Biosphere (a) – Investigating an Ecosystem

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Biosphere Summary Notes
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Biosphere (a) – Investigating an Ecosystem


Organism a living thing (animal or plant)

Habitat the place where an organism lives

Ecosystem all the living and non-living parts within a defined area


Abiotic Factor a physical factor that can affect the organisms living in a particular habitat e.g. LIGHT, MOISTURE, TEMPERATURE, OXYGEN OR CARBON DIOXIDE CONCENTRATION, pH.

A quadrat
cology is the study of the ways in which organisms interact with each other and their habitats and how physical factors within their environment affect those interactions. Ecologists need to measure the populations of organisms and the abiotic factors within an ecosystem

Sampling organisms

Organisms are sampled to give an estimate of their population size.

Sampling Plants:

A quadrat (a square, often divided into 25 smaller squares – see opposite) is used to sample plant populations

  • the quadrat is placed on the ground.

  • Abundance is found by counting the number of squares which contain the plant (maximum abundance = 25).

  • To find the total population in an area, the total number of a plant species within the whole quadrat is counted. This value is then divided by the area of the quadrat and multiplied by the total area of the habitat.

To make the results more REPRESENTATIVE or RELIABLE:

The quadrat must be thrown randomly

A number of samples within the area must be taken and the average of these results calculated.
Sampling Animals:


Pitfall Trap is a container set flush with ground level. Animals fall into the trap and cannot escape. To improve the accuracy of results obtained with the trap:

  • it needs to be properly flush with the ground.

  • Checked regularly so that the animals don’t eat each other

  • Well camouflaged

  • To make the results more REPRESENTATIVE or RELIABLEmany pitfall traps must be placed in the habitat.

Measuring Abiotic Factors

Abiotic factor

Method for Measuring


Use a light meter

Take care not to shade the meter

Always point to the brightest light source

Soil Moisture

Use a soil moisture meter

Place the probe firmly and at least 4cm into the ground

Wipe the probe clean between readings

* If the light intensity between two different areas is to be compared, to make a FAIR comparison readings must be taken:

      • at the same time of day

      • under the same weather conditions

Line Transect

A line transect is a method of investigating the distribution of organisms and how it changes as the habitat changes from one area o another. A line is stretched between the two areas and at regular intervals measurements are made. Abiotic factors and also the living organisms will be sampled. By plotting the data in bar charts a picture of how populations change and the abiotic factors influencing population distribution can be obtained.

Examples of the influence of abiotic factors

Effect of Abiotic Factor


Green plants are not found in areas with low light intensity

Green plants need light for photosynthesis

Woodlice not found in dry areas

Woodlice need moisture to allow them to breathe and so die of they dry out

Caddis fly larvae are not found in polluted rivers

Caddis fly larvae need a lot of oxygen in the water. Pollution causes the oxygen level to fall, killing the larvae.

Learning Intentions


1- Identify the main parts of an ecosystem

- Habitat (The place where an animal or a plant lives),

- Animals

- Plants

2- Describe an example of a technique which might be used for sampling organisms and describe its use


Use: estimate the number of plants in an ecosystem.

Technique: square-shaped frame throw randomly at various places. The number of plants of each type is counted → the total number of each species can be calculated.


Use: collect small animals

Technique: the branches of a tree are beaten with a stick and a tray is used to collect the falling small animals

Pitfall trap

Use: collect crawling animals

Technique: a beaker is inserted into the soil so that the rim is levelled with surrounding ground.

3- (C) Identify a possible source of error that might be involved in a sampling technique and explain how it might be reduced.

For all techniques:

The number and types of organisms might not be representative of the whole ecosystem.

an adequate number of samples should be taken


- If too few quadrats have been counted, the number of plants may not be representative as some species grow in clusters.

use large number of quadrats for study

- Some plants may be spreading on either side of the frame. → overestimation (counting them all) or underestimation numbers (not counting them).

use a rule: e.g. plants going across the top and bottom sides are counted and these going across the right and left sides are not.

Tree beating

Animals may fall beside the tray

use large tray with raised edges, empty the tray regularly using a large plastic bag

Pitfall trap

Some trapped animals might eat other smaller animals.

add 50% ethanol in the trap to kill the animals

4- Identify two abiotic factors

non-living factors: light intensity, soil-air-water temperature, soil moisture, etc…

5- Give an example of a technique which might be used to measure an abiotic factor and describe its use.

