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 becomes available again, what happens to the accumulated lactate in muscle cells?

Accepted Answer

It is converted back to pyruvate and used for 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 is experiencing muscle fatigue during a sprint. Which metabolic pathway is most responsible for the rapid but short-term supply of ATP?

Accepted Answer

Anaerobic glycolysis

Question 10

Which of the following is the correct sequence of energy systems used during exercise, from immediate to long-term supply?

Accepted Answer

Stored ATP → Stored Glycogen → Oxidative phosphorylation

Question 11

Which of the following best explains why oxidative phosphorylation cannot immediately meet the energy demands at the onset of intense exercise?

Accepted Answer

It requires time for oxygen to reach the mitochondria

Question 12

If NAD+ is not regenerated during anaerobic metabolism, what is the consequence for ATP production?

Accepted Answer

ATP production stops because glycolysis cannot proceed

Question 13

Which of the following is a real-world application of understanding lactate metabolism in clinical settings?

Accepted Answer

Diagnosing lactic acidosis in patients with impaired oxygen delivery

Question 14

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

Accepted Answer

Oxidative phosphorylation

Question 15

Which of the following statements about the conversion of pyruvate to lactate is FALSE?

Accepted Answer

It produces more ATP than oxidative phosphorylation

Question 16

During recovery after exercise, which process helps clear lactate from the muscles?

Accepted Answer

Conversion of lactate to pyruvate for entry into the Krebs cycle

Question 17

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

Question 18

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+ and reduced ATP production

Question 19

Which of the following is a direct consequence of the accumulation of lactate in muscle tissue?

Accepted Answer

Decrease in muscle pH leading to fatigue

Anaerobic Metabolism and Energy Systems in Human Physiology

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