Summary
Summary Biology Edexcel A full notes (SNAB) topics 1-8
- Module
- Topic 4
- Institution
- PEARSON (PEARSON)
Summary of 8 pages for the course Topic 4 at PEARSON (All notes)
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TOPIC 4BIODIVERSITY AND ENDEMISM
Biodiversity – the range of organisms in a given habitat
- Index of diversity takes into account the species richness and evenness
N (N −1)
D=
n(n−1)
- N = total number of organisms of all species
- n = total number of organisms of one species
- If all individuals are of the same species, the index is 1
Species diversity – the number of different species and abundance of each species in a given habitat
- Species richness – the number of different species of each species in a given habitat
Measuring species diversity in a habitat
1. Choose an area to sample randomly – to avoid bias in the results
2. Count the number of individuals of each species in the sample area e.g. quadrar, sweepnet, pitfall trap,
net
3. Repeat the process
4. Use results to estimate the total number of individuals or total number of different species in the habitat
5. Use same sampling technique for different habitats
Species evenness – a community in which most of the species have similar abundances i.e. there is not one dominant
organism
Genetic diversity – variation of alleles in the gene pool within a species
- Measure by number of different phenotypes and genotype by analysing DNA samples by investigating the
sequence of base pairs or cut into fragments and separate using electrophoresis
- The larger the number of different alleles for a single characteristics, the greater the genetic diversity
- Can also be measured using heterozygosity index – the greater the number of heterozygotes in a population, the
greater the genetic diversity
- Heterozygotes have 2 different alleles at a particular locus
number of heterozygotes
H=
number of individuals ∈ population
- An average value for H at many loci can be used to estimate the genetic diversity in the whole genome of the
population
Endemism – when a species is unique to a single place i.e. it is not found anywhere else in the world
Natural selection has increased biodiversity over time
Human activity e.g. farming and deforestation are reducing species diversity which is causing biodiversity to fall
Conservation is needed to maintain biodiversity and endemic species because they’re vulnerable to extinction
ADAPTATION AND EVOLUTION
Niche – the role of an organism and the way it interacts with other living and non living organisms within an
environment
A niche can only be occupied by one species
If 2 species try to occupy the same niche, they will compete until the better adapted outcompetes the lesser adapted so
only one species occupies the niche
Adaptation – being specialised to suit the environment to increase an organisms chance of survival and reproduction
- Behavioural – the way it acts
- Physiological – processes inside its body that increase its chances of survival
- Anatomical – structural features of its body that increase its chances of survival
Useful adaptations become more common in populations of species because of evolution by natural selection
Co – adaptation – when two species are adapted so they are dependent on each other for survival
Evolution – a change in allele frequency over time
Natural selection
1. Mutations can introduce new alleles into a population so the individuals within the population show variation in
their phenotypes. Some of the characteristics make the individual more likely to survive
2. Selection pressures e.g. predation, disease and competition create a struggle for survival as a result of a change in
environment
3. An allele that was previously of no particular advantage now becomes favourable
, 4. Individuals without advantageous alleles don’t survive so there are fewer individuals and therefore less
competition for resources
5. Individuals with selectively advantageous alleles have better adaptations so they are more likely to survive,
reproduce and pass on the selectively advantageous alleles to their offspring
6. The number of individuals with advantageous alleles increases over time
7. Over generations this leads to evolution as the frequency of advantageous alleles in the population increases and
the adaptations become more common
The ability of a population to adapt to new conditions will depend on=:
- The strength of the selection pressure
- The size of the gene pool
- The reproductive rate of the organism
Being ‘perfectly’ adapted to an environment makes the population vulnerable because they would be severely affected
by any change
A population cant be perfectly adapted to the environment because there’s a time lag before a population can adapt by
natural selection
Species – a group of similar organisms that can breed together to give fertile offspring
Speciation – the development of new species
When populations of the same species become reproductively isolated the changes in the alleles and phenotypes
prevents them from successfully breeding
- Seasonal changes – different flowering/mating seasons
- Mechanical changes – changes in genitalia
- Behavioural changes – courtship rituals are unattractive to main population
Species may become reproductively isolated due to geographical isolation or random mutations that introduce new
alleles into the population
The longer 2 groups are isolated, the more allele frequencies change and the more likely it is that speciation will occur
Speciation – geographical isolation:
1. Physical barrier divides a population of species
2. Conditions on either side of the barrier differ
3. Different selection pressures and random mutations on either side of the barrier means different characteristics
become more common due to natural selection
4. The different populations become genetically distinct so they are unable to breed successfully to produce fertile
offspring – they are reproductively isolated
5. The 2 groups have become 2 different species
CLASSIFICATION
Taxonomy – the science of classification
- Use differences and similarities in genotypes and phenotypes
8 taxonomic groups
1. Domains – bacteria, archaea or eukaryota
2. Kingdoms
Prokaryotae
- Prokaryotes, unicellular, no nucleus, less than 5µm,
- e.g. bacteria
Proctotista
- Eukaryotic cells, usually live in water, single celled or simple multicellular organisms
- E.g. algae and protozoa
Fungi
- Eukaryotic, chitin cell wall, saprotrophic
- E.g. moulds, mushrooms, yeasts
Plantae
- Eukaryotic, multicellular, cell walls made from cellulose, can photosynthesise, contain chlorophyll,
autotrophic
- E.g. mosses, ferns, flowering plants
Animalia
- Eukaryotic, multicellular, no cell walls, heterotrophic
- E.g. nematodes, molluscs, insects, fish, reptiles, birds, mammals
3. Phylum
4. Class
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