Topic 5 - Evolution and Biodiversity

Question 1

Evolution

Answer 1

The change in the heritable characteristics of biological populations over successive generations. Through evolution, new species may arise from pre-existing species

Question 2

Species

Answer 2

A group of individuals that actually (or potentially) interbreed to produce viable, fertile offspring

Question 3

Heritable Traits

Answer 3

Traits that are entirely based in genetics

Question 4

Fossil Record

Answer 4

A group of fossils which has been analysed and arranged in chronological and/or taxonomic order

Question 5

Strata

Answer 5

Fossils are often contained in rocks that build up in layers called strata. The strata provide relative timeline, with layers near the top being newer and layers near the bottom being older.

Question 6

Outline how fossils provide that evolution has occurred

Answer 6

Fossils provide evidence for the existence of now-extinct past species. Fossils can help scientists reconstruct the evolutionary histories of present-day species by providing evidence of the species changing over time

Question 7

Explain the process of artificial selection using selective breeding.

Answer 7

Selective breeding, also known as artificial selection, is a process used by humans to modify populations of organisms so they have desirable characteristics. Breeders choose which animal or plant males and females will sexually reproduce and have offspring together, yielding offspring with the desired traits and/or elimination of undesirable varieties. Selective breeding can lead to significant and rapid change over time from the original phenotype.

Question 8

Outline how artificial selection can serve as evidence for evolution

Answer 8

Changes in genotype and phenotype that are due to selective breeding show that rapid change is possible when there is differential survival and/or reproduction in a population

Question 9

Use an example to explain how selective breeding has lead to evolution in an animal species

Answer 9

Farmers breed animals in order to improve productivity (and thus profits). For example, dairy farmers will look for the cows that can produce the most milk and only breed those cows. These cows then pass their genes that contribute to higher milk production onto their offspring, increasing milk productivity each generation

Question 10

Use an example to explain how selective breeding has lead to evolution in a plant species

Answer 10

B. oleracea is a wild mustard plant that grows in the Mediterranean region. To maximize the amount of food they got, farmers preferentially planted seeds from plants that grew more leaves. After many generations, the artificial selection produced a leafy version -kale.

Later, farmers selected for variants of the plant that produced enlarged leaf buds. After many generations, this led to plants with huge heads of tightly rolled leaves — cabbage.

Other farmers selected for enlarged flowering structures (creating broccoli and cauliflower), enlarged stems (kohlrabi), many small heads (brussels sprouts).

Question 11

Homologous Structure

Answer 11

A biological structure (molecular or anatomical) that appears in different species of organisms. The commonality is evidence of descent from a common ancestor that also had the structure

Question 12

Contrast analogous structures and homologous structures

Answer 12

Homologous structures are structures that are similar in organisms because they were inherited from a common ancestor.

Analogous structures are structures that are similar but were not inherited from a common ancestor, the organisms independently evolved the characteristic (via convergent evolution).

Question 13

Adaptive Radiation

Answer 13

The process by which organisms evolve from an ancestral species into a multitude of new forms. Adaptive radiation often occurs when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches.

Question 14

Convergent Evolution

Answer 14

When different species independently evolve structures to serve a common function. The similarities are not due to inheritance from a shared common ancestor, but rather because of similar selective pressures in the environment.

Question 15

State an example of an analogous structure

Answer 15

The wings of birds, bats and butterflies are analogous. They serve a common function (flight) but are not due to inheritance of flight from a shared common ancestor.

Question 16

State an example of a homologous structure

Answer 16

The wings of bats and the arms of primates are homologous. Although these two structures do not look similar or have the same function, they are due to inheritance of a limb structure found in their last shared ancestor.

Question 17

State an example of a vestigial structure

Answer 17

Examples of vestigial structures include the pelvic bone of a whale, rudimentary leg spurs on some snakes and the wings of flightless birds

Question 18

Vestigial Structure

Answer 18

Structures that have no apparent function and appear to be residual structures inherited from a past ancestor are called vestigial structures

Question 19

Population

Answer 19

A population is organisms of the same species that live in a particular geographic area at the same time

Question 20

Speciation

Answer 20

Speciation is the process by which populations evolve to become distinct species that are reproductively isolated (no longer capable of interbreeding with each other to produce fertile offspring)

Question 21

Describe the process of gradual speciation

Answer 21

In gradual speciation, populations diverge slowly over time, accumulating changes in small steps. Eventually there is so much accumulated change that the populations are no longer capable of interbreeding with each other to produce fertile offspring. The original populations have become separate species

Question 22

Continuous Variation

Answer 22

Continuous variation within a population is when a characteristic changes gradually over a range of phenotypes

Question 23

Cline

Answer 23

A cline is a the continuous variation of a single biological trait of a species across its geographical range

Question 24

Explain how continuous variation across geographical ranges is evidence of evolutionary change

Answer 24

Natural selection causes adaptation to the local environment, resulting in different genotypes or phenotypes being favoured in different environments.

Through natural selection acting on populations in localized regions, genetic differences between populations may accumulate. The populations will gradually diverge. If the differences between populations become great enough, it may lead to speciation.

Question 25

Ring Species

Answer 25

Ring species are a distinct type of cline where the geographical distribution of a population is circular in shape, so that the two ends of the cline overlap with one another. The adjacent populations and the ends of the ring rarely interbreed due to the cumulative effect of the many changes in phenotype along the cline.

Question 26

State an example of recognizably different populations of the same species across a geographical range

Answer 26

The ponderosa pine (Pinus ponderosa) occupies a broad geographic range in western North America. Needles of ponderosa pines in the Rocky Mountains are bundled into groups of two or three, and cones of these trees are more than 9 cm long.

In contrast, needle of ponderosa pines in southern Arizona and northern Mexico are bundled in groups of five, and their cones are less than 9 cm long.

Despite the geographic variation, the two groups belong to the same species because they could produce fertile offspring if their geographic separation were overcome. They are different populations of the same species which are gradually diverging from each other.

Question 27

Pentadactyl Limb

Answer 27

Many vertebrates have a very similar bone structure despite their limbs looking very different on the outside. This structure is known as the pentadactyl limb. This suggests that many vertebrates descended from the same common ancestor.

