B6.2 Feeding the human race

Why this matters

Humans have been farming for around 12 000 years, but the scale, speed and technology have changed enormously in the last century. Selective breeding produced cattle that grow faster and crops that yield more grain. Industrial fertilisers and pesticides, machinery and irrigation pushed yields higher still — but at a cost in soil quality, biodiversity, pollinator health and water quality. Meanwhile the global population keeps climbing and richer diets demand more meat, which is biologically expensive: every trophic level loses about 90% of its biomass to respiration, faeces, movement and parts not eaten, so a hectare of wheat can feed roughly ten times as many people as the same hectare used to graze cattle. Modern food production must balance four pressures simultaneously: feeding more people, doing it sustainably (so land, oceans and climate survive), respecting animal welfare, and keeping food affordable. Biotechnology — fermenters growing fungal protein, GM crops with engineered traits, GM bacteria producing insulin and other proteins — offers some of the most promising tools, alongside smarter farming, biological pest control, and stricter fisheries management.

How to learn this topic

Build on what you already know

• OCR B4: photosynthesis as the source of all food biomass; respiration releases energy and loses some as heat.
• OCR B6.1: ecosystems, food chains, trophic levels and biomass transfer (~10% efficiency).
• OCR B2 / B6: selective breeding and genetic engineering — choosing genes and transferring them between organisms.
• OCR B2.2: recombinant DNA technology and using GM bacteria to make human insulin (cross-reference).
• KS3: ideas about sustainability, ecosystems and the carbon and nitrogen cycles.

1. Set the scene: growing population + finite land/water/fish → need sustainable methods.
2. Recall biomass losses up trophic levels — why eating producers is efficient.
3. Intensive farming: restricting movement and controlling temperature to channel biomass into meat.
4. Fertilisers — replacing nutrients, eutrophication risk if leached into rivers/lakes.
5. Pesticides — kill pests but harm non-target organisms, bioaccumulation up trophic levels, pollinator decline.
6. Biological control — natural predators/pathogens; ladybirds vs aphids, Encarsia vs whitefly.
7. Genetic engineering of crops — Bt toxin, drought tolerance, Golden Rice, herbicide resistance.
8. Sustainable fisheries: quotas and larger mesh sizes; cross-reference with biological control as both reduce environmental harm.
9. Biotechnology in fermenters — mycoprotein from Fusarium; GM E. coli producing human insulin.
10. Weigh ethical, ecological and economic trade-offs across all methods.

Key terms

biological control

Using a natural predator or pathogen to reduce the numbers of a crop pest, instead of chemical pesticides. (OCR phrase: 'natural predator/pathogen introduced to reduce pest numbers' — 'predator feeds on pest so fewer pests damage crop' — 'no chemical pollution'. Cite an example (ladybirds vs aphids, Encarsia formosa vs whitefly).)

pesticide

A chemical sprayed on crops to kill pests (insects, fungi or weeds), raising yield but often killing non-target organisms. (OCR phrase: 'pesticides kill pests' — 'can kill non-target/beneficial organisms (bees/pollinators)'. Also bioaccumulation up trophic levels.)

fertiliser

A substance added to soil to provide essential nutrients (nitrates, phosphates, potassium) so plants grow faster and larger. (OCR phrase: 'fertilisers provide essential nutrients', 'so plants grow faster/larger', 'fertiliser can leach into rivers/lakes' (causing eutrophication).)

genetic engineering

Inserting a desired/useful gene from one organism into the DNA of another (e.g. a crop plant) so the recipient gains a useful characteristic such as pest resistance, drought tolerance or higher nutritional value. (OCR phrase: 'a desired/useful gene inserted into crop plant', 'crop gains a desirable characteristic', 'pest resistance', 'more food available to feed growing population'.)

eutrophication

Excess nutrients (often from fertiliser run-off) cause rapid algal growth in a waterway; algae block light, then die; decomposers use up dissolved oxygen and fish suffocate. (Mention the chain: fertiliser leaches → algal bloom → light blocked → algae die → decomposers respire → oxygen used up → fish die.)

