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4.2.2 Classification and Evolution (natural selection (antibiotic…
4.2.2 Classification and Evolution
Theory of evolution
fossil, (genomic) DNA, molecular evidence
Charles Darwin developed the idea of natural selection; observed how species in the Galapagos Islands had developed differently to species in mainland South America
Alfred Russel Wallace independently came to same conclusion as Darwin, and published joint papers
Observations:
offspring appear similar to their parents
no two individuals are identical
organisms have the ability to produce a large number of offspring
populations in nature tend to remain fairly stable in size
Survival of the fittest
there is a struggle to survive
better adapted individuals survive and pass on their genes to their offsrping
a number of changes may give rise to a new speces
Fossil evidence
new species are similar to fossils of old species
many fossil species were much larger but appear similiar
Biological molecules
all living organisms have similar molecules; evolved from one common ancestor
two closely related species have very similar biological molecules
greater the similarity between DNA sequence, the more closely related the species
Variation
intraspecific: variation between members of the same species
interspecific: variation between members of different species
continuous: variation when there is two extremes and a full range of values in between e.g. height, length of leaves; can be shown on a histogram
discontinuous: variation when there are distinct categories and nothing in between e.g. eye colour, hair colour, blood group; can be shown on a bar chart
causes
genetic variation: variation caused by possessing a different combination of alleles
environmental variation: variation caused by response to environmental factors such as light intensity
chemicals in environment can also directly affect which genes are active
the presence of variety; difference between individuals
Adaptations
anatomical: structural adaptations
long roots: reach water that is deep underground
spread out roots: stabilise sand dunes, absorb a lot of water
curled leaves: reduces surface area exposed to the wind; decrease rate of transpiration
lower epidermis is covered in hairs: trap moisture to create humid environment
folded lower epidermis: water vapour builds up in pits
low density of stomata: less water vapour is lost
thick waxy cuticle on leaves: reduced evaporation of water from cells of leaf
behavioural: the ways that the behaviour is modified for survival
rolls leaf more tightly
close stomata
physiological: affect the way that processes work
specialised hinge cells in lower epidermis: allow leaf to be rolled up when they lose water and lose turgidity to roll leaves more tightly
guard cells gain and lose turgidity to open and close the stomata
has cell water potential lower than other plants: can survive in salty conditions by the sea
lignified cells: provide support when turgidity is lost
why organisms from different taxonomic groups may show similar anatomical features; marsupial mole and placental mole
a characteristic that enhances survival in the habitat
find food, find water, defence against pathogens and predators, survive physical condition of habitat, respond to changes in the environment, find a mate
Marram grass: very specialised plant ; is a xerophyte
species from different taxonomic groups may show similar adaptations as they may live in similar habitats, so evolve to look similar
e.g. marsupial mole and placental mole
both have cylindrical body, small eyes, strong front legs, large front claws, short fur, short tail, nose with tough skin for protection
natural selection
affect characteristics of population over time
term used to explain how features of the environment apply a selective force on the reproduction of the individuals in a population
mutation created alternate form of a gene (allele)
creates genetic variation between individuals of a species (intraspecific variation)
environment selects variation that give an advantage; selection pressure
individuals with advantageous characteristic will survive and reproduce
individuals pass on advantageous characteristics (inheritance)
next generation has a higher proportion of individuals with advantageous characteristics; organisms are well adapted to their environment over time
antibiotic resistance
small proportion of bacteria are resistant to the antibiotic so are not killed
resistant bacteria can reproduce and pass on resistant genes
Evolution
pesticide resistance in insects
pesticides kill most pests, but resistant ones remain
resistant pests survive and reproduce to pass on genes
DDT: insecticide that binds to a receptor on the plasma membrane of certain cells; mutations in insect DNA have changed the shape of the receptor molecules; DDT can no longer bind
Pyrethroid: insecticide to stop spread of malaria; mosquitoes have evolved an enzyme tp break down pyrethroids
drug resistance in microorganisms
some bacteria are resistant to antibiotics so are not killed
resistant bacteria survive and reproduce to pass on genes
creates a resistant strain of the bacteria that is unaffected by antibiotics
implications for human population
MRSA: bacteria "superbug"; is resistant to most antibiotics
need to find another antibiotic that works
resistant insects can enter food chains with pesticides still in them; humans can ingest a large amount of pesticide
Classification
Artificial classification
based on a few characteristics
does not reflect evolutionary relationships
provides limited information
is stable
Natural classification
uses many characteristics
reflects evolutionary relationships
provides a lot of useful information
may change with advancing knowledge
Phylogeny
study of evolutionary relationships between species
species that belong to the same phylogenetic group are called monophyletic
any two species have a common ancestor in the past; evolved differently
the more recent the common ancestor, the more closely related the species
Sammer Sheikh