AOS 4

Question 1

what is mass extinction

Answer 1

when a larger-than-normal number of groups become extinct on regional and global scale
* evolutionary opportunity for other species to thrive and diversify

Question 2

evidence for evolution

Answer 2

• fossils
• biogeographical distribution
• comparative
  
  • anatomy - structural morphology
  • embryology - developmental biology
  • molecular homology - DNA and amino acid sequences

Question 3

conditions that favour fossilisation

Answer 3

• rapidly buried
• protected from scavengers
• prevented from decomposition by low oxygen levels and low tempratures
• organisms having hard structures (won’t decompose as rapidly)

Question 4

process of fossilisation

Answer 4

• an organism dies and is rapidly buried
• protected from scavengers
• prevented from decomposition by low oxygen levels + low temperatures
• continued deposits of sediments bury it more and more deeply
• over time the molecules in the organism (usually the hard parts) are replaced by minerals from groundwater
• gradually, the weight of the overlying sediments compresses the original sediment layer so that it becomes rock
• over time the rock is eroded, uplifted through the movement of tectonic plates or excavated

Question 5

timeline of life on earth

Answer 5

• prokaryotes
• first unicellular eukaryotes
• first multicellular eukaryotes
• first vertebraes (jawless fish)
• first insects
• first land plants
• first amphibians
• first ferns
• first reptiles
• first conifers
• first dinosaurs
• birds
• first mammals
• first flowering plants
• primates
• humans

Question 6

mineralised/petrified fossils

Answer 6

organic material of a structure replaced by minerals

Question 7

mold fossils

Answer 7

• form when a mineralised/petrified fossil dissolves and leave an impression of the original
• these can be filled in to make cast fossils

Question 8

trace fossils

Answer 8

• form when traces of activity are buried before they are erased and turn into rock
  
  • eg footprints, teeth marks, scats (faeces)

Question 9

purpose of fossil record

Answer 9

• the fossil record reveals that over time changes have occurred in the types of organisms living on this planet
• provides evidence in support of the prediction that ancestral species will appear before the species that descend from them

Question 10

fossil/faunal succession

Answer 10

• based on the premise that strata accumalates in chronological order
• fossils in lower strata are older than fossils closer to the surface
• fossils in lower strata are less complex than strata closer to surface

Question 11

relative dating

Answer 11

• sedimentary rocks form in layers (strata)
• newer layers are at the top and the older layers are at the bottom
• can determine relative age from that (as in newer or older - not the specific time)

Question 12

index fossils

Answer 12

• index fossils can be used to determine the relative ages of rock strata anywhere in the world
• presence of index fossils in rock strata in widely separated regions of the world can identify these rocks as having the same age.
• must be
  
  • abundant
  • distributed worldwide
  • existed for only a short period of time

Question 13

transitional fossils

Answer 13

• can tell us about major changes - evidence of evolution
• is the fossilised remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group
• e.g: archaopteryx - dinosaur and modern birds (claws on wings + feathers)

Question 14

absolute dating techniques

Answer 14

• radiometric dating is the most common way to find the actual age of a fossil (rock)
• measure the relative amounts (decay) of radioactive materials (parent) and their daughter products
• the radioactive isotopes (parents) spontaneously decay or break down over time to form stable daughter products

Question 15

relative vs absolute dating

Answer 15

relative age provides a comparative age whereas absolute age provides a more precise numerical age

Question 16

half-life

Answer 16

half life → the time taken for half of the original radioactive isotope to decay

Question 17

carbon dating

Answer 17

• carbon 14 will decay into nitrogen 14 (half-life of 5700 years)
• living things take in C14 when they eat living things stop taking in C14 when they die
• by comparing the amount of C14 and N14, the time since death can be determined
• limitation: can’t be used to date fossils older than around 50000 - 60000 years, there are very small amounts of carbon 14 left in the organic matter

Question 18

speciation

Answer 18

the formation of a new species

Question 19

process of speciation

Answer 19

• variation of characteristics is present in the population
• breeding population becomes isolated
• different selective pressures applied to isolated populations, random genetic drift, mutations
• b/c of natural selection, some characteristics are favoured over others
• those best suited to the environment survive
• survivors reproduce and pass on favourable genes + traits to offspring
• frequency of genes for new traits increases
• overtime, differences and mutations accumulate resulting in speciation

Question 20

definition of species

Answer 20

organisms that can breed and produce fertile and viable offspring

Question 21

allopatric speciation

Answer 21

• Initially a population (or populations) of the same species becomes isolated by a geographical barrier.
• Over time the isolated population(s) is exposed to different selective pressures and accumulates
• sufficient differences to the original population so that it forms a new species.

Question 22

galapagos finches

Answer 22

• 13 volcanic islands w/ a variety of habitats - arid regions and mountainous regions
• after finches had arrived on an island they would become geographically isolated
• differing environmental selection pressures on each of the islands based on food availability (main environmental pressure)
  
  • caused change in beak shape bc of diff food source
  • no gene flow

Question 23

sympatric speciation

Answer 23

• members of a populations living in the same area diverge to become 2 species
• no geographical barrier - both species continue to inhabit the same geographic region
• non-geographical barrier isolates populations from each other (active day/night) - some gene flow
• isolated populations are subject to different selection pressures → different phenotypes are favoured
• over generations, genetic divergence occurs
  
  • responds to diff environmental pressures → different phenotypes and isolated populations change
• when the population come together again - can no longer interbreed - two separate species (2 distinct gene pools and different species)

Question 24

lord howe island palms

Answer 24

• there was variation in the lord howe island population
• shift in nutrient content in the soils which caused a shift in flowering times
• those that flowered at the same time would interbreed
• over time there was accumulation in the differences and mutations in the palms
• speciation occurs and the two species can no longer interbreed

Question 25

why is sympatric speciation rare?

Answer 25

* gene flow can still occur in sympatric speciation * genetic drift has less of an impact * less likely to be isolated as it requires reproductive isolation * natural selection would need to be strong to favour specific traits that then lead to a divergence and a new species evolving

Question 26

what is a common ancestor

Answer 26

* is a species that existed earlier in the fossil record * subsequently evolved into two or more different species * an ancestor shared by later species: one from which two or more species evolved

Question 27

pre-zygotic/post zygotic isolation

Answer 27

* pre-zygotic: barriers that prevent an organism from finding and securing a mate * post-zygotic: barriers that prevent fertile offspring from developing after mating

Question 28

relatedness

Answer 28

species that are **more closely related** are those that have most recently shared a **common ancestor**

Question 29

what is structural morphology

Answer 29

* the process of comparing similarities in body structures to infer relatedness * fossil record

Question 30

structural morphology - homologous structures

Answer 30

* homologous structures are those structures that have been derived from a common ancestor * would show similarities in structure * even though they may have different functions * evolution commonly occurs by modification of pre-existing structures - not by the production of TOTALLY new structures * eg. mammalian forelimbs

Question 31

structural morphology - vestigial structure

Answer 31

* structures that are non-functional remnants of structures that were functional in ancestral species * eg. tailbone in humans

Question 32

what is molecular homology

Answer 32

involves comparing the similarities in DNA and protein sequences to infer relatedness

Question 33

amino acids for molecular homology

Answer 33

* species that are more closely related are expected to have fewer differences in the amino acid sequences of their corresponding proteins than species that are more distantly related

Question 34

challenges with amino acid sequencing

Answer 34

* multiple triplets can code for a particular amino acid * genetic code is redundant * some mutations (silent mutations) aren’t visible in amino acid sequencing * also sometimes two mutations that occur in the same codon will only cause one amino acid change.