Name
Date
Class
Lab
?
INVESTIGATION How Can a Key Be Used to
Identify Organisms?
17-1
C
lassification is a way of separating a large group of closely related organisms into smaller
subgroups. The scientific names of organisms are based on the classification systems of living organisms. The identification of an organism is easy with a classification system. To identify an organism, scientists often use a key. A key is a listing of characteristics, such as structure
and behavior, organized in such a way that an organism can be identified.
O BJECTIVES
• Hypothesize how organisms can be identified
with a key.
• Use a key to identify fourteen shark families.
M ATERIALS
goggles
• Examine the method used to make a key.
• Construct your own key that will identify another
group of organisms.
PROCEDURE
1. Make a hypothesis to describe how sharks can
be identified using a key. Write your hypothesis
in the space provided.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
2. Use Figure 1 as a guide to the shark parts used in
the key on page 119.
3. Read statements 1A and 1B of the key. They
describe a shark characteristic that can be used to
separate the sharks into two major groups. Then
study Shark 1 in Figure 2 for the characteristic
referred to in 1A and 1B. Follow the directions in
these statements and continue until a family
name for Shark 1 is determined. For example, to
key a shark that has a body that is not kite shaped
and has a pelvic fin and six gill slits, follow the
directions of 1B and go directly to statements 2.
Follow statement 2B to statements 3. At statement 3A, identify the shark as belonging to
Family Hexanchidae.
4. Continue keying each shark until all have been
identified. Write the family name on the line
below each shark in Figure 2.
5. Have the teacher check your answers.
HYPOTHESIS
Figure 1
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CHAPTER 17 BIOLOGY: The Dynamics of Life
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Name
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How Can a Key Be Used to Identify Organisms?
17-1
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Figure 2
118
CHAPTER 17 BIOLOGY: The Dynamics of Life
LABORATORY MANUAL
Name
Date
Class
Lab
How Can a Key Be Used to Identify Organisms?
17-1
1. A. Body kitelike in shape (if viewed from above) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement 12
B. Body not kitelike in shape (if viewed from above) . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement 2
2. A. Pelvic fin absent and nose sawlike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Pristophoridae
B. Pelvic fin present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement
3
3. A. Six gill slits present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Hexanchidae
B. Five gill slits present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement
4
4. A. Only one dorsal fin present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Scyliorhinidae
B. Two dorsal fins present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement
5
5. A. Mouth at front of head rather than back along underside of head . . . . . . Family Rhinocodontidae
B. Mouth back along underside of head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement
6
6. A. Head expanded on side with eyes at end of expansion . . . . . . . . . . . . . . . . . . . . . Family Sphyrnidae
B. Head not expanded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement
7
7. A. Top half of caudal fin exactly same size and shape as bottom half . . . . . . . . . . . . . . Family Isuridae
B. Top half of caudal fin different in size and shape from bottom half . . . . . . . . . . . . Go to statement
8
8. A. First dorsal fin very long, almost half total length of body . . . . . . . . . . . . . Family Pseudotriakidae
B. First dorsal fin length much less than half total length of body . . . . . . . . . . . . . . . Go to statement
9
9. A. Caudal fin very long, almost as long as entire body . . . . . . . . . . . . . . . . . . . . . . . . Family Alopiidae
B. Caudal fin length much less than length of entire body . . . . . . . . . . . . . . . . . . . . . Go to statement 10
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
10. A. Nose with long needlelike point on end . . . . . . . . . . . . . . . . . . . . . . . . . Family Scapanorhynchidae
B. Nose without needlelike point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement 11
11. A. Anal fin absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Family Squalidae
B. Anal fin present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Carcharhinidae
12. A. Small dorsal fin present near tip of tail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Rajidae
B. Small dorsal fin absent near tip of tail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Go to statement 13
13. A. Hornlike appendages at front of shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Family Mobulidae
B. Hornlike appendages not present at front of shark . . . . . . . . . . . . . . . . . . . . . . . Family Dasyatidae
ANALYSIS
1. What is a classification key and how is it used?
2. List four different characteristics that were used in the shark key.
3. a. Which main characteristic could be used to distinguish shark 4 from shark 8?
b. Which main characteristic could be used to distinguish shark 4 from shark 7?
