Biology WJEC BY2 Notes for 2.1 Evolution

Got given some notes at college, decided to edit them a tad, making them a bit easier to read and getting rid of the irrelevant stuff and highlighted the main points.

I found actually making these notes, (and the rest which are still to come) good revision, so if you don't know what to do with them, edit them yourself :) or just don't listen to me.. :)

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  • Created on: 12-05-12 17:40
Preview of Biology WJEC BY2 Notes for 2.1 Evolution

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Wjec BY2.1 Evolution
Biodiversity - a measure of the number of species on the planet. The number of
species per square kilometre increases as one move from the poles to the tropics.
Tropical rain forests and coral reefs are the most diverse habitats on the planet.
Reasons for decline in numbers and extinction:
o Loss of habitat due to Deforestation/pollution/drainage of wetlands
o Over hunting by humans
o Competition from introduced species
Species - members of a species share a large number of common
characteristics and interbreed to produce fertile offspring.
Evolution - process by which new species are formed from pre-existing
ones over a period of time.
Variation - change in the organism's genotype and phenotype.
Evolutionary history shows that biodiversity has gone through several bottlenecks called
mass extinctions followed by radiations of new species:
Darwin's observations on natural selection:
o Darwin recognized that species changed
o Proposing the theory of natural selection to explain why it happened
o So that there is a large variation of genotypes in population
o Organisms overproduce offspring
o However, numbers on the population remain constant
o Therefore there is a high mortality rate

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Because only those individuals with beneficial alleles have a selective
advantage e.g. white fur in arctic
o Can withstand selection pressures i.e. a factor which increases the chances of
a beneficial allele being passed onto the next generation e.g. competition,
predation, disease
o These individuals then reproduce
o Offspring are likely to inherit the beneficial alleles, therefore characteristic
o This process repeats generation after generation
o Therefore the beneficial allele frequency increases within the gene pool
o e.g.…read more

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Greater variation
o With a higher mean
o Because there is less competition for food (with other finches)
o Therefore there is a smaller selective pressure
Helps understand relationships between ancestors
o Phylogenetics:
Based on Evolutionary History of the organisms
It shows the Ancestry of groups or Points of Divergence
E.g. mammals and birds are more closely related than fish
Organisms are classified on the basis of similar or shared
characteristics e.g.…read more

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Biochemical techniques
o Compare the sequence of bases in DNA of genes (DNA Fingerprinting) - the
more similar the sequence the more closely related the species *N.B. The
best/most accurate technique for establishing relatedness
DNA is most similar, so most
closely related
o Compare the sequence of amino acids in
proteins ­ the more similar the sequence the more closely related the
The most commonly used classification is:
o Kingdom King e.g.…read more

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Rattus norvegicus = Brown rat
o Rattus rattus = Black rat
Binomial system is used to avoid confusion of local common names and different
languages ­ uses the Latin name
Kingdom Animal
Phylum Chordata (Non-chordata)
Arthropods Annelids
Class Millipedes/ Spiders Insects Crustacea
Characteristics of the 5 Kingdoms (excluding viruses):
Animal Kingdom e.g. dog, spider, starfish
Eukaryotic cells
Heterotrophic feeding
Specialised organ systems
Nervous system
Cells do not have cell walls
Plant Kingdom e.g.…read more

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Fungi Kingdom e.g. mushrooms, yeast
Eukaryotic cells
Made up of hyphae threads forming a mycelium
Cells have Chitin cell walls
Heterotrophic feeding (often saprophytic)
Reproduce using spores
Protoctist Kingdom e.g. slime moulds, algae
Eukaryotic cells
Unicellular organisms that are Heterotrophic or Autotrophic
Multicellular organisms are autotrophic (Seaweed)
No specialised structures
Have cell walls
Prokaryote Kingdom (Bacteria) e.g.…read more

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Two important evolutionary developments are:
o jointed legs - modified to perform a variety of functions, including walking, swimming,
jumping, feeding, reproduction and where present, ventilation of the gills.
o exoskeleton - the outermost layer of cells of the body secretes a thick cuticle, which consists
mainly of chitin.…read more

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Reptiles- mainly terrestrial and have dry skin with scales. They have lungs. The eggs are
fertilised internally, covered with a shell and laid on land.
Birds- they can fly and have feathers. Forelegs develop as wings. They have lungs and their
eggs have hard shells.
Mammals- have skin with hair. Young are born alive and are fed on milk. They have lungs.
They are subdivided into 2 groups:
o Marsupials- young are born at a very immature stage and develop in femals pouch.…read more



Thank you

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