Quiz: The Respiratory Balance Sheet Quiz 1
The respiratory balance sheet is one of the most quoted calculations in biology: 38 ATP molecules per glucose during aerobic respiration. But this figure is a theoretical exercise, built on four assumptions that a living cell does not actually satisfy.
This quiz tests your understanding of:
- The four assumptions behind the net ATP calculation
- Why those assumptions fail in a living system
- The net gain of 38 ATP molecules in aerobic respiration
- How fermentation compares with aerobic respiration
- The rate of NADH oxidation in fermentation versus aerobic respiration
Read each question carefully and choose the single best answer. Explanations follow every question to reinforce the reasoning.
Q1. According to the lesson, the calculation of the net gain of ATP for every glucose molecule oxidised can, in reality, remain only:
The lesson states plainly that although calculations of net ATP gain are possible, in reality this can remain only a theoretical exercise, because they rest on assumptions a living cell does not satisfy.
Q2. Which of the following is one of the assumptions used to calculate the net gain of ATP?
The first assumption is a sequential, orderly pathway in which one substrate forms the next, with glycolysis, the TCA cycle and the ETS following one after another. The other options describe the real living system, not the assumptions.
Q3. The calculation of net ATP gain assumes that the NADH synthesised in glycolysis is:
The second assumption is that the NADH made in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation, so its ATP yield can be counted.
Q4. Which assumption states that only glucose is being respired?
The fourth assumption is that only glucose is being respired, with no other alternative substrates entering the pathway at any of the intermediary stages.
Q5. The assumption that "none of the intermediates in the pathway are utilised to synthesise any other compound" is best described as:
This is the third listed assumption. In a living cell, however, intermediates are withdrawn for synthesis, which is why the assumption is not really valid.
Q6. Why are the assumptions behind the respiratory balance sheet not really valid in a living system?
The lesson explains that in a living system all pathways work simultaneously rather than one after another, so the tidy sequential model does not hold.
Q7. In a living system, substrates enter the respiratory pathways and are withdrawn from it:
The lesson notes that substrates enter the pathways and are withdrawn from them as and when necessary, contradicting the fixed, orderly assumption.
Q8. According to the lesson, ATP in a living cell is:
The lesson states that ATP is utilised as and when needed, which is one reason the balance sheet assumptions do not hold in reality.
Q9. What is the net gain of ATP molecules during aerobic respiration of one molecule of glucose, as stated in the lesson?
The lesson concludes that there can be a net gain of 38 ATP molecules during aerobic respiration of one molecule of glucose.
Q10. Despite its limitations, why is the respiratory balance sheet exercise considered useful?
The lesson says it is useful to do this exercise to appreciate the beauty and efficiency of the living system in extraction and storing energy.
Q11. In fermentation, glucose is:
The lesson states that fermentation accounts for only a partial breakdown of glucose, whereas in aerobic respiration glucose is completely degraded to ##\ce{CO2}## and ##\ce{H2O}##.
Q12. What is the net gain of ATP in fermentation for each molecule of glucose degraded to pyruvic acid?
The lesson states that in fermentation there is a net gain of only two molecules of ATP for each molecule of glucose degraded to pyruvic acid.
Q13. How does the oxidation of NADH to ##\ce{NAD+}## differ between fermentation and aerobic respiration?
The lesson notes that NADH is oxidised to ##\ce{NAD+}## rather slowly in fermentation, whereas the reaction is very vigorous in aerobic respiration.
Q14. Which statement correctly contrasts aerobic respiration with fermentation?
The lesson contrasts the two: fermentation gives only a partial breakdown of glucose, while aerobic respiration completely degrades it to ##\ce{CO2}## and ##\ce{H2O}##.
Q15. Which of the following is NOT one of the assumptions listed for calculating the net gain of ATP?
Simultaneous operation of all pathways is a feature of the real living system that invalidates the assumptions, not one of the assumptions themselves.