Investigating an Ecosystem
Identify habitat, animals and plants as the main parts of an ecosystem
The main parts of an ecosystem are living organisms and the place where they live.
All organisms are either plants or animals
The place where an organism lives is called its habitat
There are a wide variety of habitats e.g.
fish live in water
birds live in trees
It is usually impossible to count all the plants and animals living in an ecosystem so
biologists use various methods for estimating the types and numbers of organisms in an
ecosystem.
Give an example of a technique which might be used for sampling organisms, and
describe its use
Quadrat
Quadrats are use to sample:
plants on the ground since they do not move
seashore animals since they are usually very slow moving
A quadrat marks off an exact area so that plants in an area can be
identified and counted.
Pitfall trap
Pitfall traps are used to sample small invertebrates living on
the ground. They fall into the trap and are unable to climb out
again.
Tullgren Funnel
Used to sample tiny animals that live in the air spaces in soil
They move away from the hot, dry, bright conditions and fall
through the sieve
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Water net
Used to catch pond animals that are quickly
transferred to screw-top jars containing pond water
Beating stick and tray
Tap tree branches with the stick and catch small
animals in the tray
Identify a possible source of error that might accompany a sampling technique and
explain how it might be minimised
Technique
Quadrat
Pitfall
trap
Possible error
Plants might be wrongly identified or
counted
The quadrat might not be placed randomly
Badly set traps may catch no animals
some animals may get eaten by other
animals before they are examined
results not reliable
Way of minimising the error
Take more samples to make the
results more reliable
Place the quadrat randomly
Traps should be level with the
ground
Trap should be examined often
set more traps
Identify two abiotic factors
An abiotic factor is a non-living factor (often related to the weather) which can affect
the distribution of organisms in an ecosystem. Some abiotic factors are:
Soil pH
The Sun provides light
Temperature – it cant be too hot or cold
Moisture
Oxygen is needed to release energy from aerobic respiration
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Give an example of a technique which might be used to measure an abiotic factor and
describe its use
Abiotic factors can be measured using meters
Light meters measure light intensity.
The meter is held at the soil surface and pointed in
the direction of maximum light intensity, the
reading on the meter is then noted.
Soil
moisture meters and soil pH meters
are used by pushing the probe
into the soil and reading the meter.
Temperature is measured using a thermometer. The bulb of
the thermometer is placed into the substance whose temperature
is to be taken.
Identify a possible source of error that might accompany a measurement technique and
explain how it might be minimised
Standing in front of a light meter can cause an error in the reading as this will block
the light.
When comparing light intensities of different ecosystems, you should ensure that
readings are taken at the same time of day, in similar weather conditions . This will
allow a fair comparison.
You must wipe a moisture meter probe in between sampling different areas so that you
remove moisture from a previous measurement before making the next measurement.
Try to use a meter which is as accurate as possible.
For all of the meters you could improve the reliability of your results by repeating the
experiment.
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State the effect an abiotic factor has on the distribution of an organism
Green plants are not usually found where the light intensity is too low.
Most organisms do not like too hot or too cold temperatures.
Most land organisms are not found in very wet or very dry areas.
Explain possible mechanisms by which abiotic factors might influence the distribution
of organisms
Extremes of temperature affect the numbers of organisms found in ecosystems. Many
organisms cannot survive extremes of temperature.
Many green plants are not found in areas with low light intensity as too little light limits
the rate of photosynthesis.
Most land organisms are not found in areas which are too dry as they would become
dehydrated.
Animals and plants are not found in very wet soil because they may drown.
How it works
Describe what is meant by habitat, population, community and ecosystem
An ecosystem is a natural biological unit made of living (biotic) and non-living (abiotic)
parts.
Ecosystem =
community +
habitat
A habitat is the place where an organism lives.
A community is made up of all the plant and animal populations living in the ecosystem.
A population is a group of organisms belonging to the same species.
Consider a freshwater ecosystem
There are a number of different habitats e.g.
the riverbed, the pondweed, the water surface.
There are members of the community e.g.
pondweed, plankton and fish
There are a number of different populations
e.g. plankton, pondweed
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Describe what is meant by producer and consumer
Producers make their own food by photosynthesis.
All producers are green plants. They trap light
energy from the Sun and convert it into chemical
energy.
All animals and non-green plants cannot make their own food. They obtain the energy
they need by eating green plants or animals that have eaten green plants. These
organisms are consumers.
There are 3 types of animal consumer:
carnivores eat other animals e.g. lion
herbivores eat plants e.g. sheep
omnivores eat plants & animals e.g. humans
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Give an example of both a food chain and a food web
A food chain is a diagram showing feeding relationships
between several living things. Arrows in a food chain point
from food to feeder. All of the energy in a food chain
or web comes from the Sun.
Grass - - - - - - - - - > rabbit - - - - - - - - - - - - >fox
The producer is the grass.