Question 28

List the bone structures present in the pentadactyl limb

Answer 28

The pentadactyl limb has a single proximal bone (humerus), two distal bones (radius and ulna), a series of carpals (wrist bones), followed by a series of metacarpals (palm bones) and phalanges (digits)

Question 29

Identify pentadactyl limb structures in diagrams of amphibians, reptiles, birds and mammals

Answer 29

Use different images to identify the structures

Question 30

Relate differences in pentadactyl limb structures to differences in limb function

Answer 30

The number of bones and the size of the bones in a pentadactyl limb can vary but each pentadactyl limb has the same general components no matter what the function of the limb is. This homologous structure is evidence that the organisms have a common ancestor. Each pentadactyl limb is adapted differently to help each species survive in their habitats.

Human arms are adapted for tool manipulation and grasping

Bird and bat wings are adapted for flying

Horse hooves are adapted for galloping

Whale and dolphin fins are adapted for swimming

Question 31

Industrial Melanism

Answer 31

Industrial melanism is defined as the proportional increase of dark-colored varieties of animals (especially moths) in industrial areas (with soot pollution) where they are better camouflaged against predators than paler forms.

In a population with a variety of coloration phenotypes, there will be selection for the color varieties that are best able to survive and reproduce. In a soot-polluted environment, moths with darker color variations are more likely to avoid predation by birds. Over generations, the proportion of the dark variety will increase in the population.

Question 32

Propose a mechanism that explains the pattern found in vertebrate limb structure yet allows for the specialization of different limb functions

Answer 32

The common bone structure of vertebrate limbs is due to evolution from a common vertebrate ancestor. The limbs are homologous. Natural selection has lead to the same bones and joints being adapted for different uses in different environmental conditions (such as walking, running, flying, jumping, digging, swimming and grasping).

Question 33

Variation

Answer 33

Biological variation is the genetic differences among individuals. The genetic difference can produce differences in observable phenotypes and be inherited between generations.

Question 34

Natural Selection

Answer 34

Natural selection is a process of evolution in which organisms better adapted to their environment tend to survive and produce more offspring.

Question 35

Outline the process of evolution through natural selection

Answer 35

1. populations produce more offspring than can survive;
2. individuals show variation in heritable traits;
3. there is a struggle for survival, often due to competition for resources;
4. some individuals are better suited to the environment and survive;
5. the most fit individuals survive to reproduce;
6. the advantageous variation is passed on to the next generation;
7. over time, the advantageous variation increases in frequency in the population;

Question 36

Species

Answer 36

The biological species concept defines a species as organisms that can (actually or potentially) interbreed with each other to produce fertile offspring and cannot breed with others. In other words, the organisms of the species are reproductively isolated

Question 37

Explain why natural selection can only function if there is variation in a species

Answer 37

Natural selection acts on the genetic variation between individuals in a population. Some individuals will have advantageous variations that are better adapted to the environmental conditions. Individuals with the beneficial variation will have a greater chance of survival and reproduction than others. The favorable genetic variation will be inherited by offspring in the next generation

Question 38

List sources of genetic variation

Answer 38

Genetic variation is a result of random mutation and sexual reproduction (meiosis and random fertilization).

Question 39

Outline how mutation leads to genetic variation

Answer 39

A mutation is a random change in DNA. A change in DNA may cause phenotypic variation. Mutations can occur when the DNA is replicated or as the result of environmental factors (such as UV light and cigarette smoke).

Only mutations in the DNA of germ cells or gametes effect evolution. Mutations in somatic cell DNA cannot be passed on to offspring and therefore do not matter for evolution.

Question 40

Outline how meiosis leads to genetic variation

Answer 40

Meiosis creates variation in the gametes, the sperms and eggs. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA.

Question 41

Describe how recombination during meiosis leads to genetic variation

Answer 41

Recombination (crossing over) occurs during prophase I of meiosis. Homologous chromosomes pair along their lengths, gene by gene. Breaks occur along the chromosomes, and they rejoin, trading some of their alleles. This produces a unique combination of alleles on the chromosome.

Question 42

Describe how independent assortment during meiosis leads to genetic variation.

Answer 42

Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis. Independent assortment means that each gamete will have one of many different possible combinations of chromosomes.

Question 43

Outline how sexual reproduction leads to genetic variation.

Answer 43

Sexual reproduction involves the combination of genetic material from two parents, resulting in new combinations of paternal and maternal chromosomes present in the zygote formed at fertilization. New combinations of genetic material is a source of genetic variation within the population.

Question 44

Adaptation

Answer 44

Adaptation is the result of natural selection. An adaptation is a physical structure or behavior of an organism that is common in a population because it provides some improved survival or reproduction in the habitat.

Animal camouflage is adaptation to avoid detection by both predator and prey species.

Many plants found in arid environments have spines rather than leaves. The spines minimise the surface area of the cactus reducing water loss.

Question 45

Explain the consequences of populations producing more offspring than the environment can support.

Answer 45

Overproduction of offspring can lead to competition (between offspring) for limited resources (such as water, space or food) in the habitat. Competition for resources can be a selective pressure. Some individuals will have a variation that is more suited for the environmental conditions and will be more likely to survive and reproduce. With overproduction, the population is more likely to produce a variant that can survive the environmental conditions.

Question 46

Outline an animal example to illustrate the potential for overproduction of offspring in a population.​

Answer 46

All species overproduce, since they have more offspring than can realistically reach reproductive age, based on the resources available. For example, many species of fish lay millions of eggs at one time, though only a fraction of those survive. Sea turtles can lay anywhere from 70 to 190 eggs at a time, though only about one out of 100 typically survive. Oysters can also lay 60 to 80 million eggs at a time, but again, only a few survive to reproduce themselves.

Question 47

Outline a plant example to illustrate the potential for overproduction of offspring in a population.​

Answer 47

All species overproduce, since they have more offspring than can realistically reach reproductive age, based on the resources available. For example, cottonwood trees release millions of seeds all at once, though only a fraction will germinate. Oak trees release thousands of acorn seeds each year but very few will grow to become full-sized trees.

Question 48

Selective Pressure

Answer 48

A selective pressure is any phenomena that impacts the survival and/or reproduction of organisms living within a given environment. Selective pressures can be divided into two types of pressure: biotic or abiotic.