Light intensity → Use a light meter

Temperature → use an electronic thermometer(answer valid for soil, air and water)

Soil moisture → use a soil moisture probe

6-(C) Identify a possible source of error that might occur during the measurement of an abiotic factor& explain

how it might be reduced

For all techniques:

→ make sure readings are taken when weather conditions are similar in all sites

Light intensity:

→ avoid casting a shadow on the light meter

Soil pH/humidity:

→ make sure that the probe is inserted in soil to the same depth

Measurement of temperature:

→ wait until temperature readings stop changing

Measurement of soil moisture

→ make sure that probe is inserted in soil to the same depth

7- State the effect an abiotic factor has on the distribution of organism

Combination of abiotic factors determines which plants grow in any one place (e.g. exposure to wind, moisture levels etc…). Types of plants determine type of animal.

8- (C) Explain ways in which abiotic factors can influence the distribution of organisms

Organism very susceptible to drying out → found in damp and shaded areas where little water evaporation

E.g. Pleurococcus found on the damper side of a tree trunk (i.e. exposed to the north) but not on tree trunks which are heavily shaded.

Biosphere (b) – How it works

More Definitions:

Population all the organisms of one species (kind) found in an ecosystem e.g. all the water lilies or rabbits.

Community all the organisms, of any kind found in an ecosystem i.e. all the plants and animals. (N.B., Ecosystem= Habitat + Community).

Producer a green plant that makes its own food by photosynthesis

Consumer an animal that gets its food by eating plants or animals

Food Chain a diagram which shows the flow of energy from the producers through the different levels of consumer
e.g. Grass Rabbit Fox

(Producer) (primary consumer) (secondary consumer)

(N.B. The sun is the source of Energy for all living things. The arrow shows the direction in which energy flows, from one organism to another. It points to the animal which is eating, and from the animal which is eaten.)
Food Web A diagram showing the interconnection of food chains illustrating that some animals eat and are eaten by a variety of other animals

Herbivore an animal that eats only plants

Carnivore an animal that eats only other animals

Omnivore an animal that eats both plants and animals

Predator an animal that hunts and kills other animals for food

Prey the animal which a predator kills for food


emoving a species
from a food web

(e.g. Removing quail from the food web opposite)

The food which the organism ate would now be available to other species which may increase in number as a result (i.e. roadrunners would have more insects to eat so the roadrunners may increase)

The predator that ate it may DECREASE in number as it has less food (i.e. foxes would have less to eat so they may decrease in number)

Other animals may DECREASE in number because the predator now eats more of them (i.e. roadrunners and mice may decrease in number because the fox eats more of them).

Energy loss from a food chain/web

Energy passes from one organism to another in a food chain. The body of the animal contains the energy. When the body of the animal is eaten the energy it contains is passed to the next organism. Any energy that is not put into the growth of an organism will therefore not be available for passage along the food chain. i.e. it is lost. Most energy (~90%) in a food chain is lost from the food chain, ultimately as heat energy.

The more links there are in a food chain, the greater the amount of energy which the producers (plants at the first step) need to provide. Because of this the numbers of animals at each step in a food chain will tend to decrease.

Pyramid of numbers

Pyramid of Numbers and Biomass

A pyramid of numbers is a diagram which is used to represent the change in numbers of each organism at each step in a food chain.
As you move along a food chain, the size of an organism increases, but the numbers of organisms decreases.
Occasionally, the food chain does not produce a pyramid. This could be because the producer is a tree that is consumed by insects. In order that this type of food chain makes sense, a PYRAMID OF BIOMASS must be used to represent the food chain. This a diagram which shows the total mass of the population of organisms at each s

Pyramid of numbers
tage in a food chain.

Pyramid of biomass
Pyramid of Numbers Pyramid of Biomass
The biomass decreases at each stage in a food chain due to the huge energy losses.

Population Growth

The growth of a population depends on the:

  • Birth Rate

  • Death Rate

Factors which increase the death rate will reduce the population and factors which increase the birth rate will increase the population. The growth of a population is limited by:

  • Lack of food

  • Lack of water

  • Lack of space (reduces breeding opportunities e.g. not enough nest sites)

  • Increases in the number of predators (increases death rate)

  • B

    uild up of poisonous wastes

  • Disease

Growth of a population in ideal conditions


–Lag Phase - Growth starts slowly because there are few organisms and they also take time to get ready to reproduce

B- Exponential growth phase – there are no restrictions on growth (plenty food, space etc.) growth is at its maximum

– Declining growth phase - food/ space has become limited and slows growth. This can either lead to a constant population
size or if wastes build, the population can be killed off (e.g. yeast is poisoned by alcohol it produces)


Competition occurs when organisms need the same resources (e.g. food, nest sites (space) or mates) to survive. As a result of competition, some organisms get a greater share of resources and survive, others get a smaller share and grow more slowly, become weak and can die. Competition causes the size of populations to be reduced. Plants compete for light, water mineral nutrients and space.

