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Cells and Biological Processes

Cells and Biological Processes — Free MYP5 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

2QuestionDenaturation and pH/Temperature EffectsConcept Practice

2 marks~3 minCriterion A

Two diagrams show the same enzyme. In Diagram 1, the enzyme functions normally at 37 °C, and structure X is clearly labelled. In Diagram 2, the enzyme is exposed to 70 °C; its shape has visibly changed and the substrate can no longer bind.

Identify structure X. [1]

Explain what has happened to the enzyme in Diagram 2 and why the substrate can no longer bind. [1]

Solutions

3QuestionAerobic vs Anaerobic RespirationConcept Practice

2 marks~3 minCriterion A

The diagram shows a muscle cell (left) and a yeast cell (right). Structure X is labelled inside the muscle cell.

Identify structure X. [1]

During intense exercise, muscle cells switch from aerobic to anaerobic respiration. Explain why structure X becomes less active under these conditions. [1]

Solutions

4QuestionCalculating Magnification and Image SizeConcept Practice

2 marks~3 minCriterion A

An electron micrograph of a plant cell is shown below. The scale bar represents 2 µm. Organelle X is visible within the cell.

Identify organelle X. [1]

The image length of organelle X measures 20 mm on the micrograph. Using the scale bar, deduce the actual length of organelle X in micrometres, showing your working. [1]

Solutions

5QuestionDifferences Between Prokaryotic and Eukaryotic CellConcept Practice

2 marks~3 minCriterion D

Genetically modified E. coli bacteria are used in the biotechnology industry to manufacture human insulin for people with diabetes. The human insulin gene is inserted into bacterial plasmids, enabling the bacteria to synthesise human insulin protein during fermentation.

Identify one advantage of using E. coli to produce human insulin rather than extracting insulin from animal pancreases. [1]

Discuss one ethical issue raised by the large-scale use of genetically modified E. coli in medical insulin production. [1]

Solutions

6QuestionCell Cycle and MitosisConcept Practice

3 marks~5 minCriterion A

The diagram below shows a cell during mitosis in which all chromosomes are aligned at the cell's equatorial plane, with spindle fibres from opposite poles attached to the centromere of each chromosome.

Identify the phase of mitosis shown in the diagram. [1]

Explain how the attachment of spindle fibres to chromosomes during this phase ensures that sister chromatids are distributed equally between the two daughter cells. [2]

Solutions

7QuestionActive 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

8QuestionDefinition and Examples of DiffusionConcept Practice

2 marks~3 minCriterion A

The diagram below shows an animal cell. Structure X is labelled on the diagram.

Identify structure X. [1]

Explain how structure X controls which substances can diffuse into and out of the cell. [1]

Solutions

9QuestionCharacteristics and Properties of Stem CellsConcept Practice

3 marks~5 minCriterion A

The bar graph below shows the number of cell types that can be produced by totipotent, pluripotent, multipotent, and unipotent stem cells.

State which type of stem cell produces the greatest number of cell types. [1]

Describe the trend shown in the graph between stem cell potency and the number of cell types produced. [1]

Explain why totipotent stem cells can produce more cell types than pluripotent stem cells. [1]

Solutions

10QuestionCharacteristics and Properties of Stem CellsConcept Practice

2 marks~3 minCriterion A

The diagram shows three stages of early embryonic development: a zygote, a morula, and a blastocyst (with its inner cell mass visible).

Identify the stage(s) that contain totipotent cells and the stage(s) that contain pluripotent cells. [1]

Explain why totipotent cells have greater developmental potential than pluripotent cells. [1]

Solutions

11QuestionStem Cells in Regenerative MedicineConcept Practice

2 marks~3 minCriterion D

In several countries, embryonic stem cell research is heavily restricted or banned due to ethical concerns, while adult stem cell therapies face fewer regulatory barriers.

State one ethical issue specific to the use of embryonic stem cells in regenerative medicine, and explain how this issue differs from the use of adult stem cells. [1]

Discuss how the source of stem cells — embryonic or adult — may influence the availability of regenerative treatments across different countries. [1]

Solutions

12QuestionFactors 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

13QuestionDenaturation and pH/Temperature EffectsAssessment Practice

2 marks~3 minCriterion D

A food company pasteurizes milk at

72^\circ\text{C}

for 15 seconds to eliminate harmful bacteria. At this temperature, enzymes naturally present in the milk are denatured — their active sites permanently change shape — which may alter the milk's taste and nutritional properties.

