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Edexcel IGCSE Biology revision

Genetic engineering questions

Explain how genes are transferred between organisms and interpret evidence about genetically modified crops.

Edexcel IGCSE Biology Subtopic 5.c

Genetic modification (genetic engineering) syllabus

Questions on genetic modification (genetic engineering) can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

  • 5.12 understand how restriction enzymes are used to cut DNA at specific sites and ligase enzymes are used to join pieces of DNA together
  • 5.13 understand how plasmids and viruses can act as vectors, which take up pieces of DNA, and then insert this recombinant DNA into other cells
  • 5.14 understand how large amounts of human insulin can be manufactured from genetically modified bacteria that are grown in a fermenter
  • 5.15 understand how genetically modified plants can be used to improve food production
  • 5.16 understand that the term transgenic means the transfer of genetic material from one species to a different species

How to answer genetic modification (genetic engineering) questions

  1. Describe each stage of the biological technique in order and name the cells, enzymes or vectors involved.
  2. Distinguish selective breeding, genetic engineering and cloning before comparing their outcomes.
  3. Balance a stated benefit against a specific biological, environmental or ethical limitation.
  4. Use evidence from the question when evaluating yield, disease resistance, biodiversity or food security.

Genetic modification (genetic engineering) example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Plotting the adoption of GM crops

Adapted from June 2017 (R), Paper 1B · Question 7(b)(i)

Question 1

Genetically modified (GM) crops have been developed over the last 30 years.

Farmers have been growing GM soybean and corn for a number of years.

The table shows data for soybean and corn grown in the USA from 1996 to 2014. It shows the percentage of each crop that is GM.

Year Percentage of each crop that is GM (%)
soybean corn
1996 7 3
2000 54 7
2004 85 20
2008 92 63
2012 93 73
2014 94 89

Plot a line graph of the data.

Use a ruler to join the points with straight lines.

Final answer

Label the horizontal axis Year and the vertical axis Percentage of each crop that is GM (%). Use linear scales, with 1996–2014 across the full grid width and 0–100% across the full grid height.

  • Plot and join with straight lines: soybean (1996, 7), (2000, 54), (2004, 85), (2008, 92), (2012, 93), (2014, 94).
  • Plot and join with straight lines: corn (1996, 3), (2000, 7), (2004, 20), (2008, 63), (2012, 73), (2014, 89).

Add a key identifying the soybean and corn lines. Do not extend either line to the origin.

199620002004200820122014YearGM share of crop (%) 020406080100 SoybeanCorn

Mark scheme points

  1. M1 Both axes use linear scales, and each scale uses at least half of the grid.
  2. M2 Both data lines are straight and pass through their plotted points; do not extrapolate from the origin.
  3. M3 Put year on the horizontal axis and percentage on the vertical axis.
  4. M4 Label the horizontal axis “year” and the vertical axis with percentage or % and GM.
  5. M5 Plot the data points correctly; an error of up to half a square is allowed.
  6. M6 Include a key identifying soybean and corn.

Explanation

A linear scale means equal changes in a value have equal distances on the axis. Use the year values to position points horizontally and the GM percentages to position them vertically. The year gaps are not all the same, so plot each year according to its actual value. Connect consecutive points for each crop with straight lines, then use a key to show which line represents each crop.

Common mistakes

  • Spacing all six years equally gives incorrect horizontal positions: the interval from 2012 to 2014 is two years, while the earlier intervals are four years.
  • Check that both axes are labelled and that the key identifies both crops; do not extend the lines to the origin.

Example 2: Engineering yeast to make pyrethrin

Adapted from June 2018, Paper 2B · Question 3(b)(i)

Question 2

The photograph shows the flower of a species of chrysanthemum plant that only grows in East Africa.

Photograph of a chrysanthemum flower with pale petals surrounding a dark central disk; a smaller flower is visible in the background.

The chrysanthemum plant produces an insecticide called pyrethrin. Scientists have grown genetically modified yeast cells in fermenters to produce large quantities of pyrethrin.

Explain how yeast cells can be genetically modified to produce pyrethrin.

Final answer

A restriction enzyme cuts out the DNA containing the gene needed to make pyrethrin and cuts open a plasmid. DNA ligase joins the gene into the plasmid. The recombinant plasmid is introduced into yeast cells, which use the gene to produce pyrethrin.

Mark scheme points

  1. M1 Use a restriction enzyme to cut out the gene or DNA for pyrethrin.
  2. M2 Use a plasmid to carry the gene.
  3. M3 Use ligase to join the DNA together.

Explanation

The restriction enzyme cuts the DNA containing the pyrethrin gene. A plasmid acts as a vector, carrying that gene into the yeast cell. Ligase joins the gene to the plasmid DNA, forming recombinant DNA. The yeast can then use the gene to make pyrethrin.

Common mistakes

  • Name the restriction enzyme and state that it cuts DNA containing the pyrethrin gene; naming the enzyme alone is not enough.
  • Do not confuse the enzyme roles: restriction enzymes cut DNA, while ligase joins DNA.

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