Classification Processes

Question 1

Recognise that biological classification can be hierarchical and based on different levels of similarity of physical features, methods of reproduction and molecular sequences

Answer 1

Biological classification can be hierarchical and based on different levels of similarity of physical features, methods of reproduction and molecular sequences

Question 2

Describe the classification systems for similarity of physical features

Answer 2

Uses similarity in physical form. The Linnean classification system of animal groups was based on physical features (eg. vertebrate classes and body coverings - birds (feathers), mammals (hair), reptiles (scaley skin). (Organisms with more physical similarities will share more levels in the classification hierarchy)

Question 3

Describe the classification systems for methods of reproduction

Answer 3

Members of the plant kingdom were classified into phyla according to their reproductive features / dispersal units (eg. conifers, angiosperms) while mammals were classified into subgroups based on methods of reproduction / early development (eg. egg laying monotremes, pouched marsupials and placentals)

In addition, organisms can be described as r strategists or K strategists

Question 4

Describe the classification systems for molecular sequences

Answer 4

Analysis involving DNA hybridisation, DNA profiling /sequencing, mitochondrial DNA or amino acid composition of proteins. (Organisms with more molecular similarities will share more levels in the classification hierarchy).

Question 5

Describe the classification systems for methods of species interactions

Answer 5

Organisms interact in many ways, for example predation or competition for resources.

Organisms can be described by symbiotic interactions ( eg. mutualism, commensalism, parasitism) or disease (eg infectious pathogens or parasites).

Question 6

Define the term clade

Answer 6

A group of organisms that consists of a common ancestor and all its lineal descendants

Question 7

Recall common assumptions of cladistics

Answer 7

A common ancestry - related species share a common ancestor
Bifurcation - common ancestral species evolve over time and can branch into two (bifurcate) groups, giving rise to new species. (Note: this assumption is contentious as some argue that populations can also divide into more than 2 branches simultaneously)
Physical change - populations that have diverged from a common ancestral group have undergone physical change due to genetic changes caused by mutations in DNA.

Question 8

Interpret cladograms to infer the evolutionary relatedness between groups of organisms

Answer 8

Organisms that share a more recent common ancestor are more closely related

Question 9

Analyse data from molecular sequences to infer species evolutionary relatedness

Answer 9

Fewer differences in amino acid sequences, more related

Question 10

Recognise the need for multiple definitions of species

Answer 10

There are problems with the biological species definition - because:

it requires organisms to be alive to determine reproductive capability (so not good for identification of extinct / fossil species).

many organisms don’t reproduce sexually (clonal organisms) eg. apomixis / asexual reproduction in bacteria or Paramecium (so ‘fertile offspring’ is not applicable & two different organisms are not required to breed).

-some embryos develop without an egg being fertilised eg. parthenogenesis in animals aphids & rotifers (so two different organisms are not required to breed).

Question 11

Identify one example of an interspecific hybrid that does not produce fertile offspring

Answer 11

Mule (Equus mulus)

Question 12

The Binomial naming system

Answer 12

Assigns a two part name to each individual. The first name is the genus name (begins with a capital) and the second a species name (beginning with lower case).eg. Homo sapiens.

Scientific names are written in italics.

Question 13

Taxonomy

Answer 13

Classification of organisms based on similarities of physical features, molecular sequences, species interaction and methods of reproduction.

Question 14

R-strategists

Answer 14

Are short lived, quick to mature, fast to reproduce(exponential growth), large numbers of offspring and little parental care of / involvement with offspring. eg. Bacteria, rodents, insects.

• common early in successions (are pioneer organisms)

Question 15

K-strategists

Answer 15

Are long lived, slow to mature, slow to reproduce, fewer numbers of offspring and high parental care of / involvement with offspring eg. elephants, humans, turtles (often relatively large in size).

