OCR GCSE Biology A: Food security, agricultural solutions and selective breeding (J247)

This study guide follows the OCR GCSE (9-1) Gateway Science Biology A specification (J247), Version 4.0 (August 2026), for first assessment in 2018. It covers outcomes B6.2a, B6.2b and B6.2c from topic B6.2, Feeding the human race. The specification marks none of these statements in bold, so none is labelled Higher Tier only. Genetic engineering and gene technology are taught on a separate page, so they are left out here. Revise with the revision notes, then try the practice questions. Course links: OCR GCSE Biology hub, printable checklist and the free diagnostics.

What this unit covers

Outcome	You must be able to
B6.2a	Describe biological factors affecting food security: increasing human population, changing diets in wealthier populations, new pests and pathogens, environmental change, and the sustainability and cost of agricultural inputs
B6.2b	Describe and explain possible agricultural solutions: fertilisers, pesticides, hydroponics and biological control
B6.2c	Explain the impact of selective breeding of food plants and domesticated animals

The mathematical outcome for this topic is to extract and interpret information from charts, graphs and tables. Expect percentages, ratios and simple rates too.

B6.2a Biological factors affecting food security

Food security means that people can reliably get enough safe, nutritious food. It falls when food demand rises faster than supply, or when supply becomes less reliable.

Increasing human population

More people need more food. If the population grows faster than food production, the food available per person falls.

Worked example 1. A country’s population rises from 38.0 million to 44.6 million over 20 years. Its cereal output rises from 11.4 million tonnes to 12.5 million tonnes.

1. Population increase = (44.6 - 38.0) / 38.0 × 100 = 17.4%.
2. Output increase = (12.5 - 11.4) / 11.4 × 100 = 9.6%.
3. Cereal per person before = 11.4 × 10⁹ kg / 38.0 × 10⁶ = 300 kg. After = 12.5 × 10⁹ / 44.6 × 10⁶ = 280 kg (3 significant figures).
4. Output grew more slowly than population, so cereal per person fell by about 6.6%. Food security in this country is under pressure.

Changing diets in wealthier populations

As incomes rise, many people eat more meat and dairy. Animals are fed crops, and energy is lost at each stage of a food chain. It is lost as heat from respiration, in waste, and in parts of the animal that humans do not eat. So a meat-based diet needs more farmland than a plant-based diet for the same energy.

Worked example 2. A field produces crops containing 600 000 kJ of energy. Assume 10% of the energy passes from crop to cattle and that people can use all of the energy in whatever they eat. These values are supplied for the example.

1. People eat the crop directly: up to 600 000 kJ is available.
2. Cattle eat the crop: 600 000 × 0.10 = 60 000 kJ is stored in beef.
3. The crop route gives 600 000 / 60 000 = 10 times as much energy.

New pests and pathogens

Pests (such as insects) eat or damage crops and livestock. Pathogens (fungi, bacteria, viruses) cause disease. Global trade and travel move them to places where plants and animals have no resistance. A new fungal disease can destroy a large share of a crop in a season. Pests and pathogens can also evolve resistance to the chemicals used against them.

Environmental change

Drought, flooding, higher temperatures and changing rainfall alter which crops grow where. Salty water from rising seas can ruin low-lying farmland. Extreme weather can damage a harvest in a single event. Habitat loss also reduces pollinators, and many crops need them.

Sustainability and cost of agricultural inputs

Inputs include fertilisers, pesticides, fuel, water, seed and machinery. Fertiliser production uses energy, and phosphate is mined from limited reserves. If an input becomes too expensive, farmers use less of it and yields drop. Farming is sustainable when it can continue without using up resources or harming the ecosystems it depends on.

B6.2b Agricultural solutions

Fertilisers

Fertilisers supply mineral ions that crops take up from soil. Harvesting removes these ions from a field, so they have to be replaced.

Element (ion)	Used for	Deficiency sign
Nitrogen (nitrate)	Making amino acids and proteins	Stunted growth, yellow older leaves
Phosphorus (phosphate)	DNA, ATP and cell membranes	Poor root growth, purple-tinged leaves
Potassium	Enzyme activity and water balance in cells	Yellow leaves with dead patches

Worked example 3. A trial gives the wheat yields below for different nitrogen rates. Assume wheat sells at £200 per tonne and nitrogen costs £1.20 per kg (both supplied).

Nitrogen applied (kg per hectare)	0	50	100	150	200
Yield (tonnes per hectare)	3.1	5.2	6.8	7.5	7.7

1. Gain for each extra 50 kg: 2.1, 1.6, 0.7 and 0.2 tonnes. Gains shrink, because another factor (water, light or another ion) starts to limit growth.
2. Increase from 0 to 100 kg = (6.8 - 3.1) / 3.1 × 100 = 119%.
3. From 100 to 150 kg: extra income = 0.7 × 200 = £140; extra cost = 50 × 1.20 = £60. Worth it.
4. From 150 to 200 kg: extra income = 0.2 × 200 = £40; extra cost = £60. Not worth it, and more fertiliser can run off.

