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Doc Brown's Biology AQA GCSE Additional Science-BIOLOGY 2 Revision Notes

Biology Unit B2.4 Organisms and their environment Study Notes

BIOLOGY UNIT 2 Biology 2 for GCSE Additional Science or GCSE Biology

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

AQA GCSE Science BIOLOGY 2 Unit B2.4 Organisms and their environment

  • Know that living organisms form communities, and we need to understand the relationships within and between these communities.

  • Know that these relationships are affected by external influences.

  • You should be able to use your skills, knowledge and understanding to:

    • suggest reasons for the distribution of living organisms in a particular habitat,

    • evaluate methods used to collect environmental data, and consider the validity of the method and the reproducibility of the data as evidence for environmental change,

      • at the end of an investigation and analysis, can you distinguish whether differences in distributions of an organism are due to one or more environmental factors?

      • is it possible to control, or allow for, different environmental factors?

    • and you should understand:

      • the terms mean (average of all of a data set), median (middle value in a data set) and mode (the most common value in a data set - could be more than one value)

      • that sample size is related to both validity and reproducibility,

        • the larger the sample, random sampling from many locations and the more times the experiment is repeated, the more reliable will be the final analysis and conclusions,

        • reproducibility is the key to a successful valid investigation,


AQA GCSE Science BIOLOGY Unit B2.4.1 Distribution of organisms

  • a) Know and understand the physical factors that may affect an organism in its habitat (area where the organism lives):

    • To study the distribution of a species of animal or plant you must measure the population of the organism in different sample areas.

    • A habitat is where an organism lives (plant or animal) and its distribution is the areas where the organisms live an this may depend on environmental factors such as ...

    • ambient temperature,

    • availability of nutrients in the soil or water,

    • amount of light falling on the habitat,

    • availability of water in soil for plants,

    • availability of oxygen and carbon dioxide in the air or water.

      • Organisms will be adapted by evolution to fill a niche in a particular area of the environment,

      • but if there is a change in any of the factors above, then organism populations will be affected, some will increase and some will decrease,

      • in extreme cases, one species might die out in an area and another species may take advantage and move in.

      • An organism will be more common in an area, where environmental factors make conditions more suitable for the organism to survive and reproduce e.g.

        • shade for plants that need little sunlight, or out in the open for plants that need bright sunlight,

        • some creatures may prefer damp conditions, others adapted to dry conditions,

        • greater density/availability of the organism's specific food requirements

  • b) Know and understand that quantitative data on the distribution of organisms can be obtained by:

    • (i) random sampling with quadrats to cover a large area without sampling all of it

      • A sampling quadrat is usually a 1m x 1m (1 m2) square frame of wood or plastic,

      • Therefore if you measure the number of organisms in a quadrat you get the density in organisms per square metre.

      • You can average the random individual quadrat results to get the mean value for a particular organism/m2.

      • To work out the total population of an organism in the area you have been randomly sampling, you multiply the mean by the total area.

      • The more samples you take, the more reliable is your data, and therefore any deductions made will also be more reliable, but the data is only statistical, never completely precise, but

      • In presenting data make sure you know how to use the terms mean (average of all of a data set), median (middle value in a data set) and mode (the most common value in a data set - could be more than one value).

    • (ii) sampling with quadrats along a linear transect to look for changes across an area of land e.g. to see how a population changes across a wider area.

      • You can mark out the transect with two sticks and a long piece of string.

    • Note (iii) Whatever field work you do, the only really reliable data, are data that are consistent, i.e. always show the same pattern of organism distribution (plant or animal), and in that way the data is repeatable and reproducible.

      • This involves random sampling with samples using many quadrats and transects.

      • Does the data support the question posed about organism distribution?

      • Are differences in population due to environmental factors?

      • What are the variables?

      • Have the variables been controlled properly in your survey design?


  • Your practical work to develop your skills and understanding may have included the following:

    • investigative fieldwork involving sampling techniques and the use of quadrats and transects; which might include, on a local scale, the:

      • patterns of grass growth under trees,

      • distribution of daisy and dandelion plants in a field,

      • distribution of lichens or moss on trees, walls and other surfaces,

      • distribution of the alga Pleurococcus on trees, walls and other surfaces,

      • leaf size in plants growing on or climbing against walls, including height and effect of aspect.

    • analysing the measurement of specific abiotic factors in relation to the distribution of organisms

    • the study of hay infusions

    • the use of sensors to measure environmental conditions in a fieldwork context.


keywords: gcse AQA communities physical factors temperature availability of nutrients, amount of light, water, oxygen, carbon dioxide Unit B2.4 Organisms and their environment Distribution of organisms additional science Unit 2 BIOLOGY 2


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