Evolution

Question 1

Define biological evolution

Answer 1

A change in the allele frequency of a population’s gene pool over successive generations

Question 2

How do fossils provide evidence for evolution?

Answer 2

The fossil record provides evidence by revealing the features of an ancestor for comparison against living descendants

Question 3

What is the fossil record and what does it show?

Answer 3

The totality of fossils, both discovered and undiscovered, is referred to as the fossil record

The fossil record shows that over time changes have occurred in the features of living organisms (evolution)

Question 4

What are fossils and what two categories can they be divided into? What different types of evidence may they provide?

Answer 4

A fossil is the preserved remains or traces of any organism from the remote past

Preserved remains (body fossils) provide direct evidence of ancestral forms and include bones, teeth, shells, leaves, etc.

Traces provide indirect evidence of ancestral forms and include footprints, tooth marks, burrows and faeces (coprolite)

Question 5

Explain the law of fossil succession

Answer 5

his chronological sequence of complexity by which characteristics appear to develop is known as the law of fossil succession

This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species

Question 6

Explain how strata form and how this provides information on the sequence of development

Answer 6

Fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found

Sedimentary rock layers develop in a chronological order, such that lower layers are older and newer strata form on top
Each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)

Question 7

Define transitional fossils, explain the. significance and provide an example

Answer 7

Transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken by a single genus

They establish the links between species by exhibiting traits common to both an ancestor and its predicted descendents
An example of a transitional fossil is archaeopteryx, which links the evolution of dinosaurs (jaws, claws) to birds (feathers)

Question 8

What may be a limitation to the use of fossils to evaluate evolutionary links?

Answer 8

Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered

With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms

Question 8

What may be a limitation to the use of fossils to evaluate evolutionary links?

Answer 8

Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered

With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms

Question 9

Define selective breeding and explain how it provides evidence for evolution

Answer 9

Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring

By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period

Question 10

Provide an example of selective breedng in the plant kingdom

Answer 10

Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection
This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves)

Question 11

Provide two examples of selective breeding in the animal kingdom

Answer 11

Example 1: Horse Breeding

Horses have been selectively bred across many generations to produce variation according to a targeted function

Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
Draft horses have been bred for power and endurance and hence are sturdier and stockier

Example 2: Cow Breeding

Cows have been selectively bred across many generations to produce offspring with improved milk production

Farmers have also targeted the breeding a cows with a mutation resulting in increased muscle mass

The resulting stock of cattle (termed Belgian Blue) have excessive bulk and produce more edible lean meat

Example 3: Dog Breeding

Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man

Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast
Toy dogs (e.g. chihuahuas) were selectively bred for their dimunitive size

Question 12

How may comparing anatomy allow for ancestry to be established?

Answer 12

Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry.

The more similar the homologous structures between two species are, the more closely related they are likely to be as the species would have had less time to evolve

Question 13

What are homologous structures and how why does this occur?

Answer 13

Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures

This occurs when species rapidly diversify from their common ancestor by adapting their function to a unique niche. This is known as adaptive radiation.

Question 14

Discuss homologous structures with reference to an example

Answer 14

A classical example of homologous structures is the pentadactyl limb in a variety of different animals

Mammals, birds, amphibians and reptiles all share a similar arrangement of bones in their appendages based on a five-digit limb

Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:

-Human hands are adapted for tool manipulation (power vs precision grip)
-Bird and bat wings are adapted for flying
-Horse hooves are adapted for galloping
-Whale and dolphin fins are adapted for swimming

Question 15

Discuss divergence in species [ 4 marks ]

Answer 15

Within a population of any given species there will be genetic variation (i.e. variation which is inheritable) Typically this variation will be continuous and follow a normal distribution curve as the rate of change is gradual and cumulative

If two populations of a species become geographically separated then they will likely experience different ecological conditions Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another

The degree of divergence will depend on the extent of geographical separation and the amount of time since separation occurred

Populations located in close proximity that separated recently will show less variation (less divergence) Distant populations that separated a longer period of time ago will show more variation (more divergence)

Question 16

How does speciation occur once species are geographically seperated ?

