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

These revision notes condense outcomes B6.2a, B6.2b and B6.2c of the OCR GCSE (9-1) Gateway Science Biology A specification (J247), Version 4.0 (August 2026), for first assessment in 2018. None of these statements is in bold, so none is labelled Higher Tier only. For full explanations and worked examples, read the study guide. When you are ready, use the practice questions, the OCR GCSE Biology hub, the printable checklist and the free diagnostics. Genetic engineering is on a separate page.

B6.2a Factors affecting food security

Food security: people can reliably get enough safe, nutritious food.

Factor	Why it threatens supply
Increasing population	More mouths; food per person falls if output grows more slowly
Changing diets in wealthier populations	More meat and dairy; energy is lost at each trophic level, so more land per unit of energy
New pests and pathogens	Spread by trade and travel to places with no resistance; can destroy crops or herds
Environmental change	Drought, flooding, heat, salt water; fewer pollinators
Sustainability and cost of inputs	Fertiliser, fuel, water and pesticides cost money, and some resources are limited

Method for a percentage change:

1. Subtract old from new.
2. Divide by the old value.
3. Multiply by 100.

Example: population from 7.0 to 8.0 billion gives (8.0 - 7.0) / 7.0 × 100 = 14.3%.

Energy through food chains: if 10% passes to the next stage, then 40 000 kJ in plants gives 4 000 kJ in a herbivore and 400 kJ in a carnivore that eats it. The value is supplied in questions.

B6.2b Agricultural solutions

Fertilisers

Ion	Plant uses it for	Deficiency
Nitrate	Amino acids, proteins	Stunted, yellow older leaves
Phosphate	DNA, ATP, membranes	Poor roots, purple leaves
Potassium	Enzymes, water balance	Yellow leaves, dead patches

• Benefit: replaces ions removed at harvest, so yield stays high.
• Diminishing returns: each extra dose adds less yield, so judge extra income against extra cost.
• Risk: run-off causes eutrophication.

Eutrophication in steps:

1. Fertiliser washes into water.
2. Algal bloom.
3. Light blocked, so submerged plants die.
4. Decomposers respire aerobically and use up oxygen.
5. Fish and other animals suffocate.

Pesticides

Type	Kills
Insecticide	Insects
Herbicide	Weeds
Fungicide	Fungi

• Benefit: less crop lost, so higher and steadier yields.
• Risks: harm to non-target species such as pollinators; build-up along food chains; resistance evolves; cost.
• Resistance: a few pests are resistant by chance, they survive, they breed, and resistance spreads.

Hydroponics

Roots in an aerated solution of mineral ions, with support for the plant.

Advantages	Disadvantages
Exact control of ions and pH	High set-up and energy costs
No soil pests or weeds	Skilled management
Water can be recycled	Disease spreads in shared solution
Works where soil is poor	Power failure can lose the crop

Biological control

Use a predator, parasite or pathogen of the pest.

Advantages	Disadvantages
No chemical residues	Slow and incomplete
Specific to the pest	Needs suitable conditions
Resistance less likely	Introduced species may become a pest

Examples: ladybirds against aphids; Encarsia formosa against whitefly; Bacillus thuringiensis against caterpillars. In a graph, the predator peak follows the pest peak.

B6.2c Selective breeding

Steps:

1. Choose parents with the wanted characteristic.
2. Breed them.
3. Select the best offspring and breed those.
4. Repeat for many generations.

Plants	Animals
Yield, size, taste, disease resistance, drought tolerance	Milk yield, egg numbers, meat, growth rate, wool

Impact:

• Gain: more food from the same land and inputs; uniform produce.
• Cost: less genetic variation, so a new disease can wipe out a crop or herd.
• Cost: inbreeding raises inherited disorders; fast-growing animals can have welfare problems.
• Slow: many generations are needed.
• Selection acts on alleles already present. It does not create new ones.

Worked reminders

Cost against benefit. A grower pays £1.20 per kg for nitrogen and sells grain at £200 per tonne (supplied). An extra 50 kg of nitrogen raises yield by 0.7 t.

1. Extra income = 0.7 × 200 = £140.
2. Extra cost = 50 × 1.20 = £60.
3. Income is larger than cost, so the extra fertiliser pays. If the gain were only 0.2 t, income would be £40, below the £60 cost, and it would not.

