B10: ANSWERS Human influences on the Ecosystem
1. Read “Deforestation” pages 240-241.
2.
Use the “key points” on page 241 to complete these sentences.
Deforestation is due to the world demand for TIMBER and PAPER. The land is also
cleared for FARMS, CATTLE RANCHES and new ROADS.
3.
List the undesirable effects of deforestation in the table below.
An example has been completed for you.
Effect
Description
Soil erosion
Thin soils in rainforests will be washed away when not held
together by vegetation. This forms gullies and causes loss of plant
nutrients.
Severe
storms
Loss of trees in forests can cause changes in weather patterns
(wind etc), which can increase frequency and severity of storms.
Flooding
Water runs off the land faster when it is not absorbed by plants
and transpired back into the atmosphere.
Destruction
of habitats
and
extinction
Some plants and animals live only in certain areas. If the forests
that are their homes are cut down, this can cause extinction of
many species.
Carbon
When the chopped down trees are burnt, the CO2 is
dioxide build released into the atmosphere, increasing the concentration
up
of this greenhouse gas.
4.
Pollution is the harm done to the environment by the release of substances
produced by human activities.
Pollutants affect the air, ecosystems on land and aquatic ecosystems like rivers
and the sea.
Use page 242 to give examples of sources of water and air pollution.
Water pollution can be caused by sewage and chemical waste. Sources include:
FERTILISERS, SEWAGE, INDUSTRIAL CHEMICAL WASTE, PESTICIDES
AND HERBICIDES.
Air pollution by greenhouse gases are contributing to global warming. Greenhouse gases
include METHANE and CARBON DIOXIDE.
5.
Read “Pollutions of rivers and seas” pages 248-249.
6.
Define the term ‘eutrophication’, and explain how it occurs.
definition: the enrichment of waters with plant nutrients that can stimulate
the growth of algae and plants.
1.
2.
3.
4.
5.
6.
7.
8.
9.
FERTILISERS ARE LEACHED INTO RIVERS AND STREAMS FROM THE SOIL
The fertilisers cause the growth of algae in the water
Consumers of the algae cannot eat enough to limit the algal population
Algae populations grow large enough to cover the lake surface, preventing
light from reaching the plants below the surface
The water plants die as they are not getting enough light to photosynthesise,
they rot on the lake/river bed
Algae from below the surface populations also die as they are not able to
compete against the large surface population
Decomposers feed on the dead plants and algae
The decomposers use up oxygen in the water as they respire anaerobically
The lower levels of dissolved oxygen kills off fish and invertebrates as they
cannot respire
Changing the balance of one orgnaism in the food web can have a flow-on affect
to the rest of the populations.
In this case, increasing the success of the algae by providing it with added
nutrients ultimately caused the collapse of the entire ecosystem.
7.
Read “Acid rain” pages 246-247.
8.
Draw a diagram to show the causes and effects of acid rain.
See figure 19.6.1 on p246
9.
Complete the ‘summary questions 1-2’ on page 247 to summarise the causes
and effects of acid rain, and the measures that may be taken to reduce its
incidence.
1. Fossil fuels; dioxide; nitrogen oxides; nitric; sulfuric; acid
2. a
rain water dissolves atmospheric carbon dioxide to form carbonic
acid (slightly acidic)
b
sulfur dioxide and nitrogen oxides
c
fossil fuels and exhaust fumes
d
i) kills leaves and affects ability to fight disease
ii) on soils containing hard rocks like granite, there is nothing to
neutralise the acid (unlike limestone based soils which are basic),
causing plant nuturints like potassium and calcium to wash out of the
soil
iii) acid rain washes into lakes and rivers, causing the aluminium
levels to rise and lowering the pH, killing many fish and invertebrates
e
use low sulphur fuels; remove the sulfur from power station
chimneys; fit catalytic converters to car exhausts
10. Read “The Greenhouse Effect” pages 244-245.
11. Complete the table below about the sources and effects of greenhouse gases.
Gas
Carbon
dioxide
Sources
Effect
Respiration;
Combustion of fossil
fuels
Water vapour
Respiration;
combustion
Methane
Cattle; bacteria in
wetlands and rice
fields; rotting
material in landfills;
extraction of oil and
natural gas
Excess heat energy is trapped in the
atmosphere, causing global temperature
rises
12. List some of the likely consequences of global warming.





Polar ice caps could melt
Increase sea levels
Flooding of low-lying land areas
Changes to weather patterns
Change to agricultural areas and flow on effect to political and economic
stability
13. Read “Conservation” pages 250-251 and define the following terms:
1. Conservation: the management of ecosystems and resources to meet
changing conditions and needs
2. Species: a group of organisms with similar characteristics which are
capable of interbreeding and producing fertile offspring
3. Habitat: area where a population lives
4. Endangered: at risk of becoming extinct; may have low genetic diversity
5. Biodiversity: catalogue of all the species in an area, country or the
world; as well as the habitats and genetic diversity of the species
14. Give three reasons why humans should conserve ecosystems:
i.
ii.
iii.
Provide us with areas for recreation, medicines and methods for water
treatment
Maintain nutrient cycles
Keep pests and diseases in check by not disrupting species interactions
15. Give three ways that humans are conserving ecosystems and habitats:
i.
ii.
iii.
Marine reserves and parks (fishing areas)
National parks
Rescuing and breeding endangered animals and plants
Natural resources like water and non-renewable fossil fuels should also be conserved.
Fossil fuels form over millions of years; when the current supply is finished, there will be
none left. We can use more efficient machines to conserve fossil fuels and investigate
alternative energy supplies. Water should not be wasted and care should be taken to keep
water free of pollution.