Nutrient Cycles

Nutrient cycles are the ways in which minerals essential for life (e.g. nitrogen, calcium, phosphorous) are released from the bodies of dead animals so that they can be used to grow new organisms. They are very important because they:

Get rid of the bodies of dead animals and plants

Release chemicals taken up once again by plants through their roots and used for growth.

The recycling is carried out by decomposers. They feed on dead plants and animals. Decomposers are bacteria and fungi

The Nitrogen Cycle

The Nitrogen cycle is the process by which nitrogen is moved between the bodies of plants and animals which use it to make protein. Dead organisms and wastes are decomposed by bacteria and fungi to release the nitrogen as nitrates in the soil. This can then be taken up by plants, and used to make more plant protein. Animals eat plants and make animal protein using the plant protein.

bacteria & fungi

Bacteria only

Bacteria only

By bacteria

Within the cycle:

Ammonification is carried out by bacteria & fungi

Nitrification is only carried out by bacteria
Nitrogen is an important nutrient for the growth of crop plants. Farmers can also add nitrogen to the soil:

Natural Method: Dig in manure (dung) or compost

Artificial Method: Fertilisers.

Nitrogen Cycle Summary

At the core of the cycle, Nitrogen moves from plants to animals, both of which die and are then decomposed in a 3 step process:

Bacteria & Fungi Bacteria only

Ammonification both steps called


Plant Protein  Animal Protein  Ammonium Compounds  Nitrite  Nitrate

Nitrate is removed by bacteria in denitrifcation.

Nitrate is added by lightning, which causes it to rain down to the soil (important in deserts).


itrogen Fixation also adds nitrate
. In this case, bacteria capture nitrogen from the air and join it to oxygen. Some plants (legumes e.g. peae, beans, clover) make root nodules and these bacteria live in the nodules. The bacteria provide the plants with nitrates (to make protein) and the plants give the bacteria a home and some sugar food produced from photosynthesis.

These plants are useful to farmers, as growing them in a field will improve the soil fertility by adding nitrates.
Other ways of adding nitrate to soil and improve fertiltiy are to add fertilisers.

Natural fertilisers are animal wastes (manure) and plant wastes (compost = broken down).

Artificial fertilisers are man made chemicals containing nitrates (as well as phosphates and potassium)

Learning Intentions


1- Describe what is meant by the words habitat, population, community and ecosystem

Habitat : The place where an animal or a plant lives

Population : Organism of the same species living in the same area – Community: All the populations from different species living in the same area – Ecosystem: The communities and their interaction with the physical environment where they


2- Describe what is meant by the word producer and consumer

Producer : makes its own food from the energy of sunlight (e.g. green plants).

Consumer: needs to eat other organisms to feed itself (e.g. all animals)

3- Give an example of a food chain or a food web

See jotters/books

4- State what the arrow in a food web stands for.

The direction of the flow of energy from one organism to another.

5- (C) Explain how removing one organism from a food web could affect the other organisms

Animals which normally feed on this organism will decrease in numbers. Plants/animals which are consumed by this organism will increase in number.

6- State two ways in which energy can be lost from a food web

- heat energy

- movement energy

- undigested part of food, e.g. bones

7- (C) Explain what is meant by the terms pyramid of numbers (1) and pyramid of biomass (2) (and pyramid of energy(3))

(1) shows the number of organisms at each level of a food chain.

(2) shows the total mass of organisms at each level of the food chain.

(3) shows the total energy at each level of the food chain

8- State what the growth rate of a population depends on

It depends on both:

- the birth rate (number of birth/1000/year)

- the death rate (number of death/1000/year)

9- State three factors which can limit the growth of a population

For example:

- lack of food, predators, lack of space, disease, lack of water, lack of light (for plants)

10- Describe and (C) explain the shape of the growth curve of a population, under ideal conditions

A: Flat start: few individuals so population growth is very slow because there are only few organisms to reproduce.

