Topic 4 - Evolution

Question 1

What is symbiosis?

Answer 1

Two organisms helping each other and both benefitting.

Question 2

What is endosymbiosis?

Answer 2

One organism living inside another and both benefitting.

Question 3

What is the evidence that prokaryotes existed first?

Answer 3

• prokaryotes are fundamentally simpler in structure than eukaryotes
• mitochondria and chloroplasts display an example of endosymbiosis through their presence within eukaryotic cells (both of these organelles contain DNA that resembles prokaryotes)

Question 4

What is the evidence that eukaryotes evolved by endosymbiosis?

Answer 4

• chloroplasts and mitochondria have their own DNA that is circular like prokaryotes
• both contain their own ribosomes that are smaller and have similar nucleotide sequences to bacterial ribosomes
• can self-replicate independently to the cell in a process that resembles binary fission
• both have duel membranes, the inner one containing enzymes and transport proteins whilst the outer is like the plasma membrane

Question 5

What is evolution?

Answer 5

The gradual changes to populations on Earth over long periods of time.

Question 6

What are the three factors that increase mutation rate?

Answer 6

• ionising radiation
• mutagenic chemicals
• viruses

Question 7

What is the trend in mutation rate and how does this relate to evolution?

Answer 7

The amount of mutations building up in DNA, RNA or amino acid sequences of proteins is fairly linear with time. This means that if you compare the number of mutations between two species, you can get some idea of when they diverged from a common ancestor.

Question 8

How does sexual reproduction contribute to genetic variation more than asexual reproduction?

Answer 8

Sexual reproduction provides sources of genetic variation through crossing over, independent assortment, and random fertilisation. Asexual reproduction can only provide genetic variation though mutations.

Question 9

How do alleles work for genetic diversity?

Answer 9

Alleles are variations of genes, which allows an organism to express one variation whilst still carrying the same genome.

Question 10

What does comparative genomics describe?

Answer 10

All living organisms have DNA in varying degrees of complexity. Codons (sequence of three nucleotides) code for a specific amino acid, and there are 20 amino acids for all living things. This is compelling evidence for the idea of evolution from common ancestors. Given that mutation is inevitable, as time goes on there is a greater difference in the DNA sequences between organisms. If two organisms have separated relatively recently then there will be less mutations in the DNA, meaning more homology (recent common ancestor). Thus, species that have been separated by a long period of time would have more mutations in DNA, meaning less homology (distant common ancestor).

Question 11

What are the methods of checking biochemical similarity between species?

Answer 11

DNA-DNA hybridisation, and DNA/rRNA/protein sequencing.

Question 12

How does DNA-DNA hybridisation work?

Answer 12

DNA from one species is heated, breaking the hydrogen bonds between complementary strands to prompt separation. Single-stranded DNA from the other species is mixed and the mixture is cooled to allow the DNA to form double strands again, but with one strand from one species and one from the other. Strands with high homology will bond more tightly than those with low homology, due to more complementary nucleotide pairings. The hybrid strand is then reheated, causing more poorly matched strands to separate more easily. The temperature at which these hybrid strands separate is measured to determine how closely related species are.

Question 13

What are the advantages and disadvantages of DNA-DNA hydridisation versus DNA/rRNA/protein sequencing?

Answer 13

DNA-DNA hybridisation is faster and cheaper, however DNA/rRNA/protein sequencing is higher resolution.

Question 14

How does DNA/rRNA/protein sequencing work?

Answer 14

DNA is amplified using PCR then read using electrophoresis, comparing the number of differences.

Question 15

What is the definition of a species?

Answer 15

A species that reproduces sexually can be defined by the ability of its members to actually or potentially interbreed to produce fertile offspring. Other methods of species definition must be used for those that do not reproduce sexually including morphological similarity, biochemical similarity, and sharing a common gene pool.

Question 16

What is the definition of a community?

Answer 16

All of the populations of different species in an area at a particular time.

Question 17

What is the definition of a population?

Answer 17

A group of organisms of the same species occupying a particular space at a particular time.

Question 18

What is morphological similarity?

Answer 18

The development of common characteristics that make organisms recognisably similar to one another, but there are still variations (alleles) between individuals within the species.

Question 19

What is biochemical similarity?

Answer 19

Biochemical similarity is the differences in DNA sequencing between two species. Members of the same species have much greater similarity in their DNA and amino acid sequences.

Question 20

What is a gene pool?

Answer 20

The gene pool of a population includes all alleles of all genes of all the individuals of that population. Each species has a separate gene pool and is reproductively isolated from all other species.

Question 21

How can reproductive isolation be achieved?

Answer 21

PREZYGOTIC FACTORS - behavioural isolation, mechanical isolation, temporal isolation, and gamete isolation
POSTZYGOTIC FACTORS - hybrid inviability, and hybrid sterility

Question 22

What is behavioural isolation?

Answer 22

Mating behaviour is specific to individual species, not interesting to other species.

Question 23

What is temporal isolation?

Answer 23

Species may produce gametes in different seasons, meaning flowering or mating will take place at different times.

Question 24

What is mechanical isolation?

Answer 24

Anatomical differences between genitals so the transfer of gametes cannot take place.

Question 25

What is gamete isolation?

Answer 25

Prevention of fertilisation, even if the gametes are transferred (male gametes might die due to inappropriate conditions, or male and female gametes may fail to recognise each other).

Question 26

What are prezygotic factors?

Answer 26

Factors that prevent mating and/or fertilisation.

Question 27

What are postzygotic factors?

Answer 27

Barriers that operate after fertilisation and prevent the development of fertile hybrids.

Question 28

What is hybrid inviability?

Answer 28

Even if mating does occur and gametes fertilise, the zygote or embryo may not develop normally as the genes from the parents are too different.