Answer 16

The degree of divergence between geographically separated populations will gradually increase the longer they are separated

As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases
Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment

When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species

Question 17

Define speciation

Answer 17

The evolutionary process by which two related populations diverge into separate species is called speciation

Question 18

Discuss evolution in connection to peppered moths

Answer 18

Peppered moths (Biston betularia) exist in two distinct polymorphic forms – a light colouration and a darker melanic variant

In an unpolluted environment, the trees are covered by a pale-coloured lichen, which provides camouflage for the lighter moth
In a polluted environment, sulphur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth

The frequency of the two different forms of peppered moth is dependent on the environment and evolves as conditions change

Before the industrial revolution, the environment was largely unpolluted and the lighter moth had a survival advantage
Following the industrial revolution, the environment became heavily polluted, conferring a survival advantage to the darker moth

Those possessing the advantage are more likely to survive and reproduce passing on the advantageous gene

Question 19

What are the key component of natural selcetion?

Answer 19

I - Inherited variation exists within the population
C - Competition results from an overproduction of offspring
E - Environmental pressures lead to differential reproduction
A - Adaptations which benefit survival are selected for
G - Genotype frequency changes across generations
E - Evolution occurs within the population

ICE AGE

Question 20

What two types of variation exist?

Answer 20

This variation can manifest as either discontinuous (distinct classes) or continuous (range across a characteristic spectrum)

Question 21

What are the main mechanisms by which genetic variation between individuals in a species may occur:

Answer 21

Mutations – Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring
Meiosis – Via either crossing over (prophase I) or independent assortment (metaphase I)
Sexual reproduction – The combination of genetic material from two distinct sources creates new gene combinations in offspring

Question 22

Define gene mutation

Answer 22

A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait

Question 23

How does meiosis cause genetic variation?

Answer 23

1. Crossing Over

Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase I

The exchange of genetic material occurs between non-sister chromatids at points called chiasmata

As a consequence of this recombination, all four chromatids that comprise the bivalent will be genetically different

Chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent

2. Independent Assortment

When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles is random

The orientation of each bivalent occurs independently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I

The total number of combinations that can occur in gametes is 2n – where n = haploid number of chromosomes
Humans have 46 chromosomes (n = 23) and thus can produce 8,388,608 different gametes (223) by random orientation
If crossing over also occurs, the number of different gamete combinations becomes immeasurable

Question 24

How does sexual reproduction lead to variation?

Answer 24

The fusion of two haploid gametes results in the formation of a diploid zygote This zygote can then divide by mitosis and differentiate to form a developing embryo As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes This means that individual offspring will typically show variation despite shared parentage

Question 25

How does competition form between species

Answer 25

If left to follow course, a stable population will inevitably outgrow its resource base, leading to competition for survival When there is an abundance of resources, a population will grow according to its biotic potential (exponential curve) With more offspring, there are less resources available to other members of the population (environmental resistance) This will lead to a struggle for survival and an increase in the mortality rate (causing population growth to slow and plateau)

Question 26

What are adaptations and how may they be classified?

Answer 26

Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment These adaptations may be classified in a number of different ways: -Structural: Physical differences in biological structure (e.g. neck length of a giraffe) -Behavioural: Differences in patterns of activity (e.g. opossums feigning death when threatened) -Physiological: Variations in detection and response by vital organs (e.g. homeothermy, colour perception) -Biochemical: Differences in molecular composition of cells and enzyme functions (e.g. blood groups, lactose tolerance) -Developmental: Variable changes that occur across the life span of an organism (e.g. patterns of ageing / senescence)

Question 27

Define and explain adaptive radiation with reference to one example

Answer 27

Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions Consequently, members evolve different morphological features (adaptations) in response to the different selection pressures An example of adaptive radiation can be seen in the variety of beak types seen in the finches of the Galapagos Islands These finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)

Question 27

Define and explain adaptive radiation with reference to one example

Answer 27

Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions Consequently, members evolve different morphological features (adaptations) in response to the different selection pressures An example of adaptive radiation can be seen in the variety of beak types seen in the finches of the Galapagos Islands These finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)

Question 28

Discuss antibiotic resistance in connection to evolution [ 5 marks ]

