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4.4Ecology and the Environment

Human Influences on the Environment — Edexcel Linear - OL Revision Notes & Topical Questions

5 min read 7 parts Lesson 10 of 10 Unit quiz

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Lesson summary

Air Pollution, Greenhouse Effect, Water Pollution and Deforestation — EDEXCEL LINEAR - OL notes: Explain the biological effects of air and water pollution, the enhanced greenhouse effect and deforestation.PollutantEffect Carbon monoxide (CO)Binds to haemoglobin and reduces oxygen…

  • Eutrophication
  • Sewage pollution
  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4

Part 1 of 5Air pollution

PollutantEffect
Carbon monoxide (CO)Binds to haemoglobin and reduces oxygen transport in the blood; can cause suffocation and death at high concentration
Sulfur dioxide (SO2)Combines with water vapour to form acid rain, which damages plants, aquatic life and soil, and causes respiratory problems

Both gases are produced by burning fuels. Carbon monoxide comes from incomplete combustion, for example in car engines and faulty heaters, which is why it is dangerous in poorly ventilated rooms. Sulfur dioxide comes from burning fossil fuels containing sulfur. Acid rain lowers the pH of lakes and soil, harms fish and trees, and washes minerals out of the soil.

Part 2 of 5Greenhouse gases and the enhanced greenhouse effect

Greenhouse gases (water vapour, carbon dioxide, methane, nitrous oxides, CFCs) absorb heat radiation so it stays in the atmosphere. The natural greenhouse effect keeps Earth warm enough for life:

1
The Sun's radiation enters the atmosphere.
2
The Earth's surface absorbs energy and re-emits it as infrared radiation.
3
Some is reflected into space.
4
Some is absorbed by greenhouse gases and trapped.

Human activities raise carbon dioxide (burning fossil fuels, deforestation) and methane (cattle digesting grass, rice paddy fields), causing an enhanced greenhouse effect, global warming and climate change. Consequences include warmer oceans, melting ice caps, rising sea level, flooding and coral bleaching, extreme weather (storms, floods, droughts), loss of habitats, lower biodiversity as food chains are disrupted, and species migrating, which spreads pests and disease.

Other effects of global warming include changing rainfall patterns, which can cause crop failure in some regions and flooding in others, and the melting of glaciers that supply fresh water. Reducing the enhanced greenhouse effect needs lower use of fossil fuels, protection of forests and reduced methane from farming.

Part 3 of 5Water pollution

Eutrophication happens when fertiliser run-off enters water:

1
Nitrates cause overgrowth of algae and plants at the surface.
2
Plants below die from lack of light.
3
Decomposers increase in number and use up oxygen respiring.
4
Dissolved oxygen falls and many aquatic organisms die.

Sewage pollution (from overflowing sewers or agricultural waste) increases aerobic bacteria that feed on the waste and reduce dissolved oxygen. Oxygen-sensitive organisms die, leaving only those that tolerate low oxygen, so biodiversity falls, and pathogenic bacteria may increase.

Compare the two kinds of water pollution in an exam: in both, the key chain of events ends in low dissolved oxygen.

Water pollution
In eutrophication the cause is excess nitrate and algal growth; in sewage the cause is the growth of aerobic bacteria feeding on waste.
Name the organisms that use the oxygen (decomposers or aerobic bacteria) and state that species sensitive to low oxygen disappear so biodiversity falls.
Indicator species such as certain invertebrates can show how polluted water is.

Part 4 of 5Deforestation

Deforestation is large-scale clearing of trees for farming or development.

EffectExplanation
LeachingMinerals no longer taken up by trees are washed into water
Soil erosionRoots no longer hold the soil, so it is washed or blown away
Water cycle disturbanceLess transpiration, so less cloud and rainfall
Carbon cycle disturbanceLess photosynthesis removes less CO2; burning felled trees releases CO2, increasing warming

Part 5 of 5Worked examples

  1. Explain how carbon monoxide is harmful. [2]2 marks

  2. Describe how fertiliser run-off kills fish. [4]4 marks

  3. Give two causes of increased methane in the atmosphere. [2]2 marks

  4. Explain how deforestation can increase global warming. [3]3 marks

Key terms

TermMeaning
Greenhouse gasGas that absorbs infrared radiation and traps heat.
Enhanced greenhouse effectExtra warming from raised greenhouse gas levels.
EutrophicationOvergrowth of algae and oxygen depletion from nutrient pollution.
Acid rainRain made acidic by sulfur dioxide.
DeforestationLarge-scale clearing of trees.
LeachingWashing of minerals out of soil.

Avoid these mistakes

1
Saying algae use up the oxygen directly — decomposers respiring do.
2
Confusing the natural greenhouse effect (needed for life) with the enhanced effect.
3
Saying CO binds to red blood cells in general — it binds to haemoglobin.
4
Forgetting that deforestation reduces rainfall.

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