Question 29

What is hybrid sterility?

Answer 29

If the two species differ in chromosome type - even if hybrid offspring is formed - it is sterile because the process of meiosis cannot proceed normally (homologous pairs cannot form).

Question 30

What is natural selection?

Answer 30

Even though organisms have the capacity to increase numbers from one generation to the next, not all organisms will survive to reproduce. There are a range of selection pressures that cull populations such as predators, disease, competition for resources, and environmental factors (temperature, water availability, and shelter). Organisms that are born with traits better suited to these selection pressures will survive and have an increased chance of reproducing.

Question 31

How does gene frequency work?

Answer 31

Others that do not have these traits tend to die off due to selection pressures which removes the gene from the gene pool, or reduces its frequency, for future generations. Thus, genes that convey an advantage for a particular environment stay in the gene pool and tend to be more likely passed onto the next generation, increasing gene frequency. This is natural selection and depends on the specific selection pressures.

Question 32

Why are large gene pools necessary for species survival?

Answer 32

Populations that have limited or small gene pools are less able to withstand selection pressures due to the limitations in the variation of genes to respond to these changes in environment; either more organisms will survive or most will die. Populations with diverse gene pools are more likely to have individuals with the genetic make-up to survive the selection pressures. It is the survival of these individuals that ensures the survival of the population.

Question 33

What is genetic drift?

Answer 33

The changes in frequencies of alleles in a population due to chance events.

Question 34

What is the founder effect?

Answer 34

If a small number of individuals from a population begin a new population, they may have far less genetic diversity than the original population.

Question 35

What is the bottleneck effect?

Answer 35

Species that have limited genetic diversity within the population (loss of individuals) may not have full diversity of alleles (narrowed gene pool) from the original population.

Question 36

What are some examples of species with low genetic diversity?

Answer 36

Cheetahs, european bison, and tasmanian devil.

Question 37

What is speciation?

Answer 37

The development of a new species that occurs so slowly it is almost unnoticed (natural selection alters the characteristics of a population over many generations.

Question 38

What is an explanation of speciation?

Answer 38

Initially, a single population is split into groups. This can occur through geographical isolation and changes in environmental conditions. Over thousands of years, the selection pressures drive the increase in different gene frequencies in the gene pool, driving the evolution of species (assuming no gene flow between groups).

Question 39

What is allopatric speciation?

Answer 39

Allopatric speciation is the formation of different species by geographical isolation, causing mutations to occur in these separate locations which results in reproductive isolation.

Question 40

What is sympatric speciation?

Answer 40

Evolution of two species living in the same geographical area.

Question 41

What is convergent evolution?

Answer 41

Organisms that are isolated but face similar pressures may evolve to express similar traits. The similar selection pressures mean that specific genes are favoured, resulting in similar traits being expressed and organisms that resemble one another.

Question 42

What is divergent evolution?

Answer 42

Divergent evolution involves the gradual accumulation of new characteristics culminating in the formation of a new species, as a result of different selection pressures.

Question 43

What is adaptive radiation?

Answer 43

A particular case of divergent evolution where there is the sudden emergence of a new species from a common ancestor. Adaptive radiation is usually due to a change in the environment of the organism and different selection pressures acting upon them.

Question 44

What are some human impacts?

Answer 44

• increased carbon dioxide levels
• enhanced greenhouse effect
• acid rain
• eutrophication
• soil salinity
• extinction of species (bilby, dodo, etc)

Question 45

What is biodiversity?

Answer 45

Biodiversity refers to the relative abundance of organisms on Earth.

Question 46

What are the human benefits of biodiversity?

Answer 46

• foods
• medicines
• raw materials
• clothing

Question 47

How is interconnectedness related to biodiversity?

Answer 47

Upsetting the balance of nature could have severe and unpredictable consequences on entire ecosystems.

Question 48

How do you preserve a species?

Answer 48

An organism’s habitat is the place it lives including the medium in which it lives, as well as the climate and other organisms present. By preserving the species habitat, you can preserve the species.

Question 49

What are the two accepted levels of conservation in preserving habitats?

Answer 49

1. To ensure survival, an area of land large enough for 50 of the largest carnivores in the community needs to be set aside.
2. To go beyond just secure and be reasonably confident of survival, the area needs to be large enough to support 500 of the largest carnivores within the community.

Question 50

How does recycling resources help to maintain habitats?

Answer 50

In biological terms, recycling can include more than elements and minerals but also features like nests or burrows. These resources are usually limited in a community and need to be recycled from one generation to the next. Minerals and elements used by plants and consumed are returned to the soil by death and decomposition.

Question 51

What is succession?

Answer 51

Changes in the mix of species over time due to changing selection pressures, until an established ecosystem (climax community) is formed.

Question 52

What is secondary succession?

Answer 52

The gradual re-establishment of the succession process due to a disruption in environment, prompting new species development that thrive in these new selection pressures.

Question 53

What is primary succession?

Answer 53

The establishment of plants on bare rock or sand dunes is called primary succession.

Question 54

What is a climax community?

Answer 54

A climax community is when the community is stable and reaches a natural balance where no further succession occurs.

Question 55

How does a climax community form?

Answer 55

A climax community does not form automatically as a single unit, but it is the result of species competing against each other for the resources. If resources change then the species better suited to the changed conditions may gradually overcome the pioneer and intermediate species.

Question 56

Describe the role of RNA in the first simple cells.

Answer 56

In the first simple cells, it is likely that RNA was used instead of DNA to carry inherent genetic information due to its simpler structure.

Question 57

Describe the role of ribozymes in the first simple cells.

Answer 57

Ribozymes are RNA molecules that have the ability to catalyse chemical reactions within cells. Thus, these acted like enzymes in the first simple cells.