Identify and explain one ethical issue the company should consider when deciding whether to use this pasteurization temperature. [2]

Solutions

14QuestionDenaturation and pH/Temperature EffectsAssessment Practice

5 marks~8 minCriterion C

An enzyme was tested at pH 2, pH 7, and pH 10. The graph shows product formed (mg) over time (min).

At pH 7, product formation rises steeply, reaching a plateau of 10 mg at 5 min. At pH 10, product rises to 2 mg by 2 min, then remains constant. At pH 2, no product forms throughout.

A student proposes the hypothesis: "Enzymes lose activity only at extreme pH values, and this effect is reversible."

Describe what the graph data show about enzyme activity at each pH value. [1]

Explain, at the molecular level, why enzyme activity is lost at pH 2 and pH 10. [2]

Evaluate the student's hypothesis using the graph data and your knowledge of denaturation. [2]

Solutions

15QuestionEnzyme Specificity and Active SiteAssessment Practice

3 marks~5 minCriterion C

The graph below shows the rate of reaction of the enzyme sucrase with three substrates. Substrate A (sucrose) produces a high reaction rate, substrate B produces a moderate reaction rate, and substrate C produces a reaction rate of zero.

State what the lock-and-key model proposes about the relationship between an enzyme's active site and its substrate. [1]

Using the lock-and-key model, explain why substrate B produces a lower reaction rate than substrate A. [1]

A student claims that substrate C is simply a slower-reacting version of sucrose. Evaluate this claim using evidence from the graph and the lock-and-key model. [1]

Solutions

16QuestionDenaturation and pH/Temperature EffectsAssessment Practice

6 marks~9 minCriterion D

A laundry detergent contains a heat-stable lipase enzyme that breaks down fat stains. The enzyme functions below

60^\circ\text{C}

but denatures above this temperature. The manufacturer promotes cold-water washing to reduce energy consumption and carbon emissions. However, in some cultures, water above

60^\circ\text{C}

is traditionally used to eliminate bacteria and ensure hygiene.

Refer to the diagram showing the lipase active site at $20^\circ\text{C}$ , $50^\circ\text{C}$ , and $80^\circ\text{C}$ .

Explain why the lipase enzyme loses its function at temperatures above

60^\circ\text{C}

, referring to molecular structure. [2]

Apply your understanding of energy use and carbon emissions to explain the ecological benefit of cold-water washing. [2]

Analyse the ethical conflict between promoting cold-water washing for environmental reasons and respecting cultural practices that rely on hot water for hygiene. [2]

Solutions

17QuestionFactors 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

18QuestionAerobic vs Anaerobic RespirationAssessment Practice

8 marks~12 minCriterion A

During high-intensity exercise, human muscle cells produce ATP through aerobic and anaerobic respiration. The table below summarises ATP yield per glucose molecule and lactic acid concentration in muscle tissue over 60 seconds.

Time (s)	0	10	20	30	40	50	60
ATP yield (ATP/glucose)	36	36	30	10	2	2	2
Lactic acid (mmol/L)	0.5	0.5	2	8	15	20	22

Describe the patterns in ATP yield and lactic acid concentration shown in the data. [2]

Deduce the time interval during which muscle cells transition from predominantly aerobic to predominantly anaerobic respiration. Use data from both variables to support your reasoning. [3]

Analyse how the limitation of oxygen supply during high-intensity exercise leads to the metabolic changes shown in the data, with reference to the electron transport chain and lactic acid fermentation. [3]

Solutions

19QuestionAerobic vs Anaerobic RespirationAssessment Practice

2 marks~3 minCriterion A

During a 400 m sprint, an athlete's muscles cannot receive oxygen fast enough to meet energy demands.

