The shape of the lesson
By the end of the lesson, learners can
- Three organisms, three problems solved: Choose GM salmon, herbicide-resistant soybean and Bt cotton in turn and press Apply the test.
- Ethical and social implications: The simulator ends each example with the same list of issues.
- GM salmon: Chinook growth hormone gene + pout promoter: grows all year.
- Soybean: glyphosate-resistant EPSPS: spray weeds, not the crop.
- Bt cotton: Bt toxin kills caterpillars: less insecticide.
- Always weigh benefits against gene flow, resistance, cost and choice.
One picture every idea returns to
Genetic engineering can help meet the global demand for food by improving the quality and productivity of farmed animals and crops. GM salmon carry a growth hormone gene from Chinook salmon with a promoter from ocean pout that keeps it switched on all year, so they reach market size in about half the time on less feed. Herbicide-resistant soybean carries a bacterial gene for a form of the enzyme EPSPS that is not inhibited by glyphosate, so fields can be sprayed to kill weeds without harming the crop. Insect-resistant (Bt) cotton carries a gene from Bacillus thuringiensis for a Bt toxin that kills caterpillars that eat it, so less insecticide is needed. The ethical and social implications include benefits to yield and farmers' incomes, and concerns about gene flow, effects on other species, resistance in weeds and pests, the cost of seed and control by large companies, animal welfare, labelling and consumer choice.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Feeding more people from the same land.. The world needs more food, and farmland and water are limited. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Three organisms, three problems solved | Choose GM salmon, herbicide-resistant soybean and Bt cotton in turn and press Apply the test. Project tab 8 of the lab (Genetic technology lab, GM organisms) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Ethical and social implications | The simulator ends each example with the same list of issues. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 18 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Ethical and social implications, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Herbicide-resistant crops do not kill weeds themselves. | They survive the herbicide, which allows the farmer to spray it onto the growing crop. Bt crops are the ones that make their own insecticide. |
GM crops and animals: worksheet
6 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
Explain how genetic modification has increased the productivity of farmed Atlantic salmon.
Explain how herbicide-resistant soybean allows farmers to increase yields.
State the source of the gene inserted into Bt cotton and explain how the product of this gene protects the crop.
In a trial, conventional cotton received 8 insecticide sprays per season and yielded 1.5 tonnes per hectare. Bt cotton received 2 sprays and yielded 1.8 tonnes per hectare. Calculate the percentage increase in yield and suggest two reasons why it is not certain that Bt cotton caused it.
Suggest why the widespread growing of Bt cotton may become less effective over time, and how farmers can reduce this risk.
Discuss the ethical and social implications of using genetically modified organisms in food production.
Answer key and marking notes
- A gene for growth hormone from Chinook salmon was inserted, together with a promoter from ocean pout.
- The promoter keeps the gene switched on all year, not just in the warmer months, so growth hormone is produced continuously.
- The fish reach market size in about half the time and use less feed per kilogram, so more fish are produced from the same resources.
- Glyphosate kills plants by inhibiting the enzyme EPSPS, needed to make some amino acids.
- The GM soybean has a bacterial gene for a form of EPSPS that is not inhibited, so the crop survives spraying.
- Weeds can be killed while the crop grows, reducing competition for light, water and mineral ions, so yield increases.
- The gene comes from the bacterium Bacillus thuringiensis.
- It codes for Bt toxin (a protein), which kills insect larvae such as bollworm caterpillars when they feed on the plant.
- (1.8 − 1.5) / 1.5 × 100 = 20 % increase.
- Other variables may differ between the fields, such as soil, rainfall, fertiliser or the size of the pest population that year.
- The trial may not have been repeated over several seasons or sites, so the result may not be reliable.
- Bt toxin is a selection pressure: any pests with alleles giving resistance survive and reproduce, so resistance becomes more common.
- Farmers can plant refuges of non-Bt plants nearby, so susceptible insects survive and breed with resistant ones, slowing the spread of resistance.
- Benefit: higher yields and faster growth can help meet the global demand for food from limited land.
- Benefit: less insecticide use (Bt crops) protects non-target species and farm workers; better weed control raises farmers' incomes.
- Concern: gene flow to wild relatives or wild fish, creating herbicide-resistant weeds or affecting wild populations; reduced biodiversity.
- Concern: pests and weeds may evolve resistance; seed is costly and controlled by a few companies, which may disadvantage poorer farmers.
- Concern: consumer distrust, the need for labelling and choice, animal welfare and religious or cultural objections; a balanced conclusion is expected.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
GM Atlantic salmon carry a growth hormone gene from Chinook salmon joined to a promoter from ocean pout. What is the role of the ocean pout promoter?
- Ait keeps the growth hormone gene switched on all year, including the colder months
- Bit codes for the growth hormone that makes the salmon grow faster
- Cit makes the GM salmon sterile so they cannot breed with wild fish
- Dit allows the salmon to survive in water below freezing point
How does the herbicide glyphosate kill plants?
