Name: Date: How do we use a Dichotomous Key? Lab # Introduction: All cultures have developed names for the living things found in their environments. When various everyday names are used for the same organism, confusion is possible. So, scientists have developed an international system for naming and classifying all organisms. Identification guides, called keys, have been developed to help all peoples recognize and identify organisms according to their scientific names. The word dichotomous comes from the word dichotomy, meaning two opposite parts or categories. A dichotomous key gives the reader a series of two different descriptions of basic features of an organism. The reader studies the specimen and selects the descriptions that apply to it until reaching a statement that characterizes only one species and names it. In this investigation, you will use a typical dichotomous key to identify the genus and species of several different s. Then, you will create your own dichotomous key to categorize a diverse group of fish. Problem: How is a dichotomous key used to distinguish among similar organisms? Before we begin: Read the entire investigation. Then, work with your group to answer the questions.. How many choices does a dichotomous key provide at each step? 2. What are some (name three) of the apparent differences among the s illustrated? 3. What might be a good strategy for beginning to create a dichotomous key for the types of fish shown in the diagram on pg. 5? 4. If you were to use live fish instead of diagrams, what other characteristics could you use to identify them? List 3:
Procedure: Using a dichotomous key. Examine the drawings of the s in Figure below. You and your group must work together to identify each using the key on pg. 3 (figure 2) 2
2. Use the dichotomous key below (Figure 2) to determine the genus and species of each. Step - Read statements a and b. Step 2 - One of the statements describes the ; the other statement does not. Follow the directions for the statement that applies to that & continue following the correct statements until you have identified it. Step 3- Record the scientific and common name of the in the Data Table on page 4. Repeat until all are named Statement Genus species (scientific name) Common name a Hind limbs absent Siren intermedia siren b Hind limbs present Go to 2 2 a External gills (extend out near where ears would be) present in adults Necturus maculosus mud puppy b External gills absent in adults Go to 3 3 a Large size (over 7 cm long in Figure ) Go to 4 b Small size (under 7 cm long in Figure ) Go to 5 4 a Body background black, large white spots variable (different) in size completely covering body and tail Ambystoma tigrinum tiger b Body background black, small round white spots in a row along each side from eye to tip of tail Ambystoma maculatum spotted 5 a Body background black with white spots Go to 6 b Body background light color with dark spots and/or lines on body Go to 7 6 a Small white spots on black background in a row along each side from b Small white spots scattered throughout a black background from 7 a Large irregular white spots on a black background extending from Ambystoma jeffersonianum Plethodon glutinosus Ambystoma opacum Jefferson slimy marbled b No large irregular black spots on a light background Go to 8 8 a Round spots scattered along back and sides of body, tail flattened like a tadpole Triturus viridescens newt b Without round spots and tail not flattened like a tadpole Go to 9 9 a Two dark lines bordering a broad light middorsal (mid back) stripe with a narrow dark line extending from the head onto the tail Eurycea bislineata two-lined b Without two dark lines running the length of the body Go to 0 0 a A light stripe running the length of the body and bordered by dark pigment extending downward on the sides b A light stripe extending the length of the body without dark pigment on the sides Plethodon cinereus Hemidactylium scutatum red-backed four-toed 3
3. Write the Genus and species along with the common name of each. Salamander Number 2 3 4 5 6 7 8 9 0 Scientific Name Common name 4. Name 4 of the characteristics that you looked at in order to find the names of the s. 5. How is a dichotomous key useful to scientists? 6. How many of the s belong to the same Genus? Which genus is it? 7. What was the main trait that was the difference between s, 2 and 3? 4
8. Prepare a dichotomous key for the five fish in Figure 3. REMEMBER:. Each step should only have 2 options! 2. The options should be about the same characteristic. Instead of ending with the family name for these fish, you should end with the numbers I, II, III, IV, and V. To help you get started, the first pair of statements was given to you. 3. Use the key as a model for creating your fish key 4. Check your key once you have created it by trying to re-identify the fish. A. If the fish has a long, tube like body.... If the fish does not have a tube like body.. 2. A. 3. A. 4. A. 5. Do any of the fish in figure 3 appear to be similar enough to be in the same genus? Explain why or why not 5