Biodiversity and Classification Notes

Organisms can be classified based on similarities and differences.
Taxonomy is the science of naming and classifying organisms.
A taxon is a group of organisms in a classification system.
Carolus Linnaeus developed the scientific naming system still used today.
Binomial nomenclature is a 2-part scientific naming system.
- Uses genus and species names.
- Scientific name is always written in italics.
- Two parts are the genus and species names.
- Ex: Human = Homo sapiens
A genus includes one or more similar species.
- Species in the same genus are thought to be closely related.
- Genus name is always capitalized.
A species name is the second part of a scientific name.
- Always lowercase.
- Always follows genus name; never written alone.
Scientific names help scientists to communicate.
- Example: Scientific name: Canis familiaris, Common name: Dog
Linnaeus’ classification system has seven levels.
- Each level is included in the level above.
- Levels get increasingly specific from kingdom to species.

The classification levels from broadest to most specific are:
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
Mnemonic device to remember the order: King Phillip Came Over For Good Spaghetti (or Sushi).

A dichotomous key is a series of paired statements that describe alternative characteristics of different organisms.
Each pair divides the objects to be classified into two categories based on specific characteristics.
Organisms must fit into one category or the other.

Linnaean system based only on physical similarities and differences, which are not always the result of close relationships.
Classification changes as new discoveries are made.
Modern classification systems apply Darwin’s ideas about evolution.

The most recent classification system divides life into three domains, which include six kingdoms.
Three Domains:
- Bacteria
- Archaea
- Eukarya
Six Kingdoms:
- Archaea
- Bacteria
- Protista
- Fungi
- Plantae
- Animalia

Modern classification is based on evolutionary relationships.
Phylogeny is the evolutionary history for a group of species.
Evolutionary classification groups species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences.
Phylogenetic relationships can be shown in a branching tree diagram called a cladogram.

Cladistics is classification based on common ancestry.
A cladogram is an evolutionary tree made using cladistics.
Species are placed in order that they descended from a common ancestor.
The more categories organisms share, the more recently they shared a common ancestor (they will have more characteristics in common).
If two species share many of the same taxonomic categories, this indicates they have a recent common ancestor.
A clade is a group of species that shares a common ancestor.
Each species in a clade shares some traits with the ancestor.
Each species in a clade has traits that have evolved.
Nodes represent the most recent common ancestor of a clade.
Derived characters are traits shared in different degrees by clade members.
They form the basis of arranging species in a cladogram.
More closely related species share more derived characters.
Derived characters are represented on a cladogram as branches.

A true clade must contain an ancestor and all of its descendants.
Many traditional taxonomic groups do form clades (ex: Class Mammalia = clade Mammalia).
Some traditional groups do not form valid clades (ex: Class Reptilia – not a clade because it excludes birds).

A wide range of organisms share a number of genes.
All genes mutate over time.
Shared genes that contain differences can be treated as derived characters.
The mutated gene may be passed on to each generation thereafter.
DNA analysis can be used to determine which species are more closely related by comparing the different forms of genes present in each species.

This tree of life shows evolutionary relationships among the taxa within the three domains of life.
All of the organisms in each domain share a common ancestor.

Domain Bacteria
- Includes Eubacteria and related organisms.
- Thick cell wall containing peptidoglycan.
- Corresponds to kingdom Eubacteria.
Domain Archaea
- Includes Archaebacteria and related organisms.
- Cell wall does not contain peptidoglycan.
- Live in extreme environments (ex: volcanic hot springs).
- Corresponds to kingdom Archaebacteria.
Domain Eukarya
- All eukaryotes.
- Made up of kingdom Protista, Fungi, Plantae, and Animalia.