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17-1
How Can a Key Be Used to Identify Organisms?
A NALYSIS
continued
4. Prepare your own key for the five fish in Figure 3. Use the same format as on page 119.
The family names to be used are the numbers I, II, III, IV, and V. Your key should correctly
use traits that will lead to each fish family. To help you get started, the first statements are
given. Statement 1 divides the five fish into two main groups, based on body shape. Next,
choose another characteristic that will divide the fish not having a tubelike body into two
groups. Continue to choose characteristics that will separate a group into smaller groups.
Write your key in the space below.
Figure 3
1. A. Fish with long tubelike body
B. Fish with body shape not tubelike
Key
1. A.
B.
2. A.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
B.
3. A.
B.
4. A.
B.
CHECKING YOUR HYPOTHESIS
Did your hypothesis describe the key correctly?
FURTHER INVESTIGATIONS
1. Exchange keys with a classmate. Work through it to identify the fish. Is the key correct?
2. The library will have many books that include simple keys to different plants and animals, as well as to
rocks, fossils, and stars. Select a book that includes keys to local plants or animals. Take a walk and
practice using the key to identify some of the organisms that live in your area.
120
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LABORATORY MANUAL
Teacher Guide
17-1 I NVESTIGATION
How Can a Key Be Used to
Identify Organisms?
Objectives
• Hypothesize how organisms can be identified
with a key.
• Use a key to identify fourteen shark families.
• Examine the method used to make a key.
• Construct your own key that will identify
another group of organisms.
Process Skills
observe, classify, communicate, form hypotheses
Time Allotment
1 class period
Materials
goggles (30)
Preparation
none
Teaching the Lab
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Students should work individually.
9. Dasyatidae
10. Scapanorhynchidae
11. Pseudotriakidae
12. Hexanchidae
13. Sphyrnidae
14. Mobulidae
Analysis
1. A classification key is a listing of specific charac-
teristics of a group of organisms. The characteristics are used to divide the groups into smaller and
smaller groups until each organism is identified.
2. Answers include body shape, nose shape, head
shape, presence or absence of fins, number of
gills, and position of mouth.
3. a. presence of anal fin
b. shape of caudal fin
4. Answers will vary. There is no right or wrong
grouping as long as those fish in a group fit the
description of that group. A sample key is shown.
1. A. Tubelike body . . . . . . . . . . . . . . . . . . . 1
B. Body not tubelike . . Go to statement 2
2. A. Two dorsal fins . . . . . Go to statement 3
B. One dorsal fin . . . . . Go to statement 4
• Help students with step 3 of the Procedure.
They should understand the principle of making choices on which the key is based.
3. A. Small mouth . . . . . . . . . . . . . . . . . . . . II
• Emphasize the importance of making the cor-
4. A. Large mouth . . . . . . . . . . . . . . . . . . . IV
rect decision at each step, since one wrong
choice will lead in the wrong direction.
Hypothesis
Sharks can be identified with a key that subdivides
a group into smaller and smaller groups based on
distinguishing features.
B. Large mouth . . . . . . . . . . . . . . . . . . . III
B. Small mouth . . . . . . . . . . . . . . . . . . . . V
Checking Your Hypothesis
Answers will vary. Students who hypothesized that
a key would subdivide the sharks into smaller groups
based on their distinguishing features would say that
their hypothesis is correct.
Data and Observations
1. Rajidae
2. Alopiidae
3. Pristophoridae
4. Carcharhinidae
5. Scyliorhinidae
6. Rhinocodontidae
7. Isuridae
8. Squalidae
LABORATORY MANUAL
ANSWER PAGES BIOLOGY: The Dynamics of Life
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