Hands-On Lab: Space Probes

Transcription

1 Hands-On Lab: Space Probes Summary In this activity, students model conditions for life on other planets by testing the growth of yeast under a variety of environmental conditions in various plastic-cup planets. Time Needed Preparation: 10 minutes Activity Time: one 45-minute class period Analysis Time: 10 minutes Extension: one 45-minute class period Objectives By the end of the lesson, students should: Ask a valid question about conditions that support the growth of yeast. Make a valid hypothesis about the effect of one variable on the ability to grow yeast. Test a single variable while keeping all other variables constant. Make accurate qualitative and quantitative observations about the growth of yeast. Explain how at least one variable affects the likelihood of life on other planets. Relate the results of the investigation to The Case of the Lost Space Probes. Identify problems with the investigation and propose modifications to improve the investigation. Materials List Per Group: 5 ml (1 tsp) dry baker s yeast packet 5 ml (1 tsp) sugar packet ( food ) mL medicine cups (for yeast and sugar if packets are not available) 6 clear plastic cups (ideally 6 oz) ( planets ) 100-mL beaker graduated cylinder ruler (metric, need be only 15 cm) submersible thermometer bag of ice (or other source to cool water) 50 ml hot tap water (38 o C 50 o C/ 100 o F 120 o F) 50 ml room temperature tap water (18 o C 24 o C/65 o F 75 o F) 50 ml ice water (as close to 32 o F as possible) 2 insulating Styrofoam cups student planning and data sheets Per Class: 1 insulated water jug for hot water 1 insulated water jug for ice water Note: the narrower the cups are, the more the foam will rise inside them which will make the yeast activity more obvious to young students. If large vials or 50 or 100 ml graduated cylinders are available, these are preferable. Safety Alert Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 1 of 10

2 Students will be using hot tap water. Test the temperature of your water before allowing students to handle it. Do not use water that is hotter than 50 o C (120 o F), as scalding may occur. Preparation Decide how many groups you will have. Ideally, there are 2 4 students in each group and there is at least one group for each variable. If materials allow, have students set up several planets to test different variables against the control simultaneously. 1. Obtain yeast packets, sugar packets, clear plastic cups, Styrofoam cups, ice, hot water (unless room has running hot water), and containers for hot and cold water before class. 2. Test temperature of water in classroom or from most convenient source. The hot water should be above 38 o C (100 o F) but below 50 o C (120 o F). The room temperature water should be between 18 o C (65 o F) and 24 o C (75 o F). 3. Ensure the cups used for planets fit easily in the Styrofoam cups. 4. Make sure other materials (worksheets, thermometers, beakers or graduated cylinders, and rulers) are available for each group before class. You may wish to print additional copies of the planning sheet and record sheet for students who wish to test multiple variables. Background Information for Teachers Life on Earth is possible because of a unique set of conditions that allow organisms on this planet to survive and reproduce. The existence of the sun, the location of the Earth relative to the sun, Earth s size and atmosphere, and the presence of water all contribute to the existence of life as we know it on Earth. Water is one of the most important resources for Earth-based life-forms. Water is available at nearly any point on the surface of Earth primarily because Earth s temperature range allows water to exist in all three of its phases. Without water, life on Earth as we know it would not exist. Astrobiologists have long been fascinated with the possibility of the existence of life on other planets. No clear and indisputable evidence of other life forms has ever been discovered, but there have been recent discoveries of other planets and stars beyond our own solar system. Some scientists are nearly certain that life, possibly intelligent life, exists somewhere else in the galaxy. The International Journal of Astrobiology recently suggested that there could be hundreds to thousands of planets with intelligent life in our own galaxy. Yeast are a kind of single-celled fungi. In a warm, moist environment (around 95 o F), when there is oxygen and a sugar source present, yeast carry out aerobic respiration. This means they use oxygen to get energy from carbon-based compounds. In the process, yeast produce bubbles of carbon dioxide. This is why yeast is used to make bread - the carbon dioxide bubbles help the bread to rise. When growing yeast in the lab, the amount of foam produced by the yeast is a good indication of yeast respiration - the yeast metabolism produces carbon dioxide in the process. The amount of foam on the top of a yeast culture is directly related to the growth of the yeast. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 2 of 10

