1. Core: How Humans Increase Food Production★★☆☆☆⏱ 12 min

As the human population grows, more food is needed. Syllabus 20.1 requires you to describe five specific ways humans have increased food production. Learn all five and how each one raises the quantity or quality of food produced.

• Agricultural machinery (e.g. tractors, combine harvesters): allows much larger areas of land to be farmed and improves the efficiency of sowing, treating and harvesting crops

• Chemical fertilisers: add mineral ions such as nitrate, phosphate and potassium to the soil to improve crop yields

• Insecticides: kill insect pests that eat or damage crops, improving the quality and yield of the crop

• Herbicides: kill weeds so that crop plants face less competition for light, water and mineral ions

• Selective breeding: breeding crop plants and livestock that have desired features (e.g. high yield, disease resistance) over several generations to improve production

Monocultures make farming efficient, but growing only one crop species over a large area has clear trade-offs (syllabus 20.1.2):

• Advantages: machinery can be used efficiently over large uniform areas; a single crop is easier to sow, manage and harvest; produces a high yield of one valuable crop

• Disadvantages: low biodiversity, as few other species can live there; pests and diseases spread rapidly through the uniform crop; the same mineral ions are removed from the soil each year, so more fertiliser is needed

Intensive livestock production keeps animals in controlled, often crowded, conditions to maximise food output. Its advantages and disadvantages are also examinable (syllabus 20.1.3):

• Advantages: more meat, eggs or milk produced in a smaller area and in less time; food is cheaper for consumers; restricting movement and keeping animals warm means less energy is lost, so more food energy is converted into body mass (higher efficiency)

• Disadvantages: raises animal-welfare concerns; diseases spread easily in crowded conditions, often leading to routine antibiotic use and the risk of antibiotic resistance; large amounts of animal waste can pollute the surrounding environment

Exam tip:

For 20.1, memorise the five named methods (machinery, chemical fertilisers, insecticides, herbicides, selective breeding). When asked to evaluate monoculture or intensive livestock, always give both advantages and disadvantages.

2. Core: Biodiversity and Habitat Destruction★★★☆☆⏱ 12 min

Biodiversity is the number of different species that live in an area (syllabus 20.2.1). Human activity often destroys habitats, reducing biodiversity and disrupting ecosystems.

The syllabus (20.2.2) gives three reasons for habitat destruction:

• Increased area for housing, crop plant production and livestock production (e.g. clearing forests and draining land for farms and settlements)

• Extraction of natural resources (e.g. mining and quarrying, and logging for timber)

• Freshwater and marine pollution, which damages aquatic habitats

Humans can also harm habitats indirectly: by altering food webs and food chains (for example through overharvesting a species), humans can have a negative impact on the whole habitat (syllabus 20.2.3).

Deforestation is a key example of habitat destruction. You must be able to explain its undesirable effects (syllabus 20.2.4): reducing biodiversity, extinction of species, loss of soil (erosion), flooding, and an increase of carbon dioxide in the atmosphere.

Exam tip:

For deforestation, the five mark-scheme effects are: reducing biodiversity, extinction, loss of soil, flooding, and increase of CO2. Always link the cause directly to the effect, e.g. 'roots bind soil, so removing trees leads to soil erosion'.

3. Core: Structured Exam Practice★★★☆☆⏱ 8 min

Practise writing full answers to these exam-style questions to reinforce your knowledge, as the exam includes structured response questions worth 3-8 marks.