Classification of Organisms And God said: Let the earth bring forth the living creature in its kind, Cattle and creeping things, and beasts of the earth, according to their kinds. And it was so done.and God saw that is was good. Genesis 1:24-25 Introduction Scientists have an overwhelming task when attempting to classify organisms. Several factors can be considered in separating one organism from another: physical characteristics; mode of locomotion; physiological traits; biochemical analyses; and others. Carolus Linnaeus developed a classification system in the eighteenth century, a form of which is still used today. The Linnaean Classification System formalized the science of taxonomy the science of grouping, describing, identifying and classifying all microorganisms, plants and animals. The Linnaean Classification is hierarchical with the greatest number of subjects in the first group or taxon, and increasingly more specific and narrow in the last group or taxon. Linnaeus also named organisms according to a binomial system and is known as binomial nomenclature. Individual organisms are given a Latin name with two parts. The first Latin name identifies the Genus (and is capitalized). The second name identifies the Species and is specific to the unique organism. For example, the gray wolf has the scientific Latin name, Canis lupus or C. lupus. Learning Objectives: Use of a dichotomous key to classify organisms Sort objects into groups based on similarities Materials Required: From Biology Kit Keys provided Appendices Student Supplied Scissors Experiment Part 1 Using a Dichotomous Key Introduction Many nature field guides have been written to assist the naturalist in identifying specimens encountered in the field. They typically use dichotomous keys. A dichotomous key is used to identify organisms. The word dichotomous is Greek: dikho meaning in two ; and, temnein meaning to cut. A dichotomous key is a flow chart in which a trait is examined, and specimens are split into two distinct groups each time. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
For example, look at the Partial Dichotomous Key for Insects below. This flowchart was used for an insect (pictured to the left) to determine which Order in which it belonged. The, first question asked in the flowchart was Are the wings functional?. The Yes answer led to the second question Are there scaled wing coiled mouthparts?. Here, the No answer led to the third question How many pairs of wings?. When the answer, 3 pairs, was given, the Order could be established as Diptera. By repeating this process with the appropriate dichotomous keys, groups of organisms may be divided into distinct and related categories. Table 1 in the Lab Report is a sample of a dichotomous key used to place insects into Orders. It is identical to the flowchart. Notice that Question #1 asks about the presence/absence of functional wings. You will work with this key in Part 1 below. PROCEDURE Part 1 1. Identify the Order of Sample 1 Place the figure of Sample 1 (found in Appendix A) in front of you Use the Dichotomous Key in Table 1 of the Lab Report Start at 1a and 1b of Table 1 Determine whether 1a or 1b provides the better description Under Your Notes column, note which choices were made Follow the closest match to the next number specified Continue following the key until the Order is identified Record the results in Table 2 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
2. Identify the Order of Sample 2 Place the figure of Sample 2 (found in Appendix A) in front of you Use the Dichotomous Key in Table 1 Repeat the steps that you used in step 1 to identify the insect 3. Proceed to Part 2 Experiment Part 2 Sorting Objects Introduction When scientists sort organisms, they typically place them in categories according to physical characteristics. Those organisms sharing a physical characteristic (or characteristics) will be placed in a group. In this experiment, you will sort fasteners into groups according to similarities in physical features. If you are part of a class, you may want to share your results with others. Note: Be on the lookout for a sample that may have similar physical characteristics, but has a different function from the other objects! PROCEDURE Part 2 Sorting objects 1. Obtain the set of object photographs found in Appendix B 2. Cut out the 18 samples and place them in front of you so that you can see them all The coins are only placed in the photographs to give an idea of size. The objects of interest are NOT the coins! 3. Pick up one sample object Find other samples that seem most similar to the one you have in your hand Place these cut-out objects in a pile clearly separated from the others In Table 3, write down the sample names and the properties shared between them 4. Pick up another sample object from the main pile Find samples that share physical characteristics to this sample Place these in another separate pile In Table 3, write down the sample names and the shared properties 5. Continue sorting until all 18 objects are in a group You do not need to have all rows filled in the table provided It is acceptable to have only one sample in a group 6. OPTIONAL: Share your findings with others in your class 7. Perform Data Analyses and Conclusions 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
The coins are only placed in the photographs to give an idea of size. The objects of interest are NOT the coins! 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
