using and Constructing a dichotomous KeyDichotomous keys can be used to help identify and classify a set of unfamiliar organisms. In a dichotomous key, paired statements off er choices about the presence or absence of specifi c characteristics.

PurposeTo use a dichotomous key to classify fi sh belonging to the taxonomic class Chondrichthyes and to construct a dichotomous key to identify insects

Procedure: Part Ausing a dichotomous Key 1. Use Figure 1 as a reference to help you identify the

body structures of cartilaginous fi sh (fi sh with a non-bony skeleton) referred to in the dichotomous key.

2. Th e observations for Part A of this activity are below (Figures 2 to 7). Carefully examine the images.

3. Use the dichotomous key (Table 1) to identify the cartilaginous fi sh in Figure 2. Start by reading Step (i) of the key. Select the statement in Step (i) that matches the features of the fi sh you are trying

dorsal (upper) surface

ventral (lower)surface

mouth

pectoral �n

dorsal �n

tail �n

anterior

posterior

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Figure 1 Body structures of cartilaginous fi sh

to identify. Th en follow the “Go to” direction that corresponds to that statement. Continue making choices until you have identifi ed the fi sh. Be sure to record the taxonomic order of each fi sh.

4. Repeat Step 3 for each of the fi sh shown in Figures 2 to 7.

observations: Part AUse the following images and descriptions of cartilaginous fi sh as your observations for Part A.

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Figure 4

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Figure 3

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Figure 2

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Figure 6

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Figure 7Figure 5

chApter 1 investigations

SKILLS MEnu

• Questioning• Researching• Hypothesizing• Predicting

• Planning• Controlling 

Variables• Performing

• Observing• Analyzing• Evaluating• Communicating

Investigation 1.2.1 oBserVAtionAL stuDY

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NELNEL32 Chapter 1 • Understanding Biodiversity

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Chapter 1 Investigations 33

Table 1

Dichotomous Key to Selected Cartilaginous Fish

i. body with flat dorsal and ventral surfaces ........order Myliobatiformes ....body not noticeably flattened ...........................order Selachii..................

ii. mouth opens anteriorly ...................................................................... manta ray

mouth located on ventral surface ........................................................... go to iii

iii. tail relatively stocky without a stinging spine ............................. barndoor skate

tail slender and whip-like with stinging spine ....................................... stingray

v. mouth gaping, no prominent teeth ............................................... basking shark

mouth moderate in size, many large cutting teeth .................. great white shark

go to iigo to iv

iv. head dramatically flattened and wide ...........................................hammerhead

head not dramatically flattened ............................................................. go to v

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Procedure: Part BConstructing a dichotomous Key 5. The observations for Part B of this activity are shown

in Figures 8 to 13. Working with a partner, decide on a creative binomial species name for each of the insects shown.

6. Create a dichotomous key that could be used to identify each species in Figures 8 to 13.

7. Exchange your dichotomous key with another group in the class and use each other’s keys to properly identify the species according to the other group’s assigned names.

observations: Part BUse Figures 8 to 13 as your observations for Part B.

Analyze and Evaluate(a) List all the features, or characteristics, that you used

in Part A to distinguish the fish from each other. K/u(b) Do you think the same features you listed in (a) could

be used in a key to identify all cartilaginous fish? Explain your reasoning. K/u T/I A

(c) How might a biologist benefit from using a dichotomous key with more detailed “choice statements”? K/u T/I A

(d) In Part B, how successful were the dichotomous keys created by your group and other groups in the class? If the keys were not successful, suggest one or two reasons why. K/u T/I

Apply and Extend(e) Once biologists correctly identify an organism, they

can research the species to see if it might be of special interest. Use online resources to learn more about the barndoor skate and the manta ray, two types of cartilaginous fish. Why might a biologist be particularly interested in one or both of these species? K/u T/I A

(f) Some species are easier to identify than others. Suggest some reasons for this. Brainstorm several species that you think are most difficult to tell apart. T/I A

(g) Research the scientific names for each of the insect species in Part B. As part of your research, give the English meaning of each Latin name. T/I C

Figure 11 Figure 12 Figure 13

Figure 9 Figure 10Figure 8

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Sampling the diversity of Life

Scientists have identified close to two million different species on Earth. Although some living things are easy to find, many are difficult to identify. Organisms come in all shapes and sizes: some are large and mobile; others are microscopic in size and difficult to see. The varied characteristics of organisms make field collection and identification a challenging task.

In this field study, you will choose a number of techniques to sample organisms from a chosen ecosystem. You will then use dichotomous keys and field guides to identify specimens.

PurposeTo collect and identify living organisms using appropriate sampling techniques and equipment

Study designIn a group, you will use a variety of techniques to sample organisms from an ecosystem of your choice. Before beginning your field work, investigate what sampling techniques are available to you and gather the necessary equipment. Note that some species, such as birds, may be identified in the field through direct observation.