Explain why muscles switch to anaerobic respiration during a 400 m sprint and identify one metabolic product of this process. [1]

Explain why anaerobic respiration cannot sustain high-intensity effort and describe one consequence for the athlete's performance. [1]

Solutions

20QuestionAerobic vs Anaerobic RespirationAssessment Practice

5 marks~8 minCriterion C

During 10 minutes of high-intensity exercise, the following measurements were recorded from human muscle tissue:

Time (min)	0	2	4	6	8	10
Lactate (mmol/L)	1.2	3.5	6.8	4.1	12.3	15.7
pH	7.40	7.32	7.18	7.28	6.95	6.78

Describe the overall trends in lactate concentration and pH across the 10-minute period. [2]

The data point at 6 minutes shows a lactate concentration of 4.1 mmol/L and a pH of 7.28. Explain why both values are anomalous in the context of anaerobic respiration. [2]

A student suggests that a brief recovery interval at 5 minutes could account for the anomalous values at 6 minutes. Evaluate this suggestion using your knowledge of lactate metabolism and pH regulation during exercise. [1]

Solutions

21QuestionAerobic vs Anaerobic RespirationAssessment Practice

8 marks~12 minCriterion D

A national government proposes blending 10% bioethanol — produced from sugarcane fermentation — into gasoline. Supporters claim the policy is carbon-neutral because CO2 released during combustion is reabsorbed by new sugarcane growth. Critics counter that large-scale monoculture requires deforestation and heavy fertilizer use, releasing nitrous oxide (N2O), a greenhouse gas with approximately 300 times the global warming potential of CO2.

Describe the process of anaerobic respiration in yeast that produces ethanol, including the correct word or chemical equation. [2]

Analyse the CO2 lifecycle of sugarcane bioethanol, considering both combustion emissions and photosynthetic reabsorption. [2]

Evaluate the carbon-neutrality assumption over a 50-year timescale, incorporating land-use change, N2O emissions, and the factors identified in part (b). [4]

Solutions

22QuestionAerobic vs Anaerobic RespirationAssessment Practice

5 marks~8 minCriterion C

A student investigates how oxygen availability affects respiration in yeast. Culture A receives air (aerobic); Culture B receives nitrogen gas (anaerobic). Both cultures are otherwise identical. Carbon dioxide volume is recorded every five minutes.

Time (min)	5	10	15	20	25	30
CO $_2$ produced (mL) — Culture A	2.1	4.5	6.8	9.0	11.3	13.5
CO $_2$ produced (mL) — Culture B	1.8	3.9	5.7	7.8	9.6	11.7

The student's hypothesis states: "Anaerobic respiration produces more CO $_2$ per glucose molecule than aerobic respiration."

State the balanced chemical equations for aerobic respiration and for anaerobic respiration (alcoholic fermentation) in yeast. [2]

Using your equations from (a), deduce how many CO

_2

molecules are released per glucose molecule in each pathway, and identify which pathway yields more CO

_2

per glucose. [1]

Evaluate the extent to which the experimental data supports or refutes the student's hypothesis, incorporating your answer from (b). [2]

Solutions

23QuestionAerobic vs Anaerobic RespirationAssessment Practice

4 marks~6 minCriterion A

A diagram shows two cells undergoing respiration. Cell A contains mitochondria and has access to oxygen; Cell B lacks mitochondria and has no oxygen available.

Identify the type of respiration occurring in each cell and state where in the cell each process takes place. [1]

Explain why Cell A produces 36 ATP per glucose molecule whereas Cell B produces only 2 ATP per glucose molecule. In your answer, refer to the role of oxygen in the electron transport chain. [2]

A student claims that anaerobic respiration is "simply a less efficient version of the same process." Evaluate this claim. [1]

Solutions

24QuestionInterdependence of Photosynthesis and RespirationAssessment Practice

7 marks~11 minCriterion D

A sealed aquarium contains aquatic plants and fish.

O_2

and

CO_2

concentrations (mg/L) are measured every 2 hours over 24 hours under a 12-hour light / 12-hour dark cycle. Light is on from 0 to 12 hours; dark from 12 to 24 hours.