The consumers are the rabbits and fox
There are 2 types of consumer primary and secondary.
Primary consumers eat producers. Secondary consumers eat primary consumers.
Predator and prey
Predators are animals that hunt other animals. Victims of predators are called prey.
e.g. lion and antelopes, foxes and rabbits etc.
A food chain rarely exists in isolation as
there are normally a number of consumers
eating the producer. In turn the
consumers are preyed upon by a number of
predators.
More complicated diagrams showing
interconnected food chains are called food
webs.
Explain possible effects of the removal of one species on the remaining organisms in a
food web
If one species is lost from a food web all others will be affected.
If all of the trees disappear there will be no food for the mushrooms and caterpillars
so they will die out. The animals which eat the mushrooms will also die out. The mice will
survive as they will eat more of their other foods to replace the caterpillars. This will
affect the number of other organisms in the food web.
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State that the arrows in a food web indicate the direction of energy flow
In a food chain energy is transferred from food to feeder.
State 2 ways in which energy can be lost from a food web
Only about 10% of the available energy is passed on at each stage of a food chain.
Energy is lost through:
Movement
Heat
Undigested food
Explain what is meant by the terms pyramid of numbers/biomass
Consider the following food chain existing in a field 1 square mile in size:
Grass  rabbit  fox
As you go up the food chain the size of the organism usually increases (except in food
webs where the producer is a tree). The species present in the highest number is
usually the producer (except when the producer is a tree)
It is possible to write a food chain as a
pyramid. It is called a pyramid because
there are fewer organisms at successive
levels.
As you go up the pyramid the number of
organisms at each level decreases.
An unusual pyramid of numbers
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A more accurate idea of the quantity of animal and plant
material at each level of the pyramid is obtained by
weighing all of the organisms at each level. This is
called the biomass.
As you move along a food chain the biomass decreases
State that the growth rate of a population depends on birth and death rates
Birth rate is the number of live organisms born in a certain period of time.
Death rate is the number of organisms that die every year.
The growth rate depends on both the birth rate and the death rate.
The population of India is increasing as the birth rate
is higher than the death rate.
If the death rate was higher than the birth rate then the population size would
decrease.
State three factors which can limit the growth of a population
Some factors limit the size of populations:
lack of food causes death in famines
Lack of water
animals are prey to predators
disease e.g. measles, influenza
lack of space
toxic waste produced by the population build up and poison future
generations
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Describe the growth curve of a population under ideal conditions
Under ideal conditions there are no limiting factors
and the population explodes.
Explain the growth curve of a population under ideal conditions
A small number of organisms colonise a new
environment.
Growth is slow because the population is small.
Then the numbers increase dramatically in the
absence of limiting factors.
The population stops growing because of a
shortage of resources or the accumulation of
toxic waste.
State that competition occurs when organisms have a need for the same resources
Plants might compete for:
space
light
water
minerals and other nutrients
Animals compete for:
food e.g. predators might compete for the same prey
living space
partners to mate with
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Describe some effects of competition
‘Weaker’ members of the population die before reproductive age. Stronger more
successful competitors survive and become the parents of the next generation.
Explain the importance of nutrient cycles to the organisms of an ecosystem
Living things need nutrients to stay alive and grow. Nutrients are recycled.
Decomposer organisms release nutrients from dead bodies back into the environment.
If there were no decomposers nutrients would run out. Other living things would die if
there were no decomposers.
Nutrients such as carbon and nitrogen must be recycled between living organisms, the
air and the soil so that organisms in an ecosystem will continue to have the necessary
elements to reproduce and grow.
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Describe the sequence of processes in the nitrogen cycle
Living things need nitrogen to make protein.
Lightning is a natural method of adding nitrates to the soil.
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Control and Management
State that pollution affects air (A), fresh water (W), sea (S) and land (L)
Pollution occurs when the presence of a substance (the pollutant) causes harm to
organisms, looks unsightly or causes damage to buildings.
The 4 ecosystems that are mainly affected by pollution are
Air
Land
Sea
Fresh water
State that the main sources of pollution are domestic, agricultural and industrial, giving
an example of a pollutant from each
The main three source of pollution are
domestic - the home e.g. detergents (W), household waste (L) and sewage (W)
agricultural - the farm e.g. fertilisers (W) and pesticides (W)
industrial - industry e.g. oil (S), sulphur dioxide (A), radiation (S) and heavy metals (L)
Explain an adverse effect of using fossil fuels and nuclear power as energy sources
Fossil fuels: coal, oil and gas
Most of our energy comes from power
stations which burn fossil fuels to produce
electricity.
Fossil fuels are non-renewable and are running out.
They take millions of years to form.
Burning coal produces soot. Soot covers leaves and blocks sunlight. It also
blocks the stomata so that carbon dioxide cannot enter the leaf. Both of these affect
photosynthesis.
