8-cell stage, one cell is removed from each embryo and tested for the CFTR mutation. Only embryos free of the mutation are implanted.

Refer to the diagram showing PGD on an 8-cell embryo.

Explain how the properties of mitosis and of cells at the 8-cell stage allow one cell to be removed without harming the embryo's development. [2]

Explain one health benefit of using PGD to select against the cystic fibrosis mutation, linking the benefit to the biological effects of the disease. [2]

Discuss one ethical concern raised by using PGD to select against specific genetic traits, evaluating whether this concern outweighs the medical benefit in the context of cystic fibrosis. [2]

Solutions

36QuestionFunctions of Mitosis in Growth and RepaiAssessment Practice

5 marks~8 minCriterion A

The tables below show the duration of each cell cycle phase in human skin cells under normal conditions and after a minor wound, and the total number of cells in the wound area at selected times after injury.

Cell cycle phase durations (hours):

Phase	G1	S	G2	M
Normal	11	8	4	1
After wound	8	7	3	2

Cells in wound area:

Time after wound (hours)	0	6	12	24
Number of cells	100	110	150	250

State the change in M phase duration following wounding. [1]

Explain how the phase duration data indicate that mitotic activity is specifically upregulated in response to wounding. [2]

Justify the conclusion that mitosis plays a critical role in wound repair, using both the phase duration data and the cell count data. [2]

Solutions

37QuestionActive Transport and Energy RequirementAssessment Practice

7 marks~11 minCriterion A

Fish gill cells actively regulate internal

\text{Na}^+

concentration. The table below shows sodium ion concentrations inside and outside a gill cell, and the cell's ATP level, at three water temperatures.

Temperature (°C)	10	20	30
$\text{Na}^+$ inside (mmol/L)	10	50	100
$\text{Na}^+$ outside (mmol/L)	100	100	100
ATP level (relative units)	80	50	10

Deduce the direction of net

\text{Na}^+

movement at each temperature. Use both the concentration gradient and ATP data to support your answer. [2]

Justify the relationship between ATP level and the internal

\text{Na}^+

concentration shown in the data. [2]

At 20°C, a metabolic poison that halts ATP production is added to the water. Analyse what will happen to the internal

\text{Na}^+

concentration, explaining the roles of both active transport and diffusion in your answer. [3]

Solutions

38QuestionDefinition and Examples of DiffusionAssessment Practice

3 marks~5 minCriterion C

The graph below shows the rate of diffusion of a dye across a semipermeable membrane at three concentration differences.

Concentration difference (%)	5	10	20
Rate of diffusion (arbitrary units)	2.5	5	10

State the relationship between concentration difference and rate of diffusion shown in the graph. [1]

Explain why a greater concentration difference produces a faster rate of diffusion. [1]

A student claims that doubling the concentration difference will always double the rate of diffusion for any substance crossing any membrane. Evaluate this claim. [1]

Solutions

39QuestionFactors Affecting Rate of DiffusionAssessment Practice

4 marks~6 minCriterion B

Three agar cubes with side lengths of 1 cm, 2 cm, and 3 cm are each submerged in the same blue dye solution at the same temperature. After 10 minutes, the 1 cm cube is entirely blue, the 2 cm cube has a blue outer layer with a white centre, and the 3 cm cube shows only a thin blue edge.

Calculate the surface area-to-volume ratio (

SA:V

) for each cube, using

SA = 6s^2

and

V = s^3

. [1]

Explain how the

SA:V

ratio of the 1 cm cube accounts for the dye reaching its centre faster than in the larger cubes. [2]

Analyse why increasing cube size progressively reduces the rate of complete dye penetration, referring to both diffusion distance and the data from the observations. [1]

Solutions

40QuestionFactors Affecting Rate of DiffusionAssessment Practice

8 marks~12 minCriterion D

Drug-eluting stents (DES) are implanted in narrowed coronary arteries and release anti-proliferative medication through a polymer coating directly into the arterial wall via diffusion. Cardiologists can adjust coating thickness to control drug release rates. Over the past decade, DES use has expanded globally, raising questions about long-term patient outcomes and healthcare systems. Fick's law of diffusion is commonly used to model drug release from these devices.

Explain how reducing the polymer coating thickness from 120 µm to 60 µm would affect the rate of drug diffusion from the stent into the arterial wall. [2]

Discuss one societal benefit and one societal risk associated with the widespread use of drug-eluting stents over a 10-year period. [3]

Analyse one limitation of using Fick's law to model drug release from a stent into arterial tissue, with reference to a specific assumption of the law. [3]

Solutions

41QuestionFactors Affecting Rate of DiffusionAssessment Practice

5 marks~8 minCriterion C

A student investigated how temperature affects the rate of diffusion by placing identical potassium permanganate crystals at the centre of agar plates and recording the time for the purple colour to spread 2 cm.

Temperature (°C)	10	20	30	40
Time to diffuse 2 cm (min)	48	24	16	8

The student hypothesised: "The rate of diffusion doubles for every 10°C rise in temperature."