Biotic selective pressures that affect an organism are other organisms within the same ecosystem that interact with the affected organism in a way that influences its survival or reproduction. The interaction can be between members of the same species (for example intraspecies competition for food) or between different species (for example predator and prey).

Abiotic selective pressure are non-living factors within the organism’s environment (such as light, wind, temperature and pollutants) that influence the survival and reproduction of the affected organism.

Question 49

Outline the role of competition as a selective pressure.

Answer 49

Because populations produce more offspring than the environment can support., individuals often must compete for resources required for survival and reproduction. Habitats usually have a limited supply of at least one resource (such as food, water, territory, or mates) which can lead to competition for the resource.

Question 50

Outline how a selective pressure acts on the variation in a population.

Answer 50

There is genetic variation of the traits within a population. A selective pressure causes a struggle for survival and/or reproduction. Organisms with the variation that best adapt them to survive given the selective pressure in the environment will be able to survive and reproduce, passing on the trait to the subsequent generation.

Question 51

Explain the effect of the selective pressure on the more and less adapted individuals in a population.

Answer 51

Individuals more adapted to the selective pressure will will be able to survive and reproduce, passing on the trait to the subsequent generation. The frequency of the more adapted trait will increase in the population.

Individuals less adapted to the selective pressure will not survive and/or reproduce. The frequency of the less adapted trait will decrease in the population.

Question 52

Describe an example of evolution through natural selection.

Answer 52

1. A named example of a species; //Anole lizards.//
2. An outline of the different variations of a relevant trait; //Variation in the limb length and toepad surface area which affects clinging ability.//
3. A statement that the variation is genetically inherited. //Limb length and toepad surface area are genetically controlled traits.//
4. A statement of the selective pressure; //Hurricanes in the habitat.//
5. Consequence of the selective pressure; //Lizards that can better cling onto branches are more likely to survive hurricanes.//
6. More reproduction by better adapted individuals; //Surviving lizards are able to reproduce after the hurricane.//
7. The change in the population that results. //The surviving lizard populations have larger toe pads, longer forelimbs and shorter hind limbs on average than before the storms.//

Question 53

Heritable Traits

Answer 53

Heritable traits are those that are entirely based in genetics.

Question 54

Contrast acquired characteristics with inheritable characteristics.

Answer 54

Inherited characteristics are those that are genetically passed down from parents to their offspring.

Acquired characteristic are those gained by an organism after birth due to environmental influence.

Question 55

Outline why only inherited characteristics can be acted upon by natural selection.

Answer 55

Acquired traits are not within the genetic material of an individual and therefore they cannot be passed down to offspring during reproduction. In order to be acted upon natural selection, the trait must be able to be inherited by the subsequent generation.

Question 56

Compare the reproductive success of better and less well adapted individuals in a population.

Answer 56

Individuals more adapted to the selective pressure will will be able to survive and reproduce, passing on the trait to the subsequent generation. The frequency of the more adapted trait will increase in the population.

Individuals less adapted to the selective pressure will not survive and/or reproduce. The frequency of the less adapted trait will decrease in the population.

Question 57

Evolution

Answer 57

Evolution is the change in the heritable characteristics of a population over time. Natural selection is one mechanism of evolution. Though evolution, new species can arise from pre-existing species.

Question 58

Explain the cause of the change in frequency of traits in a population through natural selection.​

Answer 58

Individuals that are better adapted for a selective pressure will be able to survive and reproduce, passing on the beneficial variation to the next generation. The frequency of the best fit variation will increase in the population and the frequency of the least fit variation will decrease in the population.

Question 59

Outline the role of natural selection in formation of new species.

Answer 59

For a variety of reasons (temporal/behavioural/geographic isolation), members of the same species will be split into separate populations resulting in a lack of interbreeding between the populations (reproductive isolation). Each population may be exposed to different selective pressures, so natural selection will act differently on the two populations, selecting for different variations in each population. Over generations, the original populations will have diverged to the point of not being able to create viable, fertile offspring if a mating was attempted. New species will have been formed.

Question 60

Use an example to outline the role of natural selection in the formation of new species.

Answer 60

Different species of Galápagos finches live on different islands in the Galápagos islands, located in the Pacific Ocean off South America. The finches are geographically isolated from one another by the ocean. Each island has unique habitat and food resources. Over millions of years, each species of finch developed a unique beak that is especially adapted to the kinds of food found on the island it inhabits. Some finches have large, blunt beaks that can crack the hard shells of nuts and seeds. Other finches have long, thin beaks that can probe into cactus flowers. Still other finches have medium-size beaks that can catch and grasp insects. Natural selection increased the frequency of traits in each finch populations that best enabled the bird to survive and reproduce given the selective pressure of food availability. Because they are isolated, the birds don’t breed with one another and have developed into unique species with unique characteristics.

Question 61

Outline the characteristics of Daphne Major.

Answer 61

Daphne Major is a small island in the Galapagos archipelago. An intensive study of ground finches was conducted here by biologists Peter and Rosemary Grant over a period of 25+ years. Daphne Major serves as an ideal site for research because the finches have few predators or competitors. The major factor selective pressure influencing survival of the finch is the weather, and thus the availability of food.

Question 62

Outline the role of Charles Darwin in the study of Galapagos finches.

Answer 62

On his visit to the Galapagos Islands (1835), Charles Darwin discovered several species of finches that varied from island to island. His observations of the variation in forms and habitats in which the birds were found helped him to develop his theory of evolution by natural selection. He theorized that the 13 distinct species were all descendants of a common ancestor which had adapted over time to each islands unique habitats and resources.

Question 63

Outline the role of Peter and Rosemary Grant in the study of Galapagos finches.

Answer 63

Peter and Rosemary Grant study the evolution of the medium ground finch on the small island of Daphne Major. The Grants have been collecting data on the birds for 25+ years and have witnessed natural selection in action.

Question 64

Explain how natural selection leads to changes in the beaks of Galapagos finches with changes in weather conditions.

