The shape of the lesson
By the end of the lesson, learners can
- Five ways to grow more food: In the sim a wheat field starts with no help at all: weeds (purple) grow between the crop and insect pests (black) swarm over it.
- Monocultures and intensive livestock: Switch the sim from crop field to intensive livestock.
- Machinery: larger areas, more efficiently.
- Fertilisers: mineral ions, better yields. Insecticides: fewer insect pests. Herbicides: less competition from weeds.
- Selective breeding: crops and livestock with higher production.
- Every advantage has a cost: biodiversity, disease spread, pollution, animal welfare.
One picture every idea returns to
Humans have increased food production by using agricultural machinery to farm larger areas efficiently, chemical fertilisers to improve yields, insecticides to improve quality and yield, herbicides to reduce competition with weeds and selective breeding to improve production by crop plants and livestock. Large-scale monocultures and intensive livestock production give high yields at low cost, but reduce biodiversity, spread disease and pollute the environment.
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, More food, at a price.. The human population keeps growing, and farmers have found ways to grow far more food on each hectare: machines, fertilisers, pesticides and selectively bred crops and animals. 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: Five ways to grow more food | In the sim a wheat field starts with no help at all: weeds (purple) grow between the crop and insect pests (black) swarm over it. Project tab 1 of the lab (Increasing food production on a farm) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Monocultures and intensive livestock | Switch the sim from crop field to intensive livestock. | Frayer Model |
| 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, 20 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 Monocultures and intensive livestock, 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.
Frayer Model
Pairs fill a four-box grid for the key term: definition, characteristics, examples and non-examples. The non-examples box is where the misconceptions surface, so give it the most time.
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 |
|---|---|
| Insecticides kill insects; herbicides kill weeds (plants). | Both are pesticides. Do not mix them up, and remember fertilisers supply mineral ions, not "food" for the plant: plants make their own food by photosynthesis. |
| "Higher profit" on its own is a weak answer. | Say why: higher yield per hectare, less labour per tonne, or less energy wasted by the animals. |
Food supply: worksheet
6 questions, 20 marks. Written in the style of the papers; no past paper question is reproduced.
State four ways in which humans have increased food production and give one reason each method raises yield.
Describe two advantages and two disadvantages of growing a crop as a large-scale monoculture.
A field produced 3.0 tonnes of wheat per hectare. After fertiliser was added the yield was 4.5 tonnes per hectare. (a) Calculate the percentage increase in yield. (b) Suggest why the farmer must also take care not to add too much fertiliser.
Discuss the advantages and disadvantages of intensive livestock production.
A farmer says: "Spraying insecticide over my whole monoculture is the best way to protect it." Give three reasons why this may harm the wider ecosystem.
Explain how selective breeding is used to improve milk production in dairy cattle.
Answer key and marking notes
- Agricultural machinery: one farmer can farm a larger area of land efficiently.
- Chemical fertilisers: supply mineral ions such as nitrate, so plants grow more.
- Insecticides: kill insect pests, so less of the crop is damaged.
- Herbicides: kill weeds that compete with the crop for light, water and ions. (Also accept selective breeding: higher-yielding varieties or breeds.)
- Advantage: machinery can be used easily for planting, spraying and harvesting.
- Advantage: high yield of a uniform crop at low cost per tonne.
- Disadvantage: low biodiversity, because hedgerows and other plants are removed, so fewer habitats and food sources.
- Disadvantage: pests and diseases of that crop spread quickly; heavy pesticide and fertiliser use can pollute nearby water.
- (a) Increase = 4.5 − 3.0 = 1.5 t/ha; (1.5 ÷ 3.0) × 100 = 50%.
- (b) Excess fertiliser is wasted money and is not taken up by the crop.
- It can be washed by rain into rivers and lakes, causing water pollution (eutrophication).
- Advantage: large amounts of meat, eggs or milk produced from a small area of land, so food is cheaper.
- Advantage: animals kept warm and with little movement waste less energy, so more of their food is converted into growth.
- Disadvantage: animals are crowded, so diseases spread easily and antibiotics are often used; animal welfare is poor.
- Disadvantage: large amounts of waste can pollute water; land is still needed to grow their feed.
- Insecticides can kill useful insects too, such as pollinators and predators of the pests.
- Removing insects reduces food for birds and other animals, altering food chains and food webs.
