Organisms and their enviroment

The distribution of living organisms in a particular habitat may be affected by physical factors such as temperature and amount of light.Transects and quadrats are used to help collect quantitative data about organisms in their habitats. The collected data can be analysed to find the mean, median and mode values of organisms in a particular area.

Physical factors The physical factors that may affect organisms include: Temperature Amount of light Availability of water Availability of nutrients Availability of oxygen and carbon dioxide.

So, for example, daisy plants need light energy from the sun to make their own food using photosynthesis. Therefore more daisies will be found where there is plenty of available light, rather than in shady places.

oSimilarly, more grass plants are found in the full sunlight of a field rather than in a semi-shaded area or in shady woodland. This is because grasses need a lot of light energy to photosynthesise.

Ecosystems The table describes some common terms used to describeliving things in their environment.Environment   -   All the conditions that surround a living organismHabitat           -   The place where an organism livesPopulation      -   All the members of a single species that live in a habitatCommunity     -   All the populations of different organisms that live together in a habitatEcosystem     -   A community and the habitat in which it lives

Collecting quantitative data It is usually not possible to count the entire population of a particular organism in its habitat. This means that the population must be sampled. It may involve transects and quadrats.

Transects A transect is a line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground. The number of organisms of each species can be observed and recorded at regular intervals along the transect.

QuadratsA quadrat is usually a square made of wire. It may contain further wires to mark off smaller areas inside, such as 5 x 5 or 10 x 10 squares. The organisms underneath, usually plants, can be identified and counted.

Quadrat

When using a quadrat: It should be placed randomly so that a representative sample is taken The validity and reproducibility of the results increases as the results from more quadrats are analysed Quadrats may also be used for slow-moving animals such as slug and snails.

Handling data The results from transects and quadrats must be analysed. This involves calculating values such as the mean, median and mode. The table shows some examples of quantitative data.

Distribution of Organsims

Ecosystems

Collecting quantative data

Handling Data