Human activity has significantly impacted ecosystems through deforestation, pollution, and climate change. Deforestation causes soil erosion, flooding, desertification, and changes rainfall patterns. Air pollution from fossil fuel combustion and vehicles releases sulfur dioxide, nitrogen oxides, and carbon dioxide, leading to acid rain and global warming. Water pollution from sewage, chemicals like pesticides and herbicides, and industrial/agricultural runoff causes eutrophication and harms aquatic life. Conservation efforts aim to protect biodiversity, ecosystems, resources and balance human needs with environmental protection through measures like sustainable fishing and recycling.

1. Effects of human activity
on the ecosystem
Biology Study Notes
GCE Study Buddy

2. Impact of Humans
●Humans pose a huge threat to lives of animals, plants and
their environment
●Our impact is so great due to:
- technologies that change the world so quickly
- population increase
- consumption of natural resources, and waste

3. Deforestation
●Reasons
○Urban development – land has to be cleared for building
houses, roads, factories etc
○Cultivation – land for growing crops
○Grazing – large open grasslands needed for grazing by
cattle, sheep, horses, etc
○Timber – wood needed for construction, paper industry,
fuel
○Fibres – plants are useful sources of fibres for producing
synthetic textiles

4. Damaging effects of
deforestation
●Soil erosion
○Forests important in soil stability
○The leafy canopy of the tress in tropical rainforests protects the
soil from the impact of falling rain
○The roots hold soil and water, and release water gradually to
the soil below and to the nearby streams and likes
○With trees removed, the soil is exposed directly to the force of
the rain
○Topsoil, the most fertile layer, gets washed away during heavy
rain especially on steep slopes
○When the whole of the topsoil is washed down – sheet erosion
○Without the trees forming a shelter belt, the soil is also exposed
to wind erosion

5. Damaging effects of
deforestation
●Flooding
○Eroded soil may be deposited in rivers and streams
blocking flow of water
○Rainwater is not retained and released slowly as trees
have been removed
○The water levels in rivers rise rapidly
○Water flows inland causing floods

6. Damaging effects of
deforestation
●Desertification
○Sunlight falls directly onto the soil and water evaporates directly
from the soil which then hardens
○With the topsoil eroded, plant life cannot be supported
○Other organisms which depend directly or indirectly upon plants
for food, also disappear – land becomes barren
○The destruction of land leading to desert-like conditions is
called desertification
○Desertification results in
■Loss of habitats
■Extinction of many species of organisms
■Loss of robust wild species of plants that may be useful in
treating diseases
■The delicate balance between oxygen and carbon dioxide
becomes upset
■Climatic changes

7. Climatic changes due to
desertification
●In the forest, rainwater is retained and absorbed by the
roots of trees
●The water is lost during transpiration
●The relative humidity of the air around the forest is high
●The water vapour eventually condenses and
precipitates as rain
●When the trees are cleared, the area becomes dry and
warm, and annual rainfall decreases

8. Pollution
●Air pollution
○Results mainly from incomplete burning of fuels such as
coal, oil petrol and wood
○The gaseous pollutants may be due to human activities or
natural occurrences such as biological decay, forest fires
or volcanic eruptions

9. Air Pollutants
●Sulphur dioxide and nitrogen oxides
○From burning of fossil fuels – coal, oil, natural gases
○Sulphur dioxide at high concentrations has damaging effects on
both plants and animals
○Sulphur dioxide penetrates the leaves through the stomata –
this damages the leaves and kills the plants
○In humans, sulphur dioxide irritates and damages the sensitive
lining of the eyes, air passages and lungs
○Acid rain: sulphur dioxide and oxides of nitrogen react with
oxygen and rainwater directly to form sulphuric acid and nitric
acid respectively
■Causes death of fish in lakes and rivers
■Acid rain dissolves aluminium salts in the soil and washes them
into rivers and lakes – poisonous to fishes

10. Air Pollutants
●Smog
○Main component is sulphur dioxide
○Smog is a mixture of smoke and fog
○Happens when a layer of warm air lies like a lid on top of
cool air – the cool air together with pollutants such as
smoke and sulphur dioxide is prevented from escaping
○They accumulate in the stagnant air until they reach such
high concentrations as to produce lethal results

11. Air Pollutants
●Lead
○May be present in the air, water and the food we eat
○Lead poisoning occurs when lead accumulates in the
body over long periods
○High concentrations of lead in the body may cause
cramps, loss of control of the hands and feet, and even
coma

12. Air Pollutants
●Carbon monoxide
○Main source is from exhaust of motor vehicles
○Carbon monoxide combines with haemoglobin in the red
blood cells to form carboxyharmoglobin
○This reduces the capacity of the blood to transport
oxygen round the body
○May be fatal in high concentrations

13. Air Pollutants
●Carbon dioxide
○Burning of organic compounds releases carbon dioxide
into the air
○Industrialization and increasing car population results in
carbon dioxide being released in increasing
concentrations into the atmosphere
○The gas forms a layer over the earth’s surface retaining
the heat radiating from the earth’s surface – greenhouse
effect
○The result may be global warming

