Download - Living Things in Their Environment
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Effects of human activity
on the ecosystem
Biology Study NotesGCE Study Buddy
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Impact of Humans
Humans pose a huge threat to lives of animals, plants andtheir environment
Our impact is so great due to:
- technologies that change the world so quickly
- population increase
- consumption of natural resources, and waste
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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 producingsynthetic textiles
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Damaging effects of
deforestation Soil erosion
Forests important in soil stability
The leafy canopy of the tress in tropical rainforests protects thesoil from the impact of falling rain
The roots hold soil and water, and release water gradually tothe soil below and to the nearby streams and likes
With trees removed, the soil is exposed directly to the force ofthe rain
Topsoil, the most fertile layer, gets washed away during heavyrain 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 exposedto wind erosion
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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
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Damaging effects of
deforestation Desertification
Sunlight falls directly onto the soil and water evaporates directlyfrom 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 dioxidebecomes upset
Climatic changes
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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 andprecipitates as rain
When the trees are cleared, the area becomes dry andwarm, and annual rainfall decreases
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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
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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
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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 ofcool 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
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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
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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 earths surface retaining
the heat radiating from the earths surface greenhouse
effect The result may be global warming
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Global Warming
Earth
s atmosphere is an insulating layer - It lets theSuns heat in but also stops some going out
Increase in carbon dioxidedue to:
1) Deforestation (loss in photosynthesis)
2) Combustion of fossil fuels
Increase in methanedue to:
1) livestock farming
2) rotting plant material
3) drilling for oil and gas
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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 ofskin cancer
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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 fuelsespecially 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
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Water pollution Waste materials dumped into rivers and streams
Sewage
Untreated sewage discharged into rivers and lakes containsbacteria
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 organicwastes releasing foul-smelling gases like hydrogen sulphideand ammonia
Untreated sewage may contain bacteria that cause diseaseslike cholera and typhoid
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Water pollution
Inorganic wastes
Poisonous metals such as mercury, arsenic and cadmium
Contaminates fish, seafood which are then consumed by
humans
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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 forthe growth of algae and plants
Rain means may wash nutrients from the fields and intorivers 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
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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
passed along food chains, increasing in concentration in the bodies of
organisms along the trophic levels
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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
Ad t d
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Advantages and
Disadvantages of PesticidesAdvantages 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
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Conservation Protection and preservation of natural resources in the environment
Reasons for conservation
Ensure protection of plant and animal species and to prevent theirextinction
Maintain a stable and balanced ecosystem prevents disruption ofnatural cycles and global warming
Maintain a large gene pool
wild plants and animals possess favorablegenes 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 majorsource of human food
Ensure conservation of tropical rainforests as they are of economicimportance sources of raw material for industries, medicinal drugs,natural insecticides and food
Scientific value useful information for Mans survival
Preserves the natural scenery and wildlife for people to appreciate,maintain natural resources for outdoor recreational activities
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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 intofishing grounds
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Recycling of materials Recycling:
Reduces waste disposal
Reduces pollution
Recycling sewage saves water
Saves energy and money