3 Note about the scenario: If children ask, it is not really possible for spacecraft to have made the round trip to planets outside our solar system within the current history of human space travel. In reality, such a trip would take hundreds if not thousands of years, given present space travel technology. Engage Present the following scenario to the students. The Case of the Lost Space Probes The head of the astrobiology lab was nervously waiting for information from four long-lost space probes. Thirty years ago, ten probes were launched into space. Their purpose was to explore planets beyond our solar system. The probes were designed to look for signs of life. The first six signaled back years ago. All six signaled no life. In the middle of the night, a lab assistant called the astrobiologist to tell her that the lost probes had signaled the lab! It sounded as if each probe was signaling life possible, but the signals were not very clear, and the astrobiologist did not think this was likely. She scanned the rest of the messages looking for clues. What was the environment like on each planet? One probe indicated moderate temperatures but no water. The second probe indicated water, but very low temperatures. The third probe had water but very high temperatures. The last probe had water, moderate temperatures, and energy-rich chemicals in the water. What could all this information mean? Introduce the term extraterrestrial. Extraterrestrial is a term used to describe objects, including possible life forms, that exist outside Earth. Assess Preconceptions and Activate Prior Knowledge: Ask students what they already know about the search for life on other planets. What life-sustaining environmental conditions should scientists be looking for? (not too hot, not too cold, presence of water, food source/energy source) Have students hypothesize about which environmental condition plays the most important role in supporting life. Ask students if they think scientists are really searching for life outside of our own planet. (Yes, they really are.) Is it important to know if there is life out there? (Student opinions may vary.) What would we gain from this knowledge? (Student opinions may vary.) At this point, you may want to show the short Discovery Education Science Library video segment Extraterrestrial Life. Introduce the Activity: Explain to students that they will be exploring the environmental conditions needed to sustain life. They will expose living organisms (yeast cells) to different sets of conditions to determine which conditions allow the yeast to thrive and grow. The different conditions include different temperatures, presence/absence of water, and amount of sugar available for food. Because it is confusing to change all of these at once, it is necessary to change only one of these conditions (called a variable) at a time while holding the others constant. Each variable can be tested systematically this way. Have each group decide on the variable they want to test first. As the activity requires observations over many minutes, they can set up and test a second and a third variable while making observations on their first variable. They will need to complete a different planning sheet for each variable they wish to test. Make sure students understand that in a fair test, they can only change one variable at a time. The other variables must remain the same. For example, in order to fairly test the effect of the presence of water, they must keep the food source and temperature constant. Have students use a new planning sheet for each variable that they test. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 3 of 10

4 Explore Hand out the Student Planning and Data Sheet(s) to each student. You will want to model the procedure below without giving away the results. Also model for students how to use the Student Planning Sheet and data sheet to plan their investigation, make and record observations. Explain that each group will choose one variable to test at a time. They can choose from temperature, amount of sugar or presence of water. Give students the opportunity to work on their planning sheet and allow time to discuss these with individual students. Then have students work in pairs. Have students take turns during each test. For example, one student will set up the planet while the other measures and records the results. The students then repeat the procedure with the roles reversed for the next test. All members of the groups should make observations. Instructions for three trials are provided, but if there is time, students should conduct additional trials, either repeating conditions or using other variables. Structured Option: 1. Organize students into 6 groups. You may wish to have all students conduct all tests. One test can be running while the next is set up to avoid down time. 2. Assign 3 groups (4 students each) to investigate the temperature of the water. Each group would have 3 cups of water with 5 ml yeast and 5 ml sugar. Each group gets the cold, room temperature and warm water. 3. Assign 3 more groups to investigate the amount of sugar. Each group would have a cup of warm water with 5 ml yeast. Group 1 = no sugar; group 2 = 5 ml sugar; group 3= 10 ml sugar. 4. To investigate the effect of the presence of water, a class set of two cups is set up. (There are only two values for this variable: water or no water.) One cup has warm water, 5 ml yeast and 5 ml sugar. The other would have no water, 5 ml yeast and 5 ml sugar. 5. Before students receive their samples, have them complete the Student Planning Sheet indicating which variable they are studying and posing their testable question. Students should also record the conditions of each planet in their Student Data Sheet. (If students are doing multiple variables, they will need a student record sheet for each one.) 6. When students are ready to begin their experiment, pass out the appropriate samples and have students label each cup they receive. Each plastic cup containing a yeast sample should be placed inside a Styrofoam cup to help maintain a constant temperature in the yeast sample. 7. Have students record the temperature of each sample at the beginning of the experiment. Have them make the following qualitative and quantitative observations at the start and every 5 minutes thereafter for 20 minutes: Quantitative observations should include the height of the contents of each cup. Qualitative observations should include any visual observations of bubbling, foaming, and movement of the samples. A final temperature reading should be taken at the very end of every trial. 8. If students are doing multiple tests, they can set up the next test while waiting to make observations from the first test. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 4 of 10

