Genetic Technology: Question 5

Worked solution

Part (a): How insect-resistant cotton increases yield

Once the Bacillus thuringiensis gene has been inserted into the cotton plant’s genome (with an appropriate promoter so it is expressed), the plant’s own cells transcribe and translate the gene, producing the toxin protein within the plant tissue. Insect larvae that feed on the leaves or other parts of the cotton plant ingest this toxin, which kills them or severely reduces their feeding.

Because fewer insect pests survive to damage the crop, less of the cotton plant’s tissue is destroyed by feeding, and fewer whole plants are lost to pest damage. A larger share of the crop therefore survives to maturity and can be harvested, increasing the overall yield of usable cotton fibre compared with a non-resistant variety grown under the same pest pressure.

Part (b): A further example of genetic engineering improving productivity

Herbicide-resistant soybean is a good named alternative. A gene (often originally from a bacterium) is inserted into soybean plants, making them resistant to a specific herbicide that would otherwise damage or kill them. This allows farmers to spray the whole field with that herbicide: the herbicide kills competing weeds, but the genetically modified soybean plants survive unharmed. With less competition from weeds for light, water and mineral ions, the soybean plants can grow more vigorously, increasing yield.

(GM salmon, in which the fish carry an inserted growth-hormone gene under a different promoter so that they grow to market size faster, is an equally acceptable named example, provided the explanation clearly links the genetic modification to increased productivity.)

Part (c): Ethical and social implications of insect-resistant GM cotton

A balanced discussion should weigh both potential benefits and potential concerns.

Potential benefits:

• Higher and more reliable yields can improve food and fibre security for a growing population, and can increase the income of farmers who grow the crop.
• Because the crop produces its own protection against certain pests, farmers may need to apply less chemical insecticide, which can reduce costs to farmers and reduce the amount of insecticide released into soil and water systems.

Potential concerns:

• The inserted gene could spread beyond the cultivated crop into wild or related plant populations through cross-pollination (gene flow), which is difficult to reverse once it has occurred.
• Insect populations exposed to the toxin over many growing seasons could evolve resistance to it through natural selection, gradually reducing the effectiveness of the modification.
• Seed for genetically modified crops is often patented and sold by a small number of companies, so farmers may become dependent on repeatedly purchasing seed each season rather than saving seed from their own harvest, as is traditional in many farming communities.
• Some consumers, communities or governments may distrust the safety of genetically modified crops for human consumption or for the environment, or may object on ethical or cultural grounds, which can limit public acceptance and market access even where the crop performs well agronomically.

A government weighing these factors has to balance the potential gains in yield and reduced insecticide use against the environmental, economic and social risks before deciding whether to approve widespread planting.

Final answers

• (a) The plant expresses the bacterial gene and produces the toxin, killing/deterring insect pests that feed on it, so less crop is lost to pest damage and yield increases.
• (b) Herbicide-resistant soybean (or GM salmon) is an acceptable further example, with the genetic modification explained as directly increasing productivity.
• (c) A balanced discussion should include benefits such as increased food/fibre security, farmer income and reduced insecticide use, alongside concerns such as gene flow to wild populations, evolving pest resistance, farmer dependence on purchased seed, and public concern over GM safety and ethics.