B: Slow rise: more and more animals are there to reproduce, growth rate increases.

C: Steep rise: the population is increasingly large so more organisms can reproduce + no factors are limiting the increase → growth rate extremely fast
After C, if conditions are not ideal, curve flattens. This is because death rate increases due to limiting factors to the point where death rate = birth rate .

12- State when competition occurs

- when resources are limited + organisms compete for the same resources e.g. food, space, nesting grounds

13- Describe some effect of competition

- slower foxes can’t catch enough rabbits to survive→ die

- plants which can’t grow tall enough → not enough light → not enough energy to reproduce successfully

14- Explain why re-cycling of nutrients is important to the organisms in an ecosystem

Nutrients (i.e. minerals such as nitrates) are in limited supply → if no re-cycling → nutrients would eventually run out.

Biosphere (c) - Control and Management


A pollutant is any substance which is harmful to plants or animals.

Pollution affects: AIR, SEA, FRESH WATER and LAND
Main Sources of Pollution:

DOMESTIC (from the home) e.g. sewage, household rubbish

AGRICULTURAL e.g. fertilisers, pesticides


NDUSTRIAL e.g. oil, sulphur dioxide, smoke, chemical wastes, nuclear waste.

Energy Production

Energy is vital for all aspects of life. The vast majority of energy comes from the burning fossil fuels such as coal oil and gas. Burning fossil fuels causes pollution:

ACID RAIN: the gases, sulphur dioxide & nitrogen oxides, produced from burning fossil fuels dissolve in rain water, causing ACID RAIN. This kills fish, and trees and also causes stonework and metal work to corrode (dissolve).
Power station chimneys are now fitted with chemical “scrubbers” to remove the sulphur and nitrogen oxides before releasing the gases into the air.

Cars are also fitted with catalytic converters to change harmful gases in exhaust fumes into less harmful gases.

: Carbon dioxide is also produced by burning fossil fuels. This acts like a “blanket” in the atmosphere insulating the earth. As a result the temperature of the planet is increasing. This may lead to flooding, hurricanes and the extinction of many species adapted to a cooler climate.
To reduce these problems alternative ways of producing energy are being developed:
NUCLEAR POWER: No Acid rain or carbon dioxide is produced by using nuclear power to generate electricity. However nuclear waste remains dangerous for a long time and is difficult to store safely.

WIND/WAVE/ SOLAR POWER These also do not release harmful gases, however it is unlikely that all our energy needs will be met by these technologies.

Water Pollution

Water is polluted when organic waste (e.g. sewage) is added to it because:

Organic waste acts as a food supply for micro-organisms (e.g. bacteria)

The micro-organisms increase in number and so require more oxygen

Consequently the oxygen in the water decreases

Fewer organisms can survive with these low oxygen levels (fish die)
The addition of phosphates (from detergent or fertilisers – also contain nitrogen) to water also causes pollution. They cause water plants to grow (algal bloom) and when the plants die, they provide food for micro-organisms leading to a reduction in oxygen as above.

Indicator species

The extent to which water is polluted can be determined by using indicator species. An indicator species is an animal which lives only in a narrow range of oxygen levels. Pollution affects the level of oxygen and so changes the types of organisms which can live in the water. Mayfly nymphs and trout are found in high levels of oxygen and so indicate that there is little pollution present. Conversely, sludge worms and rat tailed maggots like low levels of oxygen and indicate that pollution is at a higher level.

**Lichens are indicators of air pollution. The more lichens there are, the less the air pollution there is because lichens are killed off by sulphur dioxide in the air.**

Poor Management of Natural Resources.

Humans obtain many important resources from the planet(e.g. oil, timber, food). The exploitation of natural resources for human needs has lead to habitats being destroyed or polluted and many species of plants and animals are now endangered or extinct as a result:

OVERFISHING cod and other fish species in the North Sea are now very low as a result of over fishing.

OVER-GRAZING this leads to soil erosion and the formation of deserts. People become malnourished and prone to diseases as a result.

OVER-USE of FERTILISERS & PESTICIDES this cause rivers and lochs to become polluted killing fish. Pesticides can accumulate in animals in the food chain and can cause harm to the final consumer e.g. the eagle in the diagram below.

Ways of Protecting Natural resources

Set FISHING QUOTAS to limit the numbers of fish that can be caught

Increase mesh size of fishing nets so small fish can escape, allowing them to breed and increase the population.

