Classification Chapter 8
Learning Outcomes By the end of this week, you should: recognise the value of identification and scientific naming (nomenclature). develop knowledge of the principles of classification. recognise that biological classification contains a hierarchy of levels. become aware that taxonomic systems are subject to change. recognise features typically used in constructing major taxonomic groups.
Why is identification important? Endemic animals Deadly and harmless snakes Personal safety Knowing the difference between poisonous and harmless plants. Early settlers and stock Quarantine Medicine Conservation Forensics Palynology Agriculture and horticulture Pests and control measures
What do scientists use to classify organisms? Whole specimens Actual, image or verbal description Bits and pieces Microscopic – plant cell walls, leaf vein patterns, pollen grains, seed shape Macroscopic – feathers, hair, teeth, shells, fruits Molecular – genetic material Indirect evidence Track, burrows, nests, scratchings, scats, calls/songs Reference collections – herbaria, museums Keys
Dichotomous key – choosing between two alternatives Complete the key activities.
Scientific naming Based on Latin or Greek words – pages 227, 228 Two part names (binomial) – international Linnaeus’ binomial naming system 1758 Systematic First part = generic (which genus it belongs to), always begins with a capital letter Second part = specific name (which species it belongs to), lower case Informative about how closely related organisms are
Why is scientific naming important? Universal, no matter what language Common names can be reused for different species An indication of relatedness Common names may be misleading – suggesting relationships that are not valid Complete the quick- check questions on pages 224 and 229
What is classification? Naming and describing. Organising closely related species into groups. Combining these groups to form larger, more inclusive groups.
What is a species? Pages Use of structural similarities? The ability to interbreed? The use of chromosomes and DNA?
Principles of classification Separating into groups Based on the presence of absence of various features Uses a series of decisions in a dichotomous key
Features of classification Classification schemes can vary depending n their function. Usefulness of the scheme depends on the criteria selected: Objective (not subjective) – the same meaning for different people = reproducible and predictable results Meaningful (not arbitrary) – conveys useful information Schemes are not fixed, but can change when new information becomes available. Schemes can be single or multi-level (hierarchical).
Benefits of classification Easier to deal with smaller numbers of groups than very large number of separate items. Provides information about relationships between organisms. New items can be added in a predictable way. Information can be easily retrieved. Predictions can be made about an item based on its classification.
Hierarchical System Levels of classification are called taxa (sing. taxon) The closer the evolutionary relationship between two organisms, the more similar their classification. The hierarchical system of classification: Kingdom Phylum Class Order Family Genus Species Come up with a pneumonic to help you remember! Look at pages Complete the quick-check questions on page 242.
Domains Bacteria - prokaryotes Archaea – extremophiles Eukarya - eukaryotes Watch the Clickview video and answer the questions on classification.
Cladistics Identifying the relationships between various organisms and deciding which organisms should be included in particular groups. “How many derived features do they share?” Primitive characters – features that were present in a common ancestor, and so appear in all members of the group. Derived characters – advanced or modified features that evolved later and appear in some members of the group.
Cladograms Shows the evolutionary relationship between particular organisms based on the derived characters they share. A fork/branching point appears whenever a derived feature appears in some members of the group.
Classifications can change Based on further study. DNA and protein sequencing can show differences.