18.2. Classification Flashcards
1
Q
Why are organisms classified?
A
- With such a huge number of different kinds of organisms living on Earth, biologists have always wanted to arrange them into groups, a process called classification
- By grouping them into different categories, it is much easier to understand them and to remember their key features.
2
Q
Taxonomy
A
- the study and practice of classification, which involves placing organisms in a series of taxonomic units, or taxa (singular: taxon).
- In biological classification, these taxa form a hierarchy
3
Q
Taxonomic Hierarchy
A
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
acronym (NSFW) - dirty kinky people can often find great sex
4
Q
History on the types of Domain
A
- Biologists used to divide organisms into two large groupings based on their cell structure
- Prokaryotes and eukaryotes have significantly different cellular structures
- In the 1970s, prokaryotes were discovered living in extreme environments, such as hot springs where temperatures often exceed 100 °C - extremophiles
- These extremophiles, as they are known, were not like typical bacteria
- Studies revealed that the genes coding for the RNA that makes up their ribosomes were more like those of eukaryotes. They were found to share features with both typical bacteria and eukaryotes
- This meant that a new taxon, the domain, had to be introduced to reflect the differences between these extremophiles and typical bacteria
- The prokaryotes are divided between the domains Bacteria and Archaea and all the eukaryotes are placed into the domain Eukarya.
5
Q
Domain Types
A
1) Archaea
2) Bacteria
3) Eukarya
6
Q
Domain Bacteria
A
- prokaryotic as their cells have no nucleus
- small organisms that vary in size between that of the largest virus and the smallest single-celled eukaryote.
7
Q
Characteristic features of Domain Bacteria
A
- Cells with no nucleus
- DNA exists as a circular ‘chromosome’ and does not have histone proteins associated with it
- Smaller circular molecules of DNA called plasmids are often present
- No membrane-bound organelles (such as mitochondria, endoplasmic reticulum, Golgi body, chloroplasts) are present
- Ribosomes (70 S) are smaller than in eukaryotic cells
- Cell wall is always present and contains peptidoglycans (not cellulose)
- Cells divide by binary fission, not by mitosis
- Usually exist as single cells or small groups of cells
8
Q
Domain Archea
A
- Also prokaryotic as their cells have no nucleus
- Their range of size is similar to that of bacteria
- Many inhabit extreme environments (extremophiles)
9
Q
Characteristic features of Domain Archeans
A
- Cells with no membrane-bound organelles
- DNA exists as a circular ‘chromosome’ and does have histone proteins associated with it
- Smaller circular molecules of DNA called plasmids are often present
- Ribosomes (70 S) are smaller than in eukaryotic cells, but they have features that are similar to those in eukaryotic ribosomes, not to bacterial ribosomes
- Cell wall always present, but does not contain peptidoglycans
- Cells divide by binary fission, not by mitosis
- Usually exist as single cells or small groups of cells
10
Q
Domain Eukarya
A
- All the organisms classified into this domain have cells with nuclei and membrane-bound organelles
11
Q
Characteristic features of Domain Eukarya
A
- Cells with a nucleus and membrane-bound organelles
- DNA in the nucleus arranged as linear chromosomes with histone proteins
- Ribosomes (80 S) in the cytosol are larger than in prokaryotes; chloroplasts and mitochondria have 70S ribosomes, like those in prokaryotes.
- Chloroplast and mitochondrial DNA is circular as in prokaryotes
- A great diversity of forms: there are unicellular, colonial and multicellular organisms
- Cell division is by mitosis
- Many different ways of reproducing – asexually and sexually.
12
Q
Kingdoms
A
The three domains are each divided into various kingdoms
13
Q
Kingdoms of thee Domain Eukarya
A
1) Protoctista
2) Fungi
3) Plantae
4) Animalia
14
Q
Kingdom Protoctista
A
- Made up of a very diverse range of eukaryotic organisms, which includes those that are often called protozoans (‘simple animals’) and algae, such as seaweeds
- Any eukaryote that is not a fungus, plant or animal is classified as a protoctist
15
Q
Characteristic features of Kingdom Protoctista
A
- Eukaryotic
- Mostly single-celled, or exist as groups of similar cells
- Some have animal-like cells (no cell wall) and are sometimes known as protozoa
- Others have plant-like cells (with cellulose cell walls and chloroplasts) and are sometimes known as algae.
