Evolution

Question 1

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How long has life existed on Earth?

Answer 1

3.5 billion years

Question 2

What evidence is there for life on Earth 3.5 billion years ago?

Answer 2

Prokaryotic cell fossil

Question 3

What type of cell came first?

Answer 3

Prokaryotic cells

Question 4

How can membranes form spontaneously?

Answer 4

Phospholipids will spontaneously arrange themselves due to their chemical nature (to protect their hydrophobic tails from aqueous environments)

Question 5

What was the role of RNA in the first simple cells?

Answer 5

transmit and store genetic information

Question 6

What are ribozymes?

Answer 6

RNA that can act as a catalyst chemical reactions (similar to enzymes)

Question 7

Describe the evidence that prokaryotes existed before eukaryotes.

Answer 7

The oldest prokaryotic fossil is 2 billion years older that the oldest eukaryotic fossil.

(oldest prokaryotic fossil : 3.5 billion years old
oldest eukaryotic fossil: 1.5 billion years old)

Question 8

How did the nucleus/Golgi body/ER form?

Answer 8

From the in-folding of the plasma membrane – they all have the same structure as the plasma membrane.

Question 9

Describe endosymbiosis

Answer 9

A large prokaryotic cell engulfed (phagocytosed) a smaller aerobically respiring/photosynthesizing prokaryote

The smaller prokaryote survived inside the larger cell and the cells operated symbiotically

Overtime, the smaller prokaryote evolved into mitochondria/chloroplast

Question 10

What organelles evolved from endosymbiosis?

Answer 10

Mitochondria/Chloroplast

Question 11

Describe the techniques of DNA-DNA hybridization

Answer 11

• DNA from 2 species is mixed and heated to separate complementary strands
• DNA mixture is cooled to allow DNA to re-anneal, closely matched DNA will bond tightly, whilst less closely matched DNA will not bond tightly
• The newly formed Hybrid DNA is heated to see how easily the strands will separate
• Poorly matched DNA strands will separate at lower temperature than well-matched DNA strands as there is fewer bonds to break
• The higher the temperature/melting point at the point of separation, the more closely matched the DNA is.

Question 12

How can DNA-DNA hybridization show evolutionary relationships?

Answer 12

• The higher the temperature at the point of separation, the more bonds present to beak, hence the more closely matched the DNA is, thus indicating a more closely relationship and more recent common ancestor in time
• Lower temperature at the point of separation, the less closely matched the DNA is as there is fewer bonds to break thus, suggesting a less closely relationship and distant common ancestor in time

Question 13

How can sequencing of common proteins show evolutionary relationships

Answer 13

• The number of differences in amino acid sequence can be counted
• Fewer differences indicate a more closely related relationship and a more recent common ancestor

Question 14

How can DNA sequencing show evolutionary relationships?

Answer 14

• The number of differences in DNA base sequence can be counted
• Fewer differences indicate a more closely related relationship and a more recent common ancestor

Question 15

How can rRNA gene sequencing show evolutionary relationships in prokaryotes?

Answer 15

• The rRNA can be analysed. The number of differences can be counted
• Fewer differences indicate a more closely related relationship and a more recent common ancestor

Question 16

Describe the principles of a phylogenetic tree

• What does the scale represent? Time
• What is the starting point?
• What do the branches represent?
• What are the end points?
• How can you tell if organisms are closely related?

Answer 16

• What does the scale represent? Time
• What is the starting point? The most distant common ancestor
• What do the branches represent? Speciation – new species evolving
• What are the end points? The present time
• How can you tell if organisms are closely related? They have a common recent ancestor

Question 17

How can the mutation rate be used if it is known?

Answer 17

Mutations accumulate at a known rate
Can be used as a clock

Question 18

What happens to the number of mutations over time?

Answer 18

accumulate over time

Question 19

Which is most likely to have more differences in their DNA sequence:

2 distantly related species

OR

2 closely related species?

Answer 19

2 distantly related species

Question 20

Which is most likely to have more differences in their DNA sequence:

2 species with a recent common ancestor

OR

2 species with a distant common ancestor?