Answer 64

1. A named example of a species; //Medium ground finches//
2. An outline of the different variations of a relevant trait; //Variation in beak size and shape//
3. A statement that the variation is genetically inherited. //Beak size and shape are genetically controlled traits.//
4. A statement of the selective pressure; //A drought occurred in 1977. For 551 days the island received no rain. Plants withered and the tiny seeds the medium ground finches were accustomed to eating grew scarce. //
5. Consequence of the selective pressure; //Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn’t do this, so they died of starvation.//
6. More reproduction by better adapted individuals; //Surviving birds are able to reproduce.//
7. The change in the population that results. //The Grant’s measured the offspring and compared their beak size to that of the pre-drought generations. They found the offsprings’ beaks to be 3 to 4% larger than their grandparents’.//

Question 65

Explain how natural selection leads to changes in antibiotic resistance.

Answer 65

1. A named example of a species; //Bacteria, such as Staphylococcus aureus.//
2. An outline of the different variations of a relevant trait; //Within populations, bacteria vary in their resistance to antibiotics. Some varieties are more resistant to antibiotics than others;//
3. A statement that the variation is genetically inherited. //Antibiotic resistance arises by random DNA gene mutation. Resistance is passed through binary fission to subsequent generations or transferred to other bacteria by plasmids.//
4. A statement of the selective pressure; //Antibiotics, which are chemicals used to treat bacterial diseases. //
5. Consequence of the selective pressure; //Antibiotic-sensitive bacteria are killed. Antibiotic resistant bacteria survive.//
6. More reproduction by better adapted individuals; //Antibiotic resistant bacteria reproduce and pass on resistance gene(s) to the next generation.//
7. The change in the population that results. //A larger proportion of the bacteria population is antibiotic-resistant. It becomes difficult to treat some infections.//

Question 66

List reasons why evolution of antibiotic resistance has been rapid.

Answer 66

The rapid emergence of bacterial strains resistant to multiple antibiotics is posing a growing public health risk. Evolution of antibiotic resistance has been rapid because bacteria reproduce very rapidly and have high mutation rate. Additionally, there has been extensive use of antibiotics since they were first discovered (for example, in hospitals, animal feed, inappropriate prescriptions and not finishing prescriptions).

Question 67

Compare the use of the word theory in daily language and scientific language.

Answer 67

In daily use: a theory is a guess, there is doubt.

In scientific use: a theory has been shown to be true through repeated observations and experiments. There is no current doubt*. As of yet, no evidence has been collected that does not support the idea.

Question 68

Outline the role of botanical and zoological congresses in the naming of plants and animals.

Answer 68

A “congress” is a regularly occurring meeting of taxonomists attended by delegates from all over the world. At these meeting, the biologist modify the rules for naming and classifying species and approve the names of any new species that have been discovered.

Question 69

Binomial Nomenclature

Answer 69

Species are named with two name (binomial). The first name is for the genus and the second name is for the species. Together the two names make a unique combination that designate a species.

Question 70

Outline the benefits of using a system of binomial nomenclature.

Answer 70

The binomial system has been a successful system because it is functional, has been the only system that is recognized worldwide, and has been used over the last 250+ years of naming species. Having an internationally recognized system of naming species facilitates communication between people with a different language.

Scientific names are Latin or latinized names that are standardized by a series of rules that are applicable worldwide.

1. The Genus name is capitalized.
2. The species names is lower case.
3. The binomial is shown underlined if printed or italicized if typed.

Question 71

Taxa and Taxonimist

Answer 71

Taxon, plural taxa, is a grouping unit used in biological classification. There are multiple common grouping units of taxa. For example, a “species” is a taxon (group) of all the organisms that can (actually or potentially) interbreed with each other to produce fertile offspring and cannot breed with others.

A taxonomist is a biologist that groups organisms into categories.

Question 72

List the hierarchy of biological taxa, from largest to smallest.

Answer 72

The hierarchy of taxa from largest to smallest is:
1. Domain
2. Kingdom
3. Phylum
4. Class
5. Order
6. Family
7. Genus
8. Species

Question 73

List the three domains of life.

Answer 73

A domain is the broadest taxonomic grouping of organisms. The three-domain system was proposed by Carl Woese et al. in 1990. It divides cellular life forms into three domains, the archaea, eubacteria, and eukaryota.

Question 74

State the two prokaryotic domains.

Answer 74

Two domains consist of prokaryotic organisms, single-celled microorganisms whose cells have no nucleus or internal membrane bound compartments.

1. Archaea
2. Eubacteria

Archaea
DNA with histone proteins.
Usually have intron DNA sequences.
Cell walls not made of peptidoglycan.
Membrane phospholipids can be branched.
Different ribosomes than eubacteria.
Not sensitive to antibiotics that affect eubacteria.
Can live in extreme environments (hot springs, salt lakes, marshlands, oceans, gut of ruminants and humans).

Eubacteria
DNA without histone proteins.
Usually do no have intron DNA sequences.
Cell walls made of peptidoglycan.
Membrane phospholipids not branched.
Different ribosomes than archaea.
Sensitive to antibiotics that do not affect archaea.
Most do not live in extreme environments.

Question 75

Summarize the evidence that supports a three domain classification of life.

Answer 75

Genetic sequencing provided researchers a new way of analyzing relationships between organisms. The three domain system groups organisms primarily based on differences in ribosomal RNA (rRNA) structure. Ribosomal RNA is a molecular building block for ribosomes. Each of these three domains contains unique rRNA.

Question 76

Draw a tree diagram to illustrate the evolutionary relationship between the three domains.

Answer 76

There is ongoing debate about the early evolution of life on Earth and the placement of the three domains on a tree diagram. The current consensus places the last universal common ancestor (LUCA) at the root of the tree with two branches, one leading to the eubacteria (B) and the other two the archaea (A) and eukaryota (E).

Question 77

List the four kingdoms of eukaryotes.

Answer 77

The four eukaryotic kingdoms are animalia, plantae, fungi, and protista.

Question 78

Natural Classification

Answer 78

Natural classification is the grouping of organisms into taxa on the basis of their evolutionary relationships.

Question 79

Compare artificial and natural classification systems of taxonomy.”

