Topic 21.3 · Supplement
Evaluating GM Crops
“GM crops are good” and “GM crops are bad” are both answers an examiner will reject, whichever direction they lean. What earns marks here is tracing one named trait through to one specific, justified consequence — and being honest that the answer depends on which trait you’re talking about.
The evaluation chain
Cambridge’s “evaluate” and “discuss” command words expect a fixed reasoning chain, not a memorised list of pros in one paragraph and cons in another with no connection between them:
- Name the engineered trait.
- Explain its direct biological effect.
- Trace a plausible benefit or risk from that effect.
- Compare it with a realistic alternative.
- Use evidence-aware wording rather than absolute claims.
The named crop contexts for this evaluation are soya, maize and rice — the same three examples covered in genetic modification: definition and examples, and the trait named there is exactly what this evaluation chain should be applied to.
Possible benefits, depending on the trait
| Benefit | Depends on |
|---|---|
| Reduced crop loss to pests | Insect-resistant maize surviving attacks that would otherwise reduce yield. |
| Potentially higher usable yield | Less crop lost to weeds, pests, or damage overall. |
| Altered pesticide use | Herbicide-resistant soya changing which herbicide is applied, and how much. |
| Improved nutritional composition | Nutritionally enhanced rice containing a nutrient it wouldn’t otherwise have. |
Possible concerns, depending on mechanism and evidence
| Concern | Depends on |
|---|---|
| Effects on non-target organisms | An insect-resistance trait affecting insects other than the intended pest. |
| Gene flow to other populations | A herbicide-resistance gene spreading to wild relatives through pollen. |
| Selection for resistant pests or weeds | Repeated use of the same trait selecting for pests or weeds no longer affected by it. |
| Biodiversity and ecosystem effects | Changes to the surrounding ecological community over time. |
| Economic and social concerns | Seed cost, access, and farmer dependence on the seed supplier. |
Why the same trait, at the same time
A benefit or risk that’s genuinely true for herbicide-resistant soya — changed herbicide use, for instance — isn’t automatically true for insect-resistant maize, whose relevant concern is more about effects on non-target insects and resistant pest populations, and it isn’t automatically true for nutritionally enhanced rice either, whose relevant benefit is about diet rather than pesticide use at all. An examiner is checking whether you can hold one specific benefit and one specific risk in mind for the same named trait at the sametime — not whether you can recite a general list of GM pros and a general list of GM cons that never actually meet.
For example: herbicide-resistant soya makes weed control easier and reduces competition with the crop, but the same herbicide-resistance gene could spread to a related weed and produce a herbicide-resistant weed that’s harder to control. Insect-resistant maize suffers less insect damage and can yield more with potentially less insecticide use, while a changing insect population from that same trait may also affect other organisms in the surrounding ecosystem. Nutritionally enhanced rice shows a different trade-off again — a genuine improvement to the nutritional quality of a major food crop, set against the ecological consequences of growing any genetically modified plant at scale.
Don’t confuse
Never write “GM crops always have higher yield,” “GM always reduces pesticide use,” or “GM causes biodiversity loss” without naming the specific trait and mechanism involved. The skill being tested is following the chain from gene to characteristic to consequence for one named example — not recalling an isolated, unattached list of advantages and disadvantages.