Classification Candidates should be able to: (a) define the terms classification, phylogeny and taxonomy; (b) explain the relationship between classification.

Classification• Candidates should be able to: • (a) define the terms classification, phylogeny and taxonomy; • (b) explain the relationship between classification and phylogeny; • (c) describe the classification of species into the taxonomic hierarchy of

domain, kingdom, phylum, class, order, family, genus and species; • (d) outline the characteristic features of the following five kingdoms:

Prokaryotae (Monera), Protoctista, Fungi, Plantae, Animalia; • (e) outline the binomial system of nomenclature and the use of scientific

(Latin) names for species; • (f) use a dichotomous key to identify a group of at least six plants, animals

or microorganisms; • (g) discuss the fact that classification systems were based originally on

observable features but more recent approaches draw on a wider range of evidence to clarify relationships between organisms, including molecular evidence (HSW1, 7a);

• (h) compare and contrast the five kingdom and three domain classification systems (HSW4, 7a, 7b).

Key Terms

• Classification: The process of placing living things into groups- the detailed study of the individuals in a species

• Phylogeny: the study of how closely different species are related

• Taxonomy: the study of the principles behind classification (the differences between species). These differences can be used to classify species.

Phylogeny• The more closely

two species are related, the closer they appear on the evolutionary tree and the more recently they shared a common ancestor

The Current System of Classification

The current system uses eight taxa:

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

Five Kingdoms

• Traditionally, all living things have been grouped into a number of kingdoms- this used to be two- plants and animals, but not all living things can fit into these two categories, so it is now 5

• Prokaryotes, protoctists, fungi, plants, animals

Prokaryotes• No nucleus• Loop of DNA that is not

arranged in linear proteins (not associated with histone proteins- Histones are the major structural proteins of chromosomes)

• No membrane bound organelles

• Small ribosomes• Carry out respiration in special

membrane systems called mesosomes

• Have smaller cells than eukaryotes

• May be free living, parasitic, or cause disease

Protoctists• All are eukaryotes• Mostly single celled• Have a variety of forms• Show plant or animal like features• Mostly free living• Have autotrophic (photosynthesis)

or heterotrophic (ingesting prey or extracellular enzymes) nutrition

• It is sometimes referred to as the dustbin group as they have features that do not belong in any other kingdom

Fungi• Are eukaryotes

• Have a mycelium (a network of strands called hyphae)

• Have walls made of chitin (not cellulose)

• Have a multinucleate cytoplasm (more than one nucleus)

• Are mostly free living and saprophytic (cause decay of organic matter)

Plants

• Eukaryotes• Multicellular• Have a cellulose cell

wall• Produce multicellular

embryos from fertilised eggs

• Have autotrophic nutrition (carry out photosynthesis)

Animals

• Are eukaryotes• Are multicellular• Have heterotrophic

nutrition (eat other organisms, digest and absorb them)

• Have fertilised eggs that develop into a ball of cells called a blastula

• Can usually move around

Classifying a Species• A species means a group of organisms

that can breed together to produce fertile offspring

• Carl Linnaeus devised a system of naming living organisms that uses two names- called the binomial system

• Before this, scientists used to use long, detailed descriptions or a common name, however this did not work well because:

• The same organisms had different names in different parts of the country

• Translation of languages may give different names

• The same common name may be used for different species in other parts of the world

The Binomial System

• Latin is a universal language so species are given a universal name

• All scientists around the world will use the same name• Binomial means ‘two names’, the first name is for the

genus, the second is for the species e.g. Homo sapiens- Homo is the genus, sapiens is the species

• The genus name always starts with a capital letter• It is always used in a way that makes it stand out- if

typed, it is in italics, and if written it is underlined.

Identifying Organisms

• Before you collect a species sample, you must check it will not harm the environment

• You would first have to carry out an EIA- Environmental impact assessment

• Scientists need to know what species are present, if they are rare, and if habitat destruction would have a large impact

• For example: a pond that contains great crested newts must not be harmed, as it is protected under the wildlife and countryside act 1981- it is illegal to catch, possess handle, cause death, harm or disturb them

Using a Key

• A dichotomous key is a way of identifying organisms you have found

• It is based on questions and answers- usually yes or no

• The answer to each question leads to a different question and finally the name of the specimen

• A good dichotomous key has one question fewer than the number of species it can identify

You must make sure you know how to use a dichotomous key to identify a group of at least six plants, animals or microorganisms

Ancient Classification• Early classification was based on

observable features, so was limited to what you could see

• In the 17th century (1600s), they had microscopes to help so they could see cells

• Aristotle (384BC) based his observation on appearance and anatomy he said organisms were either plant or animal, then he further classified them into three groups, those that: live and move in water, live and move on land and move through the air

• Unfortunately, this meant that he grouped fish with turtles, birds with insects and mammals with frogs.

• Classification is now more accurate as more research has been carried out.

Modern Classification• Originally, one celled

organisms that were plant like were classified with plants and animal like ones classified with animals, but some unicellular organisms have features of both animal and plant, also there was the problem with fungi having hyphae and not carrying out photosynthesis.

• This is why we now have the 5 kingdom classification, however there are now even more ways of classifying organisms…

Biochemistry

• Certain large biochemical molecules are found in all living things, but they may not be identical in all living things

• This can be used to show evolutionary relationships and how closely related species are to one another

Cytochrome C

• Cytochrome C is a protein used in respiration• All living organisms except chemosynthetic

prokaryotes must respire, so must have Cytochrome C

• Cytochrome C is not identical in all species- it is a protein made from amino acids, and some of the amino acid sequences differ between species.

• If the amino acid sequence is the same, the two species must be closely related, the more differences there are, the less the species is related

DNA

• All organisms use DNA or RNA

• Comparisons of DNA sequences provides a way to classify species

• The more similar the sequence, the more closely related the species

• We can use this to clarify or correct evolutionary relationships that we are unsure about

Three Domains• In 1990, Carl Woese suggested a new classification system based on RNA

• He divided the kingdom Prokaryote into two: the bacteria (Eubacteria) and the Archaeae (Archaebacteria)

• He said that Bacteria have: a different cell membrane structure, different flagella, different enzymes for building RNA, no proteins bound to their genetic material and different DNA replication mechanisms

• He also said Archaea share features with eukaryotes e.g. similar enzymes for building RNA, similar DNA replication mechanisms and production of the same proteins that bind to DNA

• Woese suggested that the differences between Archaeae and Eubacteria are greater than the differences between Eukaryotes and bacteria- this is now widely accepted by biologists

Questions

[Total 4 marks]

Task

• Now complete the end of chapter test as an open book activity