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Lab Report for: # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 YOUR NOTES Table 1: Dichotomous Key to Order of Insects CHARACTERISTICS a. functional wings---------------2 b. without functional wings OR forewings thickened and concealing membranous hindwings------15 a. wings covered with minute scales; coiled tube mouthparts LEPIDOPTERA (butterflies/moths) b. clear wings not covered with scales; mouthparts not a coiled tube------------------3 a. one pair of wings DIPTERA (true flies) b. two pairs of wings---------------------4 a. wings are long and fringed with hair; body length < 5 mm THYSANOPTERA (thrips) b. fringed wing; body length < 5 mm----------------5 a. abdomen with 1-2 thready tails ; small hindwings EPHEMEROPTERA (mayflies) b. abdomen with short or no filaments; larger hindwings-----------6 a. forewings clearly longer than hindwings and with greater area---------------7 b. forewings not longer than hindwings and the same or less area than hindwings ------9 a. forewings hairy; antennae as long or longer than body TRICHOPTERA (caddis flies) b. translucent/transparent wings; not hairy; antennae shorter than body------8 a. tarsi 2 or 3-segmented; body not wasp-like---------------14 b. tarsi 5-segmented; wasp-like HYMENOPTERA (winged ants, bees, wasps) a. head prolonged into a beaklike structure MECOPTERA (scorpion flies) b. head not prolonged ------10 a. short bristle-like antennae; long slender abdomen ODONATA (dragonflies, damselflies) b. antennae not bristle-like; small/moderate eyes------11 a. hindwings broader than forewings; cerci present PLECOPTERA (stoneflies) b. hindwings smaller than forewings; no cerci------12 a. moth-like; hairy, opaque wings; antennae longer than body TRICOPTERA (caddis flies) b. not moth-like; wings not hairy, clear wings; antennae shorter than body--------13 a. wings with few cross-veins; 4-segmented tarsi; length up to 8 mm ISOPTERA (termites) b. wings with numerous cross-veins; 5-segmented tarsi; length up to 75 mm NEUROPTERA (lacewings) a. mouthparts sucking; beak at rear of head HOMOPTERA (cicadas, hoppers, aphids) b. mouthparts chewing; beak absent; body <7mm PSCOPTERA (book lice, bar lice) a. wings absent----------16 b. wings modified; hard, leathery forewings that cover hindwings-------27 a. narrow waist; ant-like HYMENOPTERA (ants, wingless wasps) b. not narrow-waisted--------17 a. body not flattened; usually do not jump----18 b. body flattened; small and jumping SIPHENAPTERA (fleas) a. parasitic; flattened body-----19 b. not parasitic; body not flattened-----20 a. head as wide/wider than thorax head MALOPHAGA (chewing lice) b. head narrower than thorax head ANOPLURA (sucking lice) a. abdomen with appendages; threadlike tails head THYSANURA (silverfish) b. abdomen with neither appendages or tails------21 a. abdomen with forked, tail-like jumping mechanism head COLLEMBOLA (springtails) b. abdomen lacking jumping mechanism---------------22 a. abdomen with 2 short tubes; small and plump body head HOMOPTERA (aphids) b. abdomen without tubes; not plump--------------------23 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 7
23 24 25 26 27 28 29 30 a. lacking pigment; whitish; soft body-------------------24 b. distinctly pigmented; hard body-----------------------25 a. antennae long and hair-like; 2- or 3-segmented tarsi hea PSOCOPTERA (psocids) b. antennae short and bread-like; 4-segmented tarsi head ISOPTERA (termites) a. body shape variable; length > 5mm--------------------------26 b. body narrow; length < 5mm head THYSANOPTERA (thrips) a. antennae 4 or 5 segmented; mouthparts sucking head HEMIPTERA (wingless insects) b. antennae with many segments; mouthparts chewing heorthoptera (cockroaches, walking sticks) a. abdomen with forceps-like cerci head DERMAPTERA (earwings) b. abdomen lacks cerci------28 a. mouthparts sucking; beak elongated------29 b. mouthparts chewing---------30 a. forewings thickened at base and membranous at tip; beak on head HEMIPTERA (true bugs) b. forewings of uniform texture; beak on hind part of head HOMOPTERA (hoppers) a. forewings with veins; forewings over abdomen roof-like at rest ORTHOPTERA (grasshoppers, crickets) b. forewings without veins; forewings meet in straight line down back COLEOPTERA (beetles) Table 2: Results Using Dichotomous Key Specimen Sample 1 Sample 2 Scientific Name 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 8
Group Table 3: Sorting Objects Members (Names of Samples) Shared Characteristics A B C D E F G H I J K *Not all rows need to be used. Data Analysis and Conclusions PART 1 1. Sample 1 of Appendix A a. List the steps you took to place this organism into an Order. 2. Sample 2 of Appendix A a. List the steps you took to place this organism into an Order. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 9
3. Are physical characteristics alone sufficient to place organisms into Orders? Explain. 4. What other methods or features could be used to sort organisms into related groups? 5. What makes a good dichotomous key? Data Analysis and Conclusions PART 2 6. Compare your findings with someone else. Did you place the objects into the same groups? Why do you think there may be differences of opinion in placing organisms into groups? 7. Look at your groups and answer the following: a. Are there large groups that can be split into smaller groups? b. Split one group into two smaller groups and fill out the table below (You only need to do this for one group.) GROUP NUMBER: split into: Subgroup A Members Subgroup A Shared Characteristics Subgroup A Members Subgroup A Shared Characteristics 8. Look at your groups and answer the following: a. Are there smaller groups that can be joined into a larger group? b. Join two groups into one larger group. (You only need to do this once.) c. Which two groups did you join? What are the shared features of the new, larger group? 9. Which objects were difficult to place? Explain. 10. As noted in the lab, all but one sample share a common function. What is this common function? 11. The outlier: a. Which sample did not share the function you described in question 9? b. What is the function of this sample? c. Discuss how this sample may compare with an organism that a scientists has just found in the field. It appears to have some common characteristics with the species he is studying, but many other features appear unique. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 10