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GCSE level biology:
Biological classification: Part 1.
Traditional
methods of classifying living organisms - the five 'Linnaean' kingdoms and
binomial classification of animalia, plantae,
fungi, protoctista (protists) and prokaryotes
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1.
The
traditional methods of classifying living organisms - five kingdoms
Introduction - what should a classification be about?
Classification systems aim to reflect evolutionary
relationships - from ancient organisms to contemporary
organisms.
Classification was (and to some extent still is) traditionally
based on studies of morphology and anatomy - the physical features
of organisms.
The sequences of bases in DNA and of amino acids in proteins are
now used as a more accurate means of classification and hence,
evolutionary relationships.
Organisms which share a more recent ancestor (are more closely
related) have base sequences in DNA that are more similar than those
that share only a distant ancestor.
In biology, a classification system is a way of
organising living organisms into groups.
Early classification systems used observable
features to place organisms in groups - sometimes referred to as an
artificial classification system - although now regarded as
outdated and not suitable in the light of more advanced knowledge,
such systems have their use in e.g. identifying animals using a
key system.
As we understanding of evolutionary relationships
developed there was a need for a more advanced classification system,
sometimes referred to as natural classification system.
Natural classification systems look at an
organism's common ancestors and common structural features to help
out organisms into suitable groupings.
e.g. bats and humans have many different
features, the pentadactyl hands of them means they are both grouped
together.
The traditional 'natural' system, still in wide use today,
is based on the classification work of Carl Linnaeus working in the 18th
century.
His system grouped living things according to
their particular observable physical characteristics and
structural features seen with an optical microscope.
This gives rise to the 'Linnaean system' in
which living organisms are first divided up into five kingdoms.
You are basically looking at similarities
and differences between species and the data is expressed in the
idea of a five kingdom system.
Up to the 1970s scientists considered the five
kingdoms of life were sub-divided as follows:
The
Five Kingdoms of life and their
characteristics CAN be defined as ...
1. animalia - all animals – animals are multicellular
(eukaryotic lacking cell wall material, but have a chromosome
containing nucleus), do
not have cell walls, do not have chlorophyll, feed heterotrophically (heterotrophs
can't make their own food) e.g. fish, insects, mammals, reptiles etc.
2. plantae
- all plants - are multicellular
(eukaryotic), have cell
walls (and a chromosome containing nucleus), have chlorophyll, feed autotroprically (autotrophs can make their own
food from photosynthesis) e.g. grasses, flowers, trees etc.
3. fungi - usually multicellular
(eukaryotic), have cell walls,
do not have chlorophyll e.g. mushrooms, toadstools, yeasts.
Fungi can (i) feed saprophytically - saprophytes/saprotrophs feeding
off dead organisms and decaying material, (ii) be parasite symbiont
- feeding off another living organism (at its host's expense!) or
(iii) symbiosis, where both the fungus and host benefit each other.
4. protoctista (protists) - usually
unicellular (single celled eukaryotes), have a nucleus, protists include algae
(can photosynthesise) and protozoa e.g. amoeba, paramecium, euglena.
Although algae photosynthesise, they are not really plants because
they do not form roots, stems or leaves.
A protist is any eukaryotic organism that is not
an animal, plant, or fungus. While it is likely that protists
share a common ancestor, the exclusion of other eukaryotes means
that protists do not form a natural group.
5.
Prokaryota (prokaryotes) - unicellular (single
celled prokaryotic organisms), have no nucleus e.g. bacteria,
cyanobacteria and archaea.
This 'five kingdom' system is still in
use, BUT it is getting out of date!
Note on viruses
Scientists do not classify
viruses in any of the five kingdoms and regard them as non-living.
Viruses, which are smaller than bacteria,
cannot reproduce themselves, and have protein coat containing a few genes,
they invade cells and make them reproduce the invading virus.
For see the
Note on the
structure and function of viruses
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The naming of organisms using the Linnaeus Latin names of the binomial system
based on genus and species
The naming of organisms - Linnaeus Latin names of the binomial system
The adoption by biologists of a system of strictly
binomial nomenclature is due to Swedish botanist and physician
Carl von Linné, more commonly known by his Latinized name Carl Linnaeus
(1707–1778).
In this context, the word binomial means
consisting of 'two parts' - usually two Latin words, the first has a capital
letter (upper case), the second word has a small letter (lower
case).
The name of the organism is written in
italics (I may have forgotten this sometimes!)
By using Latin, every name can be
unambiguously recognised around the world, no matter what the
native language of any scientist.
The use of a universal name avoids
confusion in scientific communication.
(I'm afraid its not quite the same in
chemistry!)
With millions of species to name, the world of
science needs a VERY systematic way of naming life forms.
Although the classification system of Carl
Linnaeus is being 'updated' on the basis of modern biological research,
his proposed system of naming living organisms is still the basis of
today's names.
The name is based on the two 'lowest' sections
of the classification systems described above:
The first part gives you the
genus of the species.
This gives you information on the
organism's ancestry.
In the case of 'us', our genus is
Homo.
The second part tells you the
specific species.
In the case of 'us', our species is
sapiens.
Therefore, as an organism, OUR two-part
name is Homo sapiens.
So, be able to explain why binomial
classification is needed to identify, study and conserve species, and can be
used to target conservation efforts.
