GM crops include ones that are resistant to insect attack or to herbicides.

The idea

Genetic modification can give a crop a gene that protects it against pests or weeds. Insect-resistant GM crops carry a gene from a bacterium that makes a protein toxic to certain insect larvae. When the insect eats the plant, it takes in the protein and dies, so less of the crop is damaged. Herbicide-resistant GM crops carry a gene that lets the plant survive a weedkiller that would normally kill it. A farmer can then spray the field to kill weeds without harming the crop.

For example: GM maize can carry a bacterial gene that kills corn borer larvae, and GM soybeans can be sprayed with a herbicide that kills surrounding weeds.

What earns the marks

• Insect-resistant GM crops contain a gene that makes a protein harmful to specific insect pests.
• The insect dies after eating the plant, so the crop suffers less damage.
• Herbicide-resistant GM crops contain a gene that allows them to survive a particular weedkiller.
• The weedkiller kills weeds that compete with the crop for light, water and nutrients.
• The resistance comes from a gene transferred from another organism, not from a chemical applied to the plant.

Common mistakes and how to put them right

• Saying insect-resistant plants repel insects.

  Put it right: The inserted gene makes a protein that harms the insect when it feeds.

• Thinking herbicide-resistant crops are not affected by any weedkiller.

  Put it right: Resistance is to one specific herbicide.

• Confusing pests with weeds.

  Put it right: Insects are pests that eat the crop, while weeds are unwanted plants that compete with it.

Exam tips

• Name the pest or weed problem before explaining how the inserted gene solves it.
• Use the terms insect-resistant and herbicide-resistant accurately and separately.
• Explain the benefit to the farmer, such as less crop damage or easier weed control.