The world needs more food, and farmland and water are limited. Genetic engineering can make farmed animals grow faster and crops resist weeds and pests, but whether it should is a question of ecology, economics and ethics as well as biology.
Genetic engineering can help meet the global demand for food by improving the quality and productivity of farmed animals and crops. GM salmon carry a growth hormone gene from Chinook salmon with a promoter from ocean pout that keeps it switched on all year, so they reach market size in about half the time on less feed. Herbicide-resistant soybean carries a bacterial gene for a form of the enzyme EPSPS that is not inhibited by glyphosate, so fields can be sprayed to kill weeds without harming the crop. Insect-resistant (Bt) cotton carries a gene from Bacillus thuringiensis for a Bt toxin that kills caterpillars that eat it, so less insecticide is needed. The ethical and social implications include benefits to yield and farmers' incomes, and concerns about gene flow, effects on other species, resistance in weeds and pests, the cost of seed and control by large companies, animal welfare, labelling and consumer choice.
Fig. 1: the three syllabus examples of genetically modified organisms in food production: where each gene comes from and what it changes
Section 01
Three organisms, three problems solved.
Choose GM salmon, herbicide-resistant soybean and Bt cotton in turn and press Apply the test. The GM salmon grows much faster than the non-GM fish of the same age; spraying kills the purple weeds and the non-GM soybean but not the GM soybean; caterpillars eat the non-GM cotton but not the Bt cotton.
Why GM food: the human population is growing, and land, water and fertiliser are limited. Higher yields per hectare or per kilogram of feed, less loss to weeds and pests, and better nutritional quality all help to meet demand.
GM salmon: Atlantic salmon normally grow mainly in the warmer months. The GM fish carry a growth hormone gene from Chinook salmon joined to a promoter from ocean pout, which keeps the gene switched on all year. They reach market size in about half the usual time and need less feed per kilogram. To reduce the risk to wild salmon they are reared as sterile females in land-based tanks.
Herbicide-resistant soybean: the herbicide glyphosate kills plants by inhibiting EPSPS, an enzyme needed to make some amino acids. A gene from a soil bacterium codes for a form of EPSPS that glyphosate does not inhibit. Farmers can spray the growing crop to kill all the weeds, which reduces competition for light, water and ions and increases yield.
Insect-resistant (Bt) cotton: a gene from the bacterium Bacillus thuringiensis codes for a Bt toxin (a protein) that kills insect larvae such as bollworm caterpillars when they eat the plant. It is harmless to mammals. Less insecticide is sprayed, so fewer non-target insects are killed, farmers are less exposed, and yields rise.
Examiner trap
Herbicide-resistant crops do not kill weeds themselves. They survive the herbicide, which allows the farmer to spray it onto the growing crop. Bt crops are the ones that make their own insecticide.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
In the simulator, what makes the GM salmon keep growing all year?
Quick check+10 XP
When you press Apply the test for the soybean, the purple weeds and the non-GM soybean wilt. What has been applied?
Quick check+10 XP
In the Bt cotton test, what happens to the caterpillars that feed on the Bt cotton?
Quick check+10 XP
The simulator states how GM salmon are farmed to protect wild fish. Which method does it describe?
Section 02
Ethical and social implications.
The simulator ends each example with the same list of issues. In the exam, discuss both sides and link each point to a specific example where you can.
Possible benefits
Possible concerns
more food from the same land and feed; can help reduce hunger
gene flow: pollen from GM crops may carry the new gene to wild relatives, for example making herbicide-resistant weeds; escaped GM fish could breed with wild fish
less insecticide sprayed (Bt cotton), which protects non-target insects and farm workers
resistance: pests can evolve resistance to Bt toxin, and weeds to glyphosate when it is used heavily
better weed control and higher yields; higher incomes for farmers
biodiversity: killing all weeds removes food and habitats for other species; possible effects on non-target organisms
faster-growing salmon reduce pressure on wild fish stocks
economic: GM seed is expensive and often must be bought every year; a few large companies control the seed supply, which can disadvantage poor farmers
crops can be made more nutritious or tolerant of drought
social: some consumers distrust GM food; labelling and the right to choose; animal welfare in GM animals; religious and cultural objections
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to A Level Paper 4 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
How does herbicide-resistant soybean increase crop yield?
Exam style+20 XP
Which is the strongest ecological concern about growing herbicide-resistant crops?
Exam style+20 XP
Why might growing Bt cotton reduce harm to non-target insects compared with conventional cotton?
Exam style+20 XP
Which is a social or economic concern about GM crops rather than an ecological one?
Skill unlocked
GM crops and animals, mastered.
This skill is now recorded on your profile. Keep the chain going.