Time (hours): 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24

O_2

(mg/L): 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 8.5, 8.0, 7.0, 6.0, 5.5, 5.0, 5.0

CO_2

(mg/L): 4.0, 3.5, 3.0, 2.5, 2.0, 2.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 4.5

Describe the changes in

O_2

and

CO_2

concentrations during the light period (0–12 h) and the dark period (12–24 h). [2]

Justify the prediction that

O_2

concentration would approach zero if the aquarium were kept in constant darkness for 48 hours, by discussing the roles of photosynthesis and respiration. [3]

Analyse how the balance between photosynthesis and respiration determines whether

O_2

rises or falls at any point in the 24-hour cycle, and evaluate whether this sealed aquarium can sustain its organisms indefinitely. [2]

Solutions

25QuestionUsing 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

26QuestionCalculating Magnification and Image SizeAssessment Practice

5 marks~8 minCriterion A

A transmission electron micrograph of a chloroplast contains a scale bar representing 2 µm, which measures 40 mm in the image. A thylakoid stack (granum) measures 15 mm in the image.

\text{magnification} = \frac{\text{image size}}{\text{actual size}}

Using the scale bar, calculate the magnification of the image. Show your working. [2]

Calculate the actual length of the thylakoid stack in micrometres (µm). Show your working. [2]

A second micrograph of the same chloroplast is produced at a magnification of ×5 000. The granum still measures 15 mm in this image. Deduce whether this second micrograph is consistent with your answer to part (b), and justify your reasoning. [1]

Solutions

27QuestionCalculating Magnification and Image SizeAssessment Practice

5 marks~8 minCriterion C

An electron micrograph of a mitochondrion shows a scale bar of 200 nm. A student measures the width of one crista in the image as 8 mm and calculates the actual width to be 0.05 µm (50 nm). The student concludes that this mitochondrion originates from a liver cell rather than a muscle cell.

State what cristae are and explain their role in ATP synthesis. [1]

Explain how crista density differs between liver cells and muscle cells, and link this difference to each cell's energy demands. [2]

Justify whether the student's conclusion is valid, using the calculated crista width and your knowledge of what evidence would be required to identify the cell type. [2]

Solutions

28QuestionCell Membrane and Fluid Mosaic ModelAssessment Practice

4 marks~6 minCriterion C

The diagram shows a cell membrane in which small nonpolar molecules (

O_2

and

CO_2

) pass directly through the phospholipid bilayer, while larger polar molecules (glucose and

Na^+

) cannot.

Describe the molecular structure of the phospholipid bilayer, including the orientation of its hydrophilic and hydrophobic regions. [1]

Using the fluid mosaic model, explain why

O_2

crosses the membrane freely whereas glucose cannot. [2]

A student claims that selective permeability depends only on molecular size. Evaluate this claim, using evidence from the molecules shown in the diagram. [1]

Solutions

29QuestionCalculating Magnification and Image SizeAssessment Practice

8 marks~12 minCriterion D

A public health agency uses light microscopes to monitor a parasitic infection in a remote village. The actual size of a parasite is

50 \, \mu\text{m}

; its measured image size on a slide is

5 \, \text{mm}

\text{magnification} = \frac{\text{image size}}{\text{actual size}}

Calculate the magnification of the light microscope image. [2]

Identify one resolution-related limitation of light microscopy and explain how it could lead to misidentification of the parasite species during disease monitoring. [2]

Evaluate the long-term societal impact of repeated misidentification on community health outcomes, and the environmental impact of disposing staining chemicals in a remote village with limited waste infrastructure. [4]

Solutions

30QuestionCalculating Magnification and Image SizeAssessment Practice

3 marks~5 minCriterion A

A student photographs a chloroplast through a light microscope at a fixed magnification. The graph shows the relationship between actual chloroplast length (μm) on the x-axis and image length (mm) on the y-axis. Data points at actual lengths of 2, 4, 6, 8, and 10 μm produce image lengths of 10, 20, 30, 40, and 50 mm respectively, forming a straight line through the origin with a slope of 5 mm μm⁻¹.

Calculate the magnification used to produce these images. [1]

Explain what the straight line passing through the origin indicates about the relationship between actual length and image length. [1]

A second microscope produces images of the same chloroplasts at a magnification of 2000×. Analyse how the graph would differ, and explain what this reveals about the effect of magnification on the image-to-actual-size relationship. [1]

Solutions

31QuestionCell Cycle and MitosisAssessment Practice

3 marks~5 minCriterion B

The table below shows the average time (in hours) spent in each phase of the cell cycle for three human cell types.