Question 21

How is a species defined (if it is able to reproduce sexually)

Answer 21

A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding to produce fertile offspring

Question 22

Explain why the ‘traditional’ definition of a species cannot be used for all organisms.

Answer 22

Cannot apply to asexually reproducing organisms/species

Question 23

What are the 3 other criteria used to define a species

Answer 23

Morphological similarity, biochemical similarity, sharing a gene pool

Question 24

Define the term ‘prezygotic isolation’

Answer 24

A mechanism that prevents the fusing of gametes to form zygote

Question 25

Describe temporal isolation, give an example.

Answer 25

The timing of gamete release is so different that gamete never meet e.g., different breeding season

Question 26

Describe behavioral isolation, give an example.

Answer 26

When a behaviour is not recognised before mating occurs e.g., different mating calls, different dance/song rituals for birds

Question 27

Describe mechanical isolation, give an example.

Answer 27

Anatomical differences in the genitals preventing the meeting of gametes e.g., snail reproductive do not align.

Question 28

Describe gamete isolation, give an example.

Answer 28

Gametes are unable to recognise or fuse with each other

Question 29

Define the term ‘post-zygotic’ isolation

Answer 29

A mechanism preventing the production of fertile offspring after the fusion of gametes

Question 30

Describe hybrid in-viability, give an example.

Answer 30

When the formation of embryo cannot reach full term development e.g., lion and leopard breading but pregnancy always ends in miscarriage

Question 31

Describe hybrid sterility, give an example.

Answer 31

The production of infertile hybrid species that is unable to produce offspring on its own

Question 32

What is a mutation? Explain why mutations are the ‘ultimate source of genetic variation’.

Answer 32

Change in base sequence of DNA All other genetic variation (crossing over etc.) rely on the existence of different alleles. These arise from mutations.

Question 33

In what type of species is mutation the ONLY source of genetic variation?

Answer 33

Asexual reproducing organisms

Question 34

Other than mutation, what are the additional sources of genetic variation in sexually reproducing species?

Answer 34

Crossing over, independent assortment, random fertilisation

Question 35

Explain crossing over and how this contributes to genetic diversity.

Answer 35

During meiosis 1, homologous pairs of chromosomes align There is exchange of genes between homologous pairs of chromosomes This creates new combinations of maternal and paternal alleles never seen before.

Question 36

Explain independent assortment and how this contributes to genetic diversity.

Answer 36

During anaphase of meiosis, homologous pairs of chromosomes are separated into different daughter cells The assortment of maternal and paternal chromosomes is independent to the next This creates a random assortment of paternal and maternal alleles in the daughter cells

Question 37

Explain random fertilisation and how this contributes to genetic diversity.

Answer 37

Any sperm can fertilise any egg When this happens, never-seen-before combinations of maternal and paternal alleles can be formed.

Question 38

Define the term ‘gene pool’.

Answer 38

The total of the genes within a population

Question 39

Define the term ‘selection pressure’

Answer 39

Biotic and abiotic factors/pressures that create a struggle for survive. Not all organisms can survive these selective pressures.

Question 40

Define the term ‘allele’

Answer 40

A version of a gene

Question 41

Explain how a large gene pool in a population means that population is more likely to survive selection pressures.

Answer 41

A large gene pool within a population, that population is considered diverse Diversity is an advantage as when there is changes, it is more likely that there is an allele that suits the change and allows the population to survive and adapt.

Question 42

Describe natural selection in 4 steps.

Answer 42

**Variation** : there is a difference in the alleles of individuals within a population **Selective pressure** : abiotic and biotic factors/pressures creating a struggle for survive (e.g., predators, limited food). Not all organisms can survive the selective pressure. **Survival of the fittest** : individuals with favourable genes are able to survive, reproduce, and pass on their favourable genes to the next generation **Change in allele frequency** : over many generations, there is an increase in the favourable gene within the population (become more prevalent within the population)

Question 43

Explain how sexual reproduction can affect evolution

Answer 43

Crossing over, independent assortment, and random fertilisation ensure that every gamete is different This creates new combinations of maternal and paternal alleles within the population that can be removed by chance

Question 44

Describe genetic drift and how this can affect evolution.

