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Powerpoint Presentation: Plant Diversity
Powerpoint Presentation: Taxonomy

Evolution Index

The origins of life
Evolution and Fixity
Natural selection
Lamarkian Evolution
Antibiotic Resistance
Industrial melanism
Palaeontology : The study of fossils
The C-14 Decay Curve
In Search of Deep Time
Evolution of the Horse
Punctuated Equilibrium
Humans: Neotonous, bipedal African apes
The Hominids
The Changing Trees of Human Evolution
Genetic verses Cultural Evolution
Phenylketonuria (PKU) Fact Sheet
Cystic Fibrocis (CF) Fact Sheet

Topic Chapters Index

 

THE FIVE KINGDOM SYSTEM

1. MONERA (PROKARYOTES):

Bacteria, including cyanobacteria and archea.

  • Heterotrophic or autotrophic
  • Naked DNA
  • No membranous organelles
  • Cell wall of murin

2. PROTOCTISTA:

Protozoa and unicellular algae multicellular algae such as seaweeds)

  • All those eukaryotes which do not fit in the animal, plant or fungal kingdoms
  • Heterotrophic or autotrophic
  • Eukaryotic structure
  • Unicellular and multicellular

3. FUNGI:

  • Heterotrophic
  • Acellular, eukaryotes
  • No cilia or flagella (undulipodia)
  • Develops from a spore
  • Cell wall of chitin

4. PLANTS (PLANTA):

  • Autotrophic
  • Multicellular, eukaryotes
  • Develops from an embryo
  • Show alternation of generations (haploid-diploid phases)
  • Cell wall of cellulose

5. ANIMALS (ANIMALIA):

  • Heterotrophic
  • Multicellular, eukaryotes
  • Develops from a blastula (blastocyst in mammals)
  • Diploid life cycle except for sex cells.

VIRUSES remain unclassified within these kingdoms. They are non-cellular.

 

KINGDOM: PLANTA

Bryophyta: Small terrestrial plants restricted to damp habitats. Gametophyte generation dominant. Water is needed for fertilisation. Sporophyte = spore capsule.

Phyla

Classes

Hepaticae:

Liverworts: Prostrate thallus with rhizoids.

Musci:

Mosses. Erect stem with leaflets +/- rhizoids

Vascular plants: Sporophyte generation dominant, differentiated into: leaves, stem, roots, rhizome. Lignified tissue (wood) may be present

Filicinophyta: Ferns Water still needed for fertilisation.

Phyla

Classes

Sphenophyta:

Horsetails

Lycopodophyta:

Clubmosses Heterosporous: big megaspores (ovules) and small microspores (pollen)

Seed plants: Water no longer needed for fertilisation. Gametophyte very reduced, sporophyte is the plant. Female gametophyte becomes a seed which contains a food store and protective coat.

Coniferophyta: (conifers) Naked seeds born in cones.

Angiospermophyta: Flowering plants. Seeds protected by an ovary which becomes a fruit

Phyla

Classes

Dicotyledons:

Plants with two seed leaves.

Monocotyledons:

Plants with one seed leaf.

 

 

EVOLUTION

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Taxonomy or Systematics: The study of classification.

Why classify organisms?

  • With over a million species so far identified and estimates of up to 30 million species on Earth there is a great need to organise this biodiversity.

  • Systematics tells us about the patterns in nature, the way organisms are related and how they evolve.

  • Systematics can be used to identify organisms, which are important to us. Useful organisms which could be sources of materials for us (e.g. pharmaceuticals). Harmful organisms which may cause disease in ourselves or in livestock and crops.

 

The unit of taxonomy :The SPECIES.

It has biological significance:

  • Species form populations of individuals which may interbreed to form fully fertile offspring.

  • Problem: Some species only use asexual reproduction or rarely use sexual reproduction.

  • Taxonomists compare a new specimen with given characteristics: morphology, anatomy, behaviour, embryology, protein structure, karyotypes, DNA sequence (DNA fingerprints).

 

The binomial system of classification

Species are grouped by levels of relationship called TAXA (sing. TAXON):

Kingdom; Phylum; Class; Order; Family; Genus; Species.

(Subdivisions of these may be necessary: e.g. sub phyla or superfamily)

Each species is given two names: The genus it belongs to and the name of the species (e.g. Homo sapiens). This is called the binomial system of nomenclature. Notice the species name does not carry a capital letter and it is printed in italics.

Example:

classification

All taxa, other than species, are completely arbitrary in the way taxonomists decide which species fits into which group. As our knowledge improves a species may be moved from one taxon to another but it will always keep its species name.

 

How taxonomy works

The aim is to group organisms according to their evolutionary relationship (phylogeny). This is established by studying fossils or more recently from DNA sequencing. It uses characteristic features to group organisms together (e.g. all animals with feathers = Birds). It is the taxonomists who decide which are the most significant or "important" characteristic by the way it occurs in different groups of organisms.

Recently a method of systematics called cladistics has become an accepted way of classifying organisms. This method uses many different characteristics not just one to define a taxon. One character is not enough.

The characteristics are grouped in a hierarchy. So having four legs with five toes is common to all land vertebrates and their fish ancestor. This would be used to group the animals we call tetrapods. Having a nerve cord running down the back is a feature common to all the tetrapods but also all the rest of the vertebrates. So it can be used to group all the vertebrates but not the tetrapods alone.

This type of classification is expressed as a branching diagram called a cladogram. Each branch point or node indicates that above it all the organisms share a number of features.

Thus, birds are birds not just because they have feathers but because the have: hollow bones, flexible wrists, they are endothermic (warm-blooded), they have fused clavicles (the "wishbone"), a characteristic egg shell, three toes pointing forwards and one toe pointing back.

This method has lead to some surprising discoveries. All of the characteristics of birds listed above have been found in fossils of a group of dinosaurs called the theropods (which includes Tyrannosaurus rex). This led the taxonomists to the conclusion that birds are really dinosaurs.

In fact birds seem to possess only a few characteristics which are really their own:

  • a very short tail (the parson's nose) to manage the tail feathers,

  • fused fingers and a "thumb wing" for slow flight,

  • a deep keel to the sternum (breast bone) to attach the flight muscles,

  • a complex breathing system to manage at high altitudes.

In cladistics the absence of a characteristic is not considered relevant. It is often said that a characteristic of birds is that they lack teeth. Anteaters and tulips do not have teeth either and you would not call them birds.

Reference: Paladian & ChiappeThe Origin of Birds and Their Flight Sci Amer (1998) Feb p 28

 

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