GM Crops — Genetic Engineering | IGCSE Biology

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 10% of your exam marks.

increasing

Medium

Increasing10%

Insulin production by bacteria and GM crops are growing in exam frequency.

Genetic engineering of plants has produced genetically modified crops with useful new traits.

Common GM traits in crops

Trait	Source of gene	Why it matters
Insect resistance	The Bt gene from the bacterium Bacillus thuringiensis makes a protein toxic to caterpillars but harmless to humans	The plant produces its own insecticide; less chemical pesticide needed; less crop loss
Herbicide resistance	Genes that allow the plant to break down a specific weedkiller	Farmers can spray the herbicide on the whole field, killing weeds but not the crop
Drought tolerance	Genes that help the plant cope with low water	Crops can be grown in drier regions or use less irrigation
Vitamin A production	"Golden rice" carries genes from another plant + a bacterium that produce beta-carotene (a vitamin A precursor)	Could prevent vitamin A deficiency, which causes blindness and death in poor regions
Disease resistance	Genes for resistance to specific viral or fungal pathogens	Less crop lost to disease; less need for fungicides
Longer shelf life	Genes that slow down ripening	Reduces food waste

Examples in practice

Bt cotton and Bt maize (corn) are grown widely in the USA, China, India and South America. They are resistant to the bollworm and corn borer respectively, both major insect pests.
Glyphosate-resistant ("Roundup Ready") soybeans, maize and oilseed rape make up the majority of these crops grown in the USA and South America.
Golden rice was developed in 1999 to combat vitamin A deficiency in Asia, but it has been slow to deploy due to regulatory and political controversy.

Advantages of GM crops

Advantage	Explanation
Higher yields	Less crop lost to pests, weeds and disease
Less pesticide use	Bt crops produce their own insecticide; less chemical needed
Reduced labour and cost for farmers	Herbicide-resistant crops are easier to weed
Better nutrition	Crops like golden rice can deliver missing vitamins to populations who need them
Drought tolerance	Allows farming in dry regions that traditional varieties cannot tolerate
Less land needed	Higher yields per hectare reduce pressure on rainforests for new farmland

Disadvantages and concerns

Concern	Explanation
Cost	GM seeds are more expensive; large agribusinesses develop them and charge accordingly. Small farmers may be priced out
Cross-contamination	Pollen from GM crops can fertilise wild relatives or organic neighbouring crops, spreading the engineered genes
Loss of biodiversity	Heavy use of herbicide-resistant crops kills off most weeds in the field, reducing food for insects and the birds that eat them
Pest resistance	Insects can evolve resistance to the Bt toxin if they are exposed to it constantly (natural selection in action: see topic 14)
Dependence on agribusiness	Farmers in poorer countries may become locked into buying seed each year from a single company
Long-term human health unknown	GM food has been eaten for decades with no proven harm, but long-term effects are not certain
Ethical concerns	Some people feel that humans should not "play God" with the natural genome

The scientific consensus is that current GM crops are safe to eat. The bigger debates are about social, economic and environmental impacts rather than direct health risks.