OCR Biology AS UNIT 2 - Biodiversity

AS biology module 3 (Biodiversity) notes according to the latest OCR Specification

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  • Created by: shanae
  • Created on: 29-11-11 10:24

Biodiversity: Define the terms


  • The range of organisms that can be found in a habitat


  • The place where an organism lives


  • A group of individual organisms similar in appearance, anatomy, physiology, biochemistry and genetics.
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Explain how biodiversity may be considered at diff

Habitat Biodiversity:

  • This is the range of habitats where an organism lives

Species Biodiversity:

  • The differences between species found in a habitat

Genetic Biodiversity:

  • Genetic variation between the individuals of a species
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Explain the importance of sampling in measuring th

  • Human activities affect the environment in many ways


  • We study these affects in order to assess the impact that we have


  • Environmental impact assessments are vital parts of planning processes
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Describe how random samples can be taken when meas

  • Random samples - selecting portions of the habitat, at random, and studying them in detail.
  • Random samples = more representative, less bias.
  • Method: Take samples at regular distances across the habitat

In Plants:

  • Random Quadrats - Quadrat is placed at random on the habitat, the plants within the quadrat are identified.

e.g.  Measure their abundance... An Abundance scale involves applying an abundance score to each species in the quadrat.

  • Transects: Stretching a long tape measure across the habitat & samples along that line are taken.

e.g. Line Transect: Record the plants touching the line at set intervals.


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In Animals:

  • Smaller animals can be trapped, observed & have their numbers estimated
  • Larger animals cannot be trapped, instead, carefully observed


  • Sweep netting: Sweep net through vegetation. Release the organisms onto white sheet to be counted.
  • Collecting from trees: A white sheet is held underneath a branch. The branch is knocked, so any small animals drop onto the sheet and counted.
  • Light trap: UV light attracts insects, which eventually fall into a vessel of alcohol below so that they can be counted.
  • Pitfall trap: Animals fall into a container buried in the soil.
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Describe how to measure species richness and evenn

Species richness:

The number of species in a habitat. The more species present, the richer the habitat. (Use previous methods to measure this)

Species evenness:

The relative abundance of individuals in each species

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Measuring species richness & evenness in animals;

     Smaller animals: Mark & recapture technique:


- C1 = capturing a sample of animals & marking them in a non-harmful way.

            Then release them and leave more traps

- C2 = The number of organisms recaptured.

- C3  = The number of marked animals in the second capture.

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Using Simpson's Index of Diversity (D) to calculat


D= 1-(∑(n/N2 )

n = the number of individuals in a particular species

N = the TOTAL number of individuals for all species

  • High value = A diverse habitat stable enough to withstand change.
  • Low value = Dominated by a few species, so change could damage/ destroy the whole habitat.
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Discuss the current estimates of global biodiversi


We can not be sure how accurate they are because:

  • They do not include marine species
  • We can not be sure that all species on Earth have been found
  • Evolution & speciation are continuing
  • Many species are endangered
  • Some species are becoming extinct
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  • The process of placing living organisms into groups according to their similarities.
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Define Phylogeny & explain its relationship betwee


Phylogeny - The study of evolluntionary relationships between organisms



  • Closely related species are placed in groups together.
  • By knowing the relationships between each species one can put them in the correct group.
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Describe the classification of species into the ta

  • Taxonomy - The study of the principles of classification.









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Outline the characteristics of the 5 Kingdoms...


  • No nucleus
  • Loop of naked DNA
  • No chromosomes
  • No membrane-bound organelles
  • Smaller ribosomes & cells
  • May be free living or parasitic


  • Eukaryote
  • Mostly single-celled
  • Show various plant or animal-like features: e.g. Have autotrophic or heterotrophic nutrition
  • Mostly free living


  • Eukaryote
  • Have mycelium consisting of hyphae
  • Cell walls - chitin
  • Cytoplasm is multi-nucleated
  • Mostly free living

To be continued...

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  • Eukaryote
  • Cell wall - Cellulose
  • Multi-cellular
  • Autotrophic nutrition


  •  Eukaryote
  • Multi-cellular
  • Usually able to move around
  • Most do not have cells with cell walls
  • Heterotrophic nutrition
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The changes in evidence for Classification:


  • Classification based on observable features e.g. single celled organisms with animal-like features were classed as animals
  • Those with feautures like plants were classed as plants
  • But microscopes showed that some organisms acted like BOTH
  • In the end this system was overhauled


  • 5 Kingdoms
  • Biochemistry can be used to show evolutionary relationships between 2 species = classification by genetics
  • The domain - Archaea, Bacteria & Eukaryotes


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Continuous Variation

- This occurs when there is a complete range of values/ measurements from one extreme to another:

  • Height e.g. 1.63cm, 164.1 cm, 164.3 cm etc
  • Length of leaves in a tree
  • Weight
  • Shoe size

- When this type of data is plotted on a histogram, it shows a bell-shaped normal distribution curve.

