IGCSE Biology Notes on Human Influences on Ecosystem

 Bio notes

• Impact of intensive livestock production

•   Rearing of calves and chickens on a large scale production is called factory farming. They are reared in large sheds instead of open fields and their urine and faeces are washed off leading to the formation of a slurry which if it finds its way to rivers and streams can lead to eutrophication. 
• If the animals are kept on a pasture, it can lead to overgrazing where the animals can eat the grass down to the roots and their hooves can trample the surface into a hard layer. This prevents the penetration of rainwater resulting in soil erosion. 
• Factors that contribute to famine

• Climate change and natural disasters such as excessive rainfall which can cause the soil to be water logged and infertile 
• Pollution 
• Water shortage because of it being used for other purposes like building dams and diversion of rivers. 
• Seed shortage 
• Poor soil due to lack of inorganic ions and fertilisers
• Desertification due to soil erosion 
• Economic implications of famine 

1. Detrimental effect on country’s economy 
2. Countries with large debts export cash crops even though the local people need it. 

Buffer- A solution that resists a change in pH (chemistry)

Food supply

• Intensification of agriculture

• Machinery 
• Pesticides
• Fertilisers
• Selective breeding 

1. Mono cultures
2. Factory Farming 
3. Famine 

Habitat Destruction 

• Reason for habitat destruction 
• Increased area for food crop growth ;Livestock production and growth :

 Large areas of land are cleared to provide space for growing food crops in order to meet the increased demand of food. This results in the loss of habitat in a wide variety of plants and animals, however, farmers can be educated about techniques of land management which include leaving strips of uncultivated land between the fields and around its margins. Eg: The Farming and Wildlife Advisory Group(FWAG) is an institution which educates farmers on these cultivation techniques. 

• Extraction of Natural resources:

The extraction of fossil fuels causes damage to habitats. The dumping of rocks and soil in big heaps also prevents the process of redevelopment. It also results in scraping of soil from the surface of the land. Oil spills are also toxic and can destroy habitats when the oil seeps into the soil and water systems. 

• Marine pollution:

Aquatic systems can be polluted with human debris that include, untreated sewage, agricultural fertilisers and pesticides. Artificial fertilisers create a dead zone where there is no oxygen due to eutrophication.  Oil spills can also kill seaweeds which provide nutrients to aquatic life. Plastics are non-bio degradable and hence persist in the environment for a very long time. They are also often mistaken for food by marine organisms causing sickness. 

Any form of Habitat destruction, even if it wipes out a single species, can have signaficant negative impact on food chians and food webs.

• Deforestation as a method of Habitat Destruction 

• Deforestation is the removal of large number of trees. 
• Significance of forests: oxygen, food resources, habitat(home)(known as biodiversity”hot spots” eg. Approx. 5 million different species are present in the tropical rainforests), climate control(environmental buffers), , soil maintenance(roots of trees hold the soil and prevent soil erosion), water supply
• Why does Deforestation occur?

1. To provide for timber
2. For firewood
3. For agriculture, roads and settlements. 

• Impacts of deforestation 

1. Loss of habitats 
2. Increase in soil erosion 
3. Increase in soil erosion because there are no roots to hold soil in place. The soil can be washed into rivers and lakes which also destroys the habitats there and can also result in floods. 
4. Carbon dioxide levels increase in the atmosphere leading to global warming. 
5. There are other climate change the result in habitat destruction. 

Climate Control:

• Environmental Buffers

1. Transpiration leads to rainfall 
2. Clouds don’t reflect the sunlight and hence keep the region cool
3. Reduce levels of carbon dioxide since increased carbon dioxide levels results in global warming as it is a greenhouse gas.

