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20. Human influences on ecosystems

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  1. 20.1 Food supply

    1. • Describe how humans have increased food production, limited to: (a) agricultural machinery to use larger areas of land and improve efficiency (b) chemical fertilisers to improve yields (c) insecticides to improve quality and yield (d) herbicides to reduce competition with weeds (e) selective breeding to improve production by crop plants and livestock

    2. • Describe the advantages and disadvantages of large-scale monocultures of crop plants

    3. • Describe the advantages and disadvantages of intensive livestock production

  2. 20.2 Habitat destruction

    1. 20.2.1Biodiversity as the number

      • Describe biodiversity as the number of different species that live in an area

    2. 20.2.2Reasons for habitat destruction

      • Describe the reasons for habitat destruction, including: (a) increased area for housing, crop plant production and livestock production (b) extraction of natural resources (c) freshwater and marine pollution

    3. 20.2.3Through altering food webs and food

      • State that through altering food webs and food chains, humans can have a negative impact on habitats

    4. 20.2.4Undesirable effects of deforestation

      • Explain the undesirable effects of deforestation as an example of habitat destruction, to include: reducing biodiversity, extinction, loss of soil, flooding and increase of carbon dioxide in the atmosphere

  3. 20.3 Pollution

    1. • Describe the effects of untreated sewage and excess fertiliser on aquatic ecosystems

    2. • Describe the effects of non-biodegradable plastics, in both aquatic and terrestrial ecosystems

    3. • Describe the sources and effects of pollution of the air by methane and carbon dioxide, limited to: the enhanced greenhouse effect and climate change

    4. • Explain the process of eutrophication of water, limited to: • increased availability of nitrate and other ions • increased growth of producers • increased decomposition after death of producers • increased aerobic respiration by decomposers • reduction in dissolved oxygen • death of organisms requiring dissolved oxygen in water

  4. 20.4 Conservation

    1. • Describe a sustainable resource as one which is produced as rapidly as it is removed from the environment so that it does not run out

    2. • State that some resources can be conserved and managed sustainably, limited to forests and fish stocks

    3. • Explain why organisms become endangered or extinct, including: climate change, habitat destruction, hunting, overharvesting, pollution and introduced species

    4. • Describe how endangered species can be conserved, limited to: (a) monitoring and protecting species and habitats (b) education (c) captive breeding programmes (d) seed banks

    5. • Explain how forests can be conserved using: education, protected areas, quotas and replanting

    6. • Explain how fish stocks can be conserved using: education, closed seasons, protected areas, controlled net types and mesh size, quotas and monitoring

    7. • Describe the reasons for conservation programmes, limited to: (a) maintaining or increasing biodiversity (b) reducing extinction (c) protecting vulnerable ecosystems (d) maintaining ecosystem functions, limited to nutrient cycling and resource provision, including food, drugs, fuel and genes

    8. • Describe the use of artificial insemination (AI) and in vitro fertilisation (IVF) in captive breeding programmes

    9. • Explain the risks to a species if its population size decreases, reducing genetic variation (knowledge of genetic drift is not required)