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DEFINE: This is the presence of variety - the differences between individual organisms of the same species.

Variation occurs:

  • Within a species - eye/hair colour
  • Between species - Birds fly but cats do not
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Discontinuous Variation

- This is where individuals fall into a number of distinct categories,

- There are no intermediate values/ values measured across a complete range,

- Either you have the characteristic or you don't.


For example:

  •  Sex: Male of Female in mammals, in plants, feamle or hermaphrodite
  • Human Blood groups: A, B, AB, O
  • Some bateria have flagella & others do not.
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Explain the genetic & environmental causes of vari


  • We inherit a combination of unique alleles from our parents
  • Differences occurs the exchange of genes during Meiosis
  • Unless you are an identical twin - the chances of having the same alleles are very small
  • Therefore, we have unique characteristics.


  •  If a tree that would normally grow at 6m was planted where there was a lack of water or soil, it may only grow to 1.5 m
  • An overfed pet = Obesity
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Adaptions to the environment:


  • An aspect of behaviour of an organisim that helps it survive in the conditions it lives in
  • e.g. lizards basking in the sun to get warmer


  • An adaptation that ensures the cell processes are functioning
  • e.g. Yeast can produce enzymes to respire sugars that are present


  • A structure that enhances the chances of survival of an organism
  • e.g. Bacteria have flagella to enable them to move independently
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Charles Darwin proposed the Theory of Evolution...


Darwin observed that:

  • Offspring appear genetically similar to their parents
  • No two individuals are identical
  • Organisms have the ability to produce large numbers of offspring
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This led him to conclude that:

    • There is a struggle to survive
    • This is because more offspring are produced than the habitat can sustain = Competition for food & resources
    • All individuals are different; some better adapted than others
    • Better adapted individuals = get food & resources = live & reproduce = pass on their characteristics
    • LESS well adapted = more likely to die before reproducing
    • Over time, a number of changes will give rise to a new species .
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Evidence of Speciation ( forrmation of new specie


  • Found to show similar organisms over a period of time;
  •  Slow changes & different environmental adaptions are shown
  • They have been compared to modern species,  showing similarities


  • Comparing Genes by sequencing DNA bases
  • Most distant related species show differences in DNA; did they evolve?


  • 2 closely related species will have similar biological molecules
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Discuss why the evolution of pesticide resistance

  • An insecticide applies a strong selection pressure;
  • Susceptible insects die
  • Those who can resist survive.

These resistant insects:

  • Pass on the resistance to next generation,
  • Therefore, the whole population is resistant,
  • Insecticide is no longer effective.


Note: This is the same concept for antibiotics & bacteria.

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Maintaining biodiversity: Why conserve animals & p

Economic reasons:

  • Evolution provides answers to technological questions such as the best aerodynamic shape in water, the best shape for a wing etc.

Ecological reasons:

  • Natural ecosystems perform processes valuable to humans;

          - Without soil - No growing crops = No food

          -  Purification & retention of fresh water

          - The regulation of atmosphere & climate

          -  Plants photosynthesise to remove CO2  and replace it with O2

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Ethical Reasons:

  • All living organisms have the right to survive & live in the way which they have become adapted
  • A lost of habitat & biodiversity = organisms not living in natural habitat
  •  Can lead to endangered species/ Extinction

Aesthetic Reasons:

  • Studies show that patients recover quicker from stress & injury when exposed to pleasing natural environmental conditions.
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Discuss the consequences of global climate change

  • Species who have lost their habitat will be unable to evolve to adapt to the change in temperature & rainfall;


  • migration could lead to obstructions such as: humans, large amounts of water, human developments etc.
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Affects of changing patterns of agriculture & spre

Domesticated plants have been bred to produce the best yield in specific conditions so...

- Change in climate = plant unable to adapt to new conditions

- Result: Farmers grow plants in new environments = plants exposed to new diseases & pests which they have no resistance

- Higher temperature = longer growth & breeding for pests

- Milder temperature = Not cold enough to kill pests

- Plant produces less yield = not enough for everyone

- Human diseases migrate, tropical diseases could become a problem in UK.

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Expalin the benefits for agriculture of maintainin


  • Agricultural crops have little diversity;
  • As the climate changes they may longer be able to grow in their current location;
  • Farmers could breed their agricultural plants with wild species that can grow in a new climate.
  • The offspring will have a high yield & able to grow in warmer conditions,
  • Species resistant to disease could be bred to prevent extinction.
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This is great! Thanks so much!! Really helps with revision :) 

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