B4 OCR Gateway

Ecology in the Environment

The distribution of organisms is affected by the presence of other organisms and physical factors such as soil type and water availability. 

Ecosystems can be natural or artificial. A garden is an example of an ecosystem. All the living things in the garden and the garden itself make up the ecosystem. Where a plant or animal lives is called its habitat and all the animals and plants in the ecosystem are called the community. The number of particular organisms present is called the population. 

The distribution of organisms in an ecosyetm can be mapped using a transect line. At regular intervals along the line the number of organisms are counted and plotted on either side of the line using a 5 point scale. This produces a kite diagram. They show zonation of organisms. Zonation depends on abiotic factors (not living) like water availability, exposure and soil type.

Natural ecosystems have a great biodiversity than artificial ecosystems because: there is awide variety of food, food throughout the year, shelter at different heights above and below grounds and it is free from artificial pesticides and fertilisers.

Plants and animals depend on each other for oxygen and carboin dioxide, food, fertilisation and pollination and seed dispersal. There is also the recycling of carbon and nitrogen.

To collect organisms you can use pooters, nets or pitfall traps.

Counting organisms is difficult because they do not stand still. As a result, you can find the amount in a 1m sqaured area and multiply it up. A small error in the sample, would create a large error in the final estimation.

A scientific method used is capture/recapture. Organisms are captured, marked and released. The traps are reset and organisms are recaptured. You then see how many of the organisms have been marked. To work out the overall population you use the equation:

population size= number in 1st sample x number in second sample/ number marked in second sample

This is only an estimation because not all of the organisms are captured. To increase the accuracy of tests like this the sample is as big as possible.

Population sizes are always changing because animals are born and are dying and there is emmigration and immigration. When using capture/recapture it is assumed that: there has been no deaths, births or emmigration, identical sampling methods have been used and marking the animal has not affected their survival.

Photosynthesis

Glucose and Starch produced in photosynthesis are converted into cellulose for cell wallls, proteins for growth and repair and fats and oils for storage.

Glucose is not suitable for storage because it is soluble so is easily lost from the cell and it also increases the concentration of cells, which can damage them. Starch molecules are much better because they are insoluble so are not easily lost from the cell solution, they do not react and they do not affect the water concentration of the cells. 

Photosynthesis is a two stage process. This was discovered when…