• common in later stages of successions

Question 16

Biological species concept

Answer 16

A species is a group of organisms that can potentially interbreed in nature to produce viable, fertile offspring and are reproductively isolated from other groups. …Ernst Mayr in 1942

(ie. organisms belong to the same species if they can breed under natural conditions and produce fertile offspring)

Question 17

Morphological species concept

Answer 17

Organisms of the same species have more structural features (eg body plan, colour) in common than organisms of different species. (Useful when looking at fossil remains when reproduction not possible and sometimes organisms that can interbreed to produce fertile offspring have large morphological differences eg. dog breeds)
There are problems with this biological species definition - because:

• some organisms physically mimic (have evolved physical similarities) other organisms that they are not closely related to
• difficult to apply as there is a degree of physical variation in all populations

Question 18

Phylogenetic species concept

Answer 18

Organisms of the same species are the smallest group of organisms that share a common ancestor and can be distinguished from others (smallest possible clade) eg. domestic dogs of species Canis familiaris all share a common ancestor that existed around 15,000 years ago and all Homo sapiens share a common ancestor that existed around 200,000 years ago.

(To determine whether organisms belong to the same species using this definition requires analysis of fossil morphology, DNA sequence and geographic location evidence)

While this definition can be used with asexually reproducing organisms, there are problems with the phylogenetic species definition - because:

• many organisms have not had their evolutionary history determined

Question 19

Hybrid organisms

Answer 19

Produced by crossing (breeding) two different sub-species (breeds, varieties, races, strains), species or genera via sexual reproduction.
Crossing two different species produces interspecific hybrids which are sterile (not fertile).

Male Horse (Equus ferus) and Female donkey (Equus asinus) produce a hinny which are generally sterile.

Female horse (Equus ferus; 2n = 64) and male donkey (Equus asinus; 2n = 62) produce a mule which are generally sterile.

Question 20

Dichotomous Keys

Answer 20

Can be used to identify organisms that have already been classified (eg. during field work).

A dichotomous (2 options) key provides users with two pathways or options to follow. There are two main types: Branching dichotomous keys and Written / Numbered dichotomous keys

Question 21

Phylogenetic Trees

Answer 21

Show evolutionary relationships. Can be represented in different ways (horizontally or vertically) and branches may be diagonal or square.

The major components of a phylogenetic tree (see diagram to the right) include:

branches- hypothesised evolutionary pathways.

a root- hypothesised ancestral lineage. (The initial ancestor).

leaves- at the end of each branch is an organisms name.

nodes- points where two branches diverge (represents an inferred last common ancestor that diverging branches share).

outgroups- diverged in distant past and are the least closely related to other groups in the tree. Used as a reference group.

sister taxa- are groups of taxa that are closely related (diverged recently).

Question 22

The major levels in the classification hierarchy

Answer 22

Domain, kingdom, phylum, class, order, family, genus, species
NOTE: if organisms belong to the same class they must also belong to the same taxa above that level in the hierarchy (eg. phylum, kingdom, and domain) but not necessarily the same taxa below that level (eg. order, family or genus).

Question 23

Cladogram

Answer 23

Cladograms are unscaled taxonomic diagrams depicting inferred relationships within a clade. Each branch point (node) represents divergence / a speciation event by which distinct species are formed via divergent evolution.

Constructed cladograms all typically share certain key features: a root, nodes, outgroups and clades. (see ‘phylogenetic trees’ above for explanations for these terms)

Question 24

Constructing Cladograms

Answer 24

Identify the organisms to be put in a cladogram.

List these organisms in a table and on the other axis all features / characteristics to be used. (A cladogram data table)… see the table to the right

Decide which characteristic is the most primitive / ancestral (probably one shared by all of the organisms ie. the shared ancestral characteristic) and which are the most derived (fewer organisms possessing these characteristics ie. shared derived characteristics). An organism that only possesses the ancestral characteristic will branch off first and is referred to as an outgroup.

Question 25

Classifying Ecosystems

Answer 25

In your response 4 points are needed. Please outline that:

classification / research enables decision making

classification / research allows stake holders to appreciate ecosystem significance and make decisions that serve a range of values.

classification / research allows for effective management strategies.

classification / research allows for better understanding of possible human impacts and longer term survival / resilience of the ecosystem.