- Ait inhibits the enzyme EPSPS, which plants need to make certain amino acids
- Bit breaks down cellulose so that the plant cell walls collapse
- Cit blocks the uptake of nitrate ions by the root hair cells
- Dit is a toxin that kills the insects that pollinate the plants
Bt toxin made by Bt cotton kills caterpillars that eat the plant, but it is considered safe for mammals. Which is the best explanation?
- Athe toxin binds to specific receptors in the gut of certain insect larvae, which mammals do not have
- Bmammals have the Bt gene in their own DNA, so they are immune to the toxin
- Cthe toxin is made only in the roots, which mammals do not eat
- Dthe toxin is a carbohydrate, which mammals digest into glucose
The bar chart compares the number of insecticide sprays per season on conventional cotton and on Bt cotton. Calculate the percentage decrease in sprays when Bt cotton is grown.
- A70 %
- B30 %
- C233 %
- D7 %
Which is an ecological risk of farming GM salmon in open sea cages rather than in land-based tanks?
- Aescaped fish could compete with wild salmon, or pass the transgene on if they were fertile
- Bpeople eating the salmon would take up the growth hormone gene into their cells
- Cthe salmon would produce Bt toxin that kills other fish nearby
- Dthe salmon would become resistant to herbicides used on nearby farmland
The graph shows the mean mass of GM and non-GM salmon. At 18 months the GM salmon have a mean mass of 4.0 kg and the non-GM salmon 1.6 kg. By what percentage is the mean mass of the GM salmon greater than that of the non-GM salmon at 18 months?
- A150 %
- B60 %
- C250 %
- D2.4 %
Glyphosate has been sprayed for ten years on fields of herbicide-resistant soybean. Some weed species in these fields are no longer killed by it. Which explanation is correct?
- Aweeds that happened to carry resistance alleles survived spraying and reproduced, so resistance became common
- Bglyphosate caused mutations in the weeds that made them resistant
- Cthe weeds took up the resistance gene from the soybean roots in the soil
- Dthe weeds learned to close their stomata when the herbicide was sprayed
A small-scale farmer is deciding whether to grow Bt cotton. Which is a valid economic disadvantage?
- Athe GM seed costs more and may have to be bought from a company every season
- BBt cotton needs more insecticide sprays than conventional cotton
- Ccotton fibre from Bt plants is toxic to people who wear it
- DBt cotton always gives a lower yield of cotton fibre
Quiz key
A promoter is where RNA polymerase binds to start transcription; the ocean pout promoter keeps the inserted gene transcribed all year, so the salmon grow continuously instead of mainly in summer. The hormone itself is coded for by the Chinook gene. Sterility is produced separately (the fish are reared as sterile females). Ocean pout produce antifreeze proteins, but only the promoter was used here, not an antifreeze gene.
Glyphosate inhibits EPSPS, an enzyme in the pathway that makes some amino acids, so the plant cannot make proteins and dies. GM soybean has a bacterial form of EPSPS that glyphosate does not inhibit. It does not digest cellulose or block nitrate uptake. Killing insects is the role of an insecticide or Bt toxin, not a herbicide.
Bt toxins are proteins that become active in the alkaline gut of particular insect larvae and bind to receptors on their gut cells; mammals lack these receptors (and digest the protein in an acidic stomach). Mammals do not carry the bacterial Bt gene. In Bt cotton the toxin is made in the leaves and bolls that caterpillars eat, not just the roots. Bt toxin is a protein, not a carbohydrate.
Conventional cotton receives 10 sprays and Bt cotton 3. Decrease = (10 − 3) / 10 × 100 = 70 %. 30 % is the Bt value as a percentage of the conventional value, not the decrease. 233 % divides the decrease by the new value instead of the original. 7 is the difference in the number of sprays, not a percentage.
Fast-growing escapees could outcompete wild fish for food, and fertile escapees could breed with wild salmon, spreading the transgene (gene flow); this is why they are reared as sterile females on land. Genes in food are digested; they are not taken up into human cells. GM salmon carry a growth hormone gene, not a Bt toxin gene. Herbicide resistance is a feature of GM soybean, not salmon.
(4.0 − 1.6) / 1.6 × 100 = 2.4 / 1.6 × 100 = 150 %. 60 % divides the difference by the GM mass instead of the non-GM mass. 250 % is the GM mass as a percentage of the non-GM mass (4.0 / 1.6 × 100), not the increase. 2.4 is the difference in kg, not a percentage.
Repeated spraying is a strong selection pressure: rare weeds with alleles giving resistance survive and pass them on, so the resistant proportion rises (natural selection). Mutations arise randomly; glyphosate does not cause the specific mutations needed. Plants do not take up genes from neighbouring roots in this way (gene flow by pollen is possible only to closely related species). Plants cannot learn; a stomatal response is not inherited resistance.
GM seed is patented and usually more expensive; farmers are often required, or find it necessary, to buy new seed each year, which can be a burden for poorer farmers and concentrates control in a few companies. Bt cotton usually needs fewer insecticide sprays, not more. Bt toxin affects certain insect larvae and is not toxic to people. Yields usually rise where bollworm is a problem, although they depend on conditions.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.