18.2. Classification

Question 1

Why are organisms classified?

Answer 1

• 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.

Question 2

Taxonomy

Answer 2

• 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

Question 3

Taxonomic Hierarchy

Answer 3

• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

acronym (NSFW) - dirty kinky people can often find great sex

Question 4

History on the types of Domain

Answer 4

• 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.

Question 5

Domain Types

Answer 5

1) Archaea
2) Bacteria
3) Eukarya

Question 6

Domain Bacteria

Answer 6

• 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.

Question 7

Characteristic features of Domain Bacteria

Answer 7

• 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

Question 8

Domain Archea

Answer 8

• Also prokaryotic as their cells have no nucleus
• Their range of size is similar to that of bacteria
• Many inhabit extreme environments (extremophiles)

Question 9

Characteristic features of Domain Archeans

Answer 9

• 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

Question 10

Domain Eukarya

Answer 10

• All the organisms classified into this domain have cells with nuclei and membrane-bound organelles

Question 11

Characteristic features of Domain Eukarya

Answer 11

• 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.

Question 12

Kingdoms

Answer 12

The three domains are each divided into various kingdoms

Question 13

Kingdoms of thee Domain Eukarya

Answer 13

1) Protoctista
2) Fungi
3) Plantae
4) Animalia

Question 14

Kingdom Protoctista

Answer 14

• 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

Question 15

Characteristic features of Kingdom Protoctista

Answer 15

• 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.

Question 16

Kingdom Fungi

Answer 16

• Have some similarities with plants, but none of them is able to photosynthesise
• All heterotrophic, obtaining energy and carbon from dead and decaying matter or by feeding as parasites on living organisms
• Vast range in size from the microscopic yeasts to what may be the world’s largest organism - like a specimen of the honey fungus

Question 17

Characteristic features of Kingdom Fungi

Answer 17

• Have some similarities with plants, but none of them is able to photosynthesise
• All heterotrophic, obtaining energy and carbon from dead and decaying matter or by feeding as parasites on living organisms
• Vast range in size from the microscopic yeasts to what may be the world’s largest organism - like a specimen of the honey fungus

Question 18

Kingdom Plantae

Answer 18

• Plantae (plants) are all multicellular photosynthetic organisms
• They have complex bodies that are often highly branched both above and below ground.

Question 19

Characteristic features of Kingdom Plantae

Answer 19

• Multicellular eukaryotes with cells that are differentiated to form tissues and organs
• Few types of specialised cells
• Some cells have chloroplasts and photosynthesise
• Cells have large, often permanent vacuoles for support
• Autotrophic nutrition
• Cell walls are always present and are made of cellulose
• Cells may occasionally have flagella – for example, male gametes in ferns.

Question 20

Kingdom Animalia

Answer 20

• The Animalia are multicellular organisms that are all heterotrophic with many ways of obtaining their food
• There is a great diversity of forms within this kingdom
• The nervous system is unique to the animal kingdom

Question 21

Characteristic features of Kingdom Animalia

Answer 21

• Multicellular eukaryotes with many different types of specialised cells
• Cells that are differentiated to form tissues and organs
• Cells do not have chloroplasts and cannot photosynthesise (although some, such as coral polyps have photosynthetic protoctists living within their tissues)
• Cell vacuoles are small and temporary (for example, lysosomes and food vacuoles)
• Heterotrophic nutrition
• Cells do not have cell walls
• Communication is by the nervous system
• Cells sometimes have cilia or flagella

Question 22

Viruses

Answer 22

• Structure is only visible with electron microscopes
• Acellular – they do not have a cellular structure like bacteria and fungi
• Viruses are not in the classification system we have discussed so far
• This is because viruses have none of the features that we traditionally use for classification
• When they are free in the environment, they are infectious, but they have no metabolism
• When they infect cells, they make use of the biochemical machinery of the host cell to copy their nucleic acids and to make their proteins, often leading to destruction of the host cells
• The energy for these processes is provided by respiration in the host cell.

Question 23

Classifying Viruses

Answer 23

• The taxonomic system for classifying viruses is based on the diseases which they cause, the type of nucleic acid they contain (DNA or RNA) and whether the nucleic acid is single-stranded or double-stranded. In cellular organisms,
• DNA is double-stranded and RNA is single stranded but in viruses both can be either single-stranded or double-stranded.