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Science at key stage 3    (Year 9)

Unit 9D: Plants for food
Section 9: b. How do pests affect plant growth?

QCA

Objectives
Children should learn:
  • that toxins enter a food chain when plants take them in or are in contact with them
  • that as animals feed on plants they may accumulate toxins taken in by the plant
  • that at each step of the food chain persistent toxins are accumulated in the carnivores and that this process is bio-accumulation
  • about advantages and disadvantages of using pesticides

Activities

Outcomes
Children:
  • Remind pupils how to select information from a text and ask them to suggest ways in which information about toxins in food chains might depend on the author of the text. Provide pupils with secondary sources of information, eg textbooks, videos, environmental leaflets, about the effects on the wild bird population of bio-accumulation of toxins in the food chain, eg the effect of DDT used as a pesticide on the heron population, the osprey and other birds of prey such as sparrowhawks, and the decline in populations of some UK native birds as a result of pesticide use on farms.
  • Ask pupils to consider and evaluate the information provided, and to extract from it the key points to explain why the bird populations have declined.
  • Provide pupils with secondary sources of information about the use of pesticides, eg in controlling populations of locusts, malarial mosquitoes. Ask pupils to consider and evaluate the information provided and to extract from it the key points about which pesticides were used and why they were used.
  • describe how a persistent toxic material passes up a food chain
  • explain why pesticides and weedkillers are used, identifying the dangers
  • evaluate the information provided, relating it to the standpoint of the author of the text

Points to note
  • Not all toxins used as herbicides or pesticides will be passed on to animals that feed on them. Many biodegrade over very short periods; it is only those containing persistent substances that bio-accumulate.
  • As an alternative, pupils working in groups could be given information, presented as single sentences on cards, about the effect of pesticides on the wild bird population. Ask pupils to put together the evidence to describe and explain what happened to the birds. A similar set of cards could be produced about the effect of a plague of locusts.

Sections in this unit

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This unit is divided into sections. Each section contains a sequence of activities with related objectives and outcomes. You can view this unit by moving through the sections or print/download the whole unit.
1. a. Where does our food come from?
2. b. Where does our food come from?
3. Checking progress
4. a. How do fertilisers affect plant growth?
5. b. How do fertilisers affect plant growth?
6. a. How does competition with other plants affect plant growth?
7. b. How does competition with other plants affect plant growth?
8. a. How do pests affect plant growth?
9. b. How do pests affect plant growth?
10. c. How do pests affect plant growth?
11. a. What is the perfect environment for growing plants?
12. b. What is the perfect environment for growing plants?
13. Reviewing work