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A2 · Practice questions · GM crops and animals

More food, at what cost?

Six original Cambridge-style questions on genetically modified organisms in agriculture, including data analysis and an extended discussion.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Gene, trait, benefit, risk.

01
Explain
[3 marks]

Explain how genetic modification has increased the productivity of farmed Atlantic salmon.

  • A gene for growth hormone from Chinook salmon was inserted, together with a promoter from ocean pout. ✓
  • The promoter keeps the gene switched on all year, not just in the warmer months, so growth hormone is produced continuously. ✓
  • The fish reach market size in about half the time and use less feed per kilogram, so more fish are produced from the same resources. ✓
02
Explain
[3 marks]

Explain how herbicide-resistant soybean allows farmers to increase yields.

  • Glyphosate kills plants by inhibiting the enzyme EPSPS, needed to make some amino acids. ✓
  • The GM soybean has a bacterial gene for a form of EPSPS that is not inhibited, so the crop survives spraying. ✓
  • Weeds can be killed while the crop grows, reducing competition for light, water and mineral ions, so yield increases. ✓
03
Recall
[2 marks]

State the source of the gene inserted into Bt cotton and explain how the product of this gene protects the crop.

  • The gene comes from the bacterium Bacillus thuringiensis. ✓
  • It codes for Bt toxin (a protein), which kills insect larvae such as bollworm caterpillars when they feed on the plant. ✓
04
Data
[3 marks]

In a trial, conventional cotton received 8 insecticide sprays per season and yielded 1.5 tonnes per hectare. Bt cotton received 2 sprays and yielded 1.8 tonnes per hectare. Calculate the percentage increase in yield and suggest two reasons why it is not certain that Bt cotton caused it.

  • (1.8 − 1.5) / 1.5 × 100 = 20 % increase. ✓
  • Other variables may differ between the fields, such as soil, rainfall, fertiliser or the size of the pest population that year. ✓
  • The trial may not have been repeated over several seasons or sites, so the result may not be reliable. ✓
05
Explain
[2 marks]

Suggest why the widespread growing of Bt cotton may become less effective over time, and how farmers can reduce this risk.

  • Bt toxin is a selection pressure: any pests with alleles giving resistance survive and reproduce, so resistance becomes more common. ✓
  • Farmers can plant refuges of non-Bt plants nearby, so susceptible insects survive and breed with resistant ones, slowing the spread of resistance. ✓
06
Analysis
[5 marks]

Discuss the ethical and social implications of using genetically modified organisms in food production.

  • Benefit: higher yields and faster growth can help meet the global demand for food from limited land. ✓
  • Benefit: less insecticide use (Bt crops) protects non-target species and farm workers; better weed control raises farmers' incomes. ✓
  • Concern: gene flow to wild relatives or wild fish, creating herbicide-resistant weeds or affecting wild populations; reduced biodiversity. ✓
  • Concern: pests and weeds may evolve resistance; seed is costly and controlled by a few companies, which may disadvantage poorer farmers. ✓
  • Concern: consumer distrust, the need for labelling and choice, animal welfare and religious or cultural objections; a balanced conclusion is expected. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.