Evolution 2

Question 1

What is Natural Selection?

Answer 1

environmental or selective pressures act on the phenotype of individuals in a population

lead to changes in allele frequency.

Certain alleles will be favoured and others are selected against

Question 2

Variation -

Answer 2

• presence of variation in a population is what allows natural selection to occur.

naturally present in sexually reproducing organisms and then selection allows organisms with certain characteristics to survive and then pass on their genes to the next generation.

The features which are selected to ensure that the organism is well suited or adapted to its environment

Question 3

Selection: Biotic Factors

Answer 3

• Predators
• Disease-causing organisms
• Competition from members of the same or different species
• Symbiotic relationships with other organisms

Question 4

Selection: Abiotic Factors

Answer 4

• Rainfall
• Temperature
• Nutrient levels
• Light intensity
• Medical drugs like antibiotics, or chemicals like pesticides

Question 5

Mutations

Answer 5

permanent changes in the sequence of nucleotides of DNA

source of genetic variation in the species, new forms of a particular gene (alleles).

Mutations in germline cells can be passed on to the next generation.

Question 6

Variation in Offspring

Answer 6

asexually reproducing organisms = offspring genetically identical, unless mutation has occurred.

sexually reproducing organisms = offspring not genetically identical

Question 7

Four main factors which contribute to variation among offspring:

Answer 7

Mutations
Crossing over
Independent assortment
Random fertilisation

sexual reproduction allows for the ‘re-shuffling’ of genes from parents to give rise to new combinations in their offspring.

Question 8

Gene pool

Answer 8

sum of all of the alleles of all of the individuals in that population.

Question 9

Population

Answer 9

group of individuals of the one species that breed together in a particular habitat.

Question 10

The genotype of an organism

Answer 10

determines the appearance or phenotype of the individual.

Question 11

Allele frequency

Answer 11

relative proportion of a particular allele in the population.

Question 12

Large/small gene pool

Answer 12

Populations with large gene pools = large diversity of alleles , more likely to survive in harsh conditions.

Populations with; small gene pool = are at greater risk of extinction. less genetic diversity

Question 13

Changes in the gene pool of a population can be brought about by several factors:

Answer 13

Gene Flow – Movement of alleles between different populations of the same species.

Increased gene flow between populations reduces differences between populations.

Genetic Drift – changes in the frequency of alleles in a population.

Question 14

Speciation

Answer 14

process that gives rise to the origin of new species.

result from an accumulation of genetic changes influenced by different selection pressures or genetic drift in geographically isolated populations

Question 15

Allopatric Speciation

Answer 15

involves members of the original population being separated by a geographical barrier.

Question 16

Sympatric speciation

Answer 16

is where one population gives rise to two or more species while still inhabiting the same region

• no geographical isolation.

If occurs = gene flow still needs to be prevented, leading to reproductive isolation.

Question 17

Sympatric speciation can occur through hybridisation and…

Answer 17

Asexual Reproduction

Question 18

Sympatric speciation can occur through Polyploidy

Answer 18

where organisms possess more than two sets of chromosomes.

result of a malfunction during meiosis where chromosomes fail to separate properly.

organism can’t interbreed with an organism with the normal diploid number

• gene flow is immediately stopped.

Question 19

Convergent Evolution

Answer 19

occurs when different species of organisms develop similar (analogous) features with similar functions.

can occur as different groups of organisms often live in similar habitats with similar selective pressures.

then evolve to have similar structures/ behaviours

Species evolved in particular environments in similar - evolve similar features, undergone convergent evolution.

Question 20

Analogous Features

Answer 20

have evolved separately in different lines of evolution.

serve the same function in different species but have evolved separately.

has occurred when such features evolve independently in unrelated groups or separate species.

Birds, bats and butterflies are unrelated have all evolved wings for flight independently of one another.

Question 21

Divergent Evolution

Answer 21

process by which interbreedingspeciesdiverged into two or more evolutionary groups.

these groups of species used to be similar and related. However, they became more and more dissimilar through time.

homologous structures = indicate a species is diverging from its ancestor.

