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Science at key stage 3    (Year 9)

Unit 9D: Plants for food
Section 6: a. How does competition with other plants affect plant growth?

QCA

Objectives
Children should learn:
  • that the organisms living in a habitat compete with each other for resources from the environment
  • how treating fields with selective weedkillers affects food webs

Activities

Outcomes
Children:
  • Ask pupils to suggest what the term 'weed' means, why weeds might affect yields from food crops, and ways in which weeds compete with crop plants for resources. If possible, provide pupils with data about the yields of crops with, and in the absence of, weeds, and ask them to explain whether the data supports their ideas. Ask pupils to suggest what the effects of killing the weeds might be on other living things on the farm.
  • Provide pupils with examples, eg specimens, photographs, of weeds that often grow alongside food crops and show photographs or video clips of workers in protective gear spraying food crops with weedkiller. Ask pupils to find out about the chemicals used and their effects, eg using information from packaging, and to present this information as a table.
  • describe ways in which weeds compete with crop plants for resources from the environment
  • describe how treating fields with selective weedkillers affects specific food webs
  • explain how animals are affected by the removal of a particular food plant
  • suggest how a high crop yield might be attained alongside preservation of animals' food supply

Points to note
  • The information from packs of weedkiller could be photocopied for individuals or groups to use. This could be supplemented by further reference literature, such as leaflets and gardening books.
  • Extension: pupils could read about the possible effects of weedkillers on an ecosystem and find out about specific examples and possible solutions, eg through the internet.
  • Extension: pupils could be provided with a detailed food web found in the countryside, including many wild plants and a few crop plants. Ask them to erase some of the wild plants to show the effect of weedkiller, and to note how many animals have a reduced food supply because of this. Ask pupils to relate this to the work on yields from crops, and to suggest approaches that might combine efficient crop production with preservation of animals' food supply.

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