Cell Respiration Lab: How Honey Effects Yeast

Abstract: In this lab, we will observe the effect of honey on the process of cellular respiration performed by yeast. Sugar influences cell respiration greatly. Yeast can convert sucrose into glucose and use it during respiration. The most sugar in the test tube will create the greatest concentration of CO2 gas from respiration.

Introduction/Background

In this lab, we experiment with yeast. Yeast is a type of fungus that relies on sugar to provide it with energy so it can grow. Like bacteria, yeast can grow in or on their food source. Once they absorb the sugar, they can break down the molecules into monosaccarides and create ATP (energy). This process is called cellular respiration. Yeast can convert sucrose and fructose into glucose and use it during respiration. The first step of respiration is Glycolysis which occurs in the cytosol. Glucose (6 carbon sugar) is broken down into pyruvate (3 carbon molecule.) The second step is the Krebs cycle that takes place in the mitochondria.This is where the cell generates chemical energy (ATP) from oxidation of pyruvate. The last step is Oxidative phosphorylation which occurs in the inner mitochondrial membrane. This is when large amounts of ATP are released. In cases where there is no oxygen to perform glycolysis, yeast goes through the process of fermentation which makes it possible for ATP to be produced without oxygen. Fermentation regenerates NAD that is needed to take part in glycolysis, allowing it to create more ATP. These processes are necessary for life. Yeast produces carbon dioxide from the break down of glucose. In the lab, we add honey to the yeast. There are 3 monosaccharides that make up honey: fructose, glucose, and sucrose.

Hypothesis: Since honey has sugar in it, if it is added to the yeast, the yeast will convert the sucrose and fructose into glucose during respiration. The most honey in the test tube will create the greatest amount of CO2 gas from respiration.

Materials:

4 tubes

4 CO2 measuring pumps

Yeast

Sucrose

Warm water

Salt

Honey

Timer

Procedure:

1. Set out 4 tubes and each tube add 1g yeast, 1g sucrose, and .1g salt

2. Add warm water to all of the tubes and honey to 3 of the tubes

Tube #1- 35 mL water

Tube #2- 34 mL water, 1 mL honey

Tube #3- 32 mL water, 3 mL honey

Tube #4- 30 mL water, 5 mL honey

3. Cap the tubes and shake them all at the same time

4. After it is dissolved, uncap the tubes and let the tubes sit for 5 minutes.

5. Plug each tube with a CO2 measuring pump. Make sure the pump is set at 2 mL.

6. Every minute, mark where the base of the pump is at.

Results: CO2 Measuring Pump- Recording of each tubes CO2 every minute

Conclusion: Yeast needs glucose to perform cellular respiration. The more glucose there is, the higher energy supply there is for respiration, and the more carbon dioxide produced. So, since honey is mostly made of sugar, the tube that had the most honey (#4 had 5 mL of honey) skyrocketed up the measuring scale. Our control (#1) only had the 1g of sucrose which allowed it to get up to 3.7 mL of CO2. Test tube #2 had 1 mL of honey and went up to 4.2 mL of CO2. Test tube #3 had 3 mL of honey and went up to 5.8 mL of CO2. As you can see, sugar majorly influences the rate of cell respiration in yeast. Our control was tube #1 and the variable was the honey. A potential source of error would be not uncapping the tubes which would not let the yeast get any oxygen to perform glycolysis.