u4 vce bio ch10 changes to species over time

fossil record, age of fossil methods, patterns of biological change, how species are related

earth

formed 4.5-4.6 bya

use geological time scale to measure time scale and mark important events in earth history

• life 3.5bya

• multicellular org 1bya cyanobacteria

• land animal 450mya

• mammal 200mya

• flowering plants 100mya

whyre fossils rare

fossils → preserved remains/traces of remains of a dead org

fossilisation → rare process preserves dead org 

important factors for fossilisation

• rapid burial → avoid being eaten by scavengers, decomposers, prevents breakdown of org through weathering

• occur in water bc of sediment

• volcanic ash, tree sap

• cold env

howre fossils are formed

1. org dies and is buried in water

2. rapid sedimentation, cover body (no o2, undisturbed, mineral rich)

3. layers of sediment build up, press down buried remain & pressures it

4. chemical reactions & time turn sediment into rock and bone into fossil

5. erosion & plate movement displaces fossil and returns it to the surface

the fossil record

tells us life on earth changed overtime.

• org found in certain rock layers in consistent order → LAW OF FOSSIL SUCCESSION

• first prokaryote appear in fossil record before first eukaryote, first amphibian before first reptile

• showing evolution and look for ancestral species evolved into one or more new species.

transitional fossils

fossilised remain of an org showing links between species by showing traits common to both ancestor and predicted descendants.

• archeopteryx

• bird believed to evolve from reptile. This org has teeth, tail bone which lizards have and it has feathers for birds.

fish to amphibian

life started in water .

transitional fossil → fish like structure w gills & tail and amphibian structure like ribcage and shoulder blades to move on land

extinction & mass extinction

extinction

• complete eradication of species from world

• niches vacant for other org to occupy and evolve in

• human factors → hunting, habitat destruction

• natural factors → disease, lack of genetic diversity, cold env, ice age

mass extinction

• widespread rapid abnormally high & no. species dying over short period of time

• allows for rapid evolution of orgs to fill in vacant niches & inc in diversity of species

relative age vs absolute age

relative age → qualitative. Fossils in order of youngest to oldest, not exact age.

absolute age → quantitative. exact age of fossil

relative dating - stratigraphic method & law of fossil succession

stratigraphic method

based on principal of superposition → rock layers/strata thatre oldest are on the bottom & youngest rock strata on top.

• fossil on low layer r old. Only works in same regions.

law of fossil succession

use index fossils to see fossils age in rock strata even in diff regions.

index fossils

short lived species & appear limited time in fossil record

• distinct, abundant, lived in wide areas

• found in one layer

• used to find relative age of other fossils, if in same layer as index fossil it must be same age

absolute dating

radiometric dating.

uses half life of radioactive element → time taken for half the og radioactive isotope to decay.

• decays and turn into more stable daughter element. Carbon parent element decays into nitrogen daughter element.

carbon dating

• all org have carbon 14 and decay into nitrogen 14 with half life of 5730 years.

• eg if fossil has 100g carbon 14 and it has 50g carbon 14, it went through one half life and is 5730 yo

for fossils up 60,000yo

electron spin resonance

for fossils from 50-500k yo

used on flint tools and fossilised teeth

• object buried its bombarbed by natural radiation from soil and the electrons move from ground state to higher energy lvl and get trapped. Longer trapped in ground = more electrons in higher energy lvl

• object heated → electrons go back to ground state. Determine when flint was last used.

• more high energy electrons = older it is. 

speciation

process of formation of new species. One species become 2 new species.

• occur when same species r living under diff locations & diff selection pressures. Natural selection

• occur through reproductive isolation

• over gen the selection pressure become diff.

• ALLOPATRIC AND SYMPATRIC SPECIATION

species → org thatre able to breed and produce fertile offspring.

• if cant do that then its not a species

divergent evolution

2 or more species evolve from a common ancestors. Become dis-similar overtime due to diff env & selection pressures.

• homologous structures.

eg adaptive radiation

• new species from common ancestor and each new species occupy diff niche. EG darwin finches on galapagos islands

allopatric speciation = diff homeland

speciation where pop r geographically separated. Due to clearing or construction or formation. 

1. split of smaller group of og pop to isolate it 

2. exp diff selection pressures

3. isolated pop changes overtime and cant reproduce w other pop

4. diff gene pools & diff species

allopatric speciation galapagos finches

beaks r diff based on selection pressure food.

