Ch 3 · 19.3 Genetically modified organisms in agriculture · AS & A Level Biology 9700

Topic 3 of 3 in Genetic technology — AS & A Level Biology 9700 — 48 lessons.

Introduction

Genetic engineering can help meet the world's growing demand for food by making farmed animals and crops more productive. This lesson uses the three examples the syllabus names (GM salmon, herbicide-resistant soybean and insect-resistant cotton) and then weighs up the ethical and social arguments. (Syllabus section 19.3.)

Key ideas — Feeding a growing world: three examples

The world's population and its demand for food keep rising, while land for farming is limited. Genetic engineering can raise productivity (more food from the same land, animals or time) and quality. The syllabus names three examples:

🧑‍🏫 Teacher's explanation

Imagine the world is a giant kitchen with a growing number of hungry guests, but the pantry is running out of space. To feed everyone, we can't just buy more shelves; we have to make the food we have go further and grow faster. Genetic engineering is like upgrading the 'software' of the ingredients themselves to make them more efficient.

📖 Definitions

🔍 Worked example — Easy

A standard Atlantic salmon takes 36 months to reach market size. An AquAdvantage salmon (GM) takes 18 months. Calculate the percentage reduction in time required to reach market size.

🔍 Worked example — Standard

Explain how the insertion of a growth hormone gene from a Chinook salmon into an Atlantic salmon increases productivity.

🔍 Worked example — Exam-style

A farmer uses glyphosate herbicide on a field of GM soybean. Explain why the soybean survives while the surrounding weeds die.

⚠️ Common errors

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🎯 Exam question

Key ideas — The Ti plasmid of Agrobacterium tumefaciens

Agrobacterium tumefaciens is a soil bacterium that naturally infects wounded plant tissue and transfers a section of its Ti (tumour-inducing) plasmid, called T-DNA, into the plant cell's chromosomal DNA, where genes on the T-DNA are expressed and cause uncontrolled cell division (crown gall disease). To produce transgenic plants, genetic engineers remove the disease-causing genes from the T-DNA region and replace them with a gene of interest, such as the Bt toxin gene, together with a marker gene for selection. This disarmed recombinant plasmid is reintroduced into Agrobacterium, which is used to infect wounded plant tissue or is co-cultured with plant cells; the bacterium transfers the recombinant T-DNA into the plant genome exactly as it would its own T-DNA. Cells that have taken up the new DNA are selected using the marker gene and grown on nutrient medium to regenerate whole, fertile, genetically modified plants by tissue culture.

🧑‍🏫 Teacher's explanation

Think of Agrobacterium tumefaciens as a natural 'delivery driver' that carries a package of DNA into a plant cell. In nature, this package contains instructions for making tumours, which is bad for the plant. Genetic engineers act like clever editors: they take that package, remove the 'bad' instructions (the disease-causing genes), and replace them with 'good' instructions, such as a gene that makes the plant resistant to insects.

📖 Definitions

🔍 Worked example — Easy

A scientist uses Agrobacterium tumefaciens to create insect-resistant cotton. The gene for Bt toxin is inserted into the Ti plasmid. State the purpose of including a marker gene (e.g., antibiotic resistance) alongside the Bt toxin gene in the recombinant plasmid.

🔍 Worked example — Standard

Compare the use of GM soybean (herbicide resistance) and GM cotton (insect resistance) in addressing global food demand.

🔍 Worked example — Exam-style

A farmer observes that a field of GM insect-resistant cotton has a yield of 4.5 tonnes per hectare, whereas a non-GM field has a yield of 3.2 tonnes per hectare due to pest damage. Calculate the percentage increase in yield for the GM crop.

⚠️ Common errors

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🎯 Exam question

(a) Describe how Agrobacterium tumefaciens can be used to produce a transgenic plant. [3] (b) Discuss the ethical and social implications of using genetically modified organisms (GMOs) in food production. [4] [7 marks]

Key ideas — Benefits of GMOs in food production

GM crops can substantially increase yield by reducing losses to pests and weed competition, improving food security where population growth outpaces conventional agricultural improvement. Pest-resistant crops can reduce the volume of chemical pesticide applied, lowering costs for farmers and reducing the environmental impact and health risks associated with repeated spraying. Herbicide-resistant crops allow more efficient weed control with fewer field operations, saving fuel and labour. Genetic modification can also improve nutritional quality directly, for example inserting genes for beta-carotene synthesis to produce vitamin-A-enriched "Golden Rice" for populations at risk of dietary deficiency.

🧑‍🏫 Teacher's explanation

Imagine you are running a massive community garden. Usually, you spend half your time fighting off hungry caterpillars or pulling out weeds that steal the sunlight and nutrients from your vegetables. If you could give your plants a 'built-in' defense system—like a tiny internal shield against pests—you wouldn't need to spray toxic chemicals over the whole field every week. This makes the garden more productive and safer for everyone.

📖 Definitions

🔍 Worked example — Easy

A farmer uses GM soybean crops that are resistant to a specific herbicide. Explain how this characteristic helps improve the productivity of the farm.

🔍 Worked example — Standard

Compare the use of GM cotton (insect-resistant) with conventional cotton regarding environmental impact.

🔍 Worked example — Exam-style

A population in a developing country suffers from Vitamin A deficiency. Explain how genetic engineering could be used to address this nutritional problem.

⚠️ Common errors

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🎯 Exam question

(a) State one advantage of using GM soybean crops for the farmer. [1] (b) Explain how the use of herbicide-resistant GM crops can contribute to environmental conservation. [2] [3 marks]

Key ideas — Ethical and social concerns

Pollen from herbicide-resistant crops can cross-pollinate wild relatives or unmodified crops nearby, potentially creating herbicide-resistant weeds ("superweeds") that are harder to control. Widespread cultivation of one GM variety can reduce the genetic diversity of the crop grown across a region, increasing the risk that a new pest or disease could devastate the entire harvest. Ethical concerns include whether it is right to change the genes of animals and plants at all, the welfare of GM animals such as fast-growing salmon, and the risk of GM salmon escaping and competing or breeding with wild fish. Novel proteins introduced into food crops raise concerns about previously unknown toxicity or allergenicity in consumers, requiring careful safety testing before release. GM seed is usually patented, so farmers may become economically dependent on a single supplier and may be prohibited from saving seed from their harvest, increasing costs in future seasons; there are also concerns about the unknown long-term ecological effects on non-target species and soil organisms, and insects may evolve resistance to Bt toxin. Social concerns include consumers' right to know (labelling of GM food), public distrust, and whether the benefits reach poor farmers or mainly large companies. A balanced answer weighs these against the benefits of more food, less pesticide and lower costs.

🧑‍🏫 Teacher's explanation

Imagine you are trying to fix a recipe for a massive community banquet. You decide to add a 'super-ingredient' that makes the bread rise faster and resist mold. While this solves the immediate problem of hunger, you might accidentally spill some of that ingredient into the neighbor's garden, causing their weeds to grow uncontrollably. Or, you might find that while the bread is faster, it contains a new protein that some guests are allergic to, or the company that sells the ingredient now controls everyone's kitchen.

Ch 3 · 19.3 Genetically modified organisms in agriculture · AS & A Level Biology 9700

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