Reduce use of fertilisers/ pesticides, and use more natural methods (manure, biological controls).

Agricultural Ecosystems

In agricultural, farmers control aspects of the ecosystem to increase the productivity:

FERTILISERS are added to enrich the soil by providing minerals for plant growth.

WEEDKILLERS reduce competition between weeds and crops for space, nutrients in the soil and sunlight.

PESTICIDES are chemicals which reduce damage to crops by pests.

LIME is added to soil to reduce the acidity.

Learning Intention


What is pollution

It is the addition of a harmful substance to an environment at a rate the environment cannot cope with it.

1-State which ecosystems are affected by pollution.

Air, land, fresh water and sea water

2- State the main sources of pollution (3) and give examples of a pollutant from each category.

1- Domestic pollution (land: cans; water: sewage; air: exhaust gases)

2- Agricultural pollution (land and water: chemical pollutant e.g. fertilisers/pesticides; air: gases produced by animals and rotting food wastes; water: sewage)

3- Industrial pollution (Water: oil slicks, chemical spills, air: smoke from factories or power plants)

3- (C) Explain the undesirable effects of using (a) fossil fuels and (b) nuclear power as energy sources.

(a) Burning fossil fuels releases pollutant smokes:

- sulphur dioxide and nitrogen oxides (result in acid rain); -carbon monoxide (poisonous); carbon dioxide (global warming); lead from gas exhausts (damages the brain).

(b) Radioactive wastes emitting radiations can persist over thousand of years (enter the food chain and creates health problems such as cancers).

4- Give an example of one way in which pollution may be controlled.

- reduce fossil-fuel pollution: use of renewable energies (e.g. solar, wind); scrubbing the fumes; lead-free petrol.

- reduce domestic pollution: recycle paper, cans, glass, choose showers over baths

5- State to which organisms organic wastes are food to.

(organic wastes are materials of plants and animals: e.g. sewage, blood from slaughter houses)

They are food to micro-organisms (bacteria and fungi).

6- Describe the effect of increased number of micro-organisms on the oxygen available to other organisms

The level of oxygen dissolved in the water decreases due to the activity of micro-organisms. As a consequence, there is less dissolved oxygen for other species (e.g. invertebrates, fish).

7- (C) Explain how organic waste pollution can affect the numbers of micro-organisms and hence oxygen concentration and numbers of species.

Organic pollution enters water → provides lots of food only for micro-organism → micro-organisms reproduce rapidly consuming lots of oxygen → less oxygen available for other species → most other species die, only a few survive → the number of species is reduced

8- (C) State what is meant by “indicator species” and explain how they are affected by changing oxygen concentrations

Indicator species: gives an indication of the levels of pollution or some other abiotic factors.


May fly → unpolluted

Freshwater shrimp → unpolluted or slight pollution

Blood worm and no may fly or freshwater shrimp → very polluted


Variety of lichens → very low/no pollution with sulphur dioxide.

9- Give two examples of poor management of natural resources and suggest possible improvements

1- Overgrazing of grassland → top soil is removed by erosion leaving bare infertile land.

Possible improvement: rotation of the areas to be used for grazing

2- Overfishing → fish stocks are destroyed (e.g. cod) disturbing food chains.

Possible improvement: Fishing Regulations protecting the endangered species and encouraging the fishing of other species

10- Describe how the effect

of poor management of natural resources can lead to problems

1-Growth of crops for cash (e.g. coffee) rather than food in developing countries → need to buy food → get into debts

2-Destruction of rain forest to sell wood → once forest is destroyed, loss of species and therefore source of food → top soil rapidly eroded cannot sustain agriculture → no more natural resources for either food or sales.

11- Explain how parts of an ecosystem are controlled in either agriculture or forestry

1- Agriculture:

a/ Soil fertility → to maintain supply of minerals:

- use of fertilisers, manure

- Crop rotation

b/ Control of plant species growing on land:

- use of herbicides to kill other undesirable species

- species chosen and sown by farmer

- crop rotation to avoid establishment of a single species

c/ Control of disease causing organisms

- use of insecticides (kill insects), fungicides (prevent fungal infections) and herbicides (kill weeds)

- crop rotation to avoid establishment of a specific disease causing organism

2- Forestry:

→ protection of vulnerable young plants on exposed forestry sites

- young plants grown in nurseries and transplanted when strong enough to survive on exposed site

- young plants protected against deer grazing until big enough to survive it.

- fire breakers

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