Answer 28

Antibiotics are chemicals produced by microbes that either kill (bactericidal) or inhibit the growth (bacteriostatic) of bacteria which are prescribed to humans fighting bacterial infections In a bacterial colony, over many generations, a small proportion of bacteria may develop antibiotic resistance via gene mutation When treated with antibiotics, the resistant bacteria will survive and reproduce by binary fission (asexual reproduction) Antibiotic resistant bacteria may also confer resistance to susceptible strains by transferring plasmids via bacterial conjugation The introduction of antibiotic (selection pressure) has caused the antibiotic resistance gene to become more frequent (evolution)

Question 29

What is the binomial system of nomenclature and what is its value? [ 5 marks ]

Answer 29

The binomial system of nomenclature is the formal system by which all living species are classified (taxonomy) -It allows for the identification and comparison of organisms based on recognised characteristics -It allows all organisms to be named according to a globally recognised scheme -It can show how closely related organisms are, allowing for the prediction of evolutionary links -It makes it easier to collect, sort and group information about organisms

Question 30

How do we name organisms?

Answer 30

Genus with a capital letter first, then species from lower case Homo sapiens

Question 31

State and define the three domains of life

Answer 31

Eukarya – eukaryotic organisms that contain a membrane-bound nucleus (includes protist, plants, fungi and animals) Archaea – prokaryotic cells lacking a nucleus and consist of the extremophiles (e.g. methanogens, thermophiles, etc.) Eubacteria – prokaryotic cells lacking a nucleus and consist of the common pathogenic forms (e.g. E. coli, S. aureus, etc.)

Question 32

List the taxa in order

Answer 32

Kingdom Phylum Class Order Family Genus Species [K]aty [P]erry [C]omes [O]ver [F]or [G]reat [S]ex

Question 33

Discuss different forms of classification [ 6 marks ]

Answer 33

Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly The advantage of artificial classification is that such schemes are easy to develop and relatively stable (unlikely to change) The disadvantage is that they do not generally show evolutionary relationships and for this reason are not commonly used For example, if organisms were classified according to the presence of fins then whales would be grouped with fish If organisms were classified based on the presence of shells then snails would be grouped with turtles and not with squid Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics According to a natural classification system, all members of a particular group would have shared a common ancestor This means that natural classification schemes can be used to predict characteristics shared by species within a group A disadvantage of such schemes is that they are highly mutable and tend to change as new information is discovered A third type of classification – phylogenetic classification – is now being used to differentiate organisms based on genetics Organisms who share a greater level of homology in their DNA or amino acid sequences are expected to be more closely related

Question 34

Why may organisms be re-classified? [ 3 marks ]

Answer 34

Taxonomists will reclassify groups of species when new evidence arises to compromise the traditional classification scheme Groups of species may be separated into different genera if new evidence suggests they evolved from different ancestral species Species originally classified as figworts have been reclassified into different genera based on DNA sequence comparisons Alternatively, different species may be grouped into a shared taxon if new evidence suggests more recent common ancestry The Homininae sub-family was created to include gorillas and chimpanzees when it was deduced that they share more common ancestry with humans than with other great apes (e.g. orang-utan)

Question 35

State the characteristic features of Bryophyta

Answer 35

Bryophyta Has no vascularisation (i.e. lacks xylem and phloem) Has no ‘true’ leaves, roots or stems (are anchored by a root-like structure called a rhizoid) Reproduce by releasing spores from sporangia (reproductive stalks) Examples include mosses and liverworts

Question 36

State the characteristic features of Filicinophyta

Answer 36

Filicinophyta Has vascularisation (i.e xylem and phloem) Have leaves, roots and stems (leaves are pinnate – consisting of large fronds divided into leaflets) Reproduce by releasing spores from clusters called sori on the underside of the leaves Examples include ferns

Question 37

State the characteristic features of Coniferophyta

Answer 37

Coniferophyta Has vascularisation Have leaves, roots and stems (stems are woody and leaves are waxy and needle-like) Reproduce by non-motile gametes (seeds) which are found in cones Examples include pine trees and conifers

Question 38

State the characteristic features of Angiospermophyta

Answer 38

Angiospermophyta Has vascularisation Have leaves, roots and stems (individual species may be highly variable in structure) Reproduce by seeds produced in ovules within flowers (seeds may develop in fruits) Examples include all flowering plants and grasses

