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KGS N4N5 Unit 3 – Human Impact on the Environment
Learning Outcomes
Monoculture
 The human population is continuing to increase (called Population Explosion), this
means that there is an increased need for food
 We have grown vast monocultures, employed intensive farming techniques and
developed GM crops to try to meet demand
 A monoculture is an example of the intensive farming of plants
 It is a type of farming where only one variety of crop is grown
 Natural ecosystems have been cleared to accommodate monoculture crops
 Examples of monoculture crops: wheat, maize, rice and potatoes
 This type of farming relies heavily on the use of chemicals, even with their use,
increased food yield is now struggling to keep up with growing population
Intensive Farming
 Intensive farming techniques increase food yield from the same acreage of land
 Intensive farming involves growing high yield crops as monocultures
 Intensive farming techniques rely heavily on the use of chemicals
 Involves rearing animals indoors and often in confined spaces (battery-farming),
leaving more energy for growth than it being lost as heat/movement
 It allows more energy to be transferred to the intended consumer because pests
are removed
 Advantages:
 the crop grown is suitable for climatic conditions
 more machinery can be used, so labour costs are reduced, and planting and
harvesting are speeded up
 more than one harvest per year can occur
 Disadvantages:
 crops are genetically identical, so disease can spread more easily
 more fertilisers are used as growing the same crop year after year means that the
nutrients needed by the crop are used up
 the soil is compacted by machinery, meaning soil oxygen is reduced
 it reduces habitats available to wild animals
 reduces biodiversity (because natural ecosystems are cleared)
GM Crops
 The insertion of a useful gene from another organism into the cells of a crop plant
 It is thought that GM crops could help increase our food production to cope with
demand
 Examples of GM Crops:
 Maize resistant to insect pests
 Potatoes resistant to fungal blight
 Golden rice that contains a source of vitamin A
 Advantages:
 Some GM crops contain toxins that are harmless to humans
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GM crops reduce the quantity of crop lost
allow farmers to decrease use of chemicals without decreasing their yield
Disadvantages:
There is no guarantee that these crops will remain resistant to disease
some people believe these plants carry a risk to human health
people are concerned that genetic material being introduced into plants could lead
to undesirable strains (e.g. super-weeds)
Fertilisers & Pesticides
 A fertiliser is a chemical that improves plant growth
 It is added to the soil to increase the minerals in the soil e.g. nitrogen (nitrates) or
magnesium
 Plants require nitrates for making nucleic acids and amino acids
 Magnesium is required for the formation of chlorophyll
 Phosphorus is required for production of ATP & nucleic acids
 Potassium is required for the formation of fruit/flowers
 Fertilisers can be leached from the soil and washed into fresh water (after heavy
rainfall)
 If fertiliser leaches into a river/loch, it makes the water over-rich in nutrients
 This causes algal bloom as the algae grow rapidly
 The algae then die in huge numbers & the bacteria that decompose them undergo a
‘population explosion’ (eutrophication)
 The bacteria use up the oxygen dissolved in the water
 Plants are unable to obtain light for photosynthesis and can die
 Dead plants under the water increase the food available for bacteria, which then
multiply and use up even more oxygen
 Using natural fertilisers e.g. manure/compost, reduces the risk of algal bloom
 A pesticide is a chemical used to kill organisms that are in competition with the crop
plant
 Pesticides are specific: Fungicides kill fungi, insecticides kill insects, herbicides are
used to kill plants and bactericides are used to kill bacteria
 Some pesticides sprayed on to crops accumulate in the bodies of organisms over
time, this is called bioaccumulation
 Bioaccumulation means that the level of pesticide found in the body of organisms
increases as the position on the food chain increases
 E.g. DDT (used widely in 1950s and 1960s)
 DDT was sprayed onto plants and entered the food chain when the contaminated
plants were eaten
 DDT is now banned due to its harmful effect on biodiversity
 e.g. DDT caused the thinning of egg shells meaning that chicks hatched before they
were strong enough to survive
 It has been found in water ecosystems and traces of DDT have been found in
tissues of penguins in the antartic
Pollution
 Pollution is the addition of substances to the environment that cause harm to
organisms
 An indicator species tells us something about the level of pollution and
environmental quality
 Indicator species indicate levels of pollution by either their presence or absence
 Freshwater invertebrates and lichens are indicator species
 Polluted water has low levels of oxygen
 The presence of mayfly and stonefly larvae indicates that there are low levels of
pollution and high levels of oxygen
 However, the presence of rat-tailed maggots and sludgeworms indicates that there
is high level of pollution and low level of oxygen in the water
 Polluted air may have a high sulphur dioxide concentration
 The presence of hairy lichen indicates that there is a low level of sulphur dioxide in
the air
 The presence of only crusty lichen indicates that there is a high level of sulphur
dioxide in the air
Biological Control
 Biological control is the deliberate use of natural predators to control pests in
farming
 Ladybirds to clear greenfly and caterpillar moths have been used in biological
control
 Using biological control (BC) methods reduces the effects of harmful chemical
pesticides that may kill helpful insects that act as pollinators
 Using BC means that the pests do not usually become resistant to the treatment
 BC methods mean that bioaccumulation does not occur and pesticides do not enter
the food chain
 There is no risk to human health as chemicals are not being sprayed on the crop
 In BC, the introduced predator is specific to the pest, meaning that biodiversity is
not reduced
 BC is more effective in small growing areas, since the predator is less likely to move
out of the area
 In some cases the natural predator has become a pest itself e.g. cane toad
Human Influences on Biodiversity
 pH of habitats are affected by Acid Rain
 Acid Rain is formed when sulphur dioxide and nitrogen dioxide are released when
fossil fuels are burned
 Acid rain indirectly decreases Plant Biodiversity as the acid destroys leaves so the
plants can’t photosynthesise properly
 Acid rain decreases Fish Biodiversity as it lowers the pH of freshwater which leads
to fish deaths
 The temperature of habitats is affected by Global Warming
 Global Warming is caused when fossil fuels are burned and Carbon dioxide, Nitrous
Oxide and Water Vapour are released and form a blanket around the Earth’s
atmosphere. These gases trap heat and cause global warming.
 An increase in temperature decreases fish Biodiversity as enzyme-controlled
reactions do not work properly
 Exploitation is when something is used in order to gain a benefit e.g. humans have
used trees to make paper
 The increase in the human population has led to over-exploitation – taking too much
from the environment
 Over-exploitation has led to a decrease in Biodiversity
 Examples of over-exploitation include over-hunting, over-fishing, over-grazing,
habitat destruction (e.g. desertification, deforestation)
 Foreign (Introduced) Species cause the native species to become endangered (e.g.
White-Clawed Crayfish)
 Pollution is anything that is added to the ecosystem that causes harm
 Air, Land, Freshwater and Seawater can become polluted and Biodiversity decreases
 Organisms whose presence or absence gives information about the levels of pollution
are called Indicator Species e.g. Lichens are sensitive to Sulphur Dioxide
Natural Disasters and Biodiversity
 Forest fires, Earthquakes, Volcanic Activity, Tsunamis, and Wind all decrease
Biodiversity