© 1999 ENSI (Evolution & the Nature of Science Institutes) www.indiana.edu/~ensiweb
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WHY DON'T WHALES HAVE LEGS?

A Whale of an Exercise
in Experimental Design

Adapted by S.J. Bedell, ENSI 1992

Edited by J. Irving, J. Armstrong,
T. Evashenk, and D. Parker
ENSI 1992

 

EVOLUTION

 

Adaptations & Contrivances

 SYNOPSIS

Students are given a variety of materials and are asked to design a heat loss experiment that will result in a reasonable explanation of "Why don't whales have legs?"

 PRINCIPAL CONCEPT

Natural selection favors a body design that is energy efficient

 ASSOCIATED CONCEPTS

Science attempts to answer questions by posing plausible explanations (hypotheses) and testing them (trying to disprove them).

Part of the testing process involves predicting results of experiment if hypothesis is correct, AND DIFFERENT results if hypothesis is NOT correct.

Use of models can help to understand natural phenomena

Use of critical thinking skills can help resolve questions about natural phenomena.

ASSESSABLE OBJECTIVES

   Students will....

Propose reasonable hypotheses and design experiments to test effectively those hypotheses.

Provide a reasonable answer to the question posed in the title, based on the hypotheses proposed and the results of the experiments.

 

 MATERIALS

FOR EACH TEAM (OF 2-4)
Container that holds water (e.g., deep plastic tray or large plastic beaker)
1 latex or plastic glove
2 small zip-lock type plastic baggies
1 250 ml graduated beaker
1 Styrofoam cup (large enough to hold full plastic baggie)
hot water (or way to safely heat water)
cold water
thermometer

 TIME

Three 45 minute teaching periods (or two 90 minute periods)
STUDENT HANDOUTS none

 

TEACHING STRATEGY

A very open-ended lab that is student-centered. There is minimal necessity for background information from the teacher. The activity may require direction and interaction by the teacher to keep some student groups on task. The "hint-giving" by teacher will be dependent upon the level of students (i.e., more in life science, less in advanced biology).

The lab is designed to demonstrate the adaptations typical of whales. The latex (or plastic) glove simulates a marine mammal with limbs. The plastic baggies simulate a marine mammal without limbs. The Styrofoam cup simulates blubber.

The goal of the lab is for students to fill the latex glove and baggies with warm water, float them in cold water and measure the rate of heat loss. Students can also put one baggie in the Styrofoam cup to insulate it against heat loss. HOWEVER, students should NOT be told the purpose of the materials as this is a structured inquiry lab. Hints can be given at teacher discretion.

There may be some question about using latex gloves and plastic baggies to represent skin. Will there be a difference in heat loss due solely to the difference in material? May not be significant, but something to keep in mind, something a curious student/team might be encouraged to determine.

WHERE TO USE: This lesson could be used during the introductory unit on the nature of science, providing an experience in doing biological science. It could also be used to bring the process of science into the context of studying variation, natural selection, and adaptations.

 

PROCEDURES

DAY 1:

 TEACHER
1. Distribute materials and ask students to design an experiment that will result in a reasonable explanation of, "Why don't whales have legs?" Instruct students to keep in mind the elements of a good experiment.

2. Circulate and give hints as needed. Approve viable experiments.

Optional Teacher Hints:
- What are the differences between a fish and a whale?
- What are the differences between a giraffe and a whale (and where each lives)?
- A good experiment should have only one variable.
- Why do you have a thermometer?

 STUDENTS

1. Look over materials and consider how they could be used to answer the question.

 

2. Work on plan during class period, bringing it to teacher for approval before end of class.

 

3. If time, students propose additional hypotheses and/or experiments to test them.

DAY 2:

 1. Instruct students to use their plan and materials to do their experiment.

2. Instruct students to prepare brief presentation when they finish doing their experiment (see details for Day 3).

 1. Students do their experiments.

2. If time, consider additional hypotheses and/or experiments to test hypotheses, getting teacher approval before proceeding.

3. When all teams have completed and recorded at least one experiment, student teams begin presenting their work to class, if time (see Day 3 below).

DAY 3:
Each student team briefly presents its hypothesis, the experiment to test that hypothesis (along with results predicted which would support AND not support the hypothesis), the results obtained, and the team's conclusion.

ASSESSMENT

Teacher can prepare a handout out (one per team) which each team can complete as part of a self-assessment, using the following guidelines:

1. Was the experimental design reasonable? Why?

2. Was the execution of the experiment successful? How could you tell?

3. Analysis of experiment:
- a. Did your conclusion support your hypothesis?
- b. Give your instructor a one sentence rationale of "Why don't whales have legs?"
- c. What was the probable intended purpose of the Styrofoam cup?
- d. What is the corresponding function of such a cup in common use?
- e. What is the adaptive advantage of a sea lion's legs?

4, Quality of presentation of procedure, data and conclusions to class.

EXTENSIONS

& VARIATIONS   

1. Analyze other marine animals and their adaptations to the marine environment

2. How would natural selection operate to support the evolution of the fully aquatic mammals such as whales from terrestrial mammals?

3. Consider probing deeper, using the lesson on this site "Becoming Whales", in which students can experience the recent discoveries which have begun to fill the "gap" of missing fossils linking whales to their likely terrestrial antecedents, along with the growing of clues from other fields (molecular phylogeny, comparative anatomy, development, biogeography, etc.) which have been shedding light on whale evolution

 OTHER RESOURCES

See the list of resources for "Becoming Whales" lesson.

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: Unknown; Adapted by Sandra Bedell, ENSI 1992 teacher.

2. Modified by: J. Irving, J. Armstrong, T. Evashenk, and D. Parker (all during ENSI 1992 workshop)

3. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 12/15/97

4. Edited / Revised for website by L. Flammer 3/31/02

 

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