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IGCSE · Practice questions · Genetic modification

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Six original Cambridge-style questions on genetic modification: its definition, GM bacteria and crops, the steps of making human insulin and a discussion of GM soya, maize and rice.

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

Which enzyme, which step.

01
Recall
[4 marks]

Define genetic modification and give three examples of its use.

  • Changing the genetic material of an organism by removing, changing or inserting individual genes. ✓
  • Inserting human genes into bacteria to produce human proteins such as insulin. ✓
  • Inserting genes into crop plants to give resistance to herbicides or to insect pests. ✓
  • Inserting genes into crop plants to improve their nutritional qualities, such as golden rice with extra vitamin A. ✓
02
Explain
[6 marks]

Extended. Outline how bacteria can be genetically modified to produce human insulin.

  • The human insulin gene is cut out of human DNA using restriction enzymes, forming sticky ends. ✓
  • A bacterial plasmid is cut with the same restriction enzymes, forming complementary sticky ends. ✓
  • The insulin gene is inserted into the plasmid and joined using DNA ligase, forming a recombinant plasmid. ✓
  • The recombinant plasmids are inserted into bacteria. ✓
  • The bacteria multiply rapidly (in a fermenter), copying the plasmid. ✓
  • The bacteria express the human gene and make human insulin, which is extracted and purified. ✓
03
Explain
[2 marks]

Extended. Explain what is meant by sticky ends and why they are useful.

  • Short single-stranded sections of DNA left at the ends of a cut DNA molecule by a restriction enzyme. ✓
  • Their bases are complementary to the sticky ends on the plasmid cut by the same enzyme, so the two can pair before DNA ligase joins them. ✓
04
Recall
[3 marks]

Describe how genetic modification has been used to make crop plants resistant to insect pests, and state one benefit to the farmer.

  • A gene (from a bacterium) is inserted into the crop plant, such as maize. ✓
  • The plant makes a toxin that kills insect pests that eat it. ✓
  • Benefit: less crop damage, so a higher yield, and less insecticide needs to be bought and sprayed. ✓
05
Analysis
[5 marks]

Extended. Discuss the advantages and disadvantages of growing genetically modified crops such as soya, maize and rice.

  • Advantage: higher yields because less crop is lost to weeds (herbicide-resistant soya, maize) or insect pests (insect-resistant maize). ✓
  • Advantage: less insecticide sprayed; golden rice could reduce vitamin A deficiency. ✓
  • Disadvantage: GM seed is expensive and may need to be bought every year, which is hard for poor farmers. ✓
  • Disadvantage: genes may spread to wild relatives, producing herbicide-resistant weeds; herbicide use may increase; insects that are not pests may be harmed. ✓
  • Disadvantage: reduced biodiversity, and concern about unknown long-term effects on health. (A balanced answer with a conclusion gains credit.) ✓
06
Analysis
[3 marks]

Extended. Before genetically modified bacteria were used, people with diabetes were treated with insulin extracted from the pancreas of pigs and cattle. Suggest three advantages of using insulin from GM bacteria.

  • It is human insulin, so it is identical to the patient's own and less likely to cause an immune reaction. ✓
  • Large amounts can be made quickly and cheaply because bacteria reproduce rapidly in fermenters, so supply meets demand. ✓
  • No animals need to be slaughtered, so there are fewer ethical or religious objections, and no risk of passing on animal diseases. ✓

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.