Soot also makes buildings dirty
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Burning of fossil fuels produces large amounts of gases:
carbon dioxide and sulphur dioxide. Carbon dioxide causes
global warming which is causing rising sea levels and
changing weather patterns.
Sulphur dioxide
+
water (in atmosphere)  Acid rain
When acid rain falls it decreases the pH. This kills trees, plants and animal life in lakes.
Nuclear Power
Energy comes from power stations driven by
nuclear reactors.
The great promise of nuclear fuel is that it
provides a plentiful source of energy. Although
it is not cheap its raw material is very common in
the Earth’s crust and is unlikely to ever run out.
Problems of nuclear energy
At 1.24 AM on the 26th of April 1986 there was an explosion at
the Chernobyl nuclear power plant. Scientists predict up to
75,000 people living far outside the area will die from cancer
as a result.
Waste is radioactive for many years and is difficult to get
rid of safely. If it is not disposed of carefully it can pollute air
and water and accumulate in food chains where man is often the
final consumer. This can increase the incidence of different
types of cancer.
The nuclear v. fossil fuel debate
Some people claim that nuclear fuel is better than fossil fuels. They say that it is
 safer
 produces less waste
 the only alternative to fossil fuel
 less damaging to the environment than fossil fuel power stations
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Give an example of one way in which pollution may be controlled
The environment can be damaged in many other ways.
Chemicals in aerosol cans reduce the protective ozone layer of the
atmosphere that results in higher exposure to dangerous UV rays.
Car exhausts produce poisonous carbon monoxide and lead that can damage us and
other organisms. Raw sewage released into rivers kills fish and other organisms.
Pollution could be controlled in a number of ways:
Damage to the ozone layer could be decreased by using a less harmful propellant gas in
aerosols
Acid rain could be reduced by reducing the amount of sulphur dioxide released by
power stations
Brain damage caused by lead could be stopped by using unleaded petrol
Less dead fish would be found in rivers by improving treatment of sewage before
release into rivers
State that organic waste is a food source for micro-organisms
Organic waste is the unwanted products of living organisms. Raw
sewage is a rich source of organic waste and must be treated
carefully before being released into rivers. If a sewage works is
overloaded water can become polluted by organic waste. Bacteria
will feed on the organic material, grow and multiply.
Describe the effect of increased numbers of micro-organisms on the oxygen available
to other organisms
If there are more micro-organism they will use up the available oxygen. This means that
there is less oxygen for other organisms e.g. fish. This will cause them to die.
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Explain the relationship between level of pollution with organic waste, numbers of
micro-organisms, oxygen concentration and numbers of species
An increase in organic pollution causes a large increase in the numbers of microorganisms present in water.
As they grow the bacteria use up oxygen from the water around them. This can cause
the death of other aquatic (water living) organisms that require oxygen to survive.
Explain what is meant by “indicator species”
Some organisms can only grow under certain environmental conditions. These organisms
are called Indicator species because their presence or absence in an area shows how
polluted or clean the area is.
Fresh-water species
The species present in fresh-water indicate
the varying oxygen concentrations found in
a river polluted with organic waste.
Indicators of air pollution
Different types of lichen differ in their sensitivity to sulphur dioxide (SO2) gas and
can be used to indicate the degree to which an ecosystem’s atmosphere is polluted by
this harmful gas.
Indicator species present
Crusty lichens only
Crusty and leafy lichens
Crusty, leafy and some shrubby lichens
Crusty, leafy, shrubby and hairy lichens
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SO2 concentration
(level of atmospheric pollution)
High
Medium
Low
Very low/zero
Give 2 examples of poor management of natural resources and suggest possible
improvements
Overuse of fertilisers and pesticides
Problems
Excess fertilisers are washed into rivers and lakes and cause pollution.
Pesticides that do not decompose naturally enter food chains and accumulate, causing
harm to the final consumer.
Solution
Use as little fertiliser as possible especially on land near waterways.
Develop biodegradable pesticides or use natural ones e.g. one animal to eat another
Overgrazing of grassland (developing countries)
Problems
Overgrazed plants die and no longer retain water in the soil. Land turns into a desert.
Solution
Provide economic aid to plant shelter beds of trees and resilient grass cover.
Describe how the effect of poor management of natural resources can produce
problems
In the third world lack of technology and farming know-how has led to soil erosion
and desertification causing crop failure and famine.
Lack of fertilisers and equipment mean that farmers in the Amazon destroy more and
more rainforests when the soil they are farming becomes exhausted.
Explain how components of an ecosystem are controlled in either agriculture or
forestry
When growing crops a farmer is creating and controlling an artificial ecosystem. The
farmer uses:
Fertilisers- to keep the soil fertile
Pesticides - to kill pests and prevent diseases
Herbicides - to kill any weeds that would otherwise compete with the crop for space
and nutrients
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