AS BIOLOGY - EVERYTHING on biodiversity OCR F212

These cards will help with OCR Biology AS unit F212 biodiversity. Notes are in my own words and are based upon the CGP guide and OCR textbook as well as notes from my lessons.

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  • Created by: kyle
  • Created on: 20-05-12 12:02


Biodiversity - The variety of living organisms in an area.

Species - A group of organisms with similar characteristics that can interbreed and produce fertile offspring.

Habitat - A place where an organism lives with the correct environmental conditions.

Population - Group of organisms of the same species, living in the same place at the same time.

Community - All of the different organisms of all the species living within the same habitat at the same times.

Ecosystem - A self-contained, interacting community of organisms and the environment in which they live and interact.

Niche - Place where an organism lives and the role it plays in the ecosystem.


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There are 3 main levels of biodiversity;

SPECIES DIVERSITY - the number of different species and the abundance of each species in an area.

Eg. a woodland would contain many different species of plants, insects, birds and mammals.

GENETIC DIVERSITY - the variation of alleles within a species (or a population of species).

Eg. human blood type is determined by a gene with four different alleles.

HABITAT DIVERSITY - the number of different habitats in an area.

Eg. a coastal area could contain many different habitats such as beaches, sand dunes, mudflats, salt marshes etc.

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It is important to sample when measuring biodiversity because in most cases, a habitat is too large to count every individual. So we random sample an area we have chosen to avoid bias;

1 - create a grid eg. 10 x 10 square metre area and use a random number generator to select co-ordinates.

2 - Count the number of individuals of each species in that area. Use a quadrat for plants, sweepnet for flying insects, pitfall trap for for ground insects and a net for aquatic animals.

3 - Repeat the process at many different co-ordinates. A larger sample will give you a better representation of the biodiversity of the whole habitat.

4 - Use results and the Simpson's index of diversity to estimate a value of the biodiversity.

5 - If you compare it to another area, you must carry out the exact same sampling technique for the other area.

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The co-ordinates are chosen and a chosen corner of the quadrat (red square) is placed on that exact co-ordinate (as shown);


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SPECIES RICHNESS - the number of different species in an area. The higher the number of species, the greater the species richness.

SPECIES EVENNESS - the measure of the relative abundance of each species in an area. The more similar the population size of each species, the greater the species evenness.

SIMPSON'S INDEX - This takes into account both species richness and species evenness of an area where; (Formula is next page)

n = total number of individuals of one species

N = total number of organisms of all species 

∑ = " sum of "

It always results in a value between 1 and 0. The higher the number is ie. closer to 0, then the more diverse the habitat is.

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The formula is below where D represents Diversity;


   D = 1 - ( ∑ [n/N]² )

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Global biodiversity is the total number of species on Earth. This includes the species that have been named and the species that are unnamed (as many species are still undiscovered). Scientists estimate that the total number of species on Earth to range from about 5 million to 100 million.

The reasons science opinions vary are;

1 - Different scientists have used different techniques to make their estimates.

2 - Relatively little is known about some groups of organisms (eg. bacteria and insects) - there could be many more than we think.

3 - Biodiversity varies in different parts of the world - the greatest diversity is near the equator and it decreases towards the poles. Tropical rainforests are largely unexplored - this might mean current estimates of global biodiversity are too low.

Estimates of global biodiversity change as scientists find out new things - this is an example of the tentative nature of scientific knowledge.

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PS. The above does not include 'maintaining biodiversity'

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