01 Snails Lab - Santa Monica College

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SNAIL RACES

BACKGROUND
Much can be learned from the study of the common garden snail. For example, many of
us have used the term "slow as a snail." But what do we really mean? Just how slow is a
snail? Today we will have an opportunity to find out by using some of the procedures
involved in scientific investigation. We will also attempt to become more familiar with
the metric system.

WORKING WITH THE METRIC SYSTEM

In a world where most people use the metric system rather that the English system of
measures, it is important for Americans to know both systems, as the following report
illustrates:

MARS PROBE LOST TO SIMPLE MATH ERROR

1 October 1999: NASA lost its $125-million Mars Climate Orbiter because spacecraft engineers
failed to convert from English to metric measurements when exchanging vital data before the
craft was launched, space agency officials said. A navigation team at the Jet Propulsion
Laboratory used the metric system of millimeters and meters in its calculations, while Lockheed
Martin Aeronautics in Denver, which designed and built the spacecraft, provided crucial
acceleration data in the English system of inches, feet and pounds. As a result, JPL engineers
mistook acceleration readings measured in English units of pound-seconds for a metric measure
of force called newton-seconds. "That is so dumb," said John Logsdon, director of George
Washington University's space policy institute. Over the course of the journey, the
miscalculations were enough to throw the spacecraft so far off track that it flew too deeply into
the Martian atmosphere and was destroyed when it entered its initial orbit around Mars. John
Pike, space policy director at the Federation of American Scientists, said that it was embarrassing
to lose a spacecraft to such a simple math error. "I can’t think of another example of this kind of
large loss due to English-versus-metric confusion ... it is going to be the cautionary tale until the
end of time."

PROCEDURES
We will record some preliminary data. Name your snail. Be careful with your choice as
snails are hermaphrodites; each is both male and female. Using the small rulers at your
desk, measure the length and width of your snail’s shell, first in inches and then in
centimeters. The fleshy portion of your snail varies depending on its “mood,” so
measures of the hard shell alone are more objective. Both scales (inch and metric) are
printed on the rulers. The numbered divisions on the metric side are centimeters (the
rulers are about 15 cm in length). Record these measurements in the table provided on the
worksheet at the end of this lab.

Now determine the weight and volume of your snail in metric measures and record the
results in the DATA section of the lab worksheet. Your instructor will show you how to
use a triple beam balance and graduated cylinder for this purpose.

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Science has been defined as "organized common sense." Its purpose is to increase our
knowledge of the natural world. Any question that can be tested may be answered using
scientific methodology. A possible answer to such a question is known as a hypothesis.
Hypotheses that survive repeated, careful testing can be advanced to theories. Let's see
how this works.

The first step is to ask a question. What is the relationship between weight and speed in
snails? Are heavy snails faster than light snails, or are light snails faster than heavy
snails, or.....?? Now propose a hypothesis, a tentative explanation for your question.
What is your hypothesis regarding the relationship between weight and speed in snails?
Write your hypothesis in the space provided on the lab worksheet. We can attempt to
test your hypothesis with an experiment that has become known as the Bio 3 "snail
race."

Place your snail on the surface of the table. Hold the snail in place until the instructor
indicates the start of a race. Each race will last 60 seconds. At the end of 60 seconds,
determine how far your snail has traveled. Snails seldom run in a straight line. Their
curved path can be measured after the race by laying a string over their curved slime trail
and then stretching the string out along a meter stick.

WARM SNAIL RACES

The first race will be repeated five times with the snail’s body temperature at room
temperature. Record the results of each “warm” race in the DATA section of the lab
worksheet. After the fifth race, determine the average distance your snail traveled under
warm conditions. Add all five warm race distances and divide this figure by five. The
result is your snail’s average speed at room temperature in centimeters per minute.

COLD SNAIL RACES

Now we'll propose a second hypothesis and test it. What is the relationship between
temperature and speed in snails? We've termed the first races "warm" because room
temperature is relatively warm for snails. We can now compare these results to those
obtained from "cold" snails under the same conditions. What is your hypothesis for this
experiment? How fast will cold snails travel compared to warm snails?

Snail Races 3

For this experiment, chill your snail down by placing it in a small watch glass containing
crushed ice. The snail must be chilled for a few minutes prior to the first “cold race,” and
again before each of the cold races. Record the results of each “cold” race in the DATA
section of the lab worksheet and calculate your snail’s average cold racing speed.

Contribute your snail’s data to the table your instructor has provided on the whiteboard.
Copy the entire class’ data from the whiteboard to the chart provided in the DATA
section of the worksheet.

Now that we have compiled everyone’s snail data, it is time to process them. This will
involve some simple addition and division. Since you will use pocket calculators, which
provide what appear to be fantastically “accurate” calculations, take a moment to
consider the following points regarding significant figures and rounding off.

