A revision summary of OCR A level Biology Biodiversity 4.2.1
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Biodiversity – the variety of living organism present in an area. Genetic diversity – the variation in a species gene’s
- Ecosystems are interconnect – all depend on one another Alleles – different versions of a gene.
- Plants = food for animals, habitat for animals - ↑alleles = ↑gene pool = ↑genetic biodiversity
- Animals = recycle nutrients, make fertile soil for plants to grow - population more resistant to disease
1. Habitat biodiversity – no. of different habitats found within an Increase Decrease genetic diversity
area Mutations = new Artificial selection – only breeding
2. Species biodiversity allele advantageous alleles = ↓gene pool.
- richness - no. of different species living in an area Gene flow – Captive breeding – only a small no. of
o To measure: use identification keys. interbreeding of individuals are available for breeding
- evenness – relative abundance of each species in a community organisms Genetic bottlenecks –↓pop size, ↓gene pool
3. Genetic biodiversity – variety of genes that make up a species. Outbreeding – uses = only surviving members available for
- Greater genetic biodiversity = greater adaptations to changing alleles stored in breeding
environment = greater resistance to disease. gene/ seed banks to Artificial cloning = ↓gene pool.
Community – all the populations of organisms in a particular habitat. artificially breed Natural selection – species evolve to contain
animals. only advantageous alleles.
Calculate Biodiversity - Simpson’s Index of Diversity (D) – Genetic drift – random nature of meiosis
includes both species evenness and richness. mean allele is not passed on & lost. Common in
Habitat features Low biodiversity High biodiversity ↓pop.
Successful few Large Measuring genetic Diversity
species Polymorphic genes – have more than 1 allele
Nature on Stressful, ↓niches Not stressful, ↑niches Monomorphic gene – have only 1 allele
environment - Higher proportion of polymorphic = ↑genetic diversity.
adaptations ↓species, very ↑species live, few no . of polymorphic gene loci
specific specific adaptations Proportion of polymorphic gene loci =
total number of loci
adaptations
Food webs simple Complex
Factors effecting Biodiversity – of habitats, species, genetic.
Deforestation Agriculture Climate Change
Reduces no of trees present for habitat = Monoculture – only grows one crop. Few animals Increase in temperature of waters means less
reduced animals present = impacts species can survive of one food. animals or plants can live there
interconnected ecosystem. Only culture species with advantageous Melting of glaciers = less habitats
Reduces nutrient cycling & growth of characteristics e.g. high yield/ resistance Rising sea levels = flooding to low-lying land,
other plants = decrease biodiversity Deforestation – to increase land for animals or crops loosing habitat and killing species.
specific tree is felling – diversity is lost Remove hedgerows – to make space for their plants, Less rainfall reduces water for plants
Animals must migrate to new areas, so reducing species & habitat Increase in drought resistant plants.
biodiversity of neighbouring areas Chemicals – pesticides & herbicides kills pests,
increase which may also be a food source for others.
Compare Biodiversity
Herbicides – destroys weeds.
- Total number of organisms
Humans increase biodiversity
- Species richness of
- Farming, grazing, planting, meadow provide habitats for species.
organisms
- Sheep grazing downloads enables rare Glanville fritillary (butterfly) to survive.
- Species evenness in areas
- Grazing to maintain grass at low levels allows plantains to thrive, which caterpillars feed on.
- Index of diversity
- Biodiversity
- Habitat diversity
- Genetic diversity
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