Answer 79

Artificial classification is the grouping of organisms into groups on the basis of observable structural features (e.g. the grouping together of plants according to the number and situation of their stamens, styles, and stigmas rather than their evolutionary relationships). As knowledge of homologous structures, genetics and evolutionary relationships has grown, artificial systems have been superseded by systems of natural classification, which considers evolutionary relationships for groupings.

Question 80

List difficulties in determining the natural classification of species.

Answer 80

1. Species and their distinctive attributes are not fixed and eternal, rather species are continually changing. As a consequence, any current classification is essentially a somewhat arbitrarily defined point along an evolutionary line.
2. Species are physically and genetically diverse. What may appear to be very different are actually variations within the same species (for example, spotted and black jaguars).
3. There is debate among researchers over defining new species because it is not obvious what the most important traits are for determining classification.
4. Due to convergent evolution, distantly related organisms appear superficially similar. Likewise, adaptive radiation may make make closely related organisms appear different.

Question 81

List two situations in which the reclassification of a species may be necessary.

Answer 81

Changes to classification occurs as new discoveries are made and better methods of classification are found.

1. Sometimes new evidence indicates that members of a taxa do not share a common ancestor and therefore should not be grouped together in a natural classification scheme.
2. Sometimes new evidence indicates that species that were not thought to be related actually do share a common ancestor and therefore should grouped together in a natural classification scheme.

Question 82

Outline an example of a species (or group of species) which were reclassified when new evidence was discovered.

Answer 82

Birds were categorized in the biological class Aves in Linnaean taxonomic hierarchy, and both snakes and crocodiles were part of class Reptilia. Under this scheme, snakes and crocodiles are more similar to each other than either is to birds.

However we now understand that the bird lineage shares a more recent ancestor with some modern reptiles (crocodiles) than with others (snakes). Natural classification places birds in the same taxa as crocodiles (theropoda).

Question 83

Explain an advantage of natural classification.

Answer 83

Natural classification allows for the prediction of homologous characteristics shared by species within a group since all members of a taxa in a natural classification will have evolved from a common ancestral species.

Question 84

State the classification of a plant, from domain to species.

Answer 84

Domain: Eukaryota (all eukaryotic celled organisms)
Kingdom: Plantae (all plants)
Phylum: Angiospermatophyta (all flowering plants)
Class: Dicotyledonae (plants two to seed cotyledons)
Order: Rosales (all roses and rose like plants)
Family: Rosaceae (all roses)
Genus: Rosa
Species: gallica

Question 85

State the classification of an animal, from domain to species.

Answer 85

Domain: Eukaryota (all eukaryotic celled organisms)
Kingdom: Animalia (all animals)
Phylum: Chordata (all animals with a hollow nerve cord)
Class: Mammalia (all animals the nurse their young)
Order: Carnivora (animals with teeth for tearing meat)
Family: Felidae (cats with retractable claws)
Genus: Felis (non-roaring cats)
Species: domesticus (domesticated pet cats)

Question 86

State the four major plant phyla.

Answer 86

The major phyla (divisions) of the plant kingdom are:

Bryophyta (mosses)
Filicinophyta (ferns)
Coniferophyta (conifers)
Angiospermatophyta (flowering plants)

Question 87

Outline the characteristics of the bryophyta.

Answer 87

Bryophyta are the liverworts, hornworts and mosses.

No roots, only simple, hair-like projections called rhizoids that grow directly out of the photosynthetic tissue.

Simple leaves (or flattened leaf like structures called a thallus). Leaves do not have a cuticle layer.

Reproduce via spores. Spores are single-cells that can develop into a new organism using mitotic division.

No vascular tissue (no xylem or phloem), so have no way to transport water and nutrients.

Very short plants, since the only way to move substances through the plant body is by osmosis and diffusion from surface moisture.

Must live in moist habitats.

Question 88

Outline the characteristics of the filicinophyta.

Answer 88

Filicinophyta are the ferns and horsetails.

Have roots, stem and leaves. The leaves are often pinnate (fronds with leaflets on each side of a common axis).

Have vascular tissue that conduct water and nutrients (xylem and phloem).

Produce spores which may be visible in clusters called sori on the underside of the leaves.

Do not have flowers, fruits or seeds.

Question 89

Outline the characteristics of the coniferophyta.

Answer 89

Coniferophyta are the conifers, such as cedars, firs, cypresses, junipers, pines, hemlocks, and redwoods.

Have roots, stem and leaves. The leaves are usually evergreen (do not seasonally drop) Leaves are often needle shaped and have a waxy cuticle to limit water evaporation.

Have vascular tissue that conduct water and nutrients (xylem and phloem).

Can grow tall.

Have woody stems.

Produce seeds in cones.

Question 90

Outline the characteristics of the angiospermatophyta.

Answer 90

Angiospermatophyta are the flowering plants, such as grasses, daisies, lilies, roses, tulips.

Have roots, stem and leaves.

Have vascular tissue that conduct water and nutrients (xylem and phloem). Can grow tall.

Reproduce by seeds produced in ovules within flowers.

Produce seeds in fruits.

Question 91

State seven major animal phyla.

Answer 91

Some of the major phyla of the animal kingdom are:

Porifera
Cnidarian
Platyhelminthes
Annelida
Mollusca
Arthropoda
Chordata

Question 92

Outline the characteristics of the phylum porifera.

Answer 92

Porifera are the sponges.

Are multicellular organisms which are sessile (fixed in one place).

Predominantly marine.

Body is cylindrical and usually asymmetrical.

Feed on small organisms and organic particles which enter the body through water current.

Gas exchange takes place by diffusion of oxygen from water the flowing into the body.

Excretion of nitrogenous waste (mainly ammonia) directly from the body with outgoing water current.

Reproduction may be asexual (budding) or sexual (involves internal fertilization).

Question 93

Outline the characteristics of the phylum cnidarian.

Answer 93

Cnidaria are the anemones, jellyfish, and corals.

Two distinct morphological body plans: polyp, which are sessile as adults, and medusa, which are mobile. Some species exhibit both body plans in their lifecycle.

Predominantly marine.

Body is radially symmetrical.

Have an incomplete digestive system with only one opening; the gastrovascular cavity serves as both a mouth and an anus.

Have tentacles with stinging cells called nematocysts that they use to capture food.

Gas exchange takes place by diffusion of oxygen from water the flowing into the body.

