Ecology and the
environment
The organism in the environment:
Ecosystem - a distinct, self-supporting system of organisms interactions with
each other and with a physical environment.
Population - all the organisms of a particular species found in an ecosystem.
Community - the population of all the species in an ecosystem.
Habitat - the places where specific organisms in an ecosystem live.
Niche - the role of a certain species.
Quadrats:
1. Divide sample area into a
numbered grid using a tape measure.
2. Select pairs of coordinates at random.
3. Place each quadrant at the coordinate and count the number of each
species or percentage cover.
4. Repeat several times (at least 10).
5. Calculate the mean average.
To overcome biased data random sampling is used
though the selection of coordinates at random.
To overcome data due to chance many repeats are
done.
Feeding relationships:
Humans inhabit many of the Earth’s ecosystems.
An ecosystem is a distinct, self-supporting system interaction with each other
and with their physical environment.
Ecosystems have:
•
Producers - green plants that
photosynthesise.
•
Consumers - animals that eat
plants or other animals.
•
Decomposers - Microorganisms
that break down dead material and help in recycling nutrients.
•
Physical environment - the
non-biological components such as water, soil and air.
Plants are the source of all the food that
animals, including humans, eat. They also create oxygen which aerobic organisms
need for respiration. Plants can create oxygen from glucose, starch, sugars
such as fructose or sucrose, cellulose and lipids.
Food chains are made up of trophic levels:
Producer
—> Consumer (primary, secondary, tertiary etc.)—> Decomposers
Energy and substances are transferred along a
food chain. Every time energy is transferred a lot is lost through the lack of
digestion and therefore passes out as faeces. Some form excretory products such
as urea and some is respired to release energy. Not only this, but a large
amount of energy is also lost through respiration. Because of this, only around
10% of energy is used to create new cells and therefore can be passed on to the
next trophic level. This means that generally food chains are short as
organisms must eat many organisms from the trophic level below. This creates a
pyramid shaped pyramid of energy transfer.
Food chains - shows which organisms eats which organisms and shows the
direction in which this happens.
Food web - formed when food chains are linked together. They show a more
realistic view of a food chain as obviously most organisms eat more than one
source of food.
Pyramid of number - represent the flow of energy through a good chain by telling us
the number of organisms at each trophic level.
Pyramid of
biomass - similar to a pyramid of number except
that it uses the total amount of living material rather than number of
organisms. It is more realistic that a pyramid of number as the pyramid of
biomass will almost always be pyramid shaped. It therefore shows the efficiency
of every transfer between trophic levels better.
Pyramid of energy
transfer - similar once again to the other
pyramids except that it uses the amount of energy as the measure. It is the
most realistic way of representing energy transfer. However, it is hard to
measure and difficult to scale.
Cycles within ecosystems:
Water Cycle:
Carbon Cycle:
Nitrogen Cycle:
Carbon Monoxide:
This is a colourless, odourless and tasteless
gas which can cause death by asphyxiation. Haemoglobin bind with this rather
than oxygen and so a person may become unconscious if it’s breathed in for a
certain time as a result of a lack of oxygen.
Sulfur Dioxide:
This is a major constituent of acid rain which
kills plants and also ruins the landscape.
Green House Gases:
These include water vapour, carbon dioxide,
nitrous oxide, methane and CFCs (chlorofluorocarbons).
The level of greenhouse gases has risen rapidly
in the past 100 years. The increasing burning of fossil fuels such as coal, oil
and natural gases as well as petrol and diesel in vehicle engines has led to
this. The increasing deforestation also means that the greenhouse gas carbon
dioxide is used less in photosynthesis.
The increasing levels of greenhouse gases has
resulted in the enhanced greenhouse effect. The normal greenhouse effect is
where gases absorb some long wavelength infra-red radiation from the sun and
re-emit some as longer wavelength IR. This heats up the surface of the Earth.
However, with too much greenhouse gases, global warming has occurred where the
earth heats up quicker than it should. This has caused the melting of the ice
caps and therefore sea level rises, changing ocean currents meaning warm water
is redirected to cooler areas, more rainfall in some areas (climate changes),
species to become extinct as they cannot adapt fast enough and changes to
agricultural practices as some pests become more abundant. Furthermore, changes
to the food chain occurs as well as mass migration.
Sewage must be treated as they contain pathogenic bacteria which can cause
diseases if drunk and also because aerobic bacteria in the water will deplete
the amount of oxygen in the water by breaking down the organic material in the
sewage. This then causes death to species not adapted to low oxygen levels.
Eutrophication occurs when excess minerals such as nitrates and phosphates enter a
body of water from sewage or fertilisers. Fertilisers can enter the water
through leeching as nitrates and such are washed out of the soil by rain since
it dissolves in water. This can also occur through surface run offs. Excess
minerals stimulates the growth of algae. An algal bloom will develop and block
out the light needed for photosynthesis and are also decomposed as they die.
This is done by aerobic bacteria which uses up oxygen in the water. This causes
oxygen depletion, causing many fish and plants to die. In severe cases, the
water will become anoxic (containing very little oxygen) and become smelly from
the gases such as hydrogen sulphide and methane which are released by the bacteria.
Only anaerobic bacteria can survive conditions like these.
Deforestation:
Each year tens of thousands of hectares of
rainforests are cut down. This causes several problems:
1. Soil erosion occurs as it is exposed due to lack of a canopy meaning
the soil is down or washed away.
1. Leeching occurs where minerals are washed out by rain. This occurs
as there are no tree roots to hold the soil together.
2. Destruction of habitats and reduced biodiversity occurs. Around
50-70% of all species live in rainforests.
3. The water cycle is disturbed as trees are an important part of
returning water vapour from the soil.
4. The balance in atmosphere oxygen and carbon dioxide changes as
photosynthesis decreases. This will cause global warming
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