intensive farming

Farming methods that maximise yield from a given area by restricting animal movement, controlling temperature and using high-energy feeds. (Examiners want both: 'restrict movement' AND 'control temperature' to reduce energy lost in respiration/heat.)

fishing quota

A legal limit on the mass or number of fish that can be caught from a particular stock in a given period, used to prevent over-fishing. (Marking phrase: 'fishing quotas limit how many fish are caught' — keeps stocks at a sustainable level.)

mesh size

The size of the holes in a fishing net. Larger mesh sizes allow young (small) fish to escape so they survive to breed. (Marking phrase: 'larger mesh size lets small fish escape' — 'young fish survive to breed'.)

mycoprotein

A protein-rich food made from the fungus Fusarium grown in a fermenter on glucose syrup under aerobic conditions; sold as Quorn. (Phrases: 'grown in fermentation vats', 'Fusarium grows quickly', 'less land needed', 'high in protein'.)

fermenter

A large stirred tank in which microorganisms (Fusarium for mycoprotein, GM E. coli for insulin) are grown under controlled conditions of temperature, pH and oxygen. (Note 'sterile' and 'aerobic' for higher marks. Same technology underlies mycoprotein and recombinant insulin production.)

Bt toxin

A protein from the bacterium Bacillus thuringiensis that is lethal to insect larvae. The gene for it has been inserted into crops (Bt corn, Bt cotton) to give built-in pest resistance. (Useful concrete example of 'desired gene inserted → pest resistance'.)

Golden Rice

A GM rice variety engineered to make beta-carotene (a precursor of vitamin A) in the grain, intended to prevent vitamin-A deficiency in regions where rice is the staple. (Example of GM crop with 'improved nutritional value'.)

bioaccumulation

The build-up of a pesticide (or other persistent chemical) in the tissues of organisms; concentrations increase up the food chain (biomagnification), so top predators receive the highest dose. (Classic example: DDT in birds of prey. Links pesticides to wider ecological damage.)

sustainability

Meeting food and resource needs today without preventing future generations from doing the same — usually requires protecting land, water, biodiversity and fish stocks. (Marking phrase: 'maintained at a sustainable level' — applies to fisheries, soils and farming alike.)

Notes

Why food production is a problem

The global human population is rising past eight billion and diets are getting richer. Both trends increase pressure on land, water and wild stocks. OCR B6.2 frames the challenge as balancing yield with environmental impact: we have to grow more food without destroying the soils, pollinators, waterways and fish stocks we depend on.

Three biological levers are available: (1) make existing farming more efficient and less polluting, (2) protect wild stocks (especially fisheries), and (3) use biotechnology — fermenters, GM organisms — to grow new sources of food. Underneath everything sits trophic-level efficiency: only about 10% of biomass is transferred between levels, so eating producers directly feeds far more people per hectare than eating meat.

Trophic-level efficiency — why diet matters

At every step in a food chain about 90% of biomass is lost — through respiration (mostly heat), faeces, urine and parts not eaten. Compare two diets fed by the same hectare:

• Crops → cattle → humans (meat-based): 10 000 kg of crops → ~1 000 kg of beef → ~100 kg of human biomass.
• Crops → humans (plant-based): 10 000 kg of crops → ~1 000 kg of human biomass.

A plant-based diet supports roughly ten times as many people per hectare. Key phrases: 'biomass is lost between trophic levels', 'eating producers means more biomass is available for humans'.

Intensive farming

Intensive farming raises yield by limiting biomass losses in livestock:

• Restricting movement — less energy spent on walking, more becomes meat/milk.
• Controlling temperature — sheds are heated, so animals don't respire extra glucose to keep warm.
• High-protein feeds — speed up growth to slaughter weight.

Benefits: cheaper meat, more efficient land use. Downsides: animal welfare (stress, disease, antibiotic use), and environmental costs from the inputs (feed crops, fertilisers, energy).

Fertilisers

Fertilisers provide essential nutrients — nitrates, phosphates, potassium — that crops remove from the soil. Adding them back lets plants grow faster and larger, raising yield.

Problem: when it rains, fertiliser can leach into rivers and lakes. The extra nitrates and phosphates trigger eutrophication — algae bloom on the surface, block light, then die. Decomposing bacteria multiply and use up dissolved oxygen, suffocating fish and invertebrates. So fertiliser is a powerful tool that can wreck nearby waterways if used carelessly.