So, the binomial name of species consists of a two part
Latin name (usable in any country with its own language!).
The Latin name cannot be confused linguistically with
'local' or country names.
Study and identification produces a common data base
of information on species with a universal name.
From the database, species at threat can be
identified and preservation strategies put in place.
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Key points -
Summary of ideas
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Here are detailed
revision notes on the traditional classification of living organisms,
focusing on the five Linnaean kingdoms: Animalia,
Plantae, Fungi, Protoctista, and Prokaryotes.
Traditional
Classification of Living Organisms
Biologists classify living
organisms to understand relationships between different species.
Traditionally, organisms were classified into five kingdoms based on their
cell structure, mode of nutrition, and reproductive methods.
This system was developed by
Carl Linnaeus and refined by
Robert Whittaker.
1.
Kingdom Animalia
(Animals)
-
Cell type:
Eukaryotic (cells have a nucleus)
-
Cell structure:
Multicellular; no cell walls
-
Mode of nutrition:
Heterotrophic (consume organic material)
-
Reproduction:
Mainly sexual reproduction
-
Movement:
Most animals are motile (able to move)
-
Examples:
Mammals, birds, reptiles, fish, amphibians, insects
2.
Kingdom Plantae
(Plants)
-
Cell type:
Eukaryotic
-
Cell structure:
Multicellular; cell walls made of cellulose
-
Mode of nutrition:
Autotrophic (photosynthesis using chlorophyll)
-
Reproduction:
Sexual (flowers, seeds) and asexual (vegetative propagation)
-
Movement:
Sessile (do not move actively)
-
Examples:
Mosses, ferns, flowering plants, conifers
3.
Kingdom Fungi
-
Cell type:
Eukaryotic
-
Cell structure:
Mostly multicellular (yeasts are unicellular); cell walls made of chitin
-
Mode of nutrition:
Heterotrophic (saprotrophic—absorb nutrients from dead organisms)
-
Reproduction:
Asexual (spores) and sexual reproduction
-
Movement:
Sessile
-
Examples:
Mushrooms, yeast, moulds
4.
Kingdom
Protoctista (Protists)
-
Cell type:
Eukaryotic
-
Cell structure:
Mostly unicellular; some multicellular forms (e.g., seaweed)
-
Mode of nutrition:
Both autotrophic (photosynthesis) and heterotrophic (engulfing food)
-
Reproduction:
Asexual and sexual reproduction
-
Movement:
Some move using flagella, cilia, or pseudopodia
-
Examples:
Amoeba, algae, Plasmodium (causes malaria)
5. Kingdom Prokaryota
(Prokaryotes)
-
Cell type:
Prokaryotic (no nucleus)
-
Cell structure:
Unicellular; cell walls not made of cellulose
-
Mode of nutrition:
Some autotrophic (photosynthetic bacteria), others heterotrophic
(decomposers)
-
Reproduction:
Asexual (binary fission)
-
Movement:
Some bacteria move using flagella
-
Examples:
Bacteria, cyanobacteria (blue-green algae)
The scientific importance of
Classification
-
Allows scientists to
identify and name organisms (binomial nomenclature:
genus + species).
-
Helps understand
evolutionary relationships and shared traits.
-
Essential for
medicine, conservation, and studying biodiversity.
This classification system
has since been refined with three domains (Bacteria, Archaea,
Eukarya) based on genetic analysis.
Linnaean Binomial
System of Naming Organisms
The binomial system,
developed by Carl Linnaeus in the 18th century, is a universally accepted
method for naming species.
Each organism receives a
two-part Latin
name, ensuring consistency in identification across languages and
scientific communities.
Why Use the Binomial
System?
-
Universal Naming
Convention: Latin names
remain the same worldwide, avoiding confusion caused by local common
names.
-
Clarity and
Precision: Ensures each
species has a unique name, preventing ambiguity.
-
Reflects
Evolutionary Relationships:
Names can provide information about related species.
Structure of a
Binomial Name
Each name consists of
two parts:
-
Genus Name
(capitalized) – Indicates the broader group of related species.
-
Species Name
(lowercase) – Specifies the exact organism within the genus.
Example:
Note: The scientific name
is italicized
Linnaean
Classification & Taxonomy
The binomial system is part of
the broader Linnaean classification hierarchy:
-
Kingdom
-
Phylum
-
Class
-
Order
-
Family
-
Genus
-
Species
This system groups organisms
based on shared characteristics and evolutionary ancestry.
Importance in Modern
Science
-
Used in
Phylogenetics: Helps
scientists study evolutionary links.
-
Vital in
Conservation Biology:
Standardized naming aids in protecting endangered species.
-
Applied in Medical
Research: Accurate
identification of species is essential in studying diseases and
biodiversity.
Summary of learning objectives and key words or phrases
Know the five kingdom classification into animalia animals,
plantae plants, fungi fungus (all four are eukaryotic , usually
multicellular organisms), protoctista protists (prokaryotes - single celled
organisms with no nucleus), prokaryotes and the traditional methods of
classifying living organisms was the five kingdom classification.
Be able to understand, explain and use the naming of
organisms by the Linnaeus Latin names of the binomial system examples based
on genus and species. Examples explained.
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