Question 1

During intense exercise, muscle cells switch from aerobic to anaerobic metabolism. What is the primary reason for the conversion of pyruvate to lactate under these conditions?

Accepted Answer

To regenerate NAD+ so glycolysis can continue producing ATP

Question 2

Which enzyme catalyzes the conversion of pyruvate to lactate in human muscle cells during anaerobic conditions?

Accepted Answer

Lactate dehydrogenase

Question 3

What is the chemical equation for the conversion of pyruvate to lactate in human cells?

Accepted Answer

$\mathrm{Pyruvate} + \mathrm{NADH} + \mathrm{H}^+ \rightarrow \mathrm{Lactate} + \mathrm{NAD}^+$

Question 4

Why is lactate accumulation in muscles considered disruptive during prolonged anaerobic activity?

Accepted Answer

It leads to inefficient ATP production and can lower pH, causing muscle fatigue

Question 5

After exercise, when oxygen levels return to normal, what happens to the accumulated lactate in muscle cells?

Accepted Answer

It is converted back to pyruvate and used in oxidative phosphorylation

Question 6

Which of the following best describes the role of NAD+ in glycolysis?

Accepted Answer

NAD+ accepts electrons during glycolysis, allowing ATP production to continue

Question 7

In yeast cells, what is the end product of anaerobic metabolism of pyruvate?

Accepted Answer

Ethanol

Question 8

Which of the following equations correctly represents the net ATP yield from glycolysis per molecule of glucose?

Accepted Answer

$\mathrm{Glucose} \rightarrow 2 \mathrm{Pyruvate} + 2 \mathrm{ATP} + 2 \mathrm{NADH}$

Question 9

A patient with a genetic deficiency in lactate dehydrogenase would most likely experience which of the following during intense exercise?

Accepted Answer

Impaired ability to regenerate NAD+, leading to early muscle fatigue

Question 10

Which of the following best explains why stored ATP in muscle cells is only sufficient for a few seconds of maximal effort?

Accepted Answer

Muscle cells have limited ATP stores and must rely on other energy systems for sustained activity

Question 11

During the transition from rest to exercise, what is the primary reason for the initial lag in oxygen uptake by mitochondria?

Accepted Answer

It takes time for oxygen to diffuse from capillaries to mitochondria

Question 12

Which of the following is a correct sequence of energy system activation during prolonged exercise?

Accepted Answer

Stored ATP → Glycolysis → Oxidative phosphorylation

Question 13

If a muscle cell is unable to regenerate NAD+ during anaerobic metabolism, what is the most immediate consequence?

Accepted Answer

Glycolysis will stop, halting ATP production

Question 14

Which of the following best describes the fate of pyruvate under aerobic conditions?

Accepted Answer

It enters the mitochondria and is converted to acetyl-CoA for the Krebs cycle

Question 15

A marathon runner relies on which energy system for the majority of their race?

Accepted Answer

Oxidative phosphorylation

Question 16

Which of the following is a direct result of the conversion of pyruvate to lactate in muscle cells?

Accepted Answer

Regeneration of NAD$^+$

Question 17

Which of the following statements about glycolysis is correct?

Accepted Answer

Glycolysis produces pyruvate, ATP, and NADH

Question 18

In the context of blood donation and stem cell donation, which of the following is true regarding stem cell collection for cancer patients?

Accepted Answer

Stem cell donation usually involves a simple mouth swab for initial registration, but actual donation may require bone marrow extraction only about 10% of the time

Question 19

Which of the following best explains why the DNA of a cancer patient must match the DNA of the stem cell donor?

Accepted Answer

To prevent immune rejection and ensure successful engraftment

Cellular Energy Systems: Glycolysis, Fermentation, and ATP Production

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