Gene technology already used on farms
Definition
Transgenic organism
A transgenic organism is an organism that contains a gene transferred into it from a different species.
Definition
Herbicide
A herbicide is a chemical applied to land to kill the weeds that compete with a crop.
- A transgenic organism is an organism that contains a gene transferred into it from a different species, and every GM crop grown commercially is one.
- Insect-resistant crops carry a bacterial gene that makes the plant produce a protein poisonous to the caterpillars that eat it.
- Herbicide-tolerant crops carry a gene that lets the plant survive a herbicide, so a whole field can be sprayed and only the weeds are killed.
- Nutrient-enriched crops carry genes that let them make a substance they normally cannot, and the best known is a rice modified to make beta-carotene, which the human body converts into vitamin A.
- Slow-ripening crops carry a changed version of a ripening gene, so the fruit stays firm for longer after it is picked.
- Transgenic farm animals have been produced as well, for example to grow faster or to secrete a useful protein into their milk.
Example
Rice modified to carry vitamin A
- Vitamin A deficiency is common where rice is the main food, because rice grain contains almost none of it, and the deficiency causes blindness.
- Genes taken from a daffodil and from a soil bacterium were inserted into rice so that the grain makes beta-carotene, the orange pigment found in carrots.
- A person who eats the rice converts the beta-carotene into vitamin A, so an ordinary meal supplies a vitamin the diet had been missing.
- The crop was developed to be grown by farmers who keep their own seed rather than buying it, which was intended to make it affordable.
Practical benefits of gene technology in agriculture
- Yield rises, because less of the crop is lost to insect pests and to competition from weeds, so more food is produced from the same area of land.
- Less pesticide is sprayed on an insect-resistant crop, which lowers the cost to the farmer, reduces the fuel burned by the sprayer, and spares the insects that were not the target.
- Weed control becomes simpler with a herbicide-tolerant crop, since one spray removes the weeds that were competing for light, water and mineral ions.
- Nutrition improves where a crop is modified to supply a vitamin or mineral that the local diet lacks, so deficiency diseases become less common.
- Land that cannot currently be farmed can be used, because crops modified to tolerate drought or salty soil will grow where ordinary varieties die.
- Less food is wasted, because slow-ripening varieties survive transport and storage, which matters most where refrigeration is limited.
- Every one of these benefits raises food security, by increasing the amount of food available and by making the supply less likely to fail.
Practical risks of gene technology in agriculture
Definition
Biodiversity
Biodiversity is the variety of different species living in a habitat or ecosystem.
Definition
Monoculture
A monoculture is a large area of land planted with a single variety of one crop.
- Genes can escape into wild populations, because pollen from a GM crop is carried by wind and insects to related wild plants growing nearby.
- If a herbicide-tolerance gene reaches a wild relative, a weed that the herbicide no longer kills is created, which makes the problem worse than before.
- Insects that were not the target can be harmed, since any insect eating the leaves of an insect-resistant crop takes in the same protein, and birds that fed on those insects lose part of their food supply.
- Pests evolve resistance, because a few caterpillars carry an allele that lets them survive the protein, they breed, and within a few generations the protection stops working.
- Biodiversity can fall, because GM crops are usually grown as a monoculture, so a wide area contains one variety, few weeds and therefore few of the insects, birds and mammals that depended on them.
- Long-term effects on human health are not fully known, since a protein that is new to the food supply could act as an allergen, so GM foods are tested and monitored before approval.
- Antibiotic resistance marker genes used when the crop was made raise the concern that the resistance could pass to bacteria, which is why newer methods avoid those markers.
Common Mistake
Do not describe a risk as something that has definitely happened, since the exact wording expected is that a gene could spread or that an effect is not yet fully known.
Ethical and economic concerns
- Some people object in principle to moving genes between species, on religious grounds or because they regard it as interfering with nature.
- Seed for GM varieties is developed and sold by a small number of companies, so farmers may have to buy new seed each year rather than saving their own.
- That cost falls hardest on farmers in poorer countries, who are often the ones whose food security most needs improving.
- Consumers argue that they should be able to choose, which is why GM ingredients must be shown on food labels in the United Kingdom.
- Animal welfare is questioned where livestock are modified to grow faster or produce more, because the animal's body has to support a change it did not evolve to cope with.
- Because of these concerns, GM crops are tested in contained trials and must be approved by a government regulator before they can be grown or sold.
Example
Comparing the yield of a GM and a non-GM variety
- A trial grows a non-GM maize variety and an insect-resistant GM variety on the same farm in the same season.
- The non-GM variety yields 9.2 tonnes per hectare9.2\ \text{tonnes per hectare}9.2 tonnes per hectare and the GM variety yields 10.8 tonnes per hectare10.8\ \text{tonnes per hectare}10.8 tonnes per hectare.
- The difference is 10.8−9.2=1.6 tonnes per hectare10.8-9.2=1.6\ \text{tonnes per hectare}10.8−9.2=1.6 tonnes per hectare.
- The percentage increase is 1.69.2×100=17.4%\dfrac{1.6}{9.2}\times100=17.4\%9.21.6×100=17.4% to one decimal place.
- One season on one farm is not enough to judge the variety, because weather and pest numbers vary, so the trial has to be repeated over several years and several sites.
Exam technique
Answering evaluate questions on gene technology
- Give benefits and risks in roughly equal measure, because a one-sided answer is capped however good the points are.
- Finish with a judgement that follows from what you wrote, such as saying the benefit outweighs the risk where the crop is grown well away from wild relatives.
- Separate a practical point, such as a gene spreading to a weed, from an ethical point, such as an objection to crossing species, since questions often ask for one of each.
- Use any data in the question, quoting the figures and their units, rather than answering only from memory.
Self review
- Define a transgenic organism.
- Explain how an insect-resistant GM crop lowers the amount of pesticide a farmer has to spray.
- Describe how a herbicide-tolerance gene could reach a wild plant and why that matters.
- Give two reasons why growing a GM crop over a wide area can reduce biodiversity.
- Give one ethical and one economic concern about GM crops.
- A non-GM crop yields 4.0 tonnes per hectare4.0\ \text{tonnes per hectare}4.0 tonnes per hectare and a GM crop yields 5.2 tonnes per hectare5.2\ \text{tonnes per hectare}5.2 tonnes per hectare, so calculate the percentage increase.