Pollution 

• The presence in or introduction into the environment of a substance which has harmful or poisonous effects. 
• There are three types: Land, Air, Water 

1. Land and Water:

• Insecticides and Herbicides:

They are washed off from farms or there can be accidental leakage into water bodies. If they are persistent(they cannot be broken down)pollutants(herbicides and insecticides, they can enter the food chain. Bioaccumulation takes place as they get accumulated along the food chain. Herbicides can even even destroy the plants in water bodies, thereby removing the producers from the food chain. Eg: Bioaccumulation of DDT- when the DDT was sprayed to kill the beetle that were spreading the Dutch El disease. The fallen leaves which were contaminated with DDT were eaten by earthworms. The earthworms were eaten by the birds. Where concentrations reached lethal proportions, killing 30-90% of the birds. This also caused them to lay eggs with soft shells which broke easily and resulted in fewer chickens being hatched

• Nuclear fallout: 

This can occur due to a leakage from a nuclear power plant or from a nuclear explosion. The radioactive particles are carried by wind and water and settle in the environment or absorbed by organisms. If they have a long half life there can be bioaccumulation in food chains, leading to cancer in the top carnivores. Nuclear accident @Chernobyl led to death led to the death toll of 4000 with many suffering from birth defects and cancer. If the particles read the water bodies, the fish also become unfit for consumption. 

• Chemical waste, discarded rubbish, untreated sewage and fertilisers:
• Chemical Waste

This is the waste released from industries. These can be poisonous such as copper and cyanide, released from the electroplating industry. If released in water, it can kill animals, plants and humans if they drink this water. Eg: Hg released in water bodies and was concentrated as it passed along the food chain; causing brain damage and deformities and death in people who consumed the fish. 

• Discarded rubbish

Due to the increasing population , waste disposal is a problem. Landfill sites are used for depositing wastes; this plates the ground and attracts insects. If deposited in water it can cause severe problems in aquatic animals. 

• Untreated sewage 

If untreated sewage is let off it can spread many diseases or pathogens can be present in the faeces of diseased people. 

• Fertilisers 

Causes eutrophication(algae grow)

Eutrophication: 

Fertilisers (N, P ) run off into water bodies. 

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    |———>  They cause an algal growth(large increase in the number of algae due to excessive nutrients being washed of into water bodies)

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                            |———>  Prevents the penetration of sunlight 

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                                                                    |————-> Results in the death of plants present in lower layers 

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                                                   |

                                                                                                                       |———-> the dead plants are decomposed by bacteria(uses up all the oxygen for their respiration)

• Plastics 

They are non-biodegradable an can not be broken down by decomposers. they remain in the environment, taking up valuable space and causing visual pollution. In water, plastics can trap small animals and when burnt, plastics release toxic gases. 

1. Air Pollution: 

• Factories and motor vehicles release smoke, oxides of sulphur and nitrogen, lead compounds and carbon monoxide and dioxide 
• Oxides of Sulphur: they dissolve in rain water and fall as acid rain. This acid rain when it falls on plants, it can damage their leaves and hence reduce their growth. On buildings, it can dissolve the limestone and mortar. 
• Oxides of Nitrogen: they dissolve in rain water and falls as acid rain. This dissolves the aluminium salts in the soil which reach the water bodies in toxic levels. These can also react in the atmosphere to produce ozone which can damage trees. 
• Measures taken to reduce SO2 and NO2 pollution and reduce the impact of acid rain: 

1. Fitting desulphurisation plans in power stations
2. Changing the way to burn fuel(from coal fired to gas powered fire stations)
3. Flue gases can be treated to remove the oxides of nitrogen
4. Vehicles to be fitted with catalytic converters in their exhaust systems, this removes NO2, CO2 and unburnt hydrocarbons. Even though this increases the most of cars and can be only used with unleaded petrol.
5. Redesign cars to burn petrol at lower temperatures(lean burn), this results in the emission of less NO2

• Pollution of Air by methane and Carbon dioxide 

• Sources: Burning of fossil fuels 
• Impact : Enhanced green house effect and climate change 
• Natural Greenhouse effect:

1. Heat radiates from the Earth. Some of the heat goes to space and the atmosphere traps some heat 
2. Quite a lot of heat is trapped and the earth is warm enough for life 
3. Increase in cloud cover, reducing the heat reaching the earth from the sun 

• Enhanced Greenhouse Effect:

1. Atmosphere has more Greenhouse gases
2. Heat radiates from the earth. Less of the heat goes to space and the atmosphere traps most of the heat 
3. More heat is trapped and causes global warming 
4. Changes in climate and rainfall distribution 

Negative Impacts of Contraceptives:

• Sources: a)used in contraceptive pills, excreted in urine, present in sewage as cannot be removed in the sewage treatment b) Natural hormones of cattle present in their urine and can be washed off from farms 
• This reaches water systems 

1. In male frogs and Fish 

• Become feminised I.e, they start producing eggs in their testes instead of sperms: creating an imbalance between males and females 

1. In humans 

• Can reduce the sperm count, thereby reducing fertility 

Conservation 

• Sustainable resource- it is one which is produced as rapidly as it is removed from the environment.

