This lesson is the second of two that explore cellular respiration and population growth in yeasts. In the first lesson, students set up a simple way to indirectly observe and quantify the amount of respiration occurring in yeast-molasses cultures. Based on questions that arose during the first lesson and its associated activity, students in this lesson work in small groups to design experiments that determine how environmental factors affect yeast population growth.
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- International Technology and Engineering Educators Association: Technology
- G. Brainstorming is a group problem-solving design process in which each person in the group presents his or her ideas in an open forum. (Grades 6 - 8)  ...show
- I. Artificial ecosystems are human-made complexes that replicate some aspects of the natural environment. (Grades 6 - 8)  ...show
- Next Generation Science Standards: Science
- Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms. (Grades 6 - 8)  ...show
- North Carolina: Math
- North Carolina: Science
- Understand the processes, structures and functions of living organisms that enable them to survive, reproduce and carry out the basic functions of life. (Grade 7)  ...show
- Understand the composition of various substances as it relates to their ability to serve as a source of energy and building materials for growth and repair of organisms. (Grade 8)  ...show
- Analyze the relationships between biochemical processes and energy use in the cell. (Grades 9 - 12)  ...show
- Analyze photosynthesis and cellular respiration in terms of how energy is stored, released, and transferred within and between these systems. (Grades 9 - 12)  ...show
- Explain why scientific experiments include controls.
- Describe an example of a controlled experiment.
- Explain the role of variables in scientific experiments.
- State the variable(s) when given a description of an experiment.
- Explain why sample size can be important in a scientific experiment.
Lesson Background and Concepts for Teachers
Body of Lesson
- What is the specific question you are asking?
- How exactly will you try to answer it?
- How many trials will you do?
- How will you report your results quantitatively?
- What will be your control(s)?
- What is your hypothesis?
- "Can we obtain evidence that in the process of respiration, yeast cells convert the sugar in molasses to carbon dioxide and alcohol?"
- Students should be able to describe exactly how the experiment was set up. Important aspects of the design were that the chamber included the elements known to be needed for yeast respiration: a supply of glucose and a wet environment, as well as a way to observe and measure the carbon dioxide given off by respiring yeasts.
- The number of trials done was equal to the number of test chambers set up, since all were set up the same way and exposed to the same conditions. Point out that it is important to have several identical trials in an experiment. Three trials is generally accepted as the minimum number. Multiple trials are needed for several reasons.
- The results were reported in the form of the graphs students prepared, which showed how the sizes of the gas bubbles changed over time.
- The initial experiment had no control. However, it is very important to have one! The control that should have been used would be at least one test chamber set up and treated exactly like the rest but containing no yeast cells. The reason a control was needed was because without it, how could we know that the gas bubble collected did not simply come from a chemical reaction within the molasses? It is possible that the yeast did not respire at all, and what we observed was the product of some other reaction occurring in the solution. If a few control chambers had been used, and no bubbles formed in them, then we could state with confidence that the yeast cells in the test chambers were responsible for the gas bubbles instead of the molasses alone.
- The hypothesis was that the inverted test tube would become filled with a visible gas bubble due to the yeast respiration.
- How To Make Yeast Cells Thrive - Students set up and run the experiments they designed in the associated lesson, Population Growth in Yeasts, using simple yeast-molasses cultures in test tubes.
- What was the specific question the student was asking in this experiment?
- How did she try to answer it?
- How many trials did she do?
- How could she report her results quantitatively?
- What did she use for a control(s)?
- What is a possible hypothesis for this experiment?
Other Related Information
Mary R. Hebrank, project and lesson/activity consultant
© 2013 by Regents of the University of Colorado; original © 2004 Duke University
Engineering K-PhD Program, Pratt School of Engineering, Duke University
Last modified: February 4, 2016