Cell type	G1	S	G2	M
Skin	10	8	4	1
Liver	6	7	3	1
Nerve	20	10	5	2

Identify the longest and shortest phase of the cell cycle for each cell type. [1]

Deduce what the consistently short duration of M phase, compared with G1, suggests about the relationship between preparation for division and division itself. [1]

Explain how the differences in G1 duration among skin, liver, and nerve cells reflect the specific functions of each cell type. [1]

Solutions

32QuestionCell Cycle and MitosisAssessment Practice

6 marks~9 minCriterion A

Researchers exposed onion root tip cells to increasing concentrations of a toxin for 24 hours and recorded the following:

Toxin concentration (mg/L)	0	10	20	40
Mitotic index (%)	12	9	5	2
Total cell count ( $\times 10^3$ )	50	48	45	30

The mitotic index is the percentage of cells actively undergoing mitosis.

Describe the relationship between toxin concentration and both the mitotic index and total cell count shown in the data. [2]

Deduce which cell cycle phase (G1, S, G2, or M) is most likely arrested at 40 mg/L. Use the data to support your reasoning. [2]

Justify your deduction by explaining how checkpoint proteins, cyclins, and cyclin-dependent kinases (CDKs) regulate entry into mitosis, and how toxin-induced disruption of this system accounts for both observations at 40 mg/L. [2]

Solutions

33QuestionCell Cycle and MitosisAssessment Practice

5 marks~8 minCriterion C

A researcher investigates the role of p53 in the cell cycle. Human cells are treated with a drug that inhibits p53 activity. The percentage of cells in each phase is recorded over 24 hours. In untreated cells, G1 remains at ~60%, S phase at ~30%, and G2/M at ~10%. In p53-inhibited cells, G1 drops from 60% to 20% over 12 hours, S phase rises from 30% to 70%, and G2/M remains at ~10%.

State the role of p53 at the G1/S checkpoint. [1]

Explain what the change in G1 and S phase percentages indicates about cell behaviour when p53 is inhibited. [2]

Evaluate the hypothesis: "p53 is essential for preventing cells from entering S phase." In your answer, use the data and identify one limitation of this conclusion. [2]

Solutions

34QuestionCell Cycle and MitosisAssessment Practice

4 marks~6 minCriterion D

A cancer patient is told that their chemotherapy targets rapidly dividing cells. Because hair follicle cells and intestinal epithelial cells also divide rapidly through mitosis, the patient experiences hair loss and nausea as side effects.

Explain why chemotherapy affects both cancerous and healthy cells. [1]

Analyse the trade-off a medical team must consider when recommending chemotherapy to this patient. [1]

Evaluate the limitations of "targeting mitosis" as a strategy for selectively eliminating malignant cells, and discuss the ethical dilemma this creates for the patient and medical team. [2]

Solutions

35QuestionCell Cycle and MitosisAssessment Practice

2 marks~3 minCriterion C

The diagram shows a cell at four stages of mitosis.

Identify one key event occurring during metaphase, using appropriate biological terminology. [1]

A student claims that anaphase is the most critical stage for ensuring each daughter cell receives an identical set of chromosomes. Using evidence from the events of anaphase and telophase, evaluate this claim. [1]

Solutions

36QuestionCell Cycle and MitosisAssessment Practice

2 marks~3 minCriterion A

The diagram below shows a cell in which chromosomes are maximally condensed and aligned along the equatorial plane, with spindle fibres visible extending from both poles.

Identify the stage of mitosis shown in the diagram. [1]

Explain why correct chromosome alignment at this stage is critical before the cell proceeds to the next stage of mitosis. [1]

Solutions

37QuestionCell Cycle and MitosisAssessment Practice

2 marks~3 minCriterion D

Certain chemotherapy drugs work by blocking cell cycle checkpoints, preventing cells from completing division and triggering apoptosis. Oncologists use this mechanism to target tumour cells, which divide uncontrollably.

