Genetically modified plants and food production

A genetically modified (GM) plant is one that has had its genes (DNA) changed by scientists. Usually this is done by inserting a gene from another organism into the plant's DNA. The new gene gives the plant a useful new characteristic that it did not have before.

A few important ideas to fix in your mind:

• A gene is a section of DNA that codes for a characteristic (such as making a particular protein).
• In genetic modification, scientists cut out a useful gene from one organism and insert it into the cells of the crop plant. The gene is added while the plant is being grown from cells, so the whole plant ends up carrying it.
• Because the gene is now part of the plant's DNA, it is passed on when the plant reproduces — the offspring are GM too.

The reason we do this is to improve food production: to grow more food, better food, or food that grows in difficult conditions. The rest of this note looks at the main examples named in the specification.

Exam tip. A GM organism has had a gene inserted/added from another organism. Don't write that the plant simply "changes itself" — the new gene is put in by scientists.

Two of the most common reasons for genetically modifying crops are to make them resistant to insect pests and resistant to herbicides (weedkillers).

Pest resistance (Bt crops). A gene from the bacterium Bacillus thuringiensis (often called the Bt gene) can be inserted into a crop such as maize or cotton. This gene makes the plant produce a toxin (poison) that kills the insect pests that try to eat it. The benefits are:

• Fewer crops are eaten or damaged by insects, so the yield is higher.
• Farmers need to spray less insecticide (chemical pesticide), which saves money and reduces chemicals released into the environment.

Herbicide resistance. A crop can be modified so that it is not killed by a particular weedkiller (herbicide). The farmer can then spray the whole field: the weeds die but the crop survives. With fewer weeds competing for light, water and minerals, the crop grows better and the yield increases.

Here is how a Bt crop protects itself:

Exam tip. For Bt crops, say the plant makes a toxin that kills the insect pests, so the crop is damaged less and less insecticide needs to be sprayed. For herbicide resistance, say the weedkiller kills the weeds but not the crop.

Genetic modification can also improve crops in ways that directly increase the amount and quality of food.

Higher yield. Crops can be modified so that each plant produces more food (for example bigger grains or more fruit). More food from the same area of land helps feed a growing population.

Longer shelf life. Some GM crops are designed to ripen or rot more slowly, so they stay fresh for longer after being picked. This means less food is wasted during transport and in the shops, and food can be sent to places further away.

Added nutrients (golden rice). This is the example you are most likely to be asked about. Golden rice has been genetically modified so that it makes beta-carotene, which the human body turns into vitamin A. (The beta-carotene gives the rice its golden colour.)

• In many parts of the world people rely on rice as their main food but do not get enough vitamin A.
• A lack of vitamin A can cause blindness and other health problems, especially in children.
• Growing golden rice can help prevent these deficiency problems by adding the missing nutrient to a food people already eat.

So GM is not only about growing more food — it can also make food more nutritious and less wasteful.

Exam tip. Learn the golden rice example precisely: it makes beta-carotene, which becomes vitamin A, helping to prevent vitamin A deficiency / blindness. This is a favourite "increased nutritional value" answer.

Some land is hard to farm because it is too dry (drought) or the soil is too salty. Normal crops grow poorly or die in these conditions, but crops can be genetically modified to tolerate them.

• Drought tolerance — the GM crop can survive and grow with little water, so it can be grown in dry regions or during dry seasons.
• Salt tolerance — the GM crop can grow in salty soil where ordinary crops would not survive (for example near coasts or where irrigation has left salt in the soil).

The benefit is that food can be grown on land that was previously unsuitable for farming. This is especially useful in countries where water is scarce or where climate change is making conditions harsher, helping to provide a reliable food supply.

Exam tip. Keep these simple: a drought-tolerant crop grows with less water; a salt-tolerant crop grows in salty soil. Both let farmers grow food on poor land that ordinary crops cannot use.

The specification asks you to discuss GM crops — that means giving both sides: the benefits and the concerns. A good "discuss" answer weighs both and may give a conclusion.

Benefits.

• More food is produced (higher yields, fewer losses to pests/weeds), which helps feed a growing population.
• Less pesticide and herbicide may be sprayed (e.g. with Bt crops), reducing chemicals in the environment.
• Better nutrition — crops like golden rice can prevent deficiency diseases.
• Less waste from a longer shelf life, and food can be grown on poor land (drought/salt-tolerant crops).

Concerns and risks.

• Effect on wildlife. GM crops (or the reduced spraying/changed farming) might harm other organisms, for example insects that are not pests (such as pollinators), reducing biodiversity.
• Gene transfer to wild plants. Genes (e.g. herbicide resistance) could spread by pollination to wild plants or weeds, creating "superweeds" that are hard to control.
• Cost. GM seeds can be expensive, so poorer farmers may not be able to afford them.
• Ethics. Some people object to moving genes between species or worry about unknown long-term effects on health or the environment.
• Monopoly. A few large companies own the GM seeds (and the matching weedkiller) and control the price, which can leave farmers dependent on them.

Exam tip. For a "discuss / evaluate" question, write at least one clear benefit and one clear concern, and try to explain each (don't just list words). Strong answers name a specific concern such as gene transfer to wild plants or monopoly by large companies.