Evolution and Classification

Revision notes for evolution and classification for WJEC AS level. Whole topic condensed to 6 pages; key definitions, simplified explanations. Hope it helps!

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  • Created on: 10-04-12 18:18
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BIODIVERSITY- is the number of different species on the planet
SPECIES- a group of organisms which share a large number of characteristics and can interbreed in
natural conditions to produce fertile offspring
EXTINCTION- Is the loss of a species
Tropical rainforests and coral reefs- most diverse habitats- greatest concentration of species per
square meter but they are being destroyed to support human population.
The % of species per square km increases as we move from the poles to the tropics
Rate of extinction is now 50X what it was 100,000 years ago
Extinction is a natural processes- but rate is increasing because of human activity ­ BIODIVERSITY
CRISIS
Earlier extinctions due to;
Climatic, geological and biotic changes
Extinctions are now caused by:
OVER HUNTING BY HUMANS
COMPETION FROM INTRODUCED SPECIES
LOSS OF HABITAT
Other causes are;
DRAINAGE OF WETLANDS
POLLUTION
DEFORESTATION
This is a problem because species could be sources of...
Food
Useful chemicals- (plants used for medicinal purposes)
Disease resistant genes
So there is a need for SPECIES CONSERVATION (planned protection of wildlife)
EVOLUTION- The process by which new species are formed from pre- existing ones over a long
period of time
CHARLES DARWIN- Galapagos islands
Finches- 14 species
Finches are unable to fly long distances- so Darwin proposed one ancestral species reached
with the help of the winds
No other birds on island- so a lot of food available
Individual finches differed from one island to the next- main difference being the beak and
this was related to the type of food eaten
Characteristics that best suited a particular finch to its environment was inherited by its
offspring

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Darwin suggested all the types of Finch came from a common ancestor and that the type of
beak had developed over time and become specialised to feed on a particular food source-
This is an example of ADAPTIVE RADIATION
NATURAL SELECTION- The process that drives evolution
There is VARIATION within a population
There is a struggle for survival (competition)
The "fittest", who have most favourable characteristics survive and reproduce
Favourable genes inherited by offspring
If a group of organisms become separated into two isolated populations,…read more

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TAXONOMY is the scientific study of the diversity of living things
A CLASSIFICATION SYSTEM puts order and plan on the immense diversity of life
Scientists look for physical similarities and differences between species looking at;
Number of appendages/legs
Mouthparts
Size
Heterotrophic/autotrophic
A TAXON is a level in the classification hierarchy and is a collection of organisms sharing some basic
features
(King Philip Came Over For Great Sausages)
KINGDOM- the largest taxonomic group e.g.…read more

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Organisms which are not animals, plants or fungi
Algae, water/slime moulds, amoeba, protozoa
4. Fungi
Eukaryotic
Network of threads called hyphae form a mycelium
Cell wall made of chitin
DO NOT PHOTOSYNTHESIS- they are HETEROTROPIC- all members are either
SAPROPHYTIC (live on dead things) or PARASITIC
Mushroom, yeast, penicillium.
5. Prokaryotes;
Unicellular
Bacteria
Blue/green algae
No nucleus
No membrane bound organelles
Cell wall made of muerin
3 ANIMAL PHYLA:
1. ANNELIDS;
Earthworms, leeches etc.…read more

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FIVE CLASSES;
FISH- Scales, fins, gills
AMPHIBIAN- first land vertebrates; part aquatic, part terrestrial. Soft, moist
skin. Eggs fertilised externally in water where they develop. Young are
aquatic and have gills, adults are land and have lungs
Reptiles- terrestrial, dry skin with scales. Have lungs. Eggs fertilised
internally, covered in shell and laid on land
Birds- similar to reptiles but fly, develop feathers, with fore-legs developed as
wings. Have lungs and eggs have hard shells.…read more

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