Explain why these drugs also damage healthy tissues such as hair follicles and the digestive tract lining, and outline one consequence of this for the patient. [2]

Solutions

38QuestionFactors 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

39QuestionImportance of Transport in OrganismsAssessment Practice

3 marks~5 minCriterion C

The diagram shows an alveolus adjacent to a blood capillary. Arrows indicate that oxygen (

O_2

) concentration is higher in the alveolus than in the blood, and that carbon dioxide (

CO_2

) concentration is higher in the blood than in the alveolus.

Identify the process by which

O_2

moves from the alveolus into the blood. [1]

Explain why

O_2

moves into the capillary and

CO_2

moves into the alveolus, using concentration gradients in your answer. [1]

A student claims that increasing the breathing rate would steepen the concentration gradient for

O_2

at the alveolar surface. Evaluate this claim. [1]

Solutions

40QuestionActive Transport and Energy RequirementAssessment Practice

6 marks~9 minCriterion D

In saline soils, plant cells use ATP-driven membrane pumps to actively transport

\text{Na}^+

ions into vacuoles, preventing toxic cytoplasmic accumulation. Researchers have genetically modified (GM) crops to overexpress these pumps, enabling growth on salt-damaged farmland. Approximately one billion hectares of agricultural land worldwide are affected by soil salinity, threatening food production for vulnerable populations.

Explain one societal benefit of deploying salt-tolerant GM crops on saline farmland. [2]

Explain one environmental risk that could arise if these GM crops are grown at large scale. [2]

Evaluate the limitations of translating laboratory results for these GM crops into reliable large-scale agricultural practice. [2]

Solutions

41QuestionOsmosis in Cells and Living SystemsAssessment Practice

4 marks~6 minCriterion A

The diagram shows a plant cell before and after immersion in a concentrated sucrose solution.

Identify the term for the process in which the cell membrane pulls away from the cell wall. [1]

Explain the changes visible in the cell after immersion in the sucrose solution, referring to the vacuole, cytoplasm, and cell membrane. [1]

Analyse why the cell wall prevents a plant cell from bursting when placed in pure water, and why an animal cell placed in the same conditions does not survive. [2]

Solutions

42QuestionActive Transport and Energy RequirementAssessment Practice

6 marks~9 minCriterion D

Farmers apply herbicides that block active transport in plant root cells, preventing the energy-dependent uptake of mineral ions such as

K^+

and

NO_3^-

against their concentration gradient. Two fields are compared: one treated with herbicide (Crop A) and one untreated (Crop B). Crop A shows higher yield but reduced soil microbial diversity. Herbicide residue levels in harvested crops are recorded below.

Crop	Wheat	Rice	Corn
Residue (mg/kg)	0.05	0.12	0.03
Maximum allowed residue (mg/kg)	0.10	0.10	0.10

Explain how inhibiting active transport of mineral ions leads to the death of weeds. [2]

Using the residue data, discuss one ethical issue raised by the use of this herbicide on food crops. [2]

Evaluate the ecological significance of reduced soil microbial diversity resulting from herbicide use. [2]

Solutions

43QuestionDefinition and Examples of DiffusionAssessment Practice

8 marks~12 minCriterion C

An artificial membrane with pores of diameter 10 nm separates two compartments. Three molecules are tested: glucose (molecular diameter 1 nm), starch (molecular diameter 5 nm), and a protein (molecular diameter 8 nm). Each molecule begins at a concentration of 10 mM on one side and 0 mM on the other. Diffusion is measured at 25°C over 10 minutes. The graph shows amount diffused (micromoles) against time (minutes) for each molecule.

Identify the molecule with the highest diffusion rate and the molecule with the lowest diffusion rate. [1]

Describe the relationship between molecular size and diffusion rate shown by the data, and suggest why this relationship exists. [2]

The three molecules differ not only in size but also in shape: glucose is roughly spherical, starch is a long unbranched chain, and the protein is a folded globular structure. Analyse how molecular shape could account for the difference in diffusion rate between starch and the protein, given that both are smaller than the pore diameter. [3]

Evaluate the hypothesis that 'molecular size is the only factor affecting diffusion rate', using evidence from the graph and the information about molecular shape. [2]

Solutions

44QuestionFuture Developments in Stem Cell ScienceAssessment Practice

4 marks~6 minCriterion B

A team of scientists conducted three stem cell studies investigating the relationship between cell source, differentiation potential, and tumour formation risk.