SIGNIFICANT FIGURES AND ROUNDING OFF

Your calculator might indicate that your snail’s calculated average speed was, for example,
15.32666 cm per minute. This impressive figure suggests you were able to measure your snail’s
travel distance to the nearest hundred-thousandth of a centimeter! How can you ensure that your
reported values are within your means of accuracy? By noting the accuracy of your measuring
instrument and following the rules for significant figures. The rulers you used to measure snails
could measure only to an accuracy of 0.1 cm, the smallest marks on the ruler (note that other
measuring instruments you have used may have different levels of accuracy). This means that all
calculations from these measurements can be no more accurate that 0.1 cm. For example, if you
divide 48.7 by 5, your calculator will give you 9.74 for an average speed. The 4 (0.04) in this
figure is not a significant figure because it is smaller than 0.1 cm. The 7 that precedes the 4 is the
last significant figure you can report. So what to do with the 4? Disregard it? In this case, yes.
Because 4 is less than 5, 9.74 gets “rounded down" to 9.7. If 9.74 had been 9.76, however, it
would be “rounded up” to 9.8 because 6 is greater than 5. When it comes to rounding off 5s,
alternatively round up and then down as they are encountered.

ANALYSIS
1. Determine the average weight of snails in each of the three size classes. Do this by
separately adding up the weights of all LARGE snails first, then for all MEDIUM snails,
and finally for all SMALL snails. Divide each of these sums by the number of snails in
the respective size class. Record these averages in the spaces provided below the table of
everyone’s snail measurements.

2. Determine the average speeds of large, medium, and small snails when raced at room
temperature. Do this by separately adding up warm speeds for all LARGE snails first,
then for all MEDIUM snails, and finally for all SMALL snails. Divide each of these sums
by the number of snails in the respective size class.

3. As in number 2 above, determine the average speeds of large, medium, and small
”cold” snails.

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4. Plot the average warm and cold speeds of snails on the graph provided in the lab
worksheet. Set the minimum and maximum speeds on the y-axis of this graph according
to the minimum and maximum speeds you actually observed. Plot three dots representing
the average warm speeds. Link these dots together with a solid line. Then plot three dots
representing the average cold speeds and link them together with a dotted line
(independent of the warm race line). Different color inks can also be used rather than
solid versus dotted lines. If you look at the table of data on the whiteboard and then the
graph that you have created from the data, you will readily understand how effectively
graphs can convey the results of a study!

OBSERVATION
Louis Agassiz (1807-1873) said, "Study nature, not books." Objective observation of real
organisms and events is one of the most important aspects of science. Observational
records made by scientists must be methodical, detailed, clear, and as free from bias as
possible. Why? Scientists of the future must be able to study their predecessors’ records
efficiently, and without any misunderstanding. In your lifetime, many species will pass
into extinction with little more known of them than a scientific name and a narrative
description. Observe and describe your snail as if it were the first and last specimen ever
to be known to science. Use a dissecting microscope to observe your snail in greater
detail than your unaided eyes are capable. Your instructor will review the proper use of
this handy tool. More complete instructions for microscope use can also be found in this
manual in the chapter on Microscopic Life. Record your observations in the worksheet at
the end of this lab.

Your description of your snail should be structured. Start by describing the overall
organism; its general shape, length, width, weight, color, surface texture, etc. Then
describe each of the animal’s anatomical regions. With organisms such as a snail that
exhibit cephalization--anterior (head) and posterior (tail) ends--you might logically begin
with the anterior end and continue down the length of the animal. For each region you
should describe such aspects as relative size, shape, color, texture, etc. If you do not
know the biological name for some structures, try to use descriptive analogies, such as
“pear-shaped” or “blood red.” Actual physical measurements are preferred when it comes
to recording the size of an organism or its anatomical features, so make use of the metric
rulers provided. Make a sketch of your snail as you explore its anatomy. The act of
sketching helps focus the mind on anatomical details your eye might otherwise overlook.

An important way to remain objective in your observations is to try not to make
assumptions! For example, if you wrote that “..the snail's eyes are on the tips of two small
stalks on its head" ...you made two mistakes. You assumed that those little black specks
were eyes and guessed that the front part was the head! A more objective statement
might be; “Two small stalks on the top of the snail's front end have tiny black specks at
their tips which might be used for gathering sensory information." And be careful about
using terms that have very specific meanings in biology. For instance, only certain
arthropods (insects and crustaceans) have the segmented head appendages referred to as
antennae. Your snail, however, is a mollusc, and molluscs have fleshy head appendages

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referred to as tentacles.

After you have described your snail’s anatomy, set it down and let it resume its normal
activities. Observe and describe its behavior. How does it move? How are the various
body parts used in locomotion and how are the movements of these parts coordinated?
How does the organism respond to different environmental stimuli such as different
surfaces (e.g., wet versus dry) or contact with various objects (ice, finger, paper, another
snail). How does your snail react to light? To sound? If time permits, you should also
describe how the laboratory environment differs from the organism’s normal habitat and
how this might have influenced your observations.

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