These are detailed Revision Notes for Topic 4.2.1 of OCR A-Level Biology (Biodiversity). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
- Biodiversity
- Types of Sampling’
- Sampli...
Biodiversity
11.1 Biodiversity
11.1 Biodiversity
- Biodiversity is the variety of life in an area, which can be
measured in terms of genetic, species or habitat diversity 11.2 Types of Sampling
- Habitat biodiversity is the number of different habitats or 11.3 Sampling techniques
ecosystems in an area
- Species biodiversity has two different components: 11.4 calculating biodiversity
o Species richness – the number of different species living 11.5 calculating genetic biodiversity
in a particular area
11.6 Factors affecting biodiversity
o Species evenness – a comparison of the number of
individuals of each species 11.7 Reasons for maintaining biodiversity
- Genetic biodiversity is the variety of genes and alleles that make 11.8 methods of maintaining biodiversity
up a species
11.2 Types of Sampling
- Sampling is taking measurements of a limited number of individual organisms present in a particular area.
- It can be used to estimate the number of organisms in an area.
Random sampling:
- Random sampling means selecting individuals by chance, it removes the subjective element and make a
fair comparison between 2 areas, and this allows every organism to have the same chance of being
sampled.
- Random sampling method:
o Select the area to sample
o Generate coordinates suing a random number generator
o Define the area using a tape measure
o Take a sample at each of the coordinate pairs generated
Non-Random Sampling:
- Non-random sampling is an alternative where the sample is not chosen at random.
- There are three main techniques:
o Opportunistic – the weakest technique, uses organisms that are readily available
o Stratified – population are divided into a number of different sub-groups.
o Systematic – sampled at fixed intervals. There are 2 types:
§ Line transects – a line is made between 2 points and the types of species touching
are counted
§ Belt transect – 2 lines are made in parallel and the area between each are sampled.
Reliability:
- Larger sample sizes are more representative of the whole ecosystem
- The selection process may be biased, for example choosing a particular area because it looked more
interesting.
- The organisms selected may not be representative due to chance
11.3 Sampling Techniques
Sampling animals:
- Sampling animals must be done cautiously and with care due to ethical considerations. Handling time
needs to be minimised and animals need to be released back into original habitats.
- A pooter is used to catch small insects, a mouthpiece is sucked, drawing in insects. A filter prevents
insects from being sucked into the mouth
- Sweep nets are used to catch insects in areas of long grass
, - Pitfall traps are used to catch slugs. A hole is dug in the ground and the animals fall inside, must be
deep enough that they cannot climb out and must be covered so that they do not fill up with water
drowning the slugs.
- Tree beating is where a cloth is placed under a tree and the tree is shaken to dislodge the invertebrates.
- Kick sampling is used to study in rivers. The riverbank is kicked dislodging logs, a net is held downstream
to catch any organisms
- In a Tullgren funnel the heat and light from the lamp drives the organisms into the beaker and the
alcohol preserves them.
Sampling plants:
- Plants are normally sampled using a quadrat.
- There are two different types of quadrats:
o Point quadrat – a frame with a horizontal bar, pins are pushed through holes in the bar. All
species that touch the pins are identified and recorded.
o Frame quadrat - the normal type, the quadrat is divided into a grid of smaller squares and
species are identified and their abundance can be estimated.
- Quadrats can be used to sample density, frequency, or percentage cover
Estimating animal population:
- The capture-mark-release-recapture method is often used to estimate population sizes.
- This involves capturing organisms, marking them, and then releasing back to their habitat. Time is left
and then another sample of animals are collected.
- By looking at the number of marked organisms in the second sample can be used to estimate the size
of the population
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11.4 Calculating Biodiversity
- Simpsons Index of biodiversity is used to measure biodiversity. It considers both species richness and
species evenness.
- Its value is always between 1 and 0. 1 represents infinite diversity and 0 represents no diversity.
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- The formula is 𝐷 = 1 − Σ( 9 )
- n is the number of individuals of a particular species, and N is the total number of all individuals of all
species.
High Biodiversity Low Biodiversity
- many species present, high species richness - habitat dominated by one or a few species
and evenness - change in species is likely to affect the whole habitat
- all species evenly represented - habitat unstable, not able to withstand change and
- more stable habitat easily damaged.
- complex food webs - simple food webs
11.5 Calculating Genetic Biodiversity
- Maintaining genetic diversity is very important, to prevent in-breeding and maintain disease resistance.
- Within a population there will be a variety of alleles – genes with different alleles are polymorphic
- A huge number of genes within a species will show no variability as they are essential in maintaining the
basic structure of a species – these are called monomorphic
- The more polymorphic genes present in a population the more genetically biodiverse it is.
- The greater the number of different alleles, the better the species will be able to withstand
environmental change and therefore the less likely it will become extinct.
- Factors increasing genetic biodiversity:
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