Chapter 6. Cellular Respiration

Objectives

Laboratory 6
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By the end of the period, students should be able to:

  1. understand how cells perform cellular respiration.

  2. understand the differences between aerobic respiration and fermentation.

  3. perform an experiment that investigates yeast fermentation.

This lab is modified from a lab in Kitchen Science, written by Shar Levine and Leslie Johnstone. Used with permission.

Background

One of the most important cellular processes that occurs in living organisms is cellular respiration. All living organisms depend on some form of this process in order to produce ATP, the energy currency of the cell. The process of cellular respiration in eukaryotes occurs in the mitochondria where energy from food is converted into the energy rich molecule ATP. This ATP is then used for many cellular processes, including active transport, molecule synthesis, and muscle attachment, basically any process that requires energy. Organisms can use oxygen as the terminal electron acceptor (aerobic respiration) or another terminal electron acceptor (anaerobic respiration) such as iron, manganese, or sulfate (to name a few) in order to produce ATP.

The equation for aerobic respiration is:

C6H12O6 + O2 ⇒ ATP + water + CO2

Photosynthesis converts light energy into chemical energy that is stored in the bonds of the sugars created. We will discuss this process in great detail in next week’s lab. Cellular respiration then converts the energy stored in those bonds to create ATP.

What happens when oxygen is not available to organisms that normally perform aerobic respiration? Some organisms can undergo fermentation. These organisms are known as facultative anaerobes, meaning that they can adapt to their environmental conditions and ferment when oxygen is not available. One of the organisms capable of fermentation is the unicellular, eukaryote yeast, found in the Fungi kingdom. When oxygen is available, the yeast cells use aerobic respiration to produce ATP; when oxygen is not present, they use fermentation to produce a reduced amount of ATP. Both fermentation and respiration require sugar to produce ATP. However, fermentation produces ethanol and carbon dioxide as their waste products.

C6H12O6 ⇒ ATP + alcohol + CO2

How can we measure the rate of cellular respiration or fermentation? If you look at the equations above, you will see that there are several ways, including:

  1. The amount of oxygen consumed (for aerobic respiration)

  2. The amount of sugar consumed

  3. The amount of carbon dioxide produced

The Experiment

In this lab, you will use yeast fermentation to blow up a balloon. Remember that fermentation has carbon dioxide released as a by-product, which is the same by-product released by aerobic respiration.

MATERIALS

  • Balloons

  • Narrow funnel

  • 1 tablespoon (15 ml) active dry yeast

  • 1 teaspoon (5 ml) table sugar

  • Measuring spoons

  • Measuring cup

  • Warm water

  • Fabric ruler

PROCEDURE

  1. Place the bottom of the funnel into the opening of the balloon.

  2. Pour the properly measured yeast and table sugar into the balloon. Then put 1 cup warm water from the sink into the balloon.

  3. Remove the funnel from the balloon and try to remove as much air as possible from the balloon before tying a knot in the balloon.

  4. Measure the circumference of the balloon in cm at its largest point and record on your Hand-in (Table 6.1) as time zero.

  5. Place the balloon on the bench top and wait.

  6. Re-measure the circumference (at the widest part) every minute for 20 minutes and gently shake the balloon before placing back on the bench top.