Study 1 — Embryonic stem cells: 18 cell types produced; tumour formation risk: High
Study 2 — Adult stem cells: 5 cell types produced; tumour formation risk: Low
Study 3 — Induced pluripotent stem cells (iPSCs): 15 cell types produced; tumour formation risk: Medium

Analyse the data to identify the relationship between differentiation potential and tumour formation risk across the three stem cell sources. [2]

A fourth study introduces amniotic stem cells, reported to produce approximately 10 cell types. Deduce the expected tumour formation risk for amniotic stem cells, and justify your deduction using the relationship identified in part (a). [2]

Solutions

45QuestionEthical Considerations in Stem Cell ResearchAssessment Practice

5 marks~8 minCriterion C

A research team compared induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs) for generating pancreatic beta cells to treat type 1 diabetes.

Differentiation success rate into beta cells	iPSC 45%	ESC 72%
Immune rejection rate in animal models	iPSC 12%	ESC 35%

Ethical approval status: iPSC approved (no embryos destroyed); ESC controversial (requires embryo destruction)

State one biological advantage and one biological disadvantage of using iPSCs compared to ESCs, using data from the table. [2]

Explain how the lower immune rejection rate of iPSCs is clinically significant for patients receiving beta cell transplants. [1]

Evaluate whether the experimental evidence supports the hypothesis that iPSCs are a more ethically viable alternative to ESCs for diabetes treatment. [2]

Solutions

46QuestionEthical Considerations in Stem Cell ResearchAssessment Practice

6 marks~9 minCriterion C

Four regulatory genes —

Oct4

Sox2

Nanog

, and

Pax6

— were measured in three stem cell types. Expression levels are in relative units (RU).

$Oct4$	embryonic stem cells 95	neural stem cells 12	mesenchymal stem cells 8
$Sox2$	embryonic stem cells 90	neural stem cells 85	mesenchymal stem cells 10
$Nanog$	embryonic stem cells 88	neural stem cells 8	mesenchymal stem cells 6
$Pax6$	embryonic stem cells 5	neural stem cells 78	mesenchymal stem cells 5

Identify the two genes with high expression in embryonic stem cells but low expression in both neural and mesenchymal stem cells. Explain what this pattern indicates about the function of these genes. [2]

Sox2

is highly expressed in both embryonic and neural stem cells, yet these two cell types differ greatly in differentiation potential. Using the full gene expression profile, explain how the combination of genes expressed — rather than any single gene — determines a stem cell's potency. [2]

A researcher proposes that mesenchymal stem cells could replace embryonic stem cells in regenerative therapies because "stem cells are all essentially the same." Evaluate this claim using evidence from the gene expression data. [2]

Solutions

47QuestionCharacteristics and Properties of Stem CellsAssessment Practice

4 marks~6 minCriterion D

A 45-year-old patient with a spinal cord injury resulting in paraplegia is considering two stem cell treatments:

Option 1 — Embryonic stem cells (ESCs): pluripotent cells from donated IVF embryos. Risks include immune rejection and teratoma formation.

Option 2 — Induced pluripotent stem cells (iPSCs): the patient's own skin cells reprogrammed to pluripotency. Immune rejection is avoided, but reprogramming may introduce genetic mutations, increasing cancer risk.

Explain what pluripotency means and why it is relevant to spinal cord repair. [1]

Analyse the benefits and risks of each treatment option for this patient. [2]

Justify which option is more viable for clinical use, considering ethical, health, and practical trade-offs. [1]

Solutions

48QuestionCharacteristics and Properties of Stem CellsAssessment Practice

4 marks~6 minCriterion A

The diagram below shows a single embryonic stem cell giving rise to three specialised cell types: a neuron, a skeletal muscle cell, and a red blood cell.

Describe the process of differentiation shown in the diagram. [2]

Explain why the embryonic stem cell is classified as pluripotent rather than totipotent or multipotent. [2]

Solutions