Excretion of nitrogenous waste (mainly ammonia) directly from the body with outgoing water current.

Most polyps reproduce asexually (budding). Medusa usually reproduce sexually using eggs and sperm. Depending on the species, fertilization is either internal or external.

Question 94

Outline the characteristics of the phylum platyhelminthes.

Answer 94

Platyhelminthes are the flatworms.

May be marine, terrestrial or parasitic.

Body is bilaterally symmetrical.

Have an incomplete digestive system with only one opening serving as both a mouth and an anus.

Body is flat and not segmented.

Gas exchange takes place by diffusion of oxygen from the environment directly into the body; no cell can be too far from the outside, making a flattened shape advantageous.

Excretion of nitrogenous waste (mainly ammonia) directly from the body.

Most flatworms are hermaphrodites, having both male and female sex organs. As a result, platyhelminthes can reproduce sexually on its own or through cross fertilization with another individual (with internal fertilization). Asexual reproduction occurs through fission and regeneration (a single organism splits up into smaller fragments which each regenerates).

Question 95

Outline the characteristics of the phylum annelida.

Answer 95

Annelida are the segmented worms, like earthworms and leeches.

May be aquatic or terrestrial.

Body is bilaterally symmetrical.

May have chaetae, bristles projecting from the skin which function in locomotion.

Have a complete digestive system with seperate in and out openings.

Gas exchange takes place by diffusion of oxygen from the environment directly into the body; no cell can be too far from the outside.

Excretion of nitrogenous waste (ammonia and urea), takes place through nephridia
(a tube that opens to the exterior).

Have a closed circulatory system, blood is always contained within blood vessels.

Asexual reproduction occurs through budding or fission and regeneration (a single organism splits up into smaller fragments which each regenerates).

Sexual reproduction occurs through cross fertilization with another individual (internal or external fertilization depending on the species). Some hermaphroditic reproduction occurs.

Question 96

Outline the characteristics of the phylum mollusca.

Answer 96

Mollusca are the slugs, squid, snails, octopus and clams.

Have soft, unsegmented bodies with a head, a muscular foot and a visceral mass. This is all covered with a mantle that typically secretes a hard shell.

Occur in almost every habitat found on Earth.

Body is bilaterally symmetrical.

Have a complete digestive system with seperate in and out openings.

Circulatory system is open (do not have blood vessels and enters directly into the body chambers).

Gas exchange via gills.

Excretion of nitrogenous waste (ammonia and urea), takes place through nephridia
organized as kidneys, that collect liquid wastes from the coelom and dump them in the mantle cavity.

Primarily sexual reproduction with external fertilization. Some use internal fertilization and/or are hermaphrodites.

Question 97

Outline the characteristics of the phylum arthropoda.

Answer 97

Arthropods have jointed appendages/legs.

Body is bilaterally symmetrical.

Body is divisible into head, thorax and abdomen. Head bears a pair of compound eyes and antenna.

Body is covered with chitinous exoskeleton.

Occur in almost every habitat found on Earth.

Digestive system is complete and well developed.

Gas exchange takes place by general body surface or gills (in crustaceans) or trachea (in insects) or book-lungs (in arachnids).

Circulatory system is open (do not have blood vessels and enters directly into the body chambers).

Excretion of nitrogenous waste (uric acid) takes place through Malpighian tubules.

Sexual reproduction (fertilization is internal or external).

Question 98

Outline the characteristics of the phylum chordata.

Answer 98

Body is bilaterally symmetrical.

At some point in their life, all chordates have a notochord, a flexible rod made out of a material similar to cartilage providing skeletal support through the length of the body.

Have a dorsal hollow nerve cord, which in most chordates develops into the brain and spinal cord.

Have pharyngeal slits, openings in the pharynx that extend to the outside environment. May be present only during embryonic development.

Have a post-anal tail, an elongation of the body, extending beyond the anus. In humans, the tail is present during embryonic development and is vestigial as an adult.

Digestive system is complete and well developed.

Gas exchange takes place through skin, in gills or in lungs.

Have a closed circulatory system, blood is always contained within blood vessels.

Excretion of nitrogenous waste (ammonia, urea or uric acid) takes place through a kidney.

Primarily sexual reproduction (internal or external fertilization).

Question 99

Vertebrate

Answer 99

The vertebrate animals are all the members of the phylum chordata that possess a backbone that runs from head to tail and surrounds and protects the main nerve cord. In vertebrates the notochord becomes part of the back bone during embryonic development.

Question 100

State the major classes of chordata.

Answer 100

Class Agnatha (jawless fishes)
Class Chondrichthyes (cartilaginous fishes)
Class Osteichthyes (bony fishes)
Class Amphibia (amphibians)
Class Reptilia (reptiles)
Class Aves (birds)
Class Mammalia (mammals)

Question 101

Outline the characteristics of birds.

Answer 101

The class Aves includes all the birds. They produce an amniote egg which usually has a hard shell that protects the embryo from drying out. After internal fertilization the the amniote egg can be laid on land. Birds are descendents of theropod dinosaurs (two-legged mostly carnivorous dinosaurs).

Question 102

Outline the characteristics of mammals.

Answer 102

Dogs, whales, sloths and humans are members of the class Mammalia. All mammals have internal fertilization and after birth feed the babies milk produced by the mammary glands. Mammals are heterodonts (they have a variety of specialized teeth) which allows them to chew their food into small pieces before swallowing it. Subsequently, they can eat any size plant or animal.

Question 103

Outline the characteristics of amphibians.

Answer 103

Frogs, toads, and salamanders are amphibians. Amphibia spend part of their lives under water and part on land. Many of these species must keep their skin moist by periodically returning to wet areas. All of them must return to water in order to reproduce because their eggs would dry out otherwise. They start life with gills, like fish, and later develop lungs to breathe air.

Question 104

Outline the characteristics of reptiles.

Answer 104

Reptilia includes turtles, snakes, lizards, and alligators. All of them have lungs to breathe on land and skin that does not need to be kept wet. They produce an amniote egg which usually has a leathery shell that protects the embryo from drying out. After internal fertilization the the amniote egg can be laid on land.

Question 105

Outline the characteristics of fish.

