iGCSE Biology Notes Human influences on ecosystems

[q] Food supply

[a] 

Food supply
○ How modern technology has increased food production:
■ Agricultural machinery to use larger areas of land and improve efficiency
■ Chemical fertilisers to improve yields
■ Insecticides to improve quality and yield
■ Herbicides to reduce competition with weeds
■ Selective breeding to improve production by crop plants and livestock

[q] Large – scale Monocultures of crop plants

[a] 

○ Negative impacts on ecosystem
■ Only one type of crop is grown
■ Biodiversity is lower
■ Increase in pest population, if a particular pest feeds upon a crop there will be an abundance of that pest
■ Spraying insecticides leads to:
● Harmless insects being killed
● Pollution by pesticides
● The pests may become resistant to them, reducing their effectiveness

[q] Intensive livestock farming

[a] 

○ Large numbers of livestock are often kept in an area that would not normally be able to to support more than a very small number
○ They are often fed high energy foods
○ Given antibiotics
○ Kept in small spaces
○ Ecological issues with intensive farming:
■ Reduction in biodiversity in areas where large amounts of land are used to graze cattle
■ Overgrazing can lead to soil erosion
■ Large numbers of cattle produce large amounts of methane (greenhouse gas)

[q] Global food supply

When people do not receive enough food, famine occurs
Caused by

[a] Natural disasters 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Drought 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Flooding 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Increasing population 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Poverty 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Unequal food distribution 

[q] When people do not receive enough food, famine occurs
Caused by

[a] More land is required to grow crops and animals 

[q] When people do not receive enough food, famine occurs
Caused by

[a] Global warming

[q] Habitat destruction 

Reasons

[a] 

■ Increased area for food crop growth, livestock producing and housing
■ Extraction of natural resources
■ Marine pollution
■ deforestation

[a] Through altering food webs and food chains, Humans can have a negative impact on habitats 

[a] Undesirable effects of deforestation on habitat destruction:
■ Extinction
■ Flooding
■ Increase of carbon dioxide in the atmosphere

[a] Undesirable effects of deforestation on environment:
■ Extinction/ loss of biodiversity
■ Soil erosion
■ Flooding
■ Increase co2 in atmosphere
● Plants are unable to remove enough co2

[q] Pollution
Source and effects of pollution of land and water

[a] Insecticides, herbicides, and by nuclear fall-out (effect water bodies) 

[q] Pollution
Source and effects of pollution of land and water

[a]

• Chemical waste (water)
  
• Poison top carnivores

[q] Pollution
Source and effects of pollution of land and water

[a]

• Discarded rubbish
  
• Can get into food chains way

[q] Pollution
Source and effects of pollution of land and water

[a] ■ Untreated sewage
● Causes eutrophication

[q] Pollution
Source and effects of pollution of land and water

[a] ■ Fertilisers
● Causes algal bloom

[q] Pollution 

Eutrophication

[a] Increased availability of nitrate and other ions 

[q] Pollution 

Eutrophication

[a] Increased growth of producers (algae) 

[q] Pollution 

Eutrophication

[a] Increased decomposition after death of producers 

[q] Pollution 

Eutrophication

[a] Increased aerobic respiration by decomposers 

[q] Pollution 

Eutrophication

[a] Reduction in dissolved oxygen 

[q] Pollution 

Eutrophication

[a] Death of organisms requiring dissolved oxygen in water 

[q] Plastic pollution
In marine habitats

[a] ● Animals try to eat plastic, leading to injuries and death
● As the plastic breaks down it can release toxins these affect marine organisms

[q] Plastic pollution 

On land

[a] ● Plastic’s toxin can cause soil erosion,
○ Become no good for growing crops or grazing animals

[q] Pollution 

Female hormones

[a] ■ Female contraceptive hormones are excreted from the body in urine and then make their way into the water supply, as they are not filtered out by sewage treatment plants
■ If they reach male aquatic organisms, such as fish and frogs, they are very sensitive to hormone, it can cause feminisation
● Where males begin to produce eggs and lose the ability to reproduce
● Lose the ability to reproduce
■ Reduce the sperm count in human males and cause fertility problems

