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  1. 1-biological-molecules

    1-1-biological-molecules-carbohydrates
    11 主题
  2. 1-2-biological-molecules-lipids
    3 主题
  3. 1-3-biological-molecules-proteins
    5 主题
  4. 1-4-proteins-enzymes
    12 主题
  5. 1-5-nucleic-acids-structure-and-dna-replication
    8 主题
  6. 1-6-atp-water-and-inorganic-ions
    4 主题
  7. 2-cell-structure
    2-1-cell-structure
    7 主题
  8. 2-2-the-microscope-in-cell-studies
    4 主题
  9. 2-3-cell-division-in-eukaryotic-and-prokaryotic-cells
    8 主题
  10. 2-4-cell-membranes-and-transport
    7 主题
  11. 2-5-cell-recognition-and-the-immune-system
    7 主题
  12. 2-6-vaccines-disease-and-monoclonal-antibodies
    6 主题
  13. 3-exchange-and-transport
    3-1-adaptations-for-gas-exchange
    6 主题
  14. 3-2-human-gas-exchange
    10 主题
  15. 3-3-digestion-and-absorption
    5 主题
  16. 3-4-mass-transport-in-animals
    6 主题
  17. 3-5-the-circulatory-system-in-animals
    8 主题
  18. 3-6-mass-transport-in-plants
    6 主题
  19. 4-genetics-variation-and-interdependence
    4-1-dna-genes-and-chromosomes
    7 主题
  20. 4-2-dna-and-protein-synthesis
    6 主题
  21. 4-3-genetic-diversity-mutations-and-meiosis
    7 主题
  22. 4-4-genetic-diversity-and-adaptation
    6 主题
  23. 4-5-species-and-taxonomy
    4 主题
  24. 4-6-biodiversity
    9 主题
  25. 5-energy-transfers-in-and-between-organisms-a-level-only
    5-1-photosynthesis-a-level-only
    5 主题
  26. 5-2-respiration-a-level-only
    7 主题
  27. 5-3-energy-and-ecosystems-a-level-only
    9 主题
  28. 5-4-nutrient-cycles-a-level-only
    4 主题
  29. 6-organisms-respond-to-changes-in-their-environments-a-level-only
    6-1-response-to-stimuli-a-level-only
    12 主题
  30. 6-2-nervous-coordination-a-level-only
    10 主题
  31. 6-3-skeletal-muscles-a-level-only
    6 主题
  32. 6-4-homeostasis-a-level-only
    11 主题
  33. 7-genetics-populations-evolution-and-ecosystems-a-level-only
    7-1-inheritance-a-level-only
    6 主题
  34. 7-2-populations-a-level-only
    3 主题
  35. 7-3-evolution-a-level-only
    5 主题
  36. 7-4-populations-in-ecosystems-a-level-only
    7 主题
  37. 8-the-control-of-gene-expression-a-level-only
    8-1-genetic-mutations-a-level-only
    2 主题
  38. 8-2-regulation-of-gene-expression-a-level-only
    11 主题
  39. 8-3-using-genome-projects-a-level-only
    4 主题
  40. 8-4-gene-technologies-a-level-only
    13 主题
  41. exam-guidance-and-skills
    essay-guidance
    3 主题
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Conservation & human need

  • Humans use Earth’s resources, such as land, water, wood, and fossil fuels for various needs:

    • Buildings

    • Agriculture

    • Fuel

    • Electricity

  • As population and economic development increase, so does the demand for these resources

    • This leads to environmental damage, affecting ecosystems, climate, and biodiversity, creating a conflict between human needs and conservation

  • Conservation involves managing species and habitats sustainably, meeting present needs without compromising the future

  • Conservation of habitats frequently involves management of

    succession

    • Some oppose this due to short-term economic impacts, but careful resource management is essential to balance current use with long-term sustainability

Methods of conservation

Type of conservation

How it manages conflict & promotes sustainability

National & marine parks

Protects habitats with legal restrictions on access, development and hunting, balancing biodiversity with controlled land use

