Biology Lab 7

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Biology Lab 7

Biology Lab 7Textbook pages: Refer to pages 250-265.Pre-Lab: Identify variables and write out steps of procedure.Evaluation: Written hypothesis, procedure data tables, graph, and conclusion questionsEssential Question: How does a cell release energy with or without oxygen?Introduction:Cellular respiration is a series of metabolic reactions essential to all living cells. Respiration releases energy fromsugars and stores it in the form of adenine triphosphate (ATP). ATP is the basic energy currency for cell processes.Respiration can take place in the presence or absence of oxygen (aerobic vs. anaerobic conditions). Aerobicrespiration produces carbon dioxide and water as the primary waste products. For yeast, anaerobic respiration isknown as fermentation. During fermentation, pyruvic acid (the end product of glycolysis) is broken down andproduces carbon dioxide along with ethanol or lactate as the primary waste products (Campbell and Reece, 2008).Yeast are unicellular organisms that can break down carbohydrates in dough during aerobic or anaerobic respiration.In this lab, students will use the scientific method in a student-designed experiment to explore cellular respiration inyeast. By comparing respiration rates between different water temperature and sugar sources, students can determineoptimal conditions for yeast respiration. An environment that is too cold, too hot, or lacking in food will result inlowered rates of respiration or death.When yeast is respiring, either aerobically or anaerobically, foam (bubbles) accumulates on top of a yeast solution.What do you think the foam (bubbles) is made of? In your groups, it is your job to figure out what the best conditionsare for yeast to perform respiration.ObjectivesStudents will…1. Understand the basic concepts of aerobic cellular respiration and fermentation2. Understand the scientific method, and how to apply it3. Practice how to design a controlled lab experiment4. Practice measurement skills using thermometers and measuring devices5. Practice recording scientific data and graphing results6. Practice drawing conclusions based on data analysisMaterials:1.25 mL measuring spoon yeast - use 1.25 mL measuring spoon for yeast only2.5 mL measuring spoon sucrose (table sugar) – use 2.5 mL measuring spoon for sucrose only5 mL measuring spoon mashed up strawberries – use 5 mL measuring spoon for fruitgraduated cylinder for waterpossible alternative sugar sources (syrup, honey, corn starch, Splenda®)test tube rack with 4 test tubes room temperature water (~20°C) and/or warm water (~30°C)thermometerrulerExperimental DesignIn order to do this experiment, you will need to dissolve a small, specific amount of yeast in a few milliliters of water.You can use room temperature water or warm water from the tap. Depending on your hypothesis, you can then addspecific amounts of sugar, fruit or alternative sugar (or a combination) to some of your yeast solutions.Create a Google doc for your lab group to record your work. Title your Google doc “Respiration in Yeast” andthe last names of each of your group members and your block #. Share the Google doc with your teacher.Example: Respiration in Yeast Evashenk Yi Block 1Problem: What are the ideal conditions for yeast respiration? Discuss this as a group; decide what materials you willuse, and develop a hypothesis based on those materials. Write your hypothesis in your Google doc


Variable identification – add this information to your Google doc:Identify your independent variableIdentify your dependent variableFor this, use the ruler to measure the amount of foam (bubbles) that accumulates above your yeast solutionafter 5, 10, and 15 minutes. Measure from top of yeast solution to the top of the foam.Identify your experimental group or groupsIdentify your control groupControlled variables: In a controlled experiment (fair test) all other factors should be kept the same so that you canfairly compare the results from the control group and the experimental group.List three controlled variables - factors that were kept constant in both of the setups for this experiment.Procedure: Record the specific steps of your procedure in your Google Doc as you run your experiment.Set up your experimentData: Create a data chart with the appropriate number of rows for the number of test tubes that you use in yourexperiment. Write a caption for your data table.Height of foam in test tube in millimetersContents of test tube 0 minutes 5 minutes 10 minutes 15 minutesCaption:Analysis Questions: While your experiment is in progress, answer the following analysis questions1. What are the end products of photosynthesis?2. What substances from photosynthesis do cells use to respire? (Do you see the connection!?)3. Why do cells respire? (What product of respiration is useful to the cell?)4. In this experiment, why would measuring the height of the foam (bubbles full of a particular gas) tell usabout yeast’s respiration rates (Hint: what are in the bubbles)? Explain.5. Why do you think we use yeast to make bread? Explain.6. Why do you think we use yeast to make wine? Explain.Results and conclusions:7. Once your data is collected, create a line graph that clearly shows your results.8. In your experiment, what was the ideal condition for yeast respiration?9. Do your results support your hypothesis? Why or why not?10. Describe two specific things that you could have done to improve the reliability of this experiment.Clean up: pour the contents of the test tubes down the sink; use a test tube brush to thoroughly clean your test tubes;invert the test tubes on the pegs of the test tube rack; wash and dry your any measuring spoons you used; clean up anyspills and wipe your lab table with a damp paper towel; set up your lab table for the next group

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