Classification of organisms

C. CONSTRUCTION OF A DICHOTOMOUS KEY

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C. CONSTRUCTION OF A DICHOTOMOUS KEY
Now that you have used a key, you are asked to construct one. In this case, you are going to make a key that will allow you to separate a group of buttons. In each bag of buttons, there are 11 different buttons, labeled from A to K. We have already determined that all the ‘A’ buttons belong to the same species, all the ‘B’ buttons belong to another species, etc. If you look at the individual button groups (all members of type A, for example) you will see that there may be some variability within species as to colour, size and even shape. However, be assured that for all the bags of buttons the individuals labeled with the same letters belong to the same species.
First write your key on a spare piece of paper. You will probably have to make more than one version before you are finished. Start by picking one easily identified characteristic that divides the buttons into two groups. This characteristic should be one that emphasizes an “anatomical difference”. Colour or size are not usually good choices of characteristics, because, in living things (we are making the assumption that the buttons were once living), colour and size may vary depending upon the life cycle. Think of words that clearly and concisely describe the characteristic you have chosen and write these as the first couplet, 1a and 1b, of your key. With the buttons, a good starting place might be:

Buttons with holes through the top/Buttons with no holes through the top.

Another choice might be:

Buttons with two holes in the top/Buttons with more than 2 holes in the top

Or:

Buttons made entirely of metal/Buttons not made entirely of metal.

Or:

Buttons with cloth shank on underside/Buttons with no cloth shank on underside.

These choices are good because they are mutually exclusive, they are either/or. They are dichotomous. They divide the large group into smaller groups of items.
Work carefully and continue to choose and describe the alternatives for further dividing your initial sub-groups into still smaller groupings. The alternative characteristics you choose must be observable and clearly, concisely described, and they should be contradictory so that there is no ambiguity in the choice. When at last you have a group that contains only a single specimen, write its identification letter at that level in the key.
Some general hints about making keys: try to avoid generalities, be specific with your language; try to use positive statements; avoid statements such a “has narrow rim” versus “has wide rim” (who can tell what is narrow and what is wide? - this language is not specific enough.) Also try to avoid overlapping ranges when giving measurements.
When you think you have completed the key, test it by trying to identify one specimen chosen at random. If the key doesn’t work, revise it and clarify it until it is effective.
When you have finalized your key, trade it (your key) with another group of students. This will be a good way to see if the key can be understood and followed by people who did not construct it, as well as a way of testing a different group of buttons with your key. You may find that you need to make some clarifications to parts of your key.

LABORATORY ASSIGNMENT 2
When you are completely satisfied with your key, neatly put the final version of it on loose-leaf so that you can keep a copy. Each person should keep a copy of the key you have constructed.
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LABORATORY ASSIGNMENT 3
Pick any one of the shells you used in this laboratory and make a biological drawing of it. Refer to “BIOLOGICAL DRAWINGS” p. A-8 in your Appendix to assist you. Don’t forget to include a proper title, labels and a scale bar. Have an instructor look at your drawing and make suggestions for improvement. Hand in your completed drawing before you leave today. Be sure to put your name, seat #, Lab section (T, W, Th or F) and your room # (213 or 219) on your paper.
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LABORATORY ASSIGNMENT 4

Be sure that you can answer the questions on page 8-17 and 8-18 of this lab outline.

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D. REPRESENTATIVES OF MAJOR KINGDOMS AND PHYLA
The following is a useful division of the living organisms into 5 Kingdoms and the major taxa within these Kingdoms. This is useful to show the diversity of the living world but is certainly not meant for memorization, although you are expected to know the kingdoms and the phyla of the organisms that you use in the lab. Your text, Campbell et al is now following the three domain system which incorporates the following phyla but stresses different relationships, specifically in the Monera and Protista. (refer to your text book, Chapter 26, pg. 551-552).
KINGDOM MONERA (Now obsolete; 3,000 species) - bacteria and blue-green "algae";

- single, single celled organisms that lack nuclear membranes. The prokaryotes.