OCR mark-scheme phrases: 'fertilisers provide essential nutrients', 'so plants grow faster/larger', 'fertiliser can leach into rivers/lakes'.

Pesticides

Pesticides kill pests — insects, fungi or weeds that damage crops. Benefits are obvious: less crop damage, higher yield. Costs are equally important:

• Non-target species are killed — pesticides don't distinguish between pests and beneficial insects. Pollinators (bees) and natural predators of pests die alongside the target species.
• Bioaccumulation — fat-soluble pesticides like the old DDT build up in body tissues. Each trophic level eats many organisms from the level below, so concentrations increase up the food chain (biomagnification). Top predators (birds of prey, fish-eating birds) end up with toxic doses.
• Pollinator decline — modern neonicotinoid insecticides have been linked to declining bee colonies, which threatens pollination of many crops and wild plants.
• Pesticide resistance — pests evolve resistance, so stronger or different pesticides are needed in a chemical arms race.

OCR mark-scheme phrases: 'pesticides kill pests', 'can kill non-target/beneficial organisms (bees/pollinators)'.

Biological pest control

Biological control uses a natural predator or pathogen to reduce pest numbers instead of chemicals. Classic examples to memorise:

• Ladybirds vs aphids — ladybirds and their larvae eat aphids on crops, controlling them without spraying.
• Encarsia formosa wasp vs whitefly — this tiny parasitoid wasp lays its eggs inside whitefly larvae; the wasp larvae kill the whitefly. Widely used in greenhouse tomato production.
• Bacillus thuringiensis (Bt) — a bacterium whose spores produce a toxin lethal to caterpillars but harmless to mammals.

Advantages of biological control: no chemical pollution, no residues on food, the predator population can self-sustain so repeat applications aren't needed, and non-target organisms (bees, beneficial insects) are spared.

Disadvantages: it works more slowly than spraying, it doesn't usually wipe pests out completely (some pest is needed to keep the predator going), and the introduced predator may eat non-target species or become an invasive pest itself if it has no natural controls in the new habitat. Famous warning: the cane toad introduced to Australia to control beetles became a worse problem than the beetles.

OCR mark-scheme phrases: 'natural predator/pathogen introduced to reduce pest numbers', 'predator feeds on pest so fewer pests damage crop', 'no chemical pollution', 'introduced predator may eat non-target species'.

### Fertilisers + biological control together

A common OCR question asks how these two methods work together. The phrases: 'fertilisers provide essential nutrients', 'biological control uses natural predators/living organisms to reduce pests', 'no chemical pesticides → non-target organisms not killed', 'together: high yield + reduced pest damage'.

Genetic engineering of crops

Genetic engineering (also called genetic modification, GM) means inserting a desired/useful gene into a crop plant so it gains a desirable characteristic. The general process:

1. Identify the gene for the useful trait in some donor organism.
2. Cut it out using restriction enzymes.
3. Insert it into a vector (often Agrobacterium for plants, or a virus, or by gene gun).
4. Transform the crop cells with the vector; the gene becomes part of the crop's DNA.
5. Grow the modified cells into whole plants and select successful transformants.

Key GM crop examples to memorise:

• Bt crops (Bt corn, Bt cotton) — the Bt toxin gene from Bacillus thuringiensis makes the crop produce a protein toxic to caterpillar pests. Pest resistance built into the plant; fewer chemical pesticides needed.
• Drought-resistant crops — engineered to survive low rainfall, vital as climates dry.
• Herbicide resistance — crops survive a specific herbicide so farmers can spray weeds without killing the crop (commercial example: Roundup-Ready soy).
• Golden Rice — engineered to make beta-carotene (a precursor of vitamin A), preventing vitamin-A deficiency and childhood blindness in regions where rice is the staple.

OCR mark-scheme phrases: 'a desired/useful gene inserted into crop plant', 'crop gains a desirable characteristic', 'pest resistance', 'more food available to feed growing population'.

### Fertilisers + genetic engineering together

Another combination question. The phrases: 'fertilisers add essential nutrients', 'so plants grow faster/larger', 'desired gene inserted into crop genome', 'crop gains characteristic such as resistance to disease/pests'.