Question 22

Divergent Evolution: The forelimbs of humans and bats are

Answer 22

homologous structures.

used differently, the basic skeletal structure is the same and they are derived from the same embryonic origin.

indicate plausible evolution from a common ancestor.

Question 23

Advantages of Divergent Evolution

Answer 23

allows species with common ancestral origin to be able to adapt to their own habitats.

promotes biodiversity.

• leads to speciation,
• and a wide range of different organisms thriving in diverse habitats.

Question 24

Adaptive Radiation

Answer 24

when a single or small group of ancestral species rapidly diversifies into a large number of descendant species.

Question 25

Divergent vs Adaptive Radiation

Answer 25

adaptive radiation - small-scale evolution over a shorter span of time divergent evolution - evolution of species diverging from its ancestors over a relatively long span of time. adaptive radiation may lead to divergent evolution over time as the species become more and more distinct from its ancestors.

Question 26

Convergent Comparison

Answer 26

Species evolved from a relatively recent common ancestor. Gives rise to homologous structures; species diverge. Species become more different over time. Species are relatively closely related, as they share a recent common ancestor.

Question 27

Divergent Comparison

Answer 27

Species have relatively different common ancestors. Gives rise to analogous structures; species converge Species appear to become more similar over time. Species are less closely related, do not have a recent common ancestor.

Question 28

Issue of reduced gene pool

Answer 28

reduced genetic biodiversity = decreased chance of a population to survive and evolve in the face of changing environmental selective pressures. large gene pool - more likely that at least some members of the population will survive, pass on favoured genes to the next generation.

Question 29

Succession

Answer 29

gradual process by which species composition in a community changes. brought about by modification of the habitat caused by the organisms that live there.

Question 30

Succession: organisms can change the environment

Answer 30

can provide food or shelter for other organisms. E.g. trees are a source of food and shelter. change the soil structure by causing the breakdown of rock or increasing the amount of organic matter in the soil. decompose dead material and make nutrients available for others.

Question 31

Example of succession

Answer 31

if a lava flow kills all life in a particular area, the order which species begin to grow in the environment can be tracked over time. The first organisms which establish the area are usually able to survive in harsh conditions e.g. lichens. These colonizing species can then change the environment to allow other organisms to survive.

Question 32

There are two main types of succession:

Answer 32

Primary succession and secondary

Question 33

Primary Succession

Answer 33

where organisms establish themselves in a brand new environment.

Question 34

Example on Primary Succession

Answer 34

area where glaciers are retreating and revealing land with no life present. Species such as lichens would be able to survive on the harsh rock environment and would slowly change the environment, forming soils. This soil would then allow species like mosses to survive and over time, with further breakdown and decomposition occurring, the conditions become ripe for grasslands and shrubs. As these plants begin to survive in the environment, birds and insects can survive and change the environment further, which then allows for other plant species to be introduced. Over the succession period one type of community is replaced by another, until the ecosystem matures. At the climax stage of the community, it is dominated by generally larger, longer living and slower growing species.

Question 35

Secondary Succession

Answer 35

where changes occur in an environment which has been exposed to damage or a disaster e.g. fire, land clearance. The same pattern in the emergence of species will occur in secondary succession as in primary succession. quicker than primary succession - is a greater mix of soils - usually a greater mix of species and plants available to recolonize the area.

Question 36

Succession Characteristics

Answer 36

ecosystem matures = more biomass, but productivity decreases. more species in mature ecosystems. As the ecosystem matures the number of heterotrophic species increases more than the number of autotrophic species. Mature ecosystems are more efficient at recycling nutrients. Mature ecosystems have organisms that tend to be more specialized.

Question 37

Succession, Adaptive Radiation and Divergent Evolution…

Answer 37

When new niches become available to a species, for example as a result of succession or following an environmental change, different selection pressures may lead to divergent evolution or adaptive radiation.

Question 38

Evidence shows that life has existed on Earth for around...

Answer 38

3.5 billion years.

Question 39

All living things share many features:

Answer 39

Cell membrane composed of lipids RNA and DNA Proteins composed of the same amino acids Water composition by mass is 50%-80% for all cells and water has the same functions in all cells.

