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5.3.9Energy Transfers In and Between Organisms (A Level only)

Farming and Production — AQA A Level Biology 7402 Revision Notes & Topical Questions

5 min read 8 parts Lesson 21 of 30 1 quiz

📚 AQA A Level Biology 7402 Hub / Topical Revision
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Lesson summary

5.3.9 Farming and Production — AQA A Level Biology 7402 notes: Evaluate agricultural practices that increase net primary and secondary production and their environmental effects.The aim of intensive farming is to increase the proportion of the energy captured that ends up in a human food product.

  • increasing the energy input
  • reducing energy losses
  • Fertilisers
  • Irrigation
  • Pesticides
  • herbicides

Part 1 of 6Principle: raise NPP and reduce waste

The aim of intensive farming is to increase the proportion of the energy captured that ends up in a human food product. Farmers can increase net production by increasing the energy input to the system, such as light, water and nutrients, or by reducing energy losses to pests, weeds, disease and the animal's own respiration.

Part 2 of 6Crop production

Crop production
Fertilisers
(nitrates, phosphates, potassium) remove mineral limiting factors, increasing growth and leaf area.
Irrigation
Irrigation and greenhouse conditions prevent water shortage and allow control of temperature, carbon dioxide and light.
Pesticides
Pesticides insecticides and fungicides reduce loss of biomass to pests; herbicides reduce competition for light, water and minerals. Biological control and integrated pest management are alternatives using predators, parasites or pathogens.
Selective breeding and genetic improvement
Selective breeding and genetic improvement produce varieties with high yield, short stems, disease resistance and good partitioning of NPP into edible parts.
Crop rotation
Crop rotation and planting nitrogen-fixing legumes maintain soil nutrients and break pest cycles.

Part 3 of 6Animal production

Secondary production is raised by cutting respiratory and other losses.

1
Animals may be kept in confined indoor spaces to restrict movement, kept warm to cut the energy needed for thermoregulation, and fed a high-energy diet that is easily digested.
2
Antibiotics or vaccinations reduce loss through disease, and selective breeding gives breeds with high growth rates and food conversion.
3
Slaughtering at the stage when growth rate is highest, before adult maintenance respiration dominates, maximises production per unit of food.
4
Fish farming has efficient conversion because fish are ectotherms and buoyed by water.

Part 4 of 6Evaluating the consequences

Higher production brings costs, and evaluation questions require balanced points.

1
Fertiliser run-off causes eutrophication; pesticides can kill non-target species and accumulate in food chains; monocultures lower biodiversity and soil quality.
2
Intensive animal rearing raises ethical issues of welfare, can spread disease and the overuse of antibiotics can select for resistant bacteria.
3
On the other hand, intensive methods provide cheaper, more reliable food for a growing population and need less land per unit of food produced.

Sustainable approaches try to balance output with conservation, for example with reduced chemical use, hedgerow retention and integrated pest management.

Part 5 of 6Worked example and exam technique

Data from a trial may show that a field treated with nitrogen fertiliser produced 8.4 t ha-1 of wheat compared with 6.0 t ha-1 for an untreated control.

Worked example and exam technique
The percentage increase is (8.4 − 6.0) / 6.0 × 100 = 40%.
To judge whether the benefit justifies the cost you would also consider the price of fertiliser, the effect on neighbouring water bodies and whether a further increase in fertiliser would still raise yield (the response levels off when another factor becomes limiting).

When asked to compare the energy efficiency of two food products, for example beef and soya, trace the energy from sunlight.

Worked example and exam technique
Growing soya for direct human consumption involves one conversion, light to plant.
Producing beef adds a second, plant to cow, in which perhaps 90% of the energy in feed is lost, so many more hectares are required per unit of energy eaten.
This is why changing to a diet with more plant material can free up land and reduce emissions.

Biological control is a useful example of a sustainable alternative.

Worked example and exam technique
A predatory insect or a parasitic wasp introduced to a glasshouse can keep a pest below the level at which it harms yield, reducing the need for pesticides.
Its disadvantages are that it can be slower, may not eliminate the pest entirely, and an introduced species might become a pest itself if it feeds on non-target species.
Always weigh both sides when asked to evaluate.

Whatever the system, a good evaluation names the practice, links it to the energy loss it reduces, states the benefit to yield, then gives a named environmental or ethical cost.

Worked example and exam technique
For example, herbicides cut competition so more light reaches the crop and NPP rises, but they may reduce the number of weed species that support insects, so food for birds falls and biodiversity declines.
Structuring the answer this way earns the marks reliably.

Part 6 of 6Exam-style questions

  1. Explain how keeping cattle indoors in a warm shed can increase their net production. [3]3 marks

  2. Discuss the advantages and disadvantages of using nitrogen fertiliser on a wheat crop. [4]4 marks

Key terms

TermMeaning
MonocultureGrowing a single crop species over a large area.
Biological controlUsing a natural predator, parasite or pathogen to control a pest.
Integrated pest managementCombination of control methods to keep pests below damaging levels.
Selective breedingChoosing individuals with desired traits to breed from repeatedly.
Intensive farmingFarming that maximises yield per unit area using high inputs.
SustainableMeeting present needs without damaging future productivity.

Avoid these mistakes

1
Saying fertilisers feed the plant directly. Plants make their own food; minerals are used to build molecules.
2
Describing eutrophication without the sequence of events.
3
Giving only advantages when asked to evaluate.
4
Stating that pesticides always raise yield without mentioning non-target effects or resistance.

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