### Ethical and ecological debates around GM

• Ecological: could engineered genes spread by pollination into wild relatives? Could pest-resistant crops harm non-target insects (e.g. butterfly larvae eating Bt pollen)? Could herbicide-resistant crops promote 'superweeds'?
• Ethical: do farmers (especially in low-income countries) lose autonomy if they have to buy patented GM seed each year from large companies?
• Economic: control of food supply concentrated in a few seed companies.
• Safety: regulated commercial GM foods have not been shown to harm consumers, but some communities reject GM on principle.

A good answer acknowledges both the benefits ('more food available to feed growing population', drought/pest resistance, better nutrition) AND at least one concern.

Sustainable fisheries

Wild fish stocks are declining because adults are caught faster than they can reproduce. Two tools:

• Fishing quotas — limit how many fish (in tonnes) can be caught from a stock per year so adults survive to breed.
• Larger mesh sizes — bigger holes let young fish escape; only adults are caught, so young survive to reproduce.

Result: stocks are maintained at a sustainable level. Marking phrases: 'fishing quotas limit how many fish are caught', 'larger mesh size lets small fish escape', 'young fish survive to breed'.

Biotechnology — mycoprotein and recombinant insulin

Mycoprotein is a protein-rich food made from the fungus Fusarium venenatum. It is produced in a fermenter: glucose syrup supplies carbon and energy; nitrogen and mineral ions supply protein-building blocks; sterile oxygen is bubbled in for aerobic respiration; temperature (~30 °C) and pH are controlled. The fungus grows rapidly; biomass is harvested, purified and processed (sold as Quorn). Advantages: high in protein, low in fat, less land needed, weather-independent.

Recombinant human insulin is made by GM bacteria (E. coli): the human insulin gene is inserted into the bacterial DNA, the bacteria are grown in fermenters and produce insulin, which is purified for diabetics. Same fermenter technology, different product — and a key example of how biotechnology can solve food and medical problems.

The big picture

No single tool will feed the future. Fertilisers raise yield but can leach; pesticides kill pests but also pollinators; biological control is cleaner but slower; GM crops increase yield and nutrition but raise ecological and ethical questions; intensive farming raises efficiency but raises welfare concerns; fisheries quotas slow income now to protect stocks later. The OCR answer to 'how can we feed a growing population sustainably?' is always: combine several methods, weigh benefits against environmental and ethical costs.

Exam tips

• When OCR asks about pesticides AND fertilisers in the same question, give the benefit AND a disadvantage of each: 'pesticides kill pests | can kill non-target/beneficial organisms (bees/pollinators) | fertilisers add nutrients/nitrates to soil | fertiliser can leach into rivers/lakes'.
• For biological control always give: predator/pathogen introduced → reduces pest numbers → no chemical pollution → BUT introduced predator may eat non-target species. Add a named example (ladybirds vs aphids, Encarsia formosa vs whitefly) for credit.
• For genetic engineering questions on crops, use the four-step rubric: 'desired gene inserted into crop plant | crop gains a desirable characteristic | pest resistance (or drought tolerance / improved nutrition) | more food available to feed growing population'.
• When the question pairs fertilisers + biological control, finish with the synergy line: 'together: high yield + reduced pest damage'. Examiners look for the linkage mark.
• When the question pairs fertilisers + genetic engineering, link them as inputs: fertilisers add essential nutrients so plants grow faster/larger, AND a desired gene inserted into crop genome gives resistance to disease/pests.
• For sustainable fisheries always pair the two tools: QUOTAS (limit how many fish are caught) and LARGER MESH SIZE (lets young fish escape). Finish with 'young fish survive to breed'.
• Don't confuse the two biotechnology examples — bacteria (E. coli) produce insulin, fungus (Fusarium) produces mycoprotein. Same fermenter technology, different organism and product.

Mark-scheme phrasing

Common misconceptions

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Worked example

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Frequently asked questions

Related topics in OCR GCSE Biology A: Gateway Science (J247)

• B6.1 Monitoring and maintaining the environment
• B6.3 Monitoring and maintaining health