Question 39

State the characteristic features of Porifera

Answer 39

Porifera No body symmetry (asymmetrical) No mouth or anus (have pores to facilitate the circulation of material) May have silica or calcium carbonate based spicules for structural support Examples include sea sponges

Question 40

State the characteristic features of Cnidaria

Answer 40

Cnidaria Have radial symmetry Have a mouth but no anus (single entrance body cavity) May have tentacles with stinging cells for capturing and disabling prey Examples include jellyfish, sea anemones and coral

Question 41

State the characteristic features of Platyhelmintha

Answer 41

Platyhelmintha Have bilateral symmetry Have a mouth but no anus (single entrance body cavity) Have a flattened body shape to increase SA:Vol ratio and may be parasitic Examples include tapeworms and planaria

Question 42

State the characteristic features of Annelida

Answer 42

Annelida Have bilateral symmetry Have a separate mouth and anus Body composed of ringed segments with specialisation of segments Examples include earthworms and leeches

Question 43

State the characteristic features of Mollusca

Answer 43

Mollusca Have bilaterial symmetry Have a separate mouth and anus Body composed of a visceral mass, a muscular foot and a mantle (may produce shell) Examples include snails, slugs, octopi, squid and bivalves (e.g. clams)

Question 44

State the characteristic features of Arthropoda

Answer 44

Arthropoda Have bilateral symmetry Have a separate mouth and anus Have jointed body sections / appendages and have a hard exoskeleton (chitin) Examples include insects, crustaceans, spiders, scorpions and centipedes

Question 45

State the characteristic features of Chordata

Answer 45

Chordata Have bilateral symmetry Have a separate mouth and anus Have a notochord and a hollow, dorsal nerve tube for at least some period of their life cycle Examples include mammals, birds, reptiles, amphibians and fish (also invertebrate sea squirts)

Question 46

State the characteristic features of Fish

Answer 46

Fish Covered in scales made out of bony plates in the skin Reproduce via external fertilisation (egg and sperm released into the environment) Breathe through gills that are covered with an operculum Does not maintain a constant internal body temperature (ectothermic)

Question 47

State the characteristic features of Amohibian

Answer 47

Amphibian Moist skin, permeable to gases and water Reproduce via external fertilisation (usually spend larval state in water, adult state on land) Can breathe through skin but also possess simple lungs Do not maintain a constant internal body temperature (ectothermic)

Question 48

State the characteristic features of Reptiles

Answer 48

Reptiles Covered in scales made out of keratin Reproduce via internal fertilisation and females lay eggs with soft shells Breathe through lungs that have extensive folding (increases SA:Vol ratio) Do not maintain a constant internal body temperature (ectothermic)

Question 49

State the characteristic features of Birds

Answer 49

Covered in feathers (made out of keratin) Reproduce via internal fertilisation and females lay eggs with hard shells Breathe through lungs with parabronchial tubes Maintain a constant internal body temperature (endothermic)

Question 50

State the characteristic features of Mammals

Answer 50

Mammals Skin has follicles which produce hair made out of keratin Reproduce via internal fertilisation and females feed young with milk from mammary glands Breathe through lungs with alveoli Maintain a constant internal body temperature (endothermic)

Question 51

What is a dichotomous key and how does it work?

Answer 51

A dichotomous key is a method of identification whereby groups of organisms are divided into two categories repeatedly With each sequential division, more information is revealed about the specific features of a particular organism When the organism no longer shares its totality of selected characteristics with any organism, it has been identified

Question 52

Define clade

Answer 52

A clade is a group of organisms that have evolved from a common ancestor

Question 53

What is a cladogram? and what can be read from it?

Answer 53

Cladograms are tree diagrams that show the most probable sequence of divergence in clades. Cladograms are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor Each branch point (node) represents a speciation event by which distinct species are formed via divergent evolution Cladograms show the probable sequence of divergence and hence demonstrate the likely evolutionary history (phylogeny) of a clade The fewer the number of nodes between two groups the more closely related they are expected to be

Question 54

List and explain the key features of a cladogram?