14. Global Warming
●Earth’s atmosphere is an insulating layer - It lets the
Sun’s heat in but also stops some going out
●Increase in carbon dioxide due to:
1) Deforestation (loss in photosynthesis)
2) Combustion of fossil fuels
●Increase in methane due to:
1) livestock farming
2) rotting plant material
3) drilling for oil and gas

15. Air Pollutants
●Chlorofluorocarbons (CFCs)
○Non-toxic, unreactive chemicals
○Used as aerosol propellants, as cooling agents in
refrigerators and air conditioners, and in foam packaging
○Ozone is a gas that forms a layer over the earth. It
absorbs much of the UV rays from sunlight
○When CFCs are released into the atmosphere from
aerosols, etc, they break down the ozone layer, allowing
more UV light penetrate into the earth – increases risk of
skin cancer

16. Ways of reducing air pollution
●Use catalytic converters in cars
●Less use of cars
●Use filters or scrubbers on chimneys to remove sulphur
dioxide
●Use non-fossil fuels in factories or less use of fossil fuels
especially near more densely populated areas
●Use alkalis to neutralize acidic waste products from factories
before they are released to the environment
●Use ozone-friendly products to prevent ozone depletion

17. Water pollution
●Waste materials dumped into rivers and streams
●Sewage
○Untreated sewage discharged into rivers and lakes contains
bacteria
○Sewage is a good source of food for bacteria
○Bacteria grow and multiply rapidly using up oxygen in the water
○Other organisms, including fishes, die due to lack of oxygen
○Anaerobic bacteria then continue breaking down the organic
wastes releasing foul-smelling gases like hydrogen sulphide
and ammonia
○Untreated sewage may contain bacteria that cause diseases
like cholera and typhoid

18. Water pollution
●Inorganic wastes
○Poisonous metals such as mercury, arsenic and cadmium
○Contaminates fish, seafood which are then consumed by
humans

19. Water pollution
●Fertilisers containing plant nutrients are sprayed onto fields
so that plants can grow faster and boost crop yields.
○Contain nitrates and phosphates which are useful nutrients for
the growth of algae and plants
●Rain means may wash nutrients from the fields and into
rivers and lakes (this is called run-off).
●Eutrophication (hyper-nutrition from fertiliser pollution)
occurs
○Profuse growth and multiplication of algae and green plants occur
○Algae grows fast using up lots of oxygen and blocking sunlight
○Plants begin to die providing food for microbes
○Microbes increase the competition for oxygen
○Water becomes de-oxygenated causing aquatic life to die

20. Water pollution
●Pesticides
○used to kill insects and other crop damaging micro-organisms can effect
the food chain
○Pesticides can be absorbed by small aquatic animals
○Fish each the animals, which have eaten pesticide
○Birds eat the fish
●Insecticides
○Used to kill insects
○Some insecticides eg DDT (dichloro-diphenyl trichloroethane) are non-
biodegradable – means that cannot be broken down by bacteria
○Insecticides may be carried by rainwater into streams, rivers and lakes
○In high concentrations, they may poison fish or animals that drink the
polluted water or feed on the contaminated fish
○DDT is insoluble in water
○It is not excreted but instead is stored in the fatty tissues of animals –
accumulates in the bodies of consumer – results in the insecticide being

21. Water pollution
●Herbicides
○Used to kill weeds
○Certain herbicides eg 2:4:5T, contain an impurity called
dioxin which is harmful to human beings
○When it is washed by rainwater into streams and rivers, it
pollutes the water supply
○Dioxins may cause miscarriages in women, physical and
mental abnormalities in children and increase risk of
cancer

22. Advantages and
Disadvantages of Pesticides
Advantages Disadvantages
Healthier crops Non-biodegradable pesticides may
cause pollution, and may increase in
concentration along the food chain
Higher yields of crops Useful organisms in the environment
may be killed
Socio-economic advantages eg more
food is available, more profit for
farmers
Some pesticides are expensive
Pests may develop resistance against
the pesticides

23. Conservation
●Protection and preservation of natural resources in the environment
●Reasons for conservation
○Ensure protection of plant and animal species and to prevent their
extinction
○Maintain a stable and balanced ecosystem – prevents disruption of
natural cycles and global warming
○Maintain a large gene pool – wild plants and animals possess favorable
genes – by cross-breeding the different varieties of wild plants and
animals, can improve yield, vigor and quality of organisms
○Ensure conservation of marine life, as marine fisheries are a major
source of human food
○Ensure conservation of tropical rainforests as they are of economic
importance – sources of raw material for industries, medicinal drugs,
natural insecticides and food
○Scientific value – useful information for Man’s survival
○Preserves the natural scenery and wildlife for people to appreciate,
maintain natural resources for outdoor recreational activities

24. Conserve fishing grounds
●Measures
○Ban use of drift nets which indiscriminately trap all forms
of sea life
○Use nets with a certain mesh size so that young fish are
not caught
○Regulate size of ships allowed into fishing grounds
○Limit period of fishing in the grounds
○Ban the harvesting of endangered species, encourage
raising of these fish in hatcheries and release them into
fishing grounds

25. Recycling of materials
●Recycling:
○Reduces waste disposal
○Reduces pollution
○Recycling sewage saves water
○Saves energy and money