• og pop were at diff islands and changing climates changed env

1. one island dry & bush so bird w sharp beak can crush seed, blunt beak die

2. second island cactus long slender beak for nectar

3. each island diff alleles selected for, changing the genetics of each island pop = diff species

sympatric speciation

divergence of species within same area.

• result from reproductive isolation, chromosomal error preventing reproduction, behavioural differences

eg howea palms

• curly palm and kentia palm. Share common ancestor. Both wind pollinators and r on an island.

• 1mya calcium carbonate washed on shore where kentia palm r and became stressed and flower earlier = reproduce w stressed howea palm

• curly palm grew in volcanic soil not stressed and flower later = diff reproducing times 

convergent evolution

2 or more unrelated species adopt similar adaptations in response to environmental conditions/selection pressures

• share same function of their feature but diff structures (analogous structure)

• similar due to selection pressure but org is not related

• eg bird and moth can fly

ancestor

early type of animal/plant which other animals/plants evolve from

common ancestor → 2 or more org evolved from same ancestor

descendants → ones that evolve from ancestor

structural morphology

gives evidence for evolution → study of structure of org.

common ancestor → show similarities of bone structure.

• bone vary in size & proportion due to mutation that change where and when genes r expressed & how long.

homologous structure

characteristics thatre shared by related species bc inherited from a common ancestors.

• similar in structure but used in diff ways

• eg same bone structure for human and whale for arm but diff functions

• more similar homologous structure between 2 species then more closely related.

analogous structures

features thatre same function but very diff structures

• similarities due to similar selective pressure.

• eg bird and moth have wings but r diff structures.

vestigal organs & structures

no function in org due to changes in env making it redundant  overtime.

• gives evidence that it served function to common ancestor.

• eg whale has hind limb meaning it evolved from a footed ancestor

• wings on an emu dont work 

developmental biology

study of processes that result in growth & development of multicellular org

• compare diff species at embryo stage development, diff species share common features giving evidence for common ancestor.

• a tail, notochord for jawless fish but is the spinal cord for humans, pharyngal arches forms gills in fish and lower jaw in mammals.

how r species related

homologies → similar characteristics due to relatedness (how recently species split from a common ancestor)

• more recently split = more related.

• show it on a phylogenetic tree

degree of relatedness can be found via:

• comparing amino acid sequences

• comparing dna

• comparing karyotypes

molecular homology

all living things have DNA, DNA is universal, made of 4 bases (adenine, thymine, guanine, cytosine)

• more similar = more related and recently shared common ancestor

• more diff in DNA means more time nucleotides had to mutate

• if genes in species is unchanged = conserved

  • eg haemoglobin. Found in all related species, it has variation due to mutation as they diverged but very similar because serves important function to species

comparative genomics

genome is entire genetic sequence of an org. 

• similarities in genome/base sequences between species determine relatedness

comparing proteins

all org have same set of amino acid building blocks, same genetic code.

• fewer diff in amino acid sequence = closely related = less time passed since diverged from last common ancestor

• more diff in amino acid sequence = less related = more time passed for genes to mutate

mtDNA and molecular clock

mtdna → circular dna in mitochondria

• inherited from maternal line, the mother.

• found in teeth, bones, extracted from fossils

• unaltered, has constant rate of change,

• lots of it for sampling

• divide human population into haplogroups (shared sets of mtdna thats passed on from mother)

molecular clock

• changes at constant rate, used as clock to record time thats passed between separation of species.

• eg every 25m there is a point substitution

cladograms and phylogenetic trees

shows inferred evolutionary history of groups of orgs. 

phylogenetic trees → evolutionary trees. Uses molecular data, amino acid sequences, dna sequences

• tip = descendent of groups (taxa).

• node = ancestor of 2 or more descendents

• branch = speciation event, relationship between ancestor and descendents.

  • longer branch = longer period of time, shorter branch than everything else = extinct

• root = common ancestor of all taxa species in tree

• sister taxa = 2 groups/species with common ancestor that isnt shared with others 

cladograms 

• show relo between groups of orgs, based on shared characteristics/features of org. Structural or molecular or both

• derived traits → features evolved from og ancestor but aint feature of ancestor

• og ancestral trait → feature shared by 2+ taxa in ancestor and new species, its inherited

• clade → group includes common ancestor and all descendants