19.4 Effects of Humans on Ecosystems (Cambridge (CIE) O Level Biology): Flashcards
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Define deforestation.
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Define deforestation.
The clearing of trees, usually on a large scale.
When can deforestation be a sustainable practice?
When the trees that are cleared are replaced by replanting.
List the main undesirable effects of deforestation.
The main effects are:
extinction of species
loss of soil
flooding
increased carbon dioxide in the atmosphere
Tree roots help to stabilise the soil, preventing it from being by rain.
Tree roots help to stabilise the soil, preventing it from being eroded by rain.
How does deforestation lead to soil erosion?
Without tree roots to stabilise the soil it is washed away by rain, and its nutrients are leached out.
True or False?
Removing trees increases the risk of flooding.
True.
Loose topsoil is easily washed away, increasing the risk of flash flooding and landslides.
Why does deforestation increase carbon dioxide in the atmosphere?
Fewer trees carry out photosynthesis, so less carbon dioxide is removed; burning the trees releases more.
When cleared forest trees are burned, is released, contributing to global warming.
When cleared forest trees are burned, carbon dioxide is released, contributing to global warming.
True or False?
The loss of soil nutrients after deforestation is only temporary.
False.
The loss of soil nutrients is permanent, making it very difficult for forest trees to regrow.
Why is deforestation a particularly severe example of habitat destruction?
It destroys habitats with very high biodiversity (e.g. rainforests), causing the extinction of many species.
Give two reasons land is usually cleared by deforestation.
Reasons include:
building
grazing for cattle
planting monocultures (e.g. palm oil)
Define invasive species.
A species that has moved into an ecosystem where it was previously unknown.
Give two ways in which animals are over-harvested.
Animals can be over-harvested by:
hunting to near extinction
exploiting them for body parts (e.g. ivory)
over-fishing
What are two general consequences of all kinds of over-harvesting?
It can increase pollution and reduce biodiversity.
Over-harvesting crops can reduce the content of the soil to critical levels.
Over-harvesting crops can reduce the mineral content of the soil to critical levels.
Define monoculture.
Growing only one type of crop over a large area of land.
Why do monocultures have low biodiversity?
Only one species of plant is grown, so few other plant and animal species are supported.
True or False?
Monoculture farming tends to increase pest populations.
True.
A large, repeated supply of one crop provides an ample food source for pests.
Why can an invasive species increase in number rapidly in a new ecosystem?
It has no natural predators or competitors to keep its numbers in check.
Invasive species can out-compete native species, which may be displaced or pushed to .
Invasive species can out-compete native species, which may be displaced or pushed to extinction.
Give two harmful effects an invasive species can have on native species.
An invasive species can:
out-compete and displace them
prey on them, reducing their numbers
introduce new diseases
True or False?
Most recorded introductions of invasive species have been caused by humans.
True.
For example, through trade, accidental transport, or deliberate use as biological control.
Why do native species often have no defence against a new invasive species?
They have no natural immunity to new diseases it brings and are not adapted to compete with it.
Define eutrophication.
The enrichment of water with nutrients, leading to loss of dissolved oxygen and the death of aquatic organisms.
How does untreated sewage entering a river reduce the oxygen in the water?
It provides food for bacteria, which increase rapidly and use up the dissolved oxygen as they respire.
What causes fertiliser to enter rivers and lakes?
Runoff from agricultural land, especially when fertiliser is applied in too high a concentration.
Fertiliser runoff contains and other mineral ions that cause increased growth of algae.
Fertiliser runoff contains nitrates and other mineral ions that cause increased growth of algae.
What is an algal bloom, and what effect does it have on the water below?
A rapid growth of algae that blocks sunlight, so the water plants below begin to die.
Why do decomposing bacteria increase in number during eutrophication?
As algae and water plants die in large numbers, they provide a good source of food for the bacteria.
True or False?
During eutrophication, decomposing bacteria use up the dissolved oxygen in the water.
True.
They respire aerobically, lowering the oxygen level so that aquatic organisms may die.
As oxygen levels fall during eutrophication, aquatic organisms such as may be unable to breathe and die.
As oxygen levels fall during eutrophication, aquatic organisms such as fish may be unable to breathe and die.
Put the stages of eutrophication in order after fertiliser runoff.
The stages are:
algae grow rapidly (algal bloom)
sunlight is blocked, so water plants die
decomposing bacteria increase and use up oxygen
aquatic organisms die
True or False?
Eutrophication increases the amount of oxygen dissolved in water.
False.
Eutrophication reduces dissolved oxygen, causing aquatic organisms to die.
Name two sources of water pollution.
Sources include:
untreated sewage
chemical waste from factories
fertiliser runoff
A shortage of sewage plants means sewage may run straight into streams or rivers.
A shortage of sewage treatment plants means sewage may run straight into streams or rivers.
Name two greenhouse gases that act like a blanket around the atmosphere.
Carbon dioxide and methane
Which human activity increases the level of carbon dioxide in the atmosphere?
Burning fossil fuels
Which human activity is a major source of methane gas?
Keeping livestock (cattle)
Higher levels of carbon dioxide and methane have led to global warming and change.
Higher levels of carbon dioxide and methane have led to global warming and climate change.
True or False?
Global warming can melt permafrost, releasing even more methane into the atmosphere.
True.
This releases trapped methane, adding further to the greenhouse effect.
Define biomagnification.
The increase in concentration of a pollutant, such as a pesticide, at each trophic level of a food chain.
In biomagnification, which organism is worst affected by a pesticide?
The top predator of the food chain.
Pesticides can reach rivers and oceans in from farmland.
Pesticides can reach rivers and oceans in runoff from farmland.
Define microplastics.
Very small pieces of plastic formed as larger plastic breaks down.
True or False?
Plastics are non-biodegradable.
True.
They do not break down easily, so they can harm marine and land habitats for a long time.
Give two ways plastic harms marine animals.
Plastic can harm marine animals because they:
try to eat it
become caught in it
ingest microplastics that enter the food chain
Why is land used for plastic landfill unsuitable for crops for decades?
As the plastic breaks down it releases toxins into the surrounding soil.
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