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Summary notes for CIE IGCSE Biology Topic 21: Human influences on ecosystems

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  • Course
  • Biology
  • Institution
  • GCSE

Complete revision notes for Topic 21 of the CIE IGCSE Biology course: Human influences on ecosystems. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.

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Document information

  • April 9, 2021
  • 12
  • 2020/2021
  • Summary

Subjects

  • cie
  • igcse
  • topic 21
  • human
  • influences
  • ecosystems
  • deforestation
  • extended

Written for

  • GCSE
  • GCSE
  • Biology
  • 200
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Human influences on ecosystems

21.1 Food supply

State how modern technology has resulted in increased food production in terms of:
 Agricultural machinery to use larger areas of land and improve efficiency
 Chemical fertilisers to improve yields
 Insecticides to improve quality and yield
 Herbicides to reduce competition with weeds
 Selective breeding to improve production by crop plants and livestock, e.g. cattle,
fish and poultry

Agricultural machinery has replaced humans and improved efficiency due to the ability to
farm much larger areas of land.

Chemical fertilisers improve yields – fertilisers increase the amount of nutrients in the soil
for plants, meaning that they can grow larger and produce more fruit.

Insecticides and herbicides – these chemicals kill off unwanted insects and weed species,
meaning that there is less damage done to plants and fruit lost to insects (insecticides), as
well as reducing competition from other plant species (herbicides).

Selective breeding – animals and crop plants which produce a large yield are selectively bred
to produce breeds that reliably produce high yields.

Discuss the social, environmental and economic implications of providing sufficient food for
an increasing human global population

Social

When people do not receive enough food, famine occurs. This can be caused by a variety of
factors, including natural disasters, such as drought and flooding, increasing population,
poverty, and unequal food distribution.

Environmental

As the global human population increases, food production must also be increased to
support the increasing population
 This is a problem as more land is required to grow crops and animals, meaning
that deforestation is happening at an increasing rate, and there is also an increasing
amount of greenhouse gases emitted from animal production
 Greenhouse gases cause global warming, which is a worldwide issue that leads to
increased natural disasters, such as tropical storms and drought, as well as rising sea
levels, which floods homes and decreases the amount of habitable land

, Insecticides:
 Harmless insects being killed as well
 Pollution by pesticides (which are often persistent chemicals which accumulate in
food chains)
 In many instances where they are used repeatedly for specific pests, the pests may
eventually become resistant to them, reducing their effectiveness

Economic

Increasingly expensive to provide for an increasing human population.

Issues with the economics of food production/free trade/neo-colonialism.

Discuss the problems which contribute to famine including unequal distribution of food,
drought and flooding, increasing population and poverty

Describe the negative impacts to an ecosystem of large-scale monocultures of crop plants

Monoculture farming means that on a given area of agricultural land only one type of crop is
grown (e.g. trees for palm oil grown in Indonesian rainforest).

This large-scale growth of a single variety of plant does not happen naturally in ecosystems,
where there are usually many different species of plants growing which, in turn, support
many species of animals (high biodiversity).

In monocultures, biodiversity is much lower.

Another issue with monocultures is the increase in pest populations – if a particular pest
feeds on a crop, farming it in large areas repeatedly means there is an ample supply of food
for the pest, causing the population to increase.

Describe the negative impacts to an ecosystem of intensive livestock production

In developed countries, large numbers of livestock are often kept in an area that would not
normally be able to support more than a very small number.

They are often fed high energy foods, regularly given medication such as antibiotics as a
preventative measure against disease and kept in artificially warm temperatures and small
spaces that do not allow for much movement.

Ecological issues with intensive farming include:
 Reduction in biodiversity in areas where large amounts of land are used to graze
cattle (as only grass is grown so in effect it becomes a monoculture)
 Overgrazing can lead to soil erosion
 Large numbers of cattle produce large amounts of methane, a greenhouse gas

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