SNAIL RACES WORKING WITH THE METRIC SYSTEM

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1 SNAIL RACES 1 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.

2 Snail Races 2 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?

3 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, 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.

4 Snail Races 4 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 ( ) 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

5 Snail Races 5 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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