Answer 105

Three of the vertebrate classes are fish. The most primitive of these is Agnatha, jawless fish that do not have scales (lampreys and hagfish). Fish that have skeletons consisting of cartilage rather than bone are members of the class Chondrichthyes (sharks and rays). All of the bony fish are members of the class Osteichthyes (tuna, bass, salmon, and trout).

Question 106

Dichotomous Key

Answer 106

A dichotomous key is a tool for identification of unknown organisms. Sets of statements act as clues leading to the identification of an organism or group.

1. Observing the specimen you want to identify.
2. Look for distinguishing features.
3. Follow the pairs of “either-or” choices to the next pair of choices to the point of identification.

Question 107

Outline why the binomial naming system is used in science rather than local or common names.

Answer 107

1. Binomial names are standardized, allowing people throughout the world to communicate unambiguously about species even when they speak different primary languages.
2. Each binomial name refers to only one species. The same species can have many different local names.
3. Binomial names provide clues to the evolutionary relationships between species. Members of the same genus are more related to each other than to members of a different genus. Local names do not give clues to relationships between species.

Question 108

State the role of Carl Linnaeus in naming species.

Answer 108

Binomial nomenclature that was originally codified in the writing of Linnaeus (Systema Naturae, 1758).

In addition to a consistent binomial system of naming, Linnaeus also developed a system of organizing the diversity of life in a hierarchical classification.

Question 109

Clade and Cladistics

Answer 109

A clade is all of the organisms hypothesized to have evolved from a common ancestor. A “branch” on the tree of life.

In the example, crocodiles and birds are a in the same clade. Snakes and crocodiles are not in the same clade unless you also include birds, lizards and tuatara.

Cladistics is a way of classifying organisms into groups based on shared characteristics and common ancestry. Species in the same group (clade) are more closely related (share a more recent common ancestor) to members of the same group than to other organisms.

Question 110

Outline the relationship between time, evolutionary relationships and biological sequences.

Answer 110

Mutations in the nucleotide base sequences of DNA, and therefore differences in the amino acid sequence of proteins, accumulate gradually over time.

Therefore, the more differences there are in biological sequences, the more time has passed for the differences to accumulate. The more time that has passed since organisms have shared a common ancestor, the less evolutionarily related the organism are to each other.

Visa versa: the less differences there are in biological sequences, the less time has passed for the differences to accumulate. The less time that has passed since organisms have shared a common ancestor, the more evolutionarily related the organism are to each other.

Question 111

Summarize the use of DNA sequences as evidence for evolutionary relatedness between species.

Answer 111

The DNA base sequences of the same gene in different species is compared. Because mutations (differences) in the DNA sequence will accumulate over time, the species with more similarities in the base sequence are likely more closely related (meaning they have a more recent common ancestor; have diverged from their common ancestor more recently) than species with more differences in the base sequence. The percent similarity between species can be used as the basis for creating a cladogram of hypothesized evolutionary relationships.

Question 112

Summarize the use of amino acid sequences as evidence for evolutionary relatedness between species.

Answer 112

The amino acid sequences of the same protein in different species is compared. Differences in the amino acid sequences are due to mutations of the DNA. Because DNA mutations (and in turn amino acid sequences) will accumulate over time, the species with more similarities in the amino acid sequence are likely more closely related (meaning they have a more recent common ancestor; have diverged from their common ancestor more recently) than species with more differences in the amino acid sequence. The percent similarity between species can be used as the basis for creating a cladogram of hypothesized evolutionary relationships.

Question 113

Outline the use of a “molecular clock” to determine time since divergence between two species.

Answer 113

The “molecular clock” is a technique that uses the rate of mutation of DNA sequences (or amino acid sequences of proteins) to estimate the time when two species diverged from a common ancestor. The molecular clock hypothesis states that DNA and protein sequences change at a rate that is relatively constant over time and among different organisms. A consequence of this constancy is that the genetic difference between any two species is proportional to the time since these species last shared a common ancestor.

Question 114

State the source of differences between biological sequences (nitrogenous base or amino acid).

Answer 114

Differences in DNA (and the resulting amino acid) sequences are due to mutation. A mutation is a change that occurs either due to mistakes when the DNA is replicated or as the result of environmental factors such as UV light and cigarette smoke.

Question 115

Homologous Structure

Answer 115

A homologous structure is a biological structure (molecular or anatomical) that appears in different species of organisms. The commonality is evidence of descent from a common ancestor that also had the structure. DNA and protein sequences can be homologous.

The wings of bats and the arms of primates are homologous. Although these two structures do not look similar or have the same function, they are due to inheritance of a limb structure found in their last shared ancestor.

Question 116

State an example of a molecular homology.

Answer 116

Different species share molecular homologies as well as anatomical ones. Roundworms, for example, share 25% of their genes with humans. These genes are slightly different in each species, but their similarities are evidence of common ancestry.

The universal genetic code is a homology that links all life on Earth to a common ancestor. DNA and RNA possess a simple four-base code that provides the information for making proteins in all living things.

Question 117

Cladogram

Answer 117

Cladograms are branching diagrams where each branch represents an evolutionary lineage (a clade). Cladograms are used to show the hypothesized sequence of divergence between organisms and common ancestor(s). The names of specific taxa are put at the end of each branch and the names of the clade to which those taxa belong is often placed at the intersection of branches (nodes).

A cladogram does not really have axes, but implied in one direction (x axis in this example) is some sort of evolutionary distance from each other and implied in the other direction (y axis in this example) is relative time (the first branch at the bottom happened long ago the latter branches higher up happened more recently).

Question 118

Node

Answer 118

An internal node (branching point) is the hypothesized last common ancestor that speciated (split) to give rise to two or more daughter taxa.

Each internal node is also at the base of a clade, which includes the common ancestor (node) plus all its descendents.

Question 119

Describe how knowledge of homologous traits are used in the formation of a cladogram.

Answer 119

To build a cladogram, heritable traits are compared across organisms, such as physical characteristics (morphology), genetic sequences, and behavioral traits.

Homologous traits can be used to group organisms into clades. Traits shared among the species or groups in a dataset tend to form nested patterns that provide information about when branching events occurred in the lineage.