Question 40

Prokaryotes date back too...

Answer 40

Prokaryotes date back too...

Question 41

The oldest fossils are...

Answer 41

cyanobacteria rocks in Western Australia dated about 3.5 billion years old. formed stromatolites. photosynthetic, important for evolution on Earth as they released oxygen into the atmosphere.

Question 42

What several processes were necessary for life to begin on Earth?

Answer 42

Synthesis of simple organic molecules e.g. amino acids and ultimately the synthesis of larger organic polymers e.g. proteins. The origin of molecules that can self replicate. I.e. RNA and DNA. Packaging of these molecules into membranes with an internal environment different in composition from their surroundings. These structures are known to form spontaneously.

Question 43

It is likely that Earth was subjected to a...

Answer 43

a lengthy barrage of meteor showers and emissions from volcanoes atmosphere contained the precursors needed to make organic molecules.

Question 44

Evidence also suggests that lfie may have orinagted at the bottom of the sea. How is this possible?

Answer 44

Hydrothermal vents warm ocean water to temperatures suitable for life processes release hydrogen-rich molecules and minerals that early organisms could have used to obtain energy

Question 45

What came first DNA or RNA?

Answer 45

protein enzymes are required for DNA to be copied and replicated. RNA appeared before DNA and proteins in the evolution of life.

Question 46

The key function of RNA and ribosomes in simple cells - RNA can self replicate

Answer 46

RNA can self-replicate store information in a sequence composed of four recurring nucleotides (similar to DNA) Short sequences of RNA can be duplicated to form identical RNA molecules.

Question 47

The key function of RNA and ribosomes in simple cells - RNA can act as a catalyst

Answer 47

cells use RNA catalysts (called ribozymes) to remove introns from mRNA, help synthesise new RNA molecules In ribosomes, rRNA functions as the catalytic component - plays a pivotal role in peptide bond formation

Question 48

Prokaryotic vs. Eukaryotic Cells

Answer 48

Prokaryotes - simplest cells, lack a nucleus and membrane bound organelles. the fossil record as the oldest known microfossils are the cyanobacteria found as stromatolites.

Question 49

Evidence supporting what cell came first.

Answer 49

Fossils – earliest eukaryote fossil found, a multicellular alga – 2.1 billion years old Biomarkers – eukaryotic biomarkers have been found in sedimentary rocks in the Earth’s crust indicating 2.7 billion years ago. (Sterols – a molecule only found in eukaryotic membranes) Comparison of cell structure: DNA in eukaryotes has a higher level of organization Eukaryotes have membrane-bound organelles Eukaryotic cells are bigger

Question 50

Mechanisms for Evolution of Eukaryotic Cells from Prokaryotic Cells

Answer 50

Protists. - The oldest and most primitive eukaryotes eukaryotic cells probably originated as a collection of prokaryotes.

Question 51

The evolution of prokaryotic cells would have occurred in two steps:

Answer 51

The first step - folding of the membrane to form the endo-membrane system. - formed the endoplasmic reticulum and most other organelles. The second step - endosymbiosis - Chloroplasts and mitochondria seemed to have evolved from prokaryotes which became incorporated after being engulfed by another cell.

Question 52

Evidence supporting the evolution of prokaryotes

Answer 52

mitochondria and chloroplasts have inner membranes similar to plasma membranes of prokaryotes, replicate by splitting through binary fission, have their own circular DNA own protein manufacturing system including ribosomes.

Question 53

Endosymbiosis

Answer 53

is a a symbiotic relationship where one organism lives inside the other Primary endosymbiosis - original internalization of prokaryotes by an ancestral eukaryotic cell, resulting in the formation of the mitochondria and chloroplasts.

Question 54

Evolution

Answer 54

change in heritable characteristics of biological populations over successive generations. observed using changes in the structure or base sequence of DNA. changes in the proteins coded for, and therefore the phenotype of the organism.

