Lab 9 Cellular Respiration and Fermentation



Cellular Respiration and Carbon Dioxide Production

Pre-Lab Reading

All organisms must have a continual supply of external energy in order to maintain bodily functions and to combat entropy. Ultimately this source of energy is the sun. As you learned in the previous lab, plants can convert the sun’s energy into usable forms of chemical energy (E.g., glucose). In order for the energy to be made useful the chemical bonds that hold the atoms of these molecules together must be broken. The released energy is captured by high-energy phosphate bonds and combined with adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), which is the energy currency of the body.

There are two processes that release this energy from the photosynthetic materials to form the energy molecule ATP. Those processes are cellular respiration and fermentation. Cellular respiration is an aerobic (requires oxygen) process, while fermentation is an anaerobic (occurs without oxygen) process. There are 2 types of fermentation: lactic acid and alcohol fermentation.

When compared to fermentation, the formation of ATP via cellular respiration is a relatively efficient process, as there are 36-38 ATP molecules formed per glucose molecule. Fermentation on the other hand only generates a net of 2 ATP molecules. This may bring up the question of why the body would even bother with fermentation and not just stick with the high-energy process of cellular respiration. Recall that ATP is the body’s energy currency and energy is needed for the body to continue all of its metabolic processes. Now recall that cellular respiration requires oxygen. During times when the body is in oxygen debt (I.e., there is little oxygen available for metabolic processes) the cell still needs energy and therefore it uses its next best option for energy production and proceeds with fermentation. There are two forms of fermentation, lactic acid and alcoholic fermentation. In today’s lab we will investigate alcoholic fermentation by yeast. The carbon dioxide produced by the yeast as waste product during fermentation collects in the fermenting liquid and makes it fizzy. In producing bakery products the carbon dioxide caused the bread to rise as small air (carbon dioxide) pockets are formed and the alcohol is evaporated during the cooking process.

The equations for cellular respiration, lactic acid fermentation, and alcoholic fermentation are listed below:

Cellular Respiration

C6H12 O6 +6O2 6CO2 + 6H2O + ATP

Alcoholic Fermentation: used to make beer, wine, bread

C6H12O6 2CO2 + 2 alcohol + ATP

Lactic Acid Fermentation: used to make yogurt and in muscle cells

C6H12O6 2 lactic acid + ATP

Pre-lab Questions:

1. Where is energy captured and stored by photosynthesis?

2. Name the two processes that release the energy from ATP.

3. What is the main difference between respiration and fermentation?

4. Contrast the number of ATP released from respiration and fermentation.

5. Contrast the equations for respiration and fermentation.

6. How is the product from lactic acid fermentation different from alcoholic fermentation?

7. How is fermentation used in bakeries?

In this exercise you will determine if different carbohydrates are fermented by yeast at the same rate. Glucose is a monosaccharide and is the primary carbohydrate energy source for the cells of many organisms. Sucrose (table sugar) is a disaccharide that is composed of the monosaccharides glucose and fructose. Starch is a polysaccharide composed of many glucose subunits and acts as the primary energy storage of plants. In this lab we will be testing to see of fermentation of glucose and starch occur at the same rate.

Make a hypothesis:

Procedure:

1. Place 1/8 teaspoon of yeast in each of the three test tubes.

2. Place 10 mL of water in test tube E.

3. Place 10mL of sugar solution in test tube A.

4. Place 10 mL of starch solution in test tube B.

5. Place 10 mL of brown sugar solution in test tube C.

6. Place 10 mL of sucralose solution in test tube D.

7. Add 5 drops of bromothymol blue to each test tube.

8. Observe and record the time that it takes for each test tube to turn yellow.

Test tube A: ________ min B: _________ min C: ________ min

D: ________ min E: _________ min

Clean up your lab table and equipment.

Questions to answer

1. Did all of the yeast produce a similar color change?

2. Which carbohydrate was fermented by the yeast at the highest rate? Slowest rate? Explain why for each

3. Did the results support or refute your hypothesis? Explain.

4. What is the independent variable?

5. What is the dependent variable?

6. Do you suspect the rate of fermentation would have occurred at a different rate if the temperature was different? If yes what would you hypothesize about the rate of fermentation at a cooler temperature? At a warmer temperature?

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download