Phylum Schizomycetes - the bacteria

Phylum Cyanophyta - blue-green "algae"

KINGDOM PROTISTA (Now obsolete; 37,500 species) - protozoans and algae

- single celled, colonial and multicellular organisms with nuclear membranes. First eukaryotes

The Protozoans

Phylum Sarcodina (ll,500 species) - movement by pseudopodia

Phylum Mastigophora (l,000 species) - movement by flagella

Phylum Ciliata (6,000 species) - movement by cilia

Phylum Sporozoa (3,600 species) - parasitic sporozoans
Eukaryotic Algae

Phylum Euglenophyta (800 species) - euglenoids, Euglena

Phylum Chrysophyta (650 species) - golden, brown algae, diatoms

Phylum Pyrrophyta (l,000 species) - dinoflagellates

Phylum Chlorophyta (7,000 species) - green algae

Phylum Phaeophyta (l,500 species) - brown algae

Phylum Rhodophyta (4,000 species) - red algae
Slime Molds

Phylum Myxomycota (400 species) - true slime molds

KINGDOM FUNGI - yeasts, mushrooms, molds
Phylum Chytridiomycota -

Phylum Zygomycota (250 species ) - common bread mold

Phylum Ascomycota (2,000 species) - yeasts, truffles, Penicillium

Phylum Basidiomycota (5,000 species) - mushrooms, puffballs, bracket fungi

KINGDOM PLANTAE - the plants
Phylum (Division) Bryophyta (23,600 species) - the mosses

Class Hepatophyta (6,500 species) - the liverworts

Phylum (Division) Lycophyta (l,000 species) - the club mosses

Phylum (Division) Sphenophyta (15 species) - the horsetails

Phylum (Division) Pterophyta (l2,000 species) - the ferns

Phylum (Division) Coniferophyta (600 species) - naked-seed plants, the conifers

Phylum (Division) Anthophyta (275,000 species) - flowering plants

Class Monocotyledoneae (50,000 species)

Class Dictoyledoneae (225,000 species)
KINGDOM ANIMALIA - the animals
Phylum Porifera (5,000 species) - the sponges

Phylum Cnidaria (l0,000 species) - jellyfish, anemones, corals

Phylum Platyhelminthes (l0,000 species) - the flatworms

Phylum Nematoda (l2,000 species) - the roundworms

Phylum Rotifera (l,700 species) - multicellular, microscopic; rotifers

Phylum Annelida (l2,000 species) - segmented worms

Phylum Mollusca (50,000 species) - clams, snails, squid, octopus

Phylum Arthropoda (at least 2,000,000 species)

Class Arachnida (55,000 species) - spiders, mites

Class Crustacea (26,000 species) - crabs, lobsters

Class Insecta (at least l,000,000 species) - the insects

Phylum Echinodermata (34,000 species) - sea stars, sea urchins

Phylum Hemichordata (90 species) - acorn worms

Phylum Chordata

Subphylum Urochordata (2,000 species) - tunicates

Subphylum Cephalochordata (30 species) - Amphioxus

Subphylum Vertebrata

Superclass Agnatha (50 species) - jawless vertebrates; lamprey

Superclass Gnathostomata - vertebrates with hinged jaws

Class Chondrichthyes (800 species) - cartilaginous fishes, sharks, rays

Class Osteichthyes (l8,000 species) - bony fishes

Class Amphibia (3,l00 species) - frogs, toads, salamanders

Class Reptilia (6,500 species) - turtles, snakes, alligators

Class Aves (8,600 species) - the birds

Class Mammalia (4,l00 species) - the mammals

LABORATORY 8

ASSIGNMENT 1: IDENTIFICATION OF MOLLUSC SHELLS

Specimen Scientific Name Authority (Common Name)

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LABORATORY 8

ASSIGNMENT 1: IDENTIFICATION OF CONIFER BRANCHES

Specimen Scientific Name Authority (Common Name)

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LABORATORY 8

When you used the keys to the shells or branches, were the alternative choices equally easy

to make all the way through the key? Explain. ______________________________________________________________________
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At what point in the keys to the shells or branches, was size mentioned? Explain why there is limited use of size.

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At what point in the keys did colour become important? Did this pertain to all the specimens?

Why or why not?
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4. If you were given a shell or branch that was not in the key, could the key be fairly easily modified to include it, or would you have to construct an entirely new key? Discuss this briefly.
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In constructing the dichotomous key, when you first divided the buttons into two groups, was

it necessary for the sub-groups to contain an equal number of specimens? Explain.
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5. Evaluation of your key:

When you are making or using any key, you are making certain assumptions about

the key and the organisms involved. What are two of these assumptions?
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The alternatives at each step of the key should be mutually exclusive. Explain what is

meant by this and why it is important.
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