5 As students are conducting their investigations, make sure each group is doing the following, providing support where necessary: testing a single variable, holding other conditions constant (each cup should have the same amount of yeast and water, except for the waterless planet) collecting and recording data accurately making qualitative as well as quantitative observations (students should record any changes in appearance, temperature, and the height of the contents of the cup) reflecting on the design of the investigation as well as the results of the investigation thinking about how the investigation relates to the scenario The Case of the Lot Space Probes Explain 1. Allow groups who investigated the same variable to get together to compare results. Facilitate this process as needed. Discuss the following: How is each variable related to the support of life? (Each variable water, temperature, and energy source is important to life. If any are missing, life becomes impossible.) Which variable seems to be MOST important to support life? (the presence of water; even if energy and moderate temperatures are present, there is no life without water) Which planet showed the most signs of life? (the planet with water, moderate temperatures, and an energy source of sugar) 2. Bring the class back together so that they can share results and explain their results. 3. Apply to the Problem: Read the scenario to the class again. Have students use what they learned to decide which, if any, of the probes have found a place that could support life. Have students decide whether they should announce their findings to the rest of the world. Students should be able to explain the reasons for their decision. Elaborate/Extend Have students consider other variables to test, such as presence or absence of air, high or low pressure, high or low acidity, high or low salt, etc. Students can work out values for the variables, or you can assign values. Similarly, students can work on the design of the experiment, or you can provide the design. See ideas for creating high and low air pressure under Extended Lab in the options below. Evaluate 1. Have students evaluate their investigation. Did the investigation help answer their testable question? (The investigation should help them answer How is each variable related to the conditions for life? and Which variable seems to be MOST important to support life? and Should you let the world know you have found conditions for life?) What about the design worked well? What didn t work well? How might they change the design in the future? (The planet with the water and sugar should show a great deal of activity. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 5 of 10

6 If the tap water is too cool, there may be less activity. If the yeast is very old, it may reduce the amount of activity. If the hot water is only warm, this planet may actually be the first to show signs of activity.) What didn t the investigation tell them? What other variables could they test? (There are many other variables, such as atmospheric conditions and other chemical compounds that could be in the water. Also, planets could be MUCH colder or MUCH hotter than simulated in the classroom. Organisms may be able to adapt to a wider range of conditions than present on Earth.) How was the model like real life? How was it different? How could they make it more like real life? (The model helped to simulate several different environments, but all the environments were very Earth-like. It would be very difficult/dangerous/expensive to truly simulate other planets in the classroom, but it would be possible in a major research facility.) 2. Use the Rubric to evaluate students progress toward achieving the objectives of the lesson. Rubric Objective Full Credit Partial Credit No Credit IN GENERAL Mastery of the Process Partial Mastery of the Process Little or No Mastery of the Ask a valid question about conditions that support the growth of yeast. Make a valid hypothesis about the effect of one variable on the ability to grow yeast. Student came up with a valid scientific question about conditions that support the growth of yeast. Student developed a reasonable hypothesis based on the question and student s prior knowledge. Question was not a valid scientific question or unrelated to life and environmental conditions. Student s hypothesis was not entirely related to the question. Process No attempt made OR question not valid. No attempt made OR hypothesis wholly unreasonable. Test a single variable while keeping all other variables constant. Make accurate qualitative and Student kept all conditions constant while testing a single variable. Student made accurate observations and measurements. Student tested a single variable, but did not keep all other conditions constant. Student made observations and measurements Student did not attempt to control variables. No attempt made. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 6 of 10

