Sources of food
Plant needs, limiting factors, raising food production, environmental impacts and sustainable farming.
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Before you begin
Growing enough food for a rising population on limited land. This topic covers what plants need to grow, the methods farmers use to grow more food, the harm those methods can do to the environment, and more sustainable ways to control pests.
Be comfortable with: the idea that a fair test changes one thing and keeps everything else the same.
Learning goals
- Requirements for plant growth
- Why production must improve
- Fertilisers
- Pesticides and herbicides
- Slash-and-burn
- Fertiliser pollution
- Pesticide and herbicide pollution
- Slash-and-burn damage
- Biological control
- Improved varieties
- Intensive farming
- Uses of plant hormones
Syllabus statements covered
- state that plants need air, light, water, nutrients and appropriate pH for photosynthesis and growth
- show an understanding that the increase in world population and the limitation in space to grow food lead to the need to improve food production
- describe how the following methods improve crops produced: — use of fertilisers
- describe how the following methods improve crops produced: — use of pesticides and herbicides
- describe how the following methods improve crops produced: — slash-and-burn
- describe the environmental problems associated with the following methods: — use of fertilisers (water contamination leading to increased growth of algae and water weeds)
- describe the environmental problems associated with the following methods: — use of pesticides and herbicides (soil and water contamination leading to transfer of harmful substances along the food chain)
- describe the environmental problems associated with the following methods: — slash-and-burn method (haze leading to breathing difficulties and deforestation leading to soil erosion)
- explain how the use of biological control reduces the need for pesticides (limited to control of prey by their predators)
- describe how food production can be improved by: — improving varieties of plants and animals
- describe how food production can be improved by: — intensive farming methods for crops and farm animals (e.g. chicken, fish) [details of technologies are not required]
- state that plant hormones are used as weed killers, and in regulating growth and ripening of fruits
Lessons
Work through them in order.
- What plants need to growExplain the roles of air, light, water, mineral nutrients and pH, and judge plant-growth evidence from a fair test.
- Increasing food productionMatch fertilisers, pesticides, herbicides and slash-and-burn to the production problem each tackles.
- Environmental impacts of food productionTrace how fertiliser runoff, pesticides and land clearing can affect water, food chains, air and soil.
- Biological control of crop pestsExplain how predators can reduce pest numbers, crop damage and the need for pesticides, and evaluate the limits of the evidence.
- Varieties, intensive farming and plant hormonesDistinguish improved plant and animal varieties, intensive farming and agricultural uses of plant hormones by their purposes.
Practise and check
Or choose
Topic reference
Quick reference
| Problem | Method | Possible cost |
|---|---|---|
| soil lacks mineral nutrients | fertiliser | runoff makes algae grow in streams |
| insects eat the crop | pesticide | harms other living things; passes along food chains |
| weeds compete with the crop | herbicide | harms other plants and animals |
| no land to plant | slash-and-burn | haze, and soil erosion |
| pests, with less chemical use | biological control | the predator may affect other living things |
Core knowledge to remember
- Plants make their own food by photosynthesis, using light, carbon dioxide and water.
- Plants also need mineral nutrients and soil with a suitable pH.
- The limiting factor is the need that is holding growth back; adding more of something else does not help.
- An improved variety is the kind of plant or animal grown; intensive farming is how it is managed.
Common mistakes
- Saying plants get their food from the soil.
- Choosing fertiliser for a problem caused by pests or weeds.
- Saying fertiliser stays in the field.
- Calling biological control a kind of pesticide.