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(c) Identification & Taxonomy
(c) Identification & Taxonomy
This is a really wonderful section all about life: understanding the diversity of all life that has ever existed; the interconnections; the relationships. For me, it is the perfect introduction to the next Key Area on Evolution and I would like you to start by watching the TED talk below. It will open your eyes to the misconceptions you may have arrived at this page with.
This is a really wonderful section all about life: understanding the diversity of all life that has ever existed; the interconnections; the relationships. For me, it is the perfect introduction to the next Key Area on Evolution and I would like you to start by watching the TED talk below. It will open your eyes to the misconceptions you may have arrived at this page with.
It helps to explain why an internet search of evolution should never produce this image...
It helps to explain why an internet search of evolution should never produce this image...
...but perhaps should produce this kind of image instead.
...but perhaps should produce this kind of image instead.
...or better still...THIS
...or better still...THIS
" We're not the goal of evolution".
" We're not the goal of evolution".
The three domains of life
The three domains of life
Life is classified into 3 domains:
Life is classified into 3 domains:
- Archaea
- Bacteria
- Eukaryota
Archaea
Archaea
Sulphur-rich, acidic, thermal pool at Yellowstone National Park - home to many archaeal species, including Sulfolobus solfataricus.
Watch the video below to see where many archaeal species can be found - although note the mistakes made by the presenter (many of these are genetically and evolutionary distinct from bacteria and are actually archaea).
Bacteria
Bacteria
Bacteria and Archaea are both classes as prokaryotes. Most bacteria exist as single cells and some cause disease. Most bacteria can be broadly classified by their shape as rods, spheres or spirals and by their cell-surface properties. Although they lack the morphologically variety of eukaryotic cells, they display a surprising array of surface appendages that enable them to swim or to adhere to desirable surfaces.
Eukaryota
Eukaryota
Eukaryotes are organisms composed of one or more cells with a distinct nucleus and cytoplasm. It includes all forms of life except viruses and prokarotes (bacteria and archaea).
Watch the video by clicking the pink button - it is useful to fast-forward to 1min 36s.
Phyla or Kingdom?
Phyla or Kingdom?
Identification of an organism in a sample can be made using:
classification guides
biological keys
analysis of DNA or protein.
Organisms can be classified by both taxonomy or phylogenetics. Taxonomy involves the identification and naming of organisms and their classification into groups based on shared characteristics. Classic taxonomy classification is based on morphology.
The plant and animal kingdom are divided based on their morphological differences, as outlined below.
The Plant Kingdom
The Plant Kingdom
The plant kingdom is divided into 5 major divisions.
Task 5
Task 5
Read the information below to make an identification key for the plant kingdom. The video above (see pink button) is a good introduction to plant classification to support you with this task.
Suggested answers are available here.
Task 6
Task 6
Use the following information to make an identification key for the animal kingdom phyla. The video above (see pink button) is a useful introduction to the classification and identification system within the animal kingdom.
Suggested answers are available here.
Use your identification keys to try and work out the phyla that each of these organisms belong to. Click on the image to reveal the answer.
Use your identification keys to try and work out the phyla that each of these organisms belong to. Click on the image to reveal the answer.
How did you get on?
How did you get on?
Phylogenetics
Phylogenetics
Phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms.
Phylogenetics is changing the traditional classification of many organisms. It uses heritable traits, e.g. morphology, DNA sequences and protein structure to make inferences about an organism’s evolutionary history and create a phylogeny (or phylogenetic tree) – a diagrammatic hypothesis of its relationships to other organisms.
Familiarity with taxonomic groupings allows predictions and inferences to be made about the biology of an organism from better-known (model) organisms. Examples of taxonomic groups include nematodes, arthropods and chordates.
The image above shows sketches by Charles Darwin, who is considered to be the first person to use the metaphor of a tree to represent evolutionary relationships.
Convergent versus divergent evolution
Convergent versus divergent evolution
Phylogenetic analysis using genetic evidence can reveal relatedness obscured by divergent or convergent evolution.
Convergent evolution
Convergent evolution
Convergent evolution is the process in which organisms that are not closely related independently evolve similar features. Adaptions may take the form of similar body forms, colors, organs and other adaptions which make up the organism's phenotype.
Divergent evolution
Divergent evolution
Divergent evolution is the process whereby groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.
Task 7
Task 7
In this activity, you will construct a phylogenetic tree using five homologous DNA sequences from primates. It is useful to print this activity before you begin. Click on the small box that appears in the corner to open in Google Docs.
As always, answers for this task are available here.
Model Organisms
Model Organisms
Model organisms from within all taxonomic groups are used to obtain information that can be applied to species that are more difficult to study directly. Model organisms that have been very important in the advancement of modern biology include:
Bacteria E. coli
Flowering plant Arabidopsis thaliana
the nematode C. elegans
the arthropod Drosophilia melanogaster (a fruit fly)
Chordates including mice, rats and zebrafish.
Watch the YouTube video opposite - it is an excellent review of model organisms. If you use a model organism in your AH Biology project, remember to think about this section into your own introduction. Justify your choice!
Task 8
Task 8
Having watched the video above, now elaborate a bit more on what is meant by "a model organism" and give examples of those that have been used in research. Why are they useful? What might be their limitations? Consider different AH Biology projects - why might you use a model organism? Even consider the classic "effect of inhibitor XX on catalase activity". We are often investigating this because we are interested in the role of catalase in the HUMAN body - why use potato?!?
Suggested answers are available here.
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