For example, amphibians, turtles, lizards, snakes, crocodiles, birds and mammals all have (or had) four limbs. Four limbs is a homologous trait inherited from a common ancestor that helps set apart this particular clade from other vertebrates.

Question 120

Outline how computer programs analyze biological sequence data to create cladograms.

Answer 120

With sequencing technology we can compare the sequences evolutionarily related genes or proteins. Each nucleotide of a gene or amino acid of a protein can be viewed as a separate characteristic. The amount of data available from sequence comparisons is much higher than when using physical traits. To analyze sequence data and identify the most probable cladogram, biologists typically use computer programs and statistical algorithms that are able to rapidly and accurate compare sequences, compute differences between sequences and analyze most likely divergence patterns between sequences.

Question 121

Identify members of a clade given a cladogram.

Answer 121

This cladogram tells you that all the animals listed are in the mammalia clade. The koala and kangaroo are more closely related to one another than to anything else on the diagram. Their branches intersect each other before they intersect any other lineage. This indicates that they diverged from each other more recently than they diverged from any of the other animals on the diagram. Furthermore, they both belong to the Marsupialia clade. Similarly, the bat and the lion are more closely related to each other than they are to either of the marsupials. They are both in the placental mammals (eutherians) clade.

Question 122

Outline the role of technological advancements in the development of cladistics.

Answer 122

Until the early twentieth century, biology focused on the processes of living organisms and almost always involved observation and experiments in laboratories and in the field. Then, with advancements in sequencing and computer technology, scientists started accumulating, storing and sharing DNA and protein sequence data at an exponential rate.

Computer based sequence alignment and comparison has become an essential tool for biologists. Its speed and sensitivity allow scientists to compare nucleotide and protein sequences in large databases. Most importantly, the technology has helped make information accessible to any researcher over the Internet.

Question 123

Outline two limitations of only examining external morphology when hypothesizing evolutionary relationships.

Answer 123

Historically, classification was based primarily on external morphological (shape) characteristics. Closely related species were thought to show similar structural features. However, there are closely related organisms can exhibit very different structural features (due to divergent evolution) and distantly related organisms can display very similar structural features (due to convergent evolution).

Question 124

Outline an example of a difference in classification of a species in the traditional scheme compared to a cladistics based classification scheme.

Answer 124

Scientific understanding of relationships among organisms has changed dramatically since the time of Linnaeus and classical taxonomy. For example, we now understand that the bird lineage shares a more recent ancestor with some modern reptiles (crocodiles) than with others (lizards). Yet both snakes and crocodiles are part of the same Linnaean Class (reptilia) and birds are in a separate Class (aves). Modern classification schemes seeks to represent taxa in a system that reflects an understanding of their evolutionary relationships.

Question 125

Compare cladistics to traditional biological classification methods.

Answer 125

Cladistic classification is based on evolutionary history, with a variable number of clades depending on how much divergence there has been in an evolutionary lineage. Additionally, cladistics does not “rank” organisms into a set number of groups. Linnaean classification forces organisms to fit into into set kingdoms, phyla, orders, etc.

Question 126

Interpret a cladogram depicting primate species.

Answer 126

Humans belong to the biological group known as Primates. Besides similarities in anatomy and behavior, human relationship to other primate species is supported by DNA evidence.

Humans and chimpanzees are more closely related to one another than either is to gorillas or any other primate. The genetic difference between individual humans today is about 0.1%, on average. The same genes of the chimpanzee genome indicates a difference of about 1.2% with humans. The DNA difference between humans and gorillas is about 1.6%. Chimpanzees show this same amount of difference from gorillas. A difference of 3.1% distinguishes humans and the African apes from the Asian great ape, the orangutan. All of the great apes and humans differ from macaque and baboon monkeys by about 7% in their DNA sequences.

Question 127

Analyze a cladogram to describe the evolutionary relationship between species.

Answer 127

Butterflies and moths share a most recent common ancestor with flies.

Butterflies, moths and flies are all equally related to beetles.

Wasps are more closely related to butterflies, moths and flies than to beetles.

Ants share a more recent common ancestor with flies than they do with beetles.

Question 128

Outline the reason and evidence for the reclassification of the figwort family.

Answer 128

In traditional classification, Figworts were a family of flowering plants (angiosperms) grouped together based on morphology. However, scientists have used cladistics to reclassify the Figwort family. DNA analysis of three chloroplast genes revealed that the species in the Figwort family were not one clade but five clades that had been incorrectly grouped together into one family. Therefore, the entire figwort family was reclassified into six families, each composed of just one clade.

Question 129

Discuss the use of cladograms as hypotheses of evolutionary relationships.

Answer 129

Evolutionary trees are hypotheses that have been tested with evidence. Because they are supported by many lines of evidence, widely accepted cladograms are unlikely to have their branches rearranged (though new branches are likely to be added as species are discovered). However, a change in our understanding is always possible. If new evidence is discovered or old evidence is reinterpreted, adjustments to the evolutionary relationships depicted in a cladogram must be made in order to reflect the new information.

Question 130

Outline the reason why biological theories may change with time.

Answer 130

Biological theories change over time as technology advances and human ability to observe and measure the natural world improves.

Question 131

Summarize the changes in biological classification schemes over time.

Answer 131

Details of different classification schemes are beyond the scope of the IB biology curriculum. They are only included here to illustrate that ideas are superseded by others as knowledge improves over time.

In 1735, Linnaeus published Systema Naturae in which he proposed a system of categorizing and naming organisms using a standard format so scientists could discuss organisms using consistent terminology. Linnaeus’s tree of life contained just two main branches for all living things: the animal and plant kingdoms.

In 1866, Haeckel, proposed another kingdom, Protista, for unicellular organisms. He later proposed a fourth kingdom, Monera, for unicellular organisms whose cells lack nuclei, like bacteria.

In 1969, Whittaker proposed adding another kingdom—Fungi—in the tree of life. Whittaker’s five-kingdom tree was considered the standard for many years.

In the 1970s, Woese created a tree with three Domains above the level of Kingdom: Archaea, Bacteria, and Eukarya.

Hennig developed cladistics in 1950. After scientists began using molecular data in classification, Hennig’s cladistics approach to classification has become increasingly adopted.