Module 4 Section 3: Classification and Evolution Flashcards
What is classification
Classification is the act of arranging organisms into groups based on their similarities and differences
Why use classification
This makes it easier for scientists to identify them and to study them
What is taxonomy
Taxonomy is the study of classification
There are a few different classification systems in use, but they all involve placing organisms into groups in a taxonomic hierarchy
How to use the taxonomic hierarchy
There are eight levels of groups (called taxonomic groups) used in classification
Similar organisms are first sorted into one of the three very large groups called domains, e.g. animals, plants and fungi are in the Eukarya domain
Similar organisms are then sorted into smaller groups called kingdoms, e.g. all animals are in the animal kingdom
Similar organisms from that kingdom are then grouped into a phylum
Similar organisms from each phylum are then grouped into a class, and so on down the eight levels of the taxonomic hierarchy
What happens as you move down the taxonomic hierarchy and how does it end
As you move down the hierarchy, there are more groups at each level but fewer organism in each group
The hierarchy ends with species - the groups that contain only one type of organism
What are the levels of the taxonomic hierarchy
Kingdom
Phylum
Class
Order
Family
Genus
Species
General characteristics of prokaryotes
E.g. bacteria
Prokaryotic, unicellular (single-celled), no nucleus, less than 5 um
General characteristics of protoctista
E.g. Algae, Protozoa
Eukaryotic cells, usually live in water, single-celled or simple multicellular organisms
General characteristics of fungi
E.g. Moulds, yeast, mushrooms
Eukaryotic, chitin cell wall, saprotrophic (absorb substances from dead or decaying organisms), single-celled or multicellular organisms
General characteristics of plantae
E.g. Mosses, ferns flowering plants
Eukaryotic, multicellular, cell walls made of cellulose, can photosynthesise, contain chlorophyll, autotrophic (produce their own food)
General characteristics of animalia
E.g. Nematodes (roundworms), molluscs, insects, fish, reptiles, birds mammals
Eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals)
What is phylogeny
Phylogeny is the study of the evolutionary history of groups of organisms
Tells us what organisms are related and how closely related they are
Where have all organisms evolved from
All organisms have evolved from shared common ancestors (relatives)
What is a species
A species is the smallest group that shares a common ancestor (end of a branch on a phylogenetic tree)
Similar organisms (anatomically, physiologically) that can reproduce and have fertile offspring
What does a phylogenetic tree show
Shows the relationship between different organisms
The first branch point represents a common ancestor of all the members
The ancestor is normally extinct
Each of the following branch points represents another common ancestor from which a different group diverged
What is cladistics
Where the classification system take into account phylogeny when arranging organisms into groups
What is the nomenclature used for classification
The binomial system - all organisms are given one internationally accepted scientific name in Latin that has two parts
How to name organisms using binomial system
E.g. Homo sapiens (in italics or underlined if handwritten)
The first part of the name is the genus name and has a capital letter
The second part is the species name and begins with a lower case letter
Advantage of phylogenetic classification
Produces a continuous tree whereas classification requires discrete taxonomical groups
So scientists are not forced to put organisms into a specific group that they do not quite fit
How were species classified before
Early classification systems only used observable features to place organisms into groups
E.g. whether they lay eggs, can fly etc
Problems with classification using observable features
Scientists don’t always agree on the relative importance of different features
Groups based solely on physical features may not show how related organisms are
What are classification systems now based on
Observable features and other evidence such as:
Molecular evidence
Embryological evidence
Anatomical evidence
Behavioural evidence
What is molecular evidence
The similarities in proteins and DNA
You can compare how DNA is stored and the sequence of DNA bases
More closely related organisms will have more similar molecules
Can also compare the sequence of amino acids in proteins from different organisms
The more similar the amino acid sequence of a protein in two different species, the more closely related the species are likely to be
What is embryological evidence
The similarities in the early stages of an organism’s development
What is anatomical evidence
The similarities in structure and function of different body parts
What is behavioural evidence for evolution
The similarities in behaviour and social organisation of organisms
How can technology lead to new discoveries
Technologies such as DNA techniques, better microscopes can result in new relationships between organisms being clarified
Scientists can share new discoveries in meetings and scientific journals
How organisms are classified is continually revised to take account of any new findings that scientists discover
How does the five kingdoms differ from the three domain system
In the older system the largest groups were the five kingdoms - all organisms were placed into one of these groups
The three domain system was then proposed which has three domains (large superkingdoms that are above the kingdoms in the taxonomic hierarchy)
In this system, organisms that were in the kingdom prokaryotae (containing unicellular organisms without a nucleus) are separated into two domains - the Archaea and Bacteria
All organisms that contain a nucleus are placed in the domain Eukarya (this includes 4 of the 5 kingdoms)
Lower hierarchy stays the same (kingdom, phylum, class, order, family, genus, species)
Why was the three domain system first proposed
Mainly due to molecular evidence:
The enzyme RNA polymerase is different in Bacteria and Archaea
Archaea, but not Bacteria, have similar histones to Eukarya
Also due to cell membrane evidence:
The bonds of the lipids in the cell membranes of Bacteria and Archaea are different
The development and composition of flagellae are also different
Bacteria have a cell wall made of murein whereas archeae cell walls do not contain this
This shows that Bacteria and Archaea evolved separately and that Archaea are more closely related to Eukarya than Bacteria
Comparison between bacteria and archaea
Bacteria:
Peptidoglycan
Protein
Polysaccharides
Lipids
Archaea:
No peptidoglycan
Protein
Polysaccharides
Lipids
Darwin’s observations
Organisms produce more offspring than survive
There’s variation in the characteristics of members of the same species
Some of these characteristics can be passed on from one generation to the next
Individuals that are best adapted to their environment are more likely to survive
Darwin’s theory
Individuals within a population show variation in their phenotypes (genetic variation)
These new alleles are caused by genetic mutation
Selection pressures (environmental factors such as predation, disease and competition) create a struggle for survival
Individuals with better adaptations (characteristics that give a survival advantage, e.g. being able to run faster) are more likely to survive and reproduce successfully (survival of the fittest)
They can pass on their advantageous adaptations to their offspring
Overtime, the proportion of the population possessing the advantageous adaptations increases
Over generations this leads to evolution as the favourable adaptations become more common in the population
How did Wallace contribute to the theory of evolution
Independently came up with natural selection and wrote to Darwin about it
Wallace and Darwin published their papers on evolution together and acknowledged eachother’s work
Wallace’s observations provided lots of evidence to support the theory of evolution by natural selection
E.g. warning colours can be used by species to deter predators from eating them (e.g. butterflies) and this is an example of an advantageous adaptation that had evolved from natural selection
Why is Darwin more remembered than Wallace
Darwin is better remembered than Wallace because of the book On The Origin of Species where he mentioned the examples of species he had observed during the voyage to the Galápagos Islands
This is when scientists started to pay attention to the theory
Evidence to support evolution
Fossil record evidence
DNA evidence
Molecular evidence
