1. Why Is Cellular Respiration Necessary For Living Organisms

Question: Why is cellular respiration necessary for living organisms?

Answer: Cellular respiration allows for organisms to break down molecules in order to release the energy stored in the bonds in order to generate ATP which the cell can then use for its normal processes.

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Question: Why is fermentation less effective than aerobic respiration?

Answer: Fermentation is less effective because it does not have the capacity to completely break down the glucose molecule and therefore can only contribute to the production of two ATP molecules (via glycolysis), as opposed to the 36 produced during aerobic respiration (two molecules via glycolysis and 34 via the citric acid cycle).

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Question: What is the purpose of glycolysis?

Answer: Glycolysis starts the process of breaking down glucose. This takes place in the cytoplasm and can occur in the presence OR absence of oxygen. In glycolysis, glucose (a 6-carbon sugar) is broken down to 2 pyruvic acids (3-carbon sugars). A small amount of ATP is produced in the process, but more importantly the pyruvate is then available for other metabolic reactions.

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Question: In the Fermentation by Yeast lab, did you notice a difference in the rate of respiration between the various sugars? Did the artificial sugar provide a good starting material for fermentation?

Answer: The sucrose and sugar solutions should show the highest rates of respiration, followed by Splenda©, glu-cose, and then Equal©. Students should note that Splenda© does much better than Equal©. However, in general the sucrose provides the best starting materials.

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Question: Would you expect to find CO2 in your breath? Why?

Answer: Yes. Human cells metabolize sugars in the same way as beans, causing a release of CO2 . This CO2 is transferred to the blood stream, travels to the lungs and is exchanged for O2 in the lungs, thus you would expect to find CO2 in your breath.

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Question: Was anaerobic fermentation occurring in the Fermentation by Yeast experiment? How do you know (use scientific reasoning)?

Answer: Yes. The size of the air bubbles increased during the experiment - carbon dioxide was being created by the fermentation of the yeast cells.

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Question: If you observed respiration in the Fermentation by Yeast experiment, identify the gas that was produced. Suggest two methods you could use for positively identifying this gas.

Answer: Carbon dioxide is a byproduct of anaerobic respiration, and is the gas that inflates the balloons. Students can positively identify the gas with a meter connected to a computer, or by using Phenol Red or Bromo-thymol Blue, CO2 indicators and another O2 indicator to prove O2 is not elevated compared to normal levels.

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + enough energy to make 38 ATP

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Question: Hypothesize why some of the sugar or sweetener solutions in the Fermentation by Yeast experiment were not metabolized, while others were. Re-search the chemical formula of Equal© and Splenda© and explain how it would affect yeast respiration.

Answer: Interestingly, while yeast cannot metabolize artificial sweeteners like Equal ®, many of these sweetener packets contain small amounts of real sugars (dextrose) as a stabilizer, and so the balloons will inflate a little bit when the artificial sweeteners are used— this is a very surprising result!

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Question: How do the results of the Fermentation by Yeast experiment relate to the role yeast plays in baking?

Answer: In baking, yeast is used as a leavener in bread to make the bread fluffy and light. When mixed with flour and water, the yeast is activated by the water and begins to metabolize the sugars found in the flour (flour is ground wheat, wheat contains sugar). As the yeast metabolizes the flour sugar, CO2 is released which creates air pockets in the bread. These pockets will expand when the dough is placed in the oven and will be trapped as the dough bakes, creating fluffy bread.

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Question: What would you expect to see if yeast cells metabolism slowed down? How could this be done?

Answer: The amount of gas produced in the time allotted would decrease. This could be achieved by altering the temperature at which the reaction takes place, the amount of simple carbohydrates present, or the use of complex carbohydrates that the yeast would first have to break down enzymatically before metabolizing.

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