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What is classification?

The process by which different kinds of organisms are arranged into groups


Why do we group organisms into categories?

Because then it is much easier to understand them and to remember their key features


What is taxonomy?

The study and practice of classification, which involves placing organisms in a series of taxonomic units (taxa, singular: taxon)


What is the hierarchy of taxa?

1) Domain
2) Kingdom
3) Phylum
4) Class
5) Order
6) Family
7) Genus
8) Species


What are the three domains?

Bacteria, Eukarya and Archaea


Why are bacteria and archaea prokaryotic?

Because their cells have no nucleus


What are the 8 characteristic features of bacteria?

1) cells with no nucleus
2) DNA exists as a circular 'chromosome' and does not have histone proteins associated with it
3) plasmid (smaller, circular molecules of DNA) are often present
4) no membrane-bound organelles are present
5) ribosomes (70s) are smaller than in eukaryotic cells
6) cell wall is always present and contains peptidoglycans
7) cells divide by binary fission, not by mitosis
8) usually exist as single cells or small groups of cells


How are archaea similar to bacteria?

Their range of size and metabolism


How are archaea similar to eukaryotes?

The way in which transcription occurs in archness has much more in common with eukaryotes as the genes coding for the RNA that makes up their ribosomes are more like those of eukaryotes


How is it thought that the 3 domains evolved?

1) bacteria and archaea separated from each other very early in the evolution of life
2) archaea and eukarya probably diverged later


What is a characteristic of many archaea?

Inhabit extreme environments e.g. high temperatures and around deep volcanic vents, where there is no oxygen


What are 7 characteristic features of all archaea?

1) cells with no membrane-bound organelles
2) DNA exists as a circular 'chromosome' and is associated with histone proteins
3) plasmids are often present
4) 70s ribosomes, but features of ribosomes are similar to those of eukaryotic ribosomes, not to bacterial ribosomes
5) cell wall is always present, but does not contain peptidoglycans
6) cells divide by binary fission, not by mitosis
7) usually exist as single cells or small groups cells


What do all eukaryotes have?

Cells with nuclei and membrane-bound organelles


What are the 7 characteristic features of eukaryotes?

1) cells with a nucleus and membrane-bound organelles
2) DNA in the nucleus arranged as linear chromosomes with histone proteins
3) ribosomes (80s) in the cytosol are larger than in prokaryotes but chloroplasts and mitochondria have 70s ribosomes, like prokaryotes
4) chloroplast and mitochondrial DNA is circular as in prokaryotes
5) they have a great diversity of forms: unicellular, colonial and multicellular
6) cell division is by mitosis
7) many different ways of reproducing - asexually and sexually


What is the kingdom Protoctista made up of?

A very diverse range of eukaryotic organisms including protozoans (simple animals) and algae e.g. seaweed


What is a protoctist?

- Any eukaryote that is not a fungus, plant or animal is classified as a protoctist
- Many protoctists may actually be more related to organisms in other kingdoms than they are to each other


What are the 5 characteristic features of protoctists?

1) they are eukaryotic
2) mostly single-celled, or exists as groups of similar cells
3) some have animal-like cells (no cell wall) and are sometimes known as protozoa
4) others have plant-like cells (with cellulose cell walls and chloroplasts) and are sometimes known as algae


What do fungi range vastly in?



What are the 7 characteristic features of fungi?

1) they are eukaryotic
2) they do not have chlorophyll and do not photosynthesise
3) carry out heterotrophic nutrition
4) reproduce by means of spores
5) they have a simple body form, which may be unicellular or made up of long threads called hyphae (with or without cross walls) - large fungi e.g. mushrooms produce large compacted masses of hyphae called 'fruiting bodies' to release spores
6) cells have cell walls made of chitin or other substances (NOT cellulose)
7) never have cilia or flagella


What are plants?

- Multicellular photosynthetic organisms
- They have complex bodies that are often highly branched above and below ground


What are 6 characteristic features of plants?

1) multicellular eukaryotes with cells that are differentiated to form tissues and organs
2) they have few types of specialised cells
3) carry out autotrophic nutrition ∴ some cells have chloroplasts and photosynthesise
4) cells have large, often permanent vacuoles for support
5) cell walls are always present and made up of cellulose
6) cells may occasionally have flagella e.g. male gametes in ferns


What are animals?

- Multicellular organisms that are all heterotrophic with many ways of obtaining their food
- There is a great diversity of forms
- The nervous system is unique to the animal kingdom


What are the 8 characteristic features of animals?

1) multicellular eukaryotes with many different types of specialised cells
2) cells that are differentiated to form tissues and organs
3) cells do not have chloroplasts and cannot photosynthesise, however some e.g. coral polyps have photosynthetic protoctists living within their tissues
4) cell vacuoles are small and temporary e.g. lysosomes and food vacuoles
5) carry out heterotrophic nutrition
6) cells do not have cell walls
7) communication is by the nervous system
8) cells sometimes have cilia or flagella


What is heterotrophic nutrition?

- Using organic compounds made by other organisms as a source of energy and molecules for metabolism
- Obtaining energy and carbon from dead/decaying matter or by feeding as parasites on living organisms


What are viruses?

Acellular microorganisms (they do not have a cellular structure)


What is the structure of viruses only visible with?

An electron microscope


Why are viruses not in the classification system?

- Because they have none of the features traditional used for classification
- There is an argument that viruses should not be considered living organisms at all


What do viruses have in common with cellular organisms?

They have particles made of proteins and nucleic acids that are found in cellular organisms


What happens when viruses are free in the environment?

They are infectious but have no metabolism


What happens when viruses infect cells?

- They make use of the biochemical machinery of the host cell to copy their nucleic acids and make their proteins, often leading to destruction of the host cell
- The energy for these processes is provided by respiration in the host cell

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