[a] ■ Causes: Sulphur dioxide, oxides of nitrogen
■ Sources: burning of fossil fuels, combustion of petrol in car engines
■ Effects: damage to leaves, killing plants
● Acidification of lakes, killing animals
● Increased risk of asthma attacks and bronchitis in humans
● Corrosion of stonework on buildings
● Release of aluminium from the soil into lakes that are toxic to fish

[a] ■ Greenhouse gas is a gas that absorbs infrared radiation from the sun
● It remains in the Earth’s atmosphere
■ This increases the average temperature of the earth

[q] Greenhouse gases 

[a] ● Carbon dioxide
● Water vapour
● Methane
● CFCs 

[q] Consequences 

[a] ● Ocean temperatures increases
○ Causing polar ice caps to melt, increasing sea levels
● Increase temperatures cause extreme weather
● Can lead to changes in or loss of habitats
● Decrease in biodiversity
● Increase in migration
● Spread of pests and diseases

[q] Conservation

[a] ○ A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not run out
○ Some resources such as fossil fuels are non- renewable because they cannot be replaced
○ These resources, once used, cannot be produced anymore and so they need to be conserved by reducing the amount we use and finding other, sustainable resources to replace them
○ Some products like plastics or metals can be reused and recycled to make new things
○ Some resources, such as forests and fish stocks, can be maintained, Enabling us to harvest them sustainably

[q] Conservation 

Sustaining forests

[a] ■ Forests are need to produce paper and provide wood for timber
■ Much of the world’s paper is now produced from forests which replant similar trees when mature trees are cut, ensuring that there will be adequate supply in the future
■ Using these types of wood has now been made more sustainable due to schemes designed to monitor logging companies and track the wood produced
■ Education helps to ensure logging companies are aware of sustainable practices and consumers are aware of the importance of buying products made from sustainable sources 

[q] Conservation 

Sustainable development

[a] ○ Sustainable development
■ Sustainable development is defined as development providing for the needs of an increasing human population without harming the environment
■ When developing the way in which we use resources to manage them sustainably, we have to balance conflicting demands
● The need for local people to be able to to utilise the resources they have in their immediate environment with the needs of large companies to make money from forests and fishes
● Need of balancing what current populations need with what future populations might need
■ For development to occur sustainably, people need to corporate at local, national and international levels 

[a] ■ Methods to manage fish stock sustainably
● Controlling the number of fish caught each year
● Controlling the size of fish caught
● Controlling the time of year that certain fish can be caught depletion of stocks when fish come together in large numbers in certain areas
● Restocking
● Educating fishermen on local and international laws

[a] 

■ Pipes carry sewage water to treatment plants where the organic waste is removed and the water cleaned so it can be returned to natural water sources without causing eutrophication
■ Crude sewage flows through a screen in which large materials like paper and sticks are trapped
■ The sewage is passed slowly through channels where grit and other particles are picked up along the way settle to the bottom – grit is washed and returned to land
■ The channels lead to sedimentation tanks, where the solid material settles on the bottom as sludge and the liquid part, called effluent, remains on top
■ Sludge is removed by pumping it into tanks where anaerobic bacteria decompose it
● The bacteria produce methane which is then used as a energy source
■ The liquid called effluent is treated with aerobic bacteria to remove any organic waste in it
■ The liquid is then treated with chlorine to kill the bacteria
■ It can be returned to natural water systems now

[a] 

■ Species that at risk of going extinct
■ Causes
● Not enough genetic variation in the population
○ Inability to adapt
● Hunting
● Climate change
● Pollution
● Introduction of non-native species
○ Outcompetes native species
■ Solutions
● Education programmes
● Captive breeding programmers
● Monitoring and legal protection
● Seed banks
○ For plants that are going to be extinct