Reading a table or graph.

1. Read the axis titles and units.
2. State the trend in words, with figures from the data.
3. Look for where the line levels off, and name a possible limiting factor.
4. Use the numbers in any calculation, and quote units.

Explaining a pest graph. If aphid numbers climb for four weeks and then fall after ladybird numbers rise, write: ladybirds eat aphids, so more ladybirds means fewer aphids; the ladybird peak comes after the aphid peak because the predators need time to reproduce.

Selective breeding calculation. A herd’s mean milk yield goes from 5 000 to 6 200 litres per year over four generations (made-up values). Increase = 1 200 litres; percentage = 1 200 / 5 000 × 100 = 24%; gain per generation = 300 litres. To show the cause is genetic, keep feed and housing the same.

Evaluate questions. Give a benefit and a cost for each method, then a judgement that refers to the situation, such as cost, land, skills or the environment. One-sided answers rarely cover the whole question.

Command words for this topic

Command word	What to do here
Describe	Say what happens, in order, for example the steps of selective breeding
Explain	Give a reason for each point, for example why oxygen falls in a polluted lake
Suggest	Apply what you know to an unfamiliar farm or data set
Calculate	Show the working and give units
Evaluate	Weigh benefits against costs and reach a judgement

Must-know distinctions

• Fertiliser vs pesticide: a fertiliser supplies ions; a pesticide kills pests.
• Hydroponics vs soil farming: no soil, ions supplied in solution.
• Biological control vs pesticide: a living organism against a chemical.
• Selective breeding vs natural selection: humans choose the parents.

Quick self-test

1. Define food security.
2. Give two reasons why a diet rich in meat puts more pressure on farmland.
3. A farm’s untreated field loses 20% of a potential 15 t per hectare to pests. How many tonnes per hectare does a pesticide save, and what is the harvest?
4. Which mineral ion is used to make amino acids, and what is one sign of deficiency?
5. Put in order: algal bloom, fish die, fertiliser run-off, decomposers use oxygen, light blocked.
6. Give two advantages and one disadvantage of hydroponics.
7. Describe one example of biological control and one drawback of the method.
8. Explain how pesticide resistance spreads in an insect pest.
9. Mean tomato mass rises from 48 g to 66 g after selective breeding. Calculate the percentage increase.
10. Explain why selective breeding from a few parents makes a crop vulnerable to a new disease.
11. 40 000 kJ of crop energy passes to a herbivore, then to a carnivore, at 10% each time. How much energy reaches the carnivore?

Answers

1. People can reliably get enough safe, nutritious food.
2. Energy is lost at each stage, so animals need much more crop energy than humans get back; and the animals need feed crops grown on land.
3. 20% of 15 = 3 t per hectare saved; harvest 15 - 3 = 12 t per hectare.
4. Nitrate; stunted growth or yellow older leaves.
5. Fertiliser run-off, algal bloom, light blocked, decomposers use oxygen, fish die.
6. Any two: exact control of ions and pH; no soil pests; recycled water; use where soil is poor. Disadvantage: high set-up or energy cost, or disease spreading in the solution.
7. For example ladybirds against aphids; drawback: slow, or does not remove the pest completely.
8. A few insects are resistant by chance; the pesticide kills the rest; the survivors breed and pass on the resistance allele, so the proportion of resistant insects rises.
9. (66 - 48) / 48 × 100 = 37.5%.
10. Few parents means little variation, so the plants are genetically very similar. If none carries an allele for resistance, all are susceptible and the disease can spread through the whole crop.
11. 40 000 × 0.10 × 0.10 = 400 kJ.

Where marks are usually lost

• Writing that fertiliser is “plant food”. Say it supplies mineral ions.
• Leaving out the oxygen step in eutrophication: decomposers use oxygen, and that is what kills fish.
• Saying pesticides make pests “immune”. Describe survival of resistant individuals and their offspring.
• Describing a disadvantage of hydroponics as “expensive” without saying what costs.
• Dividing by the final figure in a percentage change, when the original figure is the base.
• Forgetting units: kJ, tonnes per hectare or grams.
• Stating that selective breeding is “unnatural” instead of giving a genetic reason such as lost variation.
• Reading one line of a graph. Compare the pest and predator lines.

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.