B13 : Human Influences on ecosystems Flashcards
1
Q
Carbon cycle
A
- Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
- It is passed on to animals and microorganisms by feeding
- It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
- If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels (fossilisation)
- When fossil fuels are burned (combustion), the carbon combines with oxygen and carbon dioxide is released into the atmosphere
2
Q
Effects of the combustion of fossil fuels and deforestation
A
- Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere
- Mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis
- This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are burnt down, releasing yet more carbon dioxide into the atmosphere
3
Q
Undesirable effects of deforestation
A
- Species extinction through habitat loss
- Loss of soil by soil erosion
- Flooding
- Carbon dioxide build up
4
Q
Species extinction through habitat loss
A
- Deforestation leads to a reduction of habitats or food sources for animals can result in their extinction
- Loss of forest habitat also reduces plant & animal diversity & disrupts the food chains
5
Q
Loss of soil by soil erosion
A
- Tree roots help to stabilise soil, preventing it from being eroded by rain
- Removal of trees means there are no roots to hold soil, thus the thin top layer of soil is washed away
- This causes soil erosion and leaching of minerals → leaching is when a soluble chemical or mineral is washed away from the soil by rainwater
- Loss of soil nutrients is permanent and makes it very difficult for forest trees to regrow, even if the land is not cultivated with crop plants or grass for cattle
- Desertification can eventually result (land becomes a desert)
- It can also lead to flooding
6
Q
Flooding
A
- Soil from erosion is washed into rivers, silting it (fill up / become blocked) and causing flooding
- When forest is removed there are no plant roots to take up rainwater, which instead flows into streams and rivers, causing further flooding
7
Q
Carbon dioxide build up
A
- Forests have high rates of photosynthesis so absorb large amounts of carbon dioxide from the atmosphere
- This means that a lot less carbon dioxide will be removed from the atmosphere
- Removal of forests therefore contributes to increases in atmospheric carbon dioxide
- Trees are often burned instead of being cut down → releases carbon dioxide into the atmosphere (combustion)
8
Q
Sources of pollution of water
A
- Chemical waste
- Discarded rubbish
- Untreated sewage
- Fertilisers
9
Q
Chemical waste
A
- Chemicals such as heavy metals like mercury can be released from factories into rivers and oceans or leach into land surrounding the factories
- Many heavy metals and other metals are persistent - they do not break down
- So they can build up in food chains (bioaccumulation), poisoning the top carnivores
10
Q
Discarded rubbish
A
- Much rubbish consists of plastic that is either discarded or buried in landfills
- Much rubbish is non biodegradable and remains in the environment for hundreds of years
- Animals also eat plastic as it breaks into smaller pieces and can get into food chains this way
11
Q
Untreated sewage
A
- Lack of sewage treatment plants in inhabited areas due to poor infrastructure / lack of money → sewage runs or is pumped into streams or rivers
- Provides a good source of food for bacteria which increase rapidly, depleting the oxygen dissolved in the water (as they respire aerobically)
- This causes the death of aquatic organisms such as fish → eutrophication
12
Q
Fertilisers
A
- Runoff from agricultural land if applied in too high a concentration
- Causes algal blooms, which then die and provide a good source of food for decomposing bacteria
- Bacteria increase rapidly and deplete the oxygen dissolved in the water
- Cause the death of aquatic organisms → eutrophication
13
Q
Eutrophication
A
- Runoff of fertilisers from farmland enters the water - there is an increased availability of nitrate and other ions
- This causes increased growth of algae and water plants
- The resulting ‘algae bloom’ blocks sunlight
- Water plants on the bottom start to die, as does the algae when competition for nutrients becomes too intense
- As water plants and algae die in greater numbers, decomposing bacteria increase in number and use up the dissolved oxygen whilst respiring aerobically
- As a result, there is less oxygen dissolved in water → aquatic organisms that require oxygen, such as fish and insects, are unable to survive
14
Q
Nitrogen cycle
A
- Nitrogen is present in all living organisms.
2. It moves through food chains and is recycled when organisms die.
15
Q
Water cycle
A
- This cycle describes how water moves on, above or just below the surface of our planet between different locations, such as rivers, oceans and the atmosphere.
- For this cycle to be completed, water has to change state.
