National 5 Biology
National 5 Biology
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The human population

  • Increasing human population requires an increased food yield.
  • This can involve the use of fertilisers and pesticides.
  • Fertilisers provide chemicals such as nitrates which increase crop yield.
  • Plants and animals which reduce crop yield can be killed by pesticides.

Nitrates

  • Nitrates dissolved in soil water are absorbed into plants.
  • Nitrates are used to produce amino acids which are synthesised into plant proteins.
  • Animals consume plants or other animals to obtain amino acids for protein synthesis.
  • Fertilisers can be added to soil to increase the nitrate content of the soil.

Fertilisers

  • Fertilisers can leach into fresh water, adding extra, unwanted nitrates.
  • This will increase algal populations which can cause algal blooms.
  • Algal blooms reduce light levels, killing aquatic plants.
  • These dead plants, as well as dead algae, become food for bacteria which increase greatly in number.
  • The bacteria use up large quantities of oxygen, reducing the oxygen availability for other organisms.
  • Genetically modified (GM) crops can be used to reduce the use of fertilisers.

Pesticides

  • Pesticides sprayed onto crops can accumulate in the bodies of organisms over time.
  • The build-up of toxic substances in living organisms is known as bioaccumulation.
  • As they are passed along food chains, toxicity increases and can reach lethal

Alternatives to Pesticides

  • Biological control and GM crops may be an alternative to the use of pesticides.
  • Biological control is a natural predator of the pest.

 

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