Question 55

Amino acid sequences

Answer 55

DNA and protein sequences show greater similarity between closely related groups of organisms compared to distantly related groups. Scientists can compare the sequence of amino acids in proteins of the same type. If different species produce proteins with very similar amino acid sequences, their DNA would also be very similar, species would therefore be derived from a recent common ancestor. - least accurate

Question 56

Amino acid sequences: cytochromes

Answer 56

proteins needed for aerobic respiration. varies from one species to another, degree of similarity indicates the closeness of the evolutionary relationship.

Question 57

DNA Hybridisation

Answer 57

used to compare the DNA of different species is called DNA hybridisation. DNA from two species is heated and this separates the two DNA strands Upon cooling the single strands of DNA recombine to form the DNA double helix again The degree of bonding between one species’ DNA and another gives a measure of how closely related the two species are

Question 58

DNA Hybridisation; similarity

Answer 58

If the two species are closely related, the DNA sequence will be very similar and the two strands will be difficult to separate. If the two strands are poorly matched, they will be easier to separate. - This means the two species are distantly related because the DNA sequence is very dissimilar

Question 59

DNA profiling

Answer 59

used to compare specific genes between species. Profiles obtained through gel electrophoresis can be used to compare regions of the DNA. Similarities and differences can be used to help establish patterns of evolutionary relatedness.

Question 60

DNA Sequencing

Answer 60

used to work out the actual sequence of bases in a specific gene. Software can then be used to create a phylogenetic tree of related organisms using DNA sequences.

Question 61

Phylogenetic Trees

Answer 61

shows the evolutionary relationships between a variety of organisms - based on similarities and differences in both genetic and physical features. The DNA sequences vary from one species to another - degree of closeness determines the closeness of the evolutionary relationship.

Question 62

Benefits of Comparative Genomics

Answer 62

understanding of organisms, including the human genome. Identifying genes that are essential to life Wide-ranging applications in agriculture and biotechnology.

Question 63

Species

Answer 63

is a population where the members have similar characteristics and the capacity to interbreed and produce fertile offspring.

Question 64

Problems in the Definition of a Species - Asexual Reproduction

Answer 64

Organisms that produce offspring that don’t involve the production of sperm and eggs undergo asexual reproduction. This means the species definition of interbreeding doesn’t apply.

Question 65

Problems in the Definition of a Species - Overlap of Population and Hybrids

Answer 65

difficult to examine the extent of interbreeding.

Question 66

Problems in the Definition of a Species - Fossils

Answer 66

classify fossils into particular species will not fit with the current definition of species. No evidence is available regarding interbreeding. Biologists use morphological features in this case.

Question 67

Pre-Zygotic Reproductive Isolation

Answer 67

these mechanisms prevent reproduction before the zygote is formed.

Question 68

Types of Pre-Zygotic -

Answer 68

Temporal (Time) Isolation Breeding cycles or time of fertility differs from one population of species to the next. Ecological Isolation Ecological, or habitat, isolation occurs when two species that could interbreed do not because the species live in different areas. Behavioural Isolation This occurs in populations with highly specific calls or rituals that are directed and responded to only by other members of a particular population. Mechanical (Morphological) Isolation This is related to compatible sexual organs. Gamete Isolation Incompatibility of sperm and eggs from populations of different species.

Question 69

Post-zygotic Reproductive Isolation

Answer 69

prevent a zygote from developing into a viable, fertile adult hybrid

Question 70

Post-zygotic Reproductive Isolation Factors - Hybrid inviability

Answer 70

When hybrid zygotes are formed and begin to develop, there are many instances where these individuals are weak and compete poorly for resources. unlikely to reach reproductive age and contribute to the gene pool.

Question 71

Post-zygotic Reproductive Isolation Factors - Hybrid sterility

Answer 71

hybrid formed is sterile. female horse mates with a male donkey, producing a mule. Horses have a diploid number of 64 and donkeys 62. The mule then has 63 chromosomes in each of its cells and it can’t undergo meiosis to form gametes.

Question 72

Bottleneck Affect

Answer 72

is an extreme example of genetic drift that happens when the size of a population is severely reduced. Events like natural disasters can decimate a population, killing most individuals and leaving behind a small, random assortment of survivors.