Public engagement

Generates income through tourism; provides local jobs and funding for services, increasing community support for conservation

Zoos (captive breeding)

Captive breeding helps restore species populations and supports research, reducing pressure on wild populations

Botanic gardens

Conserves rare plants using lab techniques and enables reintroduction; supports research and education to maintain biodiversity

Frozen zoos

Preserves genetic material for future reintroduction; reduces pressure on wild populations and supports long-term planning

Seed banks

Stores plant diversity safely; allows future crop restoration and species recovery; offsets habitat loss

Evaluating data about conservation issues

  • Being able to evaluate evidence and data concerning issues relating to the conservation of species and habitats is an important skill

  • The example below demonstrates these data evaluation techniques using data on white-clawed crayfish and signal crayfish

    • The signal crayfish, an invasive species from America, has caused major declines in the UK’s native white-clawed crayfish by outcompeting it for resources and spreading disease to which it is immune

Worked Example

A six-year investigation tested whether removing invasive signal crayfish could help conserve native white-clawed crayfish. Each year, random sampling was used to estimate native crayfish numbers in a 50 m stream section. After two years, signal crayfish were removed and regularly controlled thereafter. A similar 50 m stream section where no removal occurred served as the control. Results are shown below.

Describe and conclude the data.

Evaluate the method used to collect the data.

Crayfish experiment 1v, downloadable AS & A Level Biology revision notes

Step One: Describe the data

  • Over the first two years, the number of native crayfish approximately halved, decreasing from 50 to 25. After the invasive species was removed, the number of native crayfish increased from 25 to 45 in 4 years

  • The control site showed a decrease in the number of native crayfish, from 60 to 20 over the six-year period

Step Two: Draw conclusions

  • The removal of the invasive crayfish led to an increase in the number of native crayfish over a four-year period

  • This suggests that the decline in white-clawed crayfish populations in the UK could be due to competition with the signal crayfish

Step Three: Evaluate the method

  • Due to the control experiment, where the number of native crayfish continued to decrease throughout the six-year study, any other variables that could have affected the number of native crayfish (including abiotic factors such as water quality and biotic factors such as predation) can be discounted. This increases the validity of the results

  • As random sampling was used, the data will not be biased and will give a more accurate estimate of the whole area

Considering conflicting data

  • The data from just one study is not normally enough to draw sufficiently certain conclusions on which to base conservation actions

    • For example, although the results of the investigation outlined above seem to suggest that signal crayfish are causing the decline of white-clawed crayfish, it is unlikely that this one study would lead to conservation action to remove signal crayfish all across the UK

  • Instead, the results from multiple similar studies are normally required, and if these results appear to agree, then a more certain conclusion can be drawn

  • Sometimes, however, two very similar studies may give different results that do not appear to agree

  • Being able to consider this conflicting evidence and its implications is an important skill

Worked Example

Another investigation into the effect of invasive crayfish on the numbers of native crayfish was carried out in a 20m section of a stream in a different part of the UK over a period of 18 months. The results are shown below.

Describe and conclude the data, then evaluate the method used to collect the data.

Crayfish experiment 1 (1), downloadable AS & A Level Biology revision notes

Step One: Describe the data

  • Over the first six months, the number of native crayfish decreased from 25 to around 13. After the invasive species was removed, the number of native crayfish continued to decrease from 13 to around 9 over the next 12 months

Step Two: Draw conclusions

  • The removal of the invasive crayfish did not affect the declining native crayfish population

  • The conflicts with the results of the previous study, which suggested that the decline in white-clawed crayfish populations in the UK could be due to competition with the signal crayfish

Step Three: Evaluate the method

  • There was no control site in this investigation, so the continuing decline of the native crayfish after the invasive species was removed could be due to another biotic or abiotic factor, such as the presence of a new predator or a change in the water quality or temperature

  • The length of this investigation was much shorter than the previous study, so the decline in native crayfish could simply be due to a natural population fluctuation, meaning that the population may increase again if studied over a longer time period

  • The study area was much smaller than in the previous study, so the estimated population size values may be less accurate