18.2.2
Linnaean Classification System
Traditional Classification System
Traditional Classification System
Classification in biology involves the identifying, naming and sorting of organisms in a process called taxonomy. Organisms are classified into groups called taxa.


Taxa
Taxa
- Closely related organisms are grouped together into groups called taxa (singular = taxon).
- The phylogeny of organisms (their evolutionary relationships) is important for determining which taxa an organism is a part of.


Hierarchy
Hierarchy
- Each taxon is arranged into a hierarchy.
- The hierarchy divides into smaller, more specific taxa at each level.
- There is no overlap between taxa at the same level.
- Organisms can only belong to one taxon at each level.


Stages in the Linnaean hierarchy
Stages in the Linnaean hierarchy
- The traditional classification system, devised by Carl Linnaeus, categorises organisms based on their structure and characteristics. Linnaeus created 7 different groups:
- Kingdom.
- Phylum.
- Class.
- Order.
- Family.
- Genus.
- Species.
- The five kingdoms are : Animalia, Plantae, Protoctista, Fungi and Prokaryotae.


E.g. Humans
E.g. Humans
- Humans can be classified in the hierarchy system as:
- Kingdom = Animalia.
- Phylum = Chordata.
- Class = Mammalia.
- Order = Primates.
- Family = Hominidae.
- Genus = Homo.
- Species = sapiens.


Binomial names
Binomial names
- The naming system used in classification is called the binomial system.
- The binomial system consists of the genus and the species of an organism.
- The names are always written in italics if they are typed or they are underlined if hand-written.
- E.g. The binomial name for humans is Homo sapiens.
Animals and Plants
Animals and Plants
Animals and plants are eukaryotes; their cells contain mitochondria (for respiration) and a nucleus (containing DNA).


Animals
Animals
- Animal cells have no cell wall and no chloroplasts (so do not carry out photosynthesis).
- Animals are multicellular (made of many cells) and they don't make their own food, but they store carbohydrates as glycogen.
- They often have nervous coordination (using nerves) and are able to move around.
- Mammals (like whales) and insects (like mosquitoes) are examples.


Plants
Plants
- Plant cells are surrounded by cell walls (made of a substance called cellulose) and contain chloroplasts (carry out photosynthesis).
- Plants are multicellular (many cells) and they make their own carbohydrate food, which they store as sucrose or starch.
- Plants can be divided into flowering and non-flowering plants.
- Flowering plants include cereals (e.g. maize) and herbaceous legumes (e.g. peas).
- Non-flowering plants include pines and ferns.
Fungi, Protoctists and Bacteria
Fungi, Protoctists and Bacteria
Fungi and protoctists are eukaryotic organisms, but bacteria are prokaryotes.


Fungi
Fungi
- Fungi cells have cell walls (that contain a substance called chitin) and no chloroplasts.
- Fungi can be multicellular or unicellular and they are saprotrophic (they feed by secreting digestive enzymes and absorbing broken down decaying matter), and often store carbohydrates as glycogen.
- Their bodies are made up of mycelium, which contains many thread-like structures called hyphae.
- Mushrooms and single-celled yeast are examples.


Bacteria
Bacteria
- Bacteria are unicellular and they have cell walls and circular loops of DNA (which is not inside a nucleus).
- Some bacteria photosynthesise, and some feed off decaying matter.
- Bacteria can be rod-shaped (like Lactobacillus which turns milk into yoghurt)or spherical (like Pneumococcus which causes pneumonia).


Protoctists
Protoctists
- Protoctists are unicellular, and their cells have nuclei (membrane-bound structures that contain the cell's genetic materials).
- Some, like Amoeba, are similar to animal cells.
- Some, like Chlorella, are like plant cells and have chloroplasts.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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