Sewage Treatment:

THE ACTIVATED SLUDGE PROCESS 

1. Screening: 

• Made to flow through a metal grid to remove solids like rags, plastics, wood, etc 
• These substances are disposed off by incineration 

1. Grit:

• The sewage is made to flow through long channels and the grit settles down and removed from time to time. The grit is used for landfills 

1. First Settling Tanks:

• 40% of the organic matter settles down, remaining passes with the liquid into the next stage 

1. Aeration Tanks:

• Oxygen is added to the sewage liquid because of his the aerobic microorganisms begin to grow and reproduce.
• The organic matter is clumped; the solids are digested by enzymes released by these micro-organisms
• Some bacteria convert urea into nitrates and further into nitrogen gas 
• Protoctists eat the bacteria 
• Final products: N2,CO2 and the cytoplasm of bacteria and Protoctists(hence, water is fairly pure)

1. Second Settling Tank: 

• Micro organisms are made to settle out and returned to the aeration tanks to maintain their population.this is known as “activated sludge”
• The effluent joins a nearby river/water body 
• The sludge passes to a digester where it is used t produce methane(biogas)

Why organisms become endangered and extinct?

• The main reasons for organisms coming endangered or extinct are factors that reduce their population. They include 

1. CLIMATE CHANGE

• Due to global warming, in oceans a continued increase of even 1C can have devastating effects

1. HABITAT DESTRUCTION 

• Due to deforestation 

1. HUNTING/INTERNATIONAL TRADE 

• Tigers are hunted for their skins and bones and some body parts that are used in traditional Chinese medicines. 

1. POLLUTION 

• Increased CO2 levels, in oceans can cause decrease in pH and dissolves the calcium carbonate deposited in the corals, making them collapse

1. INVASIVE SPECIES

• Some species may be introduced accidentally or deliberately but once they find their way to the food chain and upset the natural balance. They would have no natural predators and so their numbers/population would definitely increase thus resulting in a reduction in the population of their prey 

Risks to a species upon decrease in population size

• Reduction in population size reduces the variation in the species and any changes in the environmental conditions puts them at a risk of extinction 
• It is very important because:

• It helps to reduce extinction 
• Protect vulnerable environments
• Maintain ecosystem functions such as nutrient cycling and resource provision(such as food, drugs, fuel and genes)

How can we conserve endangered species?

• Monitoring and protecting species 

• By making laws that make killing an offence; laws to protect the habitat 
• By international agreements on global bans or trading restrictions 
• Use wardens to protect the habitat 
• Reduce or control public access to the habitat 
• Control factors such as water drainage and grazing that may otherwise destroy the habitat 

• Education 
• Captive breeding 
• Can boost the numbers of the species by breeding in captivity and then releasing them back to the environment. It is important that:

      A) Animals do not become dependent on humans for food 

       B) there are suitable habitats left for them to inhabit 

• Seed banks acct as “gene banks”

• Are a way of protecting plant species from extinction 
• They include seeds from food crops and rare species 
• The Millennium Seed Bank Partnership was set up by Kew Botanical Gardens in London and involves. 80 countries are involved. It involves the conservation of 25% of the world’s plant species’.e, about 75,000 plant species 

Sustainable development

• Is the development providing for the needs of an increasing human population without harming the environment

• It requires the management of conflicting demands
• As the world’s population grows, the demand for the extraction of natural resources also increases; including food, housing 
• However , industry and agriculture should use natural resources sparingly and avoid damaging natural habitats and the organisms in them. This requires planning and voluntary organisations that work for wildlife conservation. 
• These include: Friends of the Earth, WWF(World Wildlife Fund), Green Peace