Cell Respiration Lab

Cell Respiration and Carbohydrate Processes in a Yeast Lab

Abstract:

This is a lab that demonstrates the reactions with yeast and cell respiration. We tested different carbohydrates to see how much gas it would emit. We found that the more we increased content of glucose and the less complex (disaccharide compared to polysaccharide) they were more quickly used in yeast cell respiration.

Introduction:

Cell respiration is the release of CO₂ and energy from organisms. Cellular respiration can take place in prokaryote and eukaryotic cells. The process of cell respiration involves glucose and oxygen to produce CO₂ and water and ATP energy. The formula for cellular respiration is C₆H₁₂O₆ (s) + 6 O₂ (g) → 6 CO₂ (g) + 6 H₂O (l) + Energy 36/38(ATP). Chemical energy that is released can be stored and used by the organism. There are three main steps in cellular respiration. Glycolysis is when the monosaccharide glucose is split. Glucose which is originally a six carbon sugar gets broken down into 2 sets of a 3 carbon sugar. When this occurs there is a reduction reaction and a hydrogen is gained to form water. 2 pyruvates are also formed, along with NAD⁺, and 2 ATP. The citric acid cycle is the next process sometimes it is known as the Kreb’s cycle. The 2 three carbons that were produced in glycolysis gets converted into acetyl Co A and lose a carbon to co2 in oxidation. The NAD⁺ also gets converted into NADH because it attracts hydrogen and electrons and is a good carrier.  Then the 2 carbon acetyl Co A molecules are added to a 4-carbon molecule to produce a 6-carbon compound, which is the citric acid. This citric acid produced is broken down to from a 4-carbon atom so that it can be used for the next acetyl CoA molecules. The enzymes of NAD and FAD work to remove hydrogen atoms and high-energy electrons from the broken citric acid. These electrons and atoms will move to the next phase, which is the Electron transport chain (ETC). Two more ATP molecules of energy are produced finally. The enzymes NADH and FADH in the inner membrane pass the hydrogen atoms to different protein molecules. They drain the energy slowly from these hydrogen atoms. Some energy is used to create more ATP. Some hydrogen protons get pumped into the inner membrane space and don’t proceed to get transported in a chain like the electrons. In the last step of the chain the electrons are attracted to the highly negative ½ O₂ and hydrogen thus water is formed. When electrons go thru the chain there is a pH increase in the matrix. There is also chemosmosis, which is when the pumped over concentrated hydrogen atoms enter ATP synthase in the membrane and the hydrogen atoms are used with ADP to create more ATP. This process is called oxidative phosphorylation because it is powered by oxygen.

Hypothesis:

If there is more glucose then the rate of the cellular respiration will be higher. The control, which has sugar, will create gas emissions.

Materials:

·      4 test tubes

·      Potato Starch

·      Flour

·      Honey

·      Sugar

·      Salt

·      Yeast

·      Warm Water

·      4 valve stoppers with a tube and syringe attached

Procedure

1)   Collect all the supplies and label the test tubes with what substance you are testing and the control.

2)   For every test tube measure out 1 gram of the different carbohydrates. Then measure out 35 ml of warm water. 0.1 gram of salt is also needed in each test tube. You also need 1 gram of yeast.

3)   Add the water first, but do not add yeast till everything else is in the test tube.

4)   Let it breath for 5 minutes and then set a baseline on the syringe by pulling it back.

5)   Cap the test tubes and push the air in to seal it.

6)   Then in five minutes push the air down gently and let the stopper rise and record the volume of the gas.

7)   Then in minutes intervals push the stopper down again and record the volume.

8)   End after 10 minutes.

Results

Time	Potato Starch	Flour	Sugar	Honey
0	1.6	2	2	1.9
5	2	2	2	3
7		2	3	4.5
8		2	5.3	5.3
9		2	7	6.2
10		2	8	7.6

Conclusion:

We made one error in the potato starch test so we don’t have significant data for that experiment. The seal on the cap kept leaking so gas wasn’t getting recorded in volume. We had to change caps five times to fix it and then we just couldn’t record good data. We managed to get two points for the first five minutes.  The second possible error that could have affected our data is that we added the water last instead of adding the yeast last. Examining the first two data points of the potato starch we can tell that it didn’t have a large reaction with the yeast and the test tube wasn’t as warm as the others, which shows there was less energy released.  We can assume that the points would probably have followed a similar line to the flour. Flour is a type of wheat starch is also a polysaccharide. Which means it is harder to break down in cell respiration and takes longer. Eventually if we left our experiment for longer the cell respiration might have increased in flour because of the lack of oxygen, would force the yeast to use it. We thought that honey and sugar would react because they are both forms of disaccharides. Our hypothesis was correct. The glucose in the sugar control did end up reacting. However if we also left it there less energy would be produced because of used supplies. The honey was already slowing down in the rate of respiration. The test tubes were hot after the reaction, which means that a lot of heat energy was released along with ATP. Using forms of different carbohydrates along with the remaining oxygen we were able to produce that CO₂ that we could measure from cell respiration.