These ten questions are original and the data in them are invented for practice. They run from easier to harder and cover fermentation, enzymes, genetic modification, selective breeding and evaluating claims. Write each answer in full sentences first, then open the working.
Keep a note of each error in the mistake log and retest queue, so you can see whether it was a fact, a calculation or an incomplete explanation.
Questions
1. (Easy) Write the word equation for fermentation by yeast.
Show answer
glucose → ethanol + carbon dioxide (energy is released). Fermentation is anaerobic, so oxygen does not appear.
2. (Easy) Name the enzyme in a washing powder that helps remove blood stains, and state its substrate.
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Protease. Its substrate is protein, which it breaks down into smaller molecules that wash away.
3. (Easy) A baker says the dough rose because “the yeast breathed in air”. Correct this and explain why dough rises.
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The yeast respired anaerobically. It broke down sugar, releasing carbon dioxide gas. The gas formed bubbles trapped in the dough, making it expand.
4. (Medium) A student counts 24 bubbles in 4 minutes from yeast in glucose solution at 25 °C, and 50 bubbles in 4 minutes at 35 °C. Calculate each rate and describe what the results show.
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At 25 °C: 24 ÷ 4 = 6 bubbles per minute. At 35 °C: 50 ÷ 4 = 12.5 bubbles per minute. The rate is higher at 35 °C, so the enzymes in yeast work faster at the higher temperature, which gives more molecular collisions and more carbon dioxide each minute. The data cannot show the optimum, because only two temperatures were tested.
5. (Medium) A juice factory finds that 50 cm³ of juice is obtained from a sample of pulp without pectinase and 68 cm³ with pectinase, under identical conditions. Calculate the percentage increase.
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68 − 50 = 18. 18 ÷ 50 = 0.36. So the increase is 36%.
6. (Medium) A washing powder works well at 40 °C but poorly when the machine runs at 90 °C. Explain.
Show answer
At 90 °C the enzyme is denatured. The shape of its active site has changed, so the stain substrate no longer fits and the reaction stops. At 40 °C the enzyme keeps its shape and works near its optimum.
7. (Medium) Put these stages of making human insulin in bacteria into the correct order.
- (A) bacteria are grown in large numbers
- (B) the gene is cut out with a restriction enzyme
- (C) the plasmid carrying the gene is put into bacterial cells
- (D) the gene is joined into a plasmid with ligase
- (E) insulin is collected and purified.
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B, D, C, A, E. The gene is cut out (B), joined into the plasmid (D), the plasmid is put into bacteria (C), the bacteria are grown (A), then the insulin is collected (E).
8. (Medium) For each statement, decide whether it describes selective breeding or gene insertion. (a) A gene from a bacterium is added to a crop plant. (b) Farmers breed only the sheep with the thickest wool, generation after generation.
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(a) Gene insertion, because a gene from a different species is transferred directly. (b) Selective breeding, because parents are chosen and the alleles already in the flock are passed on over generations.
9. (Harder) A trial grows GM and non-GM rice on five plots each. Mean yield is 6.3 t/ha for GM and 5.4 t/ha for non-GM. The company says, “GM rice gives 20% more yield.” Is that correct? Show working.
Show answer
Difference: 6.3 − 5.4 = 0.9. 0.9 ÷ 5.4 = 0.1667, so the increase is about 16.7%, which is below the claimed 20%. The claim slightly overstates the trial result. The evidence comes from five plots, so more repeats and more locations would help.
10. (Harder) A newspaper claims “GM cotton is better for farmers and the environment”. The trial reported cotton yield and cost of pesticide per hectare for one region in one year. Evaluate the claim.
Show answer
Yield and pesticide cost are relevant to the “better for farmers” part, and the data can be checked for differences. The “environment” part is not supported unless effects on soil, insects or other species were measured, and they were not. The trial covered one region and one year, so it cannot show results in other places or over time. A fair judgement is that the evidence may support a benefit for farmers in this region and year, but it does not test the environmental claim.
If you got these wrong
| Type of error | Questions | Revise |
|---|---|---|
| Products, conditions or word equation of fermentation | 1, 3, 4 | Explain fermentation |
| Enzyme names, denaturing or percentage change in industry | 2, 5, 6 | Interpret a use of enzymes in industry |
| Order or vocabulary of genetic modification | 7 | Outline a genetic-modification concept |
| Mixing up selective breeding and gene insertion | 8 | Distinguish gene insertion from selective breeding |
| Claims, percentages and limits of evidence | 9, 10 | Evaluate a biotechnology claim |
For the earlier enzyme ideas, see biological molecules and enzymes. The wider route is on the module page.
A teacher can go through your written answers line by line and show where an explanation loses its logic, which is what online one-to-one Biology tuition is designed for.