Population Explosion (Yeast Lab) (Day #3 of 3)

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Students will plan and conduct a laboratory investigation that tests the effect of an abiotic or biotic factor on the size of a population of yeast cells.

Big Idea

Populations are able to produce populations of infinite size, but the environment (and its resources) is finite.

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment."

This lesson-planning template is a comprehensive overview of how I approach lesson planning. It includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

With regard to this particular lesson, students will investigate the effect of a chosen environmental factor (e.g. temperature, percent glucose solution, etc.) on the population size of yeast. In doing so, students will begin to understand the relationship between organisms and their environment and ways to create a simple model of a complex system and devise a method for measuring population changes therein.

I hope you get some value from my work!

Anticipatory Set ("Hook")

10 minutes

As students anticipate the outcome of their experiments I like to delve into the predictions that each team has made. Additionally, I reinforce that they are counting not the total number of bubbles in the test tube rather the bubbles that are emanating from the tip of the inverted pipet (the direct product of yeast inside the bulb-end of the pipet).

Quite commonly students make the mistake of counting every single bubble clinging to the inside surface of the test tube which could have been produced by the yeast but it cannot be directly confirmed by eye witness account (specifically during the observational period). I also like to brainstorm possible sources of error that students ought to be aware of avoiding such as bumping or moving the test tubes while counting bubbles, not having multiple sets of eyes on the test tube, etc.

Instructional Input/Student Activities

40 minutes

Teacher note: Use this PPT as a guideline to lead students through these phases of the lab: background context, experimental design, and execution. As you discuss each slide of the PPT, have the students complete their lab handout.

DAY #3 Activities 1: Student teams are typically excited to see the outcome of their experiment after the 24-hour waiting period. Today is when they are to measure the effect of their manipulated (independent) variable in the form of the responding (dependent) variable. Essentially students will count the number of carbon dioxide bubbles that are produced by the yeast in a set period of time. If the time period is too short or too long, students may not see the proper effect of cell respiration by the yeast or they may get bored by counting bubbles excessively. I typically set a time period of 10 minutes. Students are to then enter the data into their data table, produce a bar graph and write the conclusion section of their lab report.

Click here to see video of the lab and here to see a picture.

DAY #3 Activities 2. After all lab teams successfully completed the lab investigation, we gathered as a class and did a round-robin discussion of the various manipulated variables that were chosen, the reasons behind these selections and what information they discovered. Teams that pursued the same factors combined data. Next, we discussed the relationships between the MV (IV) and RV (DV) and I pressed students to argue the effect of their chosen factor by citing supporting evidence from their lab.

Note1: Of course you may choose to extend this lab to a fourth or fifth day is you choose to so to observe a longer time period (per your discretion).


Closure: What did we learn? Where do we go from here?

5 minutes

Finally, students ought to complete the (L) column of the KWL chart that was begun on Day #1.

Samples of student responses:

1. Yeast cells perform cellular respiration when activated.

2. NOS is not very good for yeast!

3. Not only did the lemonade become a positive addition to the yeast mixture, it also aided its growth, rather than harming it.

4. On the first day of our lab we had 4 bubbles in the experimental group and then over days 2 and 3 there were no bubbles in the experimental group concluding that the yeast had died due to the amount of caffeine.