Eutrophication is the harmful result of excess fertiliser reaching water. Explain it in order:

1. Rain washes nitrates and phosphates from fields into streams and lakes (run-off).
2. Algae grow rapidly, forming a bloom on the surface.
3. Light cannot reach plants below the bloom, so they stop photosynthesising and die.
4. Bacteria decompose the dead material and use up oxygen in aerobic respiration.
5. Fish and other animals suffocate.

Pesticides

Pesticides kill organisms that reduce yield. Insecticides kill insects, herbicides kill weeds (which compete for light, water and ions), and fungicides kill fungi.

• Benefits: less crop lost to pests, weeds and disease; higher and more reliable yields.
• Risks: they can kill harmless species, including pollinators. Some persist and build up along food chains. Pests can evolve resistance, because individuals that survive pass on resistance alleles. They cost money, and residues may reach water.

Hydroponics

In hydroponics plants grow with their roots in a solution of mineral ions instead of soil. The solution is aerated, and the plant is supported.

• Advantages: the farmer controls ion concentrations and pH exactly. Growth is fast, soil pests and weeds are avoided, water can be recycled, and food can be grown where soil is poor or land is scarce.
• Disadvantages: high set-up and energy costs (pumps, lighting, heating), skilled management, and disease can spread quickly through shared solution. A power failure can lose the crop.

Worked example 4. Five hydroponic lettuces have masses of 168, 175, 172, 160 and 165 g. The mean mass of soil-grown lettuces is 131 g.

1. Mean = (168 + 175 + 172 + 160 + 165) / 5 = 840 / 5 = 168 g.
2. Percentage greater = (168 - 131) / 131 × 100 = 28%.
3. Only five plants were measured, so repeat with more plants before judging the difference.

Biological control

Biological control uses a living organism to reduce a pest: a predator, a parasite or a pathogen of the pest. Ladybirds eat aphids. A parasitic wasp (Encarsia formosa) is used against whitefly in glasshouses. The bacterium Bacillus thuringiensis infects caterpillars.

• Advantages: no chemical residues, usually specific to the pest, and resistance is less likely to arise than with chemicals.
• Disadvantages: slow to work, rarely removes the pest completely, and depends on conditions suiting the control organism. An introduced species may harm other species. Cane toads, released in Australia to control beetles, became a pest themselves.

Pest numbers usually rise first, then the predator numbers rise, and then pest numbers fall. This delay appears in graphs, so read both lines together.

B6.2c Impact of selective breeding

Selective breeding (artificial selection) is the process by which humans choose which organisms breed, to produce offspring with desired characteristics. The steps are:

1. Choose parents with the characteristic wanted, such as disease resistance or high yield.
2. Breed them together.
3. From the offspring, select those showing the characteristic most strongly, and breed them.
4. Repeat over many generations.

Food plants are bred for yield, size, taste, ripening time, disease resistance and drought tolerance. Domesticated animals are bred for milk yield, egg numbers, meat quantity, growth rate and wool.

Worked example 5. Hens bred over eight generations raise mean egg production from 180 to 288 eggs per year.

1. Increase = 288 - 180 = 108 eggs.
2. Percentage increase = 108 / 180 × 100 = 60%.
3. Mean gain per generation = 108 / 8 = 13.5 eggs.
4. To show the rise is genetic, keep every generation on the same diet and housing.

Impact on food security: higher yields from the same land, more uniform produce, and crops suited to local conditions. Less land and fewer inputs are needed per unit of food.

Risks and costs:

• Repeatedly breeding from a few individuals reduces genetic variation. If a new disease appears and no individual carries a resistance allele, the whole crop or herd can be lost.
• Related individuals share harmful recessive alleles, so inbreeding raises the chance of inherited disorders.
• Animals bred for fast growth can suffer welfare problems, such as leg problems from heavy bodies.
• It is slow, taking many generations.

Keeping wild relatives and seed banks preserves alleles that breeders can use later.

Common errors

• Writing that fertiliser “feeds” plants. Plants make their own food by photosynthesis. Fertiliser supplies mineral ions.
• Saying eutrophication kills fish because of “toxic algae”. The main cause is oxygen use by decomposers.
• Saying selective breeding “creates new genes”. It selects alleles that already exist in the population.
• Calling hydroponics “plants grown in water”. It is a solution of mineral ions.

Test yourself with the practice questions and check weak spots with the diagnostics.

Official syllabus

OCR, GCSE (9-1) Gateway Science Biology A (J247), Version 4.0 (August 2026), for first assessment in 2018, topic B6.2 Feeding the human race, outcomes B6.2a to B6.2c.