Cellular Respiration Research Paper
4. The cell’s supply of ADP, Pi, and NAD+ is finite (limited). What happens to cellular respiration when all of the cell’s NAD+ has been converted to NADH?
If NAD is unavailable, the cell is unable to conduct any processes that involve the conversion of NAD+ to NADH. Because both glycolysis and the Krebs cycle produce
NADH, both of these processes shut down when there is no available NAD+.
5. If the Krebs cycle does not require oxygen, why does cellular respiration stop after glycolysis when no oxygen is present?
When no oxygen is present, oxidative phosphorylation cannot occur. As a result, the
NADH produced in glycolysis and the Krebs cycle cannot be oxidized to NAD+.
When no NAD+ is available, pyruvate cannot be converted to the …show more content…
6. Many organisms can withstand periods of oxygen debt (anaerobic conditions). Yeast undergoing oxygen debt converts pyruvic acid to ethanol and carbon dioxide.
Animals undergoing oxygen debt convert pyruvic acid to lactic acid. Pyruvic acid is fairly nontoxic in even high concentrations. Both ethanol and lactic acid are toxic in even moderate concentrations. Explain why this conversion occurs in organisms.
As noted in question 4, when no NAD+ is available, even glycolysis stops. No ATP will be produced and the cell (or organism) will die. The conversion of pyruvic acid
(pyruvate) to lactic acid (or ethanol) requires the input of NADH and generates
NAD+. This process, called fermentation, allows the cell to continue getting at least
2 ATP per glucose.
7. How efficient is fermentation? How efficient is cellular respiration? Remember that efficiency is the amount of useful energy (as ATP) gained during the process divided by the total amount of energy available in glucose. Use 686 kcal as the total energy available in 1 mole of glucose and 8 kcal as the energy available in 1 mol of ATP.
Efficiency of fermentation
8 kcal/mole of ATP ϫ 2 ATP ϭ 16 …show more content…
a. Why could we call photorespiration a “mistake” in the functioning of the cell?
Photorespiration could be called a “mistake” because under high O2/CO2 conditions, rubisco breaks down glucose into carbon dioxide and water but no useful energy is gained.
b. Rubisco is thought to have evolved when Earth had a reducing atmosphere. How does this help explain the photorespiration “mistake?”
When the first photosynthetic organisms arose, the early Earth’s atmosphere contained little, if any, oxygen. Rubisco would have functioned very well under these conditions. It was only later, when the concentration of oxygen in the atmosphere increased considerably, that rubisco’s ability to oxidize glucose became evident.
10.2 Test Your Understanding
The metabolic pathways of organisms living today evolved over a long period of time— undoubtedly in a stepwise fashion because of their complexity. Put the following processes in the order in which they might have evolved, and give a short explanation for your arrangement.
___
4 Krebs cycle
___
3 Electron transport
___
1 Glycolysis
___
2 Photosynthesis
60
Activity 10.2
Copyright © 2011 Pearson Education,
If NAD is unavailable, the cell is unable to conduct any processes that involve the conversion of NAD+ to NADH. Because both glycolysis and the Krebs cycle produce
NADH, both of these processes shut down when there is no available NAD+.
5. If the Krebs cycle does not require oxygen, why does cellular respiration stop after glycolysis when no oxygen is present?
When no oxygen is present, oxidative phosphorylation cannot occur. As a result, the
NADH produced in glycolysis and the Krebs cycle cannot be oxidized to NAD+.
When no NAD+ is available, pyruvate cannot be converted to the …show more content…
6. Many organisms can withstand periods of oxygen debt (anaerobic conditions). Yeast undergoing oxygen debt converts pyruvic acid to ethanol and carbon dioxide.
Animals undergoing oxygen debt convert pyruvic acid to lactic acid. Pyruvic acid is fairly nontoxic in even high concentrations. Both ethanol and lactic acid are toxic in even moderate concentrations. Explain why this conversion occurs in organisms.
As noted in question 4, when no NAD+ is available, even glycolysis stops. No ATP will be produced and the cell (or organism) will die. The conversion of pyruvic acid
(pyruvate) to lactic acid (or ethanol) requires the input of NADH and generates
NAD+. This process, called fermentation, allows the cell to continue getting at least
2 ATP per glucose.
7. How efficient is fermentation? How efficient is cellular respiration? Remember that efficiency is the amount of useful energy (as ATP) gained during the process divided by the total amount of energy available in glucose. Use 686 kcal as the total energy available in 1 mole of glucose and 8 kcal as the energy available in 1 mol of ATP.
Efficiency of fermentation
8 kcal/mole of ATP ϫ 2 ATP ϭ 16 …show more content…
a. Why could we call photorespiration a “mistake” in the functioning of the cell?
Photorespiration could be called a “mistake” because under high O2/CO2 conditions, rubisco breaks down glucose into carbon dioxide and water but no useful energy is gained.
b. Rubisco is thought to have evolved when Earth had a reducing atmosphere. How does this help explain the photorespiration “mistake?”
When the first photosynthetic organisms arose, the early Earth’s atmosphere contained little, if any, oxygen. Rubisco would have functioned very well under these conditions. It was only later, when the concentration of oxygen in the atmosphere increased considerably, that rubisco’s ability to oxidize glucose became evident.
10.2 Test Your Understanding
The metabolic pathways of organisms living today evolved over a long period of time— undoubtedly in a stepwise fashion because of their complexity. Put the following processes in the order in which they might have evolved, and give a short explanation for your arrangement.
___
4 Krebs cycle
___
3 Electron transport
___
1 Glycolysis
___
2 Photosynthesis
60
Activity 10.2
Copyright © 2011 Pearson Education,