Biodiversity

Ecology and the environment · The organism in the environment · note 4 of 6

Spec 4.3B

Biology only

Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels mean

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BiodiversitySpec 4.3B

In short

Biodiversity is the variety of all the different species of organisms in an ecosystem, a habitat or on Earth. It depends on the number of different species present, not the number of individual organisms. A field with a million plants of one species has low biodiversity, while a hedgerow with many plant and insect species has high biodiversity.

Biodiversity: The variety of all the different species of organisms in an ecosystem, habitat or on Earth.

Biodiversity depends on how many different species are present. A habitat with many species has high biodiversity. A habitat with only a few species has low biodiversity.

Biodiversity is about the number of different species, not the number of individuals. A field containing a million plants of one species has low biodiversity. A hedgerow with a dozen different plant species and the insects that feed on them has high biodiversity.

Exam tip:

If asked for the meaning of biodiversity, mention the variety of different species. Do not write about the number of organisms.

Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026

Frequently asked questions

What is the difference between a population and a community?

A population is all the organisms of one species living in the same area, such as all the badgers in a wood. A community is all the populations of different species living in that area, such as the badgers, foxes, oak trees, insects and fungi. If more than one species is mentioned, it is a community.

How do you estimate population size using quadrats?

Place quadrats randomly, count the organisms in each and calculate the mean number per quadrat. Then multiply the mean by the total area divided by the area of one quadrat. For example, a mean of 4 per 0.25 m² quadrat in a 100 m² field gives an estimate of 4 × 400 = 1600.

Why are quadrats placed randomly and how many should you use?

Quadrats are placed randomly, using coordinates from a random number generator, so the sample is not biased by the person choosing where to put them. You should use as many as possible, at least 10, because a bigger sample is more representative, reduces the effect of anomalies and gives a more reliable mean.

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