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The Biosphere


  • The biosphere is the part of the planet where organisms are found.
  • The biosphere can be divided into smaller units called ecosystems (i.e an ecosystem is a smaller unit of the biosphere, which consists of a community + a habitat).
  • The place where an organism (i.e animal or plant) lives is called a habitat.

If we want to learn about a particular habitat, we need to carry out an investigation which involves:
1. collecting the organisms 2. identifying the organisms 3. measuring the physical conditions.

Sampling Techniques

We cannot collect all the organisms within a habitat, so we must take a sample.

Using a Quadrat: A quadrat is used to take plant samples.
A quadrat is a frame divided into squares. It is thrown randomly on the area being sampled. The number of squares which contain the plant being studied are counted, not the number of plants in each square.

Using a Pitfall Trap: A pitfall trap is used to take animal samples.
A cup is placed in a hole, making sure that the top is level with the ground so that the animals fall i. However, some animals that fall in may be eaten by predators, such as spiders, which also fall in.

Identifying Organism

To identify organisms in a sample a key must be used.

A Branching Key:

A Paired Statement Key (credit ):

1. with prickles ..... Holly
with no prickles ..... 2
2. jagged edge ..... Elm
Smooth edge ..... 3
3. lobes ..... Oak
no lobes ..... Beech 

Measuring Abiotic Factors

An abiotic factor is a physical factor, such as light, moisture, oxygen, concentration or temperature.
Abiotic factors affect the organisms living in a particular habitat.

An abiotic factor can normally be measured using a meter.

Measuring Moisture: A moisture meter is used. To avoid errors, you must be careful that you place the moisture probe firmly in the ground and wipe it dry afterwards.

Measuring Light: A light meter is used. To avoid errors, you must be careful not to shade the meter and always hold it the same way when you are making the reading.

Effects of Abiotic Factors

  • Effect of Abiotic Factor: Green plants are not found in areas of low light intensity.
    Reason Why: Plants need light for photosynthesis.
  • Effect of Abiotic Factor: Most land organisms are not found in very dry or very wet areas.
    Reason Why: In very dry conditions they become dehydrated. In very wet conditions plant roots are deprived of oxygen.

How an Ecosystem Works

What is an Ecosystem?

An ecosystem is made up of living and non-living things. All the parts of an ecosystem are inter-related.
Ecosystems can be divided into types such as coastal, mountain, river or forest ecosystems.
i.e A pond is a habitat.
All the organisms of one kind make up a population.
All the organisms of the pond make up a community (the pond community).
Remember: Community + Habitat = Ecosystem.

Food and Energy in an Ecosystem

All living


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