Describe the trend shown in the data. [1]

Calculate the rate of diffusion (in cm min

^{-1}

) at each temperature and explain how increasing temperature produces this trend, using kinetic energy. [2]

Evaluate whether the data support the student's hypothesis, identifying any anomaly and justifying your conclusion with numerical evidence. [2]

Solutions

42QuestionOsmosis in Cells and Living SystemsAssessment Practice

4 marks~6 minCriterion D

A student places strips of potato into sucrose solutions of five different concentrations. The bar chart shows the percentage change in mass of each strip after 30 minutes.

Deduce the sucrose concentration at which the potato strip shows no change in mass. [1]

The strip placed in 0.6 mol/L sucrose had an initial mass of 4.0 g and a final mass of 3.4 g. Calculate the percentage change in mass of this strip, showing your working. [1]

Evaluate whether the concentration identified in (a) is equal to the solute concentration of the potato cell sap, using your understanding of osmosis and water potential to justify your reasoning. [2]

Solutions

43QuestionFactors Affecting Rate of DiffusionAssessment Practice

3 marks~5 minCriterion B

The graph below shows the relationship between surface area-to-volume ratio (SA:V) and rate of diffusion for three agar cubes with side lengths of 1 cm, 2 cm, and 3 cm.

State the trend shown in the graph. [1]

Explain why a smaller cube has a higher SA:V ratio than a larger cube. [1]

Explain why a higher SA:V ratio leads to a faster rate of diffusion, and discuss why this places a limit on maximum cell size. [1]

Solutions

44QuestionStem Cell Differentiation and SpecializationAssessment Practice

4 marks~6 minCriterion A

The diagram shows a blastocyst with two labeled regions: the inner cell mass (ICM) and the trophoblast layer.

Identify the potency level of ICM cells and of trophoblast cells. [2]

A research team is developing a therapy to replace damaged cardiac muscle, liver tissue, and neurons following multi-organ injury. Justify which cell population from the blastocyst — ICM cells or trophoblast cells — is more appropriate as the cell source for this therapy. [2]

Solutions

45QuestionRole of Stem Cells in Growth and DevelopmentAssessment Practice

5 marks~8 minCriterion C

A study investigated how growth factors influence the fate of mouse neural stem cells. Cells were treated with BMP4, Shh, FGF2, or no factor (control) for 7 days. The percentage of cells differentiating into neurons, astrocytes, or oligodendrocytes was recorded and is shown in the bar chart below.

Control	neurons 10%	astrocytes 40%	oligodendrocytes 50%
BMP4	neurons 5%	astrocytes 85%	oligodendrocytes 10%
Shh	neurons 60%	astrocytes 20%	oligodendrocytes 20%
FGF2	neurons 30%	astrocytes 30%	oligodendrocytes 40%

State the differentiation outcome for neural stem cells in the control condition. [1]

Identify which growth factor most strongly promotes neuronal differentiation and describe how the data for that factor differs from the control. [2]

Evaluate the hypothesis that extracellular signals direct neural stem cell fate, using evidence from all four conditions. [2]

Solutions

46QuestionEthical Considerations in Stem Cell ResearchAssessment Practice

3 marks~5 minCriterion D

The diagram shows two structures. On the left is a blastocyst: a hollow ball of cells with an inner cell mass labelled A and an outer trophoblast layer labelled B. On the right is a bone marrow sample containing a hematopoietic stem cell labelled C.

Identify which labelled structure contains embryonic stem cells. [1]

Identify which labelled structure contains adult stem cells, and state one difference in potency between the stem cells in structure A and structure C. [1]

Evaluate one ethical concern associated with obtaining embryonic stem cells from a blastocyst, considering both a supporting and an opposing viewpoint. [1]

Solutions

47QuestionStem Cell Differentiation and SpecializationAssessment Practice

5 marks~8 minCriterion A

The diagram below shows four stages of neural stem cell differentiation.

Stage 1	Stem cell: Sox2 expressed; pluripotent
Stage 2	Progenitor: Pax6 expressed; multipotent

Stage 3 — Neuroblast: Neurogenin expressed; restricted potential
Stage 4 — Neuron: NeuroD expressed; fully specialised

Explain how the sequential expression of Sox2, Pax6, Neurogenin, and NeuroD demonstrates that cell potential becomes progressively restricted during differentiation. [2]

Using the terms transcription factor and gene regulation, explain the molecular mechanism by which external developmental signals drive the transition from one stage to the next. [2]

Analyse why a mature neuron expressing NeuroD cannot be reprogrammed to become a muscle cell under normal physiological conditions, even though it contains the same DNA as a muscle cell. [1]

Solutions

48QuestionRole of Stem Cells in Growth and DevelopmentAssessment Practice

3 marks~5 minCriterion C

The graph below shows the number of specialised cell types present in a human embryo during the first 12 weeks of development.

Describe the trend shown in the graph. [1]

Explain how the activity of embryonic stem cells accounts for the trend you described in (a). [1]

After week 8, the number of specialised cell types plateaus. Analyse what this suggests about the changing role of stem cells as embryonic development progresses. [1]

Solutions