Answer 44

Change in frequencies of alleles within population due to chance events such as catastrophes Alleles can be completely removed from the population This is more likely to happen to small population

Question 45

What is speciation?

Answer 45

The process by which populations of species change of overtime, via natural selection, to the point where there are sufficiently different to be considered different species

Question 46

What must accumulate over time for speciation to occur?

Answer 46

Mutation

Question 47

State the 4 steps of speciation.

Answer 47

Geographic isolation Selective pressure Natural selection Reproductive isolation

Question 48

For speciation to occur two populations must be geographically isolated to prevent what?

Answer 48

Gene flow

Question 49

For speciation to occur, 2 geographically isolated populations must experience different conditions. Name the term for these ‘conditions’.

Answer 49

Selective pressures

Question 50

Give an example of allopatric speciation in four steps.

Answer 50

**Geographic isolation** : 2 populations of owls are separated by a physical barrier such as a desert, preventing gene flow **Selective pressure**s :the 2 populations experience different abiotic and biotic pressures/factors/conditions (e.g., food, predators, prey) **Natural selection** : the 2 populations adapt to their respective environment and develop different characteristics **Reproductive isolation** : the 2 populations become sufficiently different to be considered different species as they cannot interbreed and produce fertile offspring

Question 51

Describe divergent evolution and give an example.

Answer 51

when species evolve from a common ancestor e.g., all mammals have the same forearm bone structure. This was inherited from a common ancestor.

Question 52

Describe adaptive radiation and give an example.

Answer 52

Many species evolve from a common ancestor e.g., the many galpagos finches evolved from an ancestral mainland species in a relatively short period of time

Question 53

Explain the difference between divergent evolution and adaptive radiation.

Answer 53

In adaptative radiation, the timeframe is shorter and the number of species is far greater

Question 54

Describe convergent evolution and give an example

Answer 54

When two species evolve same adaptations/characteristics due to experiencing similar selective pressures. They did not evolve from a common ancestor that had that adaptation e.g., echidnas and hedgehogs both separately have evolved spikes as a defence mechanism against predators. They do not share a common ancestor with spikes.

Question 55

Describe primary succession and give an example

Answer 55

Primary succession occurs on newly formed land e.g. volcanic rock. 1) A pioneer species e.g., lichen is able to colonise the land. 2) Through its lifecycle and decay, it builds up a layer of soil and changes the abiotic conditions to suit other species of plant such as mosses. 3) This process continues, allowing larger species to colonies, such as grasses, then shrubs. 4) Each new species changes the abiotic and biotic conditions to better suit other species, allowing them to colonise the area. The new species often outcompete the original. 5) Over time there is a change in the mix of species inhabiting the area. 6) Until a stable climax community is reached.

Question 56

State the name of the first organisms to colonise new land.

Answer 56

Pioneer species

Question 57

State the name of the stable ‘final’ community of organisms the is established after the process of succession.

Answer 57

Climax community

Question 58

Describe secondary succession and give an example.

Answer 58

Secondary succession occurs on existing land that has been disturbed in some way. E.g. a bushfire 1) As soil is already present, the first species to grow can be larger and there may be multiple species at one time. 2) The first species change the biotic and abiotic conditions, e.g providing shelter for small mammals or reptiles. These may bring birds who drop seeds. 3) This process allows larger species to colonies, such as shrubs and trees. 4) Each new species changes the abiotic and biotic conditions to better suit other species, allowing them to recolonize the area. The new species often outcompete the original. 5) Over time there is a change in the mix of species inhabiting the area. 6) Until a stable climax community is reached.

Question 59

Describe the difference between primary and secondary succession.

Answer 59

Primary succession occurs on new land that no species has inhabited before. Secondary succession occurs on existing land which already has soil and species have inhabited the area previously. Secondary succession is a much faster process than primary succession.