Answer 54

Constructed cladograms all typically share certain key features: Root – The initial ancestor common to all organisms within the cladogram (incoming line shows it originates from a larger clade) Nodes – Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa Outgroup – The most distantly related species in the cladogram which functions as a point of comparison and reference group Clades – A common ancestor and all of its descendants (i.e. a node and all of its connected branches)

Question 55

Why may base pairs be used to analyse wether two organisms are related? [ 4 marks ]

Answer 55

All organisms use DNA and RNA as genetic material and the genetic code by which proteins are synthesised is (almost) universal This shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels of relatedness Over the course of millions of years, mutations will accumulate within any given segment of DNA The number of differences between comparable base sequences demonstrates the degree of evolutionary divergence A greater number of differences between comparable base sequences suggests more time has past since two species diverged Hence, the more similar the base sequences of two species are, the more closely related the two species are expected to be

Question 56

In practice how is the analysis of base pairs between organisms done?

Answer 56

When comparing molecular sequences, scientists may use non-coding DNA, gene sequences or amino acid sequences Non-coding DNA provides the best means of comparison as mutations will occur more readily in these sequences Gene sequences mutate at a slower rate, as changes to base sequence may potentially affect protein structure and function Amino acid sequences may also be used for comparison, but will have the slowest rate of change due to codon degeneracy Amino acid sequences are typically used to compare distantly related species (i.e. different taxa), while DNA or RNA base sequences are often used to compare closely related organisms (e.g. different haplogroups – such as various human ethnic groups)

Question 57

Discuss the use of base sequences to compare species [ 4 marks ]

Answer 57

Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. However, Different genes or proteins may change at different rates (e.g. haemoglobin mutates more rapidly than cytochrome c) The rate of change for a particular gene may differ between different groups of organisms Over long periods, earlier changes may be reversed by later changes, potentially confounding the accuracy of predictions

Question 58

Define and explain convergent evolution

Answer 58

Convergent evolution is the independent evolution of similar features in species with distinct lineages It may occur when different species occupy the same habitat and are thus subjected to the same selection pressures The shared conditions cause common adaptations to be selected in different species, resulting in structural similarity An example of convergent evolution is the development of wings in birds, bats and insects

Question 59

Define homologous and analogous structures

Answer 59

Traits that are similar because they are derived from common ancestry are termed homologous structures Traits that are superficially similar but were derived through separate evolutionary pathways are termed analogous structures

Question 60

State and explain the limitation of using morphological features for classification [ 2 marks ]

Answer 60

Closely related organisms can exhibit very different structural features due to adaptive radiation (e.g. pentadactyl limb) Distantly related organisms can display very similar structural features due to convergent evolution

Question 61

Discuss reclassification in reference to the figworts family

Answer 61

Until recently, figworts were the 8th largest family of flowering plants (angiosperms), containing 275 different genera This was problematic as many of the figwort plants were too dissimilar in structure to function as a meaningful grouping Taxonomists examined the chloroplast gene in figworts and decided to split the figwort species into five different clades Now less than half of the species remain in the figwort family – which is now the 36th largest among angiosperms

Question 62

What are the main mechanisms for change which will reduce biodiversity within a population?

Answer 62

Genetic drift: The change in the composition of a gene pool as a result of a random or chance event Natural selection: The change in the composition of a gene pool as a result of differentially selective environmental pressures

Question 63

What causes variation within a gene pool tobe reduced

Answer 63

Variation within a gene pool can be reduced if conditions promote the survival of certain traits and the removal of others

Question 64

Describe the process of fossilisation

Answer 64

1. Death and decay – Soft body parts are decomposed or scavenged, leaving only the hard body remains 2. Deposition – The hard remains are rapidly covered with silt and sand, and over time more layers continue to build 3. Permineralisation – Pressure from the covering layers of dirt/rock cause the hard organic material to be replaced by minerals 4. Erosion / exposure – Movement of earth plates may displace the fossil and return it to the surface for discovery

Question 65

Domain to species for humans

Answer 65

Domain: Eukarya Kingdom: Animalia Phylum: Chordata Class: Mammal Order: Primate Family: Hominid Genus: Homo Species: Sapiens

Question 66

Domain to species for Ruccola

Answer 66

Domain: Eukarya Kingdom: Plantea Phylum: Tracheophyta Class: Spermatophytes Order: Brassicales Family: Brassicaceae Genus: Eruca Species: Vesicaria