This set practises structure-function chains, joining a mechanism to a figure, clean diagrams, adaptation wording and repairing keyword lists. Questions run from easy to harder. All data are invented for practice.
Attempt each one before opening the answer. The overview of the topic is biological explanations and diagrams.
Questions
1. (Easy) A palisade cell has many chloroplasts, packed towards the upper surface of the leaf. Explain how this helps the plant.
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Feature: many chloroplasts near the upper surface. Property: more chlorophyll is positioned where most light arrives. Process: more light is absorbed for photosynthesis. Outcome: more glucose is made in a given time.
Full answer: “Many chloroplasts at the upper surface of the leaf absorb more of the light that reaches it, so the rate of photosynthesis is higher and more glucose is made.”
2. (Easy) A red blood cell is shaped like a disc with a dip on each side. Explain how this shape helps it take up oxygen.
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The dip gives a large surface area compared with the cell’s volume, and the cell is thin, so the diffusion distance to the centre is short. Oxygen therefore diffuses in and out quickly. Feature, property, process are all present.
3. (Medium) A student measured how long amylase took to digest all the starch in a mixture at different temperatures. Invented data: 20 °C, 12 min; 30 °C, 6 min; 40 °C, 3 min; 60 °C, starch still present after 20 min. Calculate the rate (1 ÷ time) at 30 °C and 40 °C, then explain the results.
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Rate at 30 °C = 1 ÷ 6 = 0.17 per min. Rate at 40 °C = 1 ÷ 3 = 0.33 per min. The rate roughly doubled, since 0.33 ÷ 0.17 = 2 (to the accuracy of the rounding).
Explanation: at higher temperature the enzyme and starch molecules move faster, so they collide more often and with more energy, which digests starch faster. At 60 °C the starch was not digested, because the enzyme has denatured: the active site changed shape, so the starch no longer fits.
4. (Medium) A student’s diagram of a villus has twelve labels written inside the drawing, and three label lines cross. Give three changes that would improve it.
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- Reduce the labels to those the question needs (for example wall, capillary, lacteal).
- Move the labels beside the drawing, written horizontally.
- Use a ruler so that no lines cross, with each line ending on its structure.
5. (Medium) A drawing of a cell is 40 mm long. The real cell is 0.05 mm long. Calculate the magnification.
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Magnification = drawn size ÷ actual size = 40 ÷ 0.05 = ×800. Check: 0.05 × 800 = 40 mm.
6. (Medium) Write a correct explanation for: “Bacteria became resistant to an antibiotic because they wanted to survive it.”
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“In the population there was variation, and a few bacteria had an allele that made them resistant. When the antibiotic was used, these bacteria survived and reproduced while the others died. They passed on the allele, so the proportion of resistant bacteria increased.”
7. (Medium) Find the two errors in: “Polar bears evolved thick fur because they needed to keep warm.”
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“Needed to keep warm” is purpose wording, and “evolved because they needed” suggests that need causes change. The correct chain is variation in fur thickness, better survival and reproduction of the thicker-furred bears in the cold, inheritance of the allele and an increase in its frequency.
8. (Harder) Turn this keyword list into an explanation for “Explain why fish may die after too much fertiliser runs into a pond”: nitrates, algae, light, death, bacteria, oxygen.
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“Extra nitrates from fertiliser make algae grow quickly, and a thick layer of algae blocks light from plants below, so those plants die. Bacteria decompose the dead material and use up oxygen by respiration. The lower oxygen concentration means fish cannot respire enough, so they die.”
9. (Harder) Invented data: potato cylinders (initial mass 2.0 g) in sucrose solutions gave changes in mass of +0.30 g in 0.0 M, +0.10 g in 0.2 M, −0.12 g in 0.4 M and −0.31 g in 0.6 M. Estimate the concentration where there is no change in mass, and explain the trend using the figures.
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Zero change lies between 0.2 M (+0.10 g) and 0.4 M (−0.12 g). Assuming a straight line, the fraction of the way is 0.10 ÷ (0.10 + 0.12) = 0.45, so concentration = 0.2 + 0.45 × 0.2 = 0.2 + 0.09 = about 0.29 M. This is an estimate, because it assumes a straight-line change.
Explanation: in 0.0 M the solution has a higher water potential than the cells, so water enters by osmosis and mass rises by 0.30 g. At 0.6 M the solution has a lower water potential, so water leaves and mass falls by 0.31 g. At about 0.29 M the water potentials are equal, so there is no net movement.
10. (Harder) Explain how the structure of the alveoli makes gas exchange efficient. Then list the labels you would add to a diagram to support your answer.
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“The alveolus wall is one cell thick, as is the capillary wall, so the diffusion distance is short. The alveoli are very numerous, giving a large surface area. A dense network of capillaries carries blood away, which keeps a steep concentration gradient for oxygen and carbon dioxide. A moist lining lets oxygen dissolve before it diffuses. Together these make gas exchange fast.”
Diagram labels (four): alveolus wall, capillary, air in alveolus, direction of oxygen diffusion. Short names, ruled lines, none crossing.
11. (Harder) A cross of Aa × Aa pea plants is predicted by a model to give dominant and recessive offspring in a 3 : 1 ratio. Of 20 offspring, 12 were dominant and 8 recessive. Is the model wrong?
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The model predicts 15 dominant and 5 recessive from 20. The observed 12 and 8 differ, but fertilisation is random, so a small sample will often vary from the prediction. One sample of 20 does not show the model is wrong. A larger sample would be expected to be closer. You can test the model with the inheritance model board.
If you got these wrong
| Type of slip | Go to |
|---|---|
| Feature named but no link to the job (Q1, Q2, Q10) | Develop a structure-function explanation |
| Theory without a quoted figure, or figures with no mechanism (Q3, Q9, Q11) | Link a mechanism with observed evidence |
| Crowded or crossing labels, magnification errors (Q4, Q5) | Label an original diagram without overcrowding |
| “In order to”, “needed to” or “wanted to” (Q6, Q7) | Avoid teleological language |
| A list of words with no chain (Q8) | Repair a correct keyword list |
Record each repeated slip in the mistake log and retest it with a fresh question in a few days.
What next?
Go back to the module overview to choose what to revise. If the same slip returns in every answer, a teacher reading your writing can see the pattern faster than you can alone. That is what online one-to-one Biology tuition is designed for.