There are many inventive sampling techniques available for collecting different types of organisms. For example, various sizes of nets, dredges, and minnow traps can be used to sample an aquatic environment. Pitfall and sticky traps, sweep nets, and even black lights may be useful for collecting terrestrial insects. Some interesting traps can be made at home (Figure 1). Most plants can be sampled using just a pair of pruning shears.

Figure 1 Many insect traps, such as this malaise trap, can be made at home.

You must consider how you will handle and observe your specimens. Will you capture live specimens and

bring them back to the lab for identification? Will you attempt to identify some or all of your specimens in the field? Remember to respect the ecosystem you are working in—be gentle with the plants and animals you collect, and if possible return them to where you found them. Do not collect more than you need to.

You will also need an appropriate set of field guides and/or dichotomous keys to use in identification.

Equipment and Materials• approvedsamplingequipment• equipmentforsafehandlingoforganisms,suchas

gloves and suitable containers• dissectingmicroscopes,magnifyinglenses,and

binoculars as needed• markersandtags• fieldguidesanddichotomouskeys• notebookandpencil• digitalcamera(optional)

Procedure 1. As a group, decide on a suitable sampling location to

conduct your field study. If you are not going as a class, obtain your teacher’s approval before finalizing your plans.

2. Research sampling devices that are available for collecting specimens from an ecosystem such as the one you have chosen for your field study. Choose two or more methods that you will use in your field work.

3. Seek approval from your teacher before acquiring or constructing the necessary equipment.

4. Organize all the equipment and materials you will need to take into the field. Be prepared for poor weather, strong sun, and the possibility of biting flies.

5. When you arrive at your chosen field location, be sure to orient yourself and inspect your surroundings. Note any potential danger or safety hazards. If necessary, adjust your plans to avoid them.

Alert your teacher if you have any medical conditions that may be affected by your field work.

6. Perform your field work, being careful to avoid contact with potentially irritating organisms.

SKILLS MEnu

• Questioning• Researching • Hypothesizing• Predicting

• Planning•  Controlling 

Variables• Performing

• Observing • Analyzing• Evaluating• Communicating

Investigation 1.4.1 FieLD stuDY

NEL34 Chapter 1 • Understanding Biodiversity

7380_UNIT01_pp002-043.indd 34 12/30/10 12:11:35 PM

Handle all organisms with care. Some animals can bite or sting. Many plants are toxic if ingested or may trigger an allergic reaction. Learn to recognize and avoid poison ivy and giant hogweed (Figure 2). Do not taste any of the samples you collect. Your teacher will provide safety instructions specifi c to your chosen site.

Figure 2 (a) Poison ivy produces an oil that can be extremely irritating. Avoid contact. Poison ivy has leaves in the form of three shiny almond-shaped leafl ets. (b) Giant hogweed is a large plant with big, deeply divided leaves. Its clear watery sap can cause severe irritation, burns, and scarring.

(a) (b)

7. Record the time and location of the specimens you collect, noting any unusual circumstances. When possible, consider photographing or making sketches of your specimens and releasing them unharmed. Th ese are your “collection notes.” Be sure to label each specimen so that it can be matched to your collection notes.

8. If possible, document all of your work with a digital camera. Photograph your sampling equipment setup and your sampling locations. Keep detailed notes of your activity in a fi eld notebook. If a camera is not available, sketch your location and equipment in your notebook.

9. Use fi eld guides and/or dichotomous keys to identify your specimens to the lowest taxa you can. Do this in the fi eld or back at the lab.

10. Consider creating a website to post and share images of your specimens. A website could be used to collaborate on the identifi cation of species with students in other classes or even other schools.

observationsWhen making your collections and identifi cations, be sure to accurately record all of your observations in an appropriate format. Include information about the time and location each specimen was collected as well as the collection method you used.

Analyze and Evaluate(a) Prepare and submit a complete write-up of your fi eld

study. Your write-up should include (i) a detailed description of your location and

sampling methodology (ii) photographs and/or illustrations of your location

and the sampling equipment in the fi eld(iii) a specimen list and images, if available, including

the name or taxon, sampling method, date, and location

(iv) a discussion section in which you describe your fi eld experience studies, being sure to describe the successes and challenges you faced and including recommendations for future fi eld work T/I C

(b) Discuss your sampling techniques with other groups. What successes and diffi culties did they have? Which new techniques would you like to try if you repeated this activity? Summarize your fi ndings in your notebook. T/I C

Apply and Extend(c) Why do you think it is necessary to use a wide variety

of sampling equipment to assess the diversity of an ecosystem? T/I

(d) Do you think there is a bias in a biologist’s ability to sample living organisms? Do you think all types of organisms are likely to be fairly represented in fi eld collections? Explain your thinking. T/I C

(e) Which kinds of organisms do you think are most diffi cult to identify? Why? T/I

(f) New species are continuously being discovered. Use the Internet and other available resources to fi nd out about some of the most recent discoveries of new species. Report your fi ndings back to the class. T/I C

Chapter 1 Investigations 35NEL

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