- Insecticide can be washed into water and harm aquatic organisms (or build up along food chains).
- Cows that produce the most milk (and bulls whose mothers did) are chosen as parents and bred together.
- Offspring with the highest milk yield are chosen to breed again, repeated over many generations.
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.
Which method of increasing food production lets one farmer work a much larger area of land efficiently?
- AAgricultural machinery
- BSelective breeding
- CChemical fertilisers
- DHerbicide sprays
Why does adding a chemical fertiliser containing nitrate increase crop yield?
- APlants use nitrate to make amino acids and proteins for growth
- BNitrate kills the insect pests that eat the crop
- CNitrate is used directly as the energy source for respiration
- DNitrate stops weeds from germinating near the crop
A farmer sprays a wheat field with a selective herbicide. How does this increase the yield of wheat?
- AWeeds are killed, so wheat has less competition for light, water and ions
- BInsects are killed, so less of the wheat is eaten
- CExtra mineral ions are added to the soil for the wheat
- DThe wheat is made resistant to all plant diseases
The bar chart shows the yield of wheat from four plots. What is the percentage increase in yield from plot A to plot D?
- A100%
- B50%
- C200%
- D4%
Which is an advantage of a large-scale monoculture?
- APlanting, spraying and harvesting can all be done by machine
- BIt supports a large number of different species
- CPests of the crop cannot spread between plants
- DIt needs no fertiliser because the soil stays rich
Hedgerows are removed to make one large field for a monoculture. Which is the most likely effect on the area?
- AFewer habitats and food sources, so biodiversity falls
- BMore species of birds nest in the open field
- CPests are controlled better by natural predators
- DSoil erosion stops because the field is larger
Chickens kept in a heated shed convert more of their food into body mass than free-range chickens. What is the best explanation?
- ALess energy is released in respiration for movement and keeping warm
- BThey digest the concentrated food without needing enzymes
- CWarm sheds let them photosynthesise in artificial light
- DThey respire anaerobically, which releases more energy
Antibiotics are often added to the food or water of animals in intensive livestock units. What is the main reason, and the main risk?
- ADisease spreads easily in crowded animals; bacteria may become resistant
- BAntibiotics speed digestion; animals may become overweight
- CAntibiotics kill viruses; the meat may become toxic
- DAntibiotics replace vitamins; animals may grow too fast
Quiz key
Tractors, ploughs and combine harvesters let one farmer cultivate and harvest a large area quickly. Selective breeding improves the organisms, fertilisers supply mineral ions and herbicides remove weeds; none of these increases the area one person can farm.
Nitrate ions are absorbed by roots and used to make amino acids, then proteins, so the plants grow more. Killing insects is the job of insecticides and stopping weeds is the job of herbicides. Nitrate is not an energy source: plants respire glucose they make by photosynthesis.
A herbicide kills weeds, so the crop no longer competes with them for light, water and mineral ions. Killing insects describes an insecticide; adding ions describes a fertiliser; herbicides give no disease resistance.
Plot A gives 4 t/ha and plot D gives 8 t/ha. The increase is 4 t/ha, and (4 ÷ 4) × 100 = 100%. 50% divides the increase by the final yield instead of the starting yield; 200% is the final yield as a percentage of the starting yield, not the increase; 4% is just the increase in tonnes.
A single crop over a large area can be managed efficiently by machine, giving a high yield at low cost. Monocultures have low biodiversity, pests spread easily because the same host plant is everywhere, and growing the same crop removes the same ions every year, so fertiliser is needed.
Hedgerows provide nesting sites, shelter and food, so removing them reduces the number of species. Birds lose nest sites rather than gaining them; natural predators of pests also lose their habitat, so pest control gets worse; and bare, open fields are more exposed to wind erosion, not less.
Free-range birds use energy from respiration to move around and to keep their body temperature up in cold weather. Restricting movement and heating the shed reduce these losses, so more food goes into growth. Digestion still needs enzymes, animals cannot photosynthesise, and anaerobic respiration releases less energy than aerobic.
Crowded animals pass bacterial diseases to each other easily, so antibiotics are used to prevent outbreaks. Heavy use selects for antibiotic-resistant bacteria. Antibiotics do not aid digestion, do not kill viruses, and are not a replacement for vitamins.
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.