7 quantitative observations about the growth of yeast. without adequate accuracy. Explain how at least one variable affects the likelihood of life on other planets. Relate the results of the investigation to The Case of the Lost Space Probes. Identify problems with the investigation and propose improvements. Student demonstrated understanding of variables that affect the likelihood of life on other planets. Student related the results of the investigation to The Case of the Lost Space Probes. Student described at least one problem with the investigation and proposed a reasonable solution. Student did not demonstrate full understanding of variables that affect the likelihood of life on other planets. Student answered questions but did not relate the results to the scenario. Student described at least one problem but did not propose a reasonable solution. Student did not attempt explanation. No attempt made. Student made no attempt to analyze the investigation or design. Options and Suggestions for Differentiation Quick Lab: Have the whole class experiment with a single variable. For example, compare effects of temperature on yeast growth. Alternatively, this can be done as a demonstration. Extended Lab: Students can consider other variables and design ways to test them. For example, students can examine the effects of high pressure on yeast growth by growing cultures in a soda bottle and using a soda bottle pump to keep the environment pressurized. Or students can examine the effect that removing air has on a yeast culture by using a glass bottle and a wine-saver pump (these pumps evacuate air from a container; a glass bottle must be used because plastic bottles will collapse). Students may also design a test to investigate additional variables to find the ideal conditions for this particular life form. Structured Option: Instead of having students choose their own variable to test, assign each group a variable, setting the values of both the variable and controls for the students. Students may also benefit from completing the Virtual Lab Is Anyone Out There? before being introduced to the handson Lab. Open-Engineering Focus: Instead of providing students with the investigation materials and directions, have them brainstorm the materials they would need and design their own activity. Time permitting, once you have evaluated their designs and helped students think through the challenges, Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 7 of 10

8 students will be able to create the activity themselves. Guide students in the design with questions like What could we use to simulate different environments on different planets? How would we measure whether or not the conditions would be good for life? Space Probes Student Planning Sheet Topic of the lab Astrobiology: The Case of the Lost Space Probe Variables (things I can change) temperature, amount of water, amount of sugar Testable question What environmental conditions help to support life? Variable I will test (variable I will change to see what happens) I will change the temperature. Variables I will not test (variables I will keep the same throughout the investigation) I will keep the amount of water the same and the amount of yeast the same. This is a fair test because I am changing just one variable. I am changing the temperature, but I am keeping the other variables the same. Hypothesis (what I think will happen and why I think so) I think that the cup with the sugar and room-temperature water will show the most life because it has more conditions that support life than the other cups. Make a sketch of your setup. Make sure to label each part. Procedures (list of the steps I will take to try to answer the question) 1. Collect cups, yeast, water, and sugar. 2. Add the proper amounts of water and yeast to each cup. 3. Take the temperature of each cup. 4. Record my observations every 5 minutes. 5. Take the temperature at the end of the investigation of each cup. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 8 of 10

9 Data Sheet Test # Variable Being Tested 1 temperature 2 temperature Variables to be kept constant Presence of water; amount of food available Presence of water; amount of food available Start Temp 100 degree s F 32 degree s F Final Temp 90 degrees F 40 degrees F Observations (every 5 minutes) Cloud y Cloud y Cloudy, bubbles Cloudy, no change Cloudy, 2 cm of foam Cloudy, no change Cloudy, 5 cm of foam Cloudy, no change Cloudy, foam overflowing cup Cloudy, no change Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 9 of 10

10 Analysis Sheet Which planet (cup) showed the most signs of life? The cup with sugar and roomtemperature water there was lots of foam. Which variable do you think is most important to the support of life, and why? Water is, because without water, life is not possible. The cup without water showed no signs of life at all. How can the information from this investigation help you decide which planets could support life? Planets that are Earth-like, with water, moderate temperatures, and sources of energy (food) would most likely have life. Discovery Education Science Copyright 2009 Discovery Communications, LLC Page 10 of 10