Question

A shift in metabolism that breaks down pyruvic acid to lactic acid is called

A. aerobic threshold.
B. lactic acid threshold.
C. pyruvic acid threshold.
D. glycogenic threshold.

Answer 1

The conversion of pyruvic acid to lactic acid when oxygen is scarce is known as the lactic acid threshold. This anaerobic process allows for a continued production of ATP and the recycling of NADH into NAD*, enabling glycolysis to carry on.

Step-by-step explanation:

The shift in metabolism that breaks down pyruvic acid to lactic acid is called B. lactic acid threshold. This occurs during conditions where there is insufficient oxygen (anaerobic conditions) for the complete aerobic breakdown of glucose.

Instead of entering the mitochondria for the aerobic respiration process, pyruvic acid is converted into lactic acid in the cytoplasm.

This process, known as lactic acid fermentation, allows for the continued production of ATP and the recycling of NADH into NAD*, which is necessary for glycolysis to continue. Lactic acid can be transported to the liver via the Cori cycle where it can be converted back to glucose when oxygen becomes available.

Answer 2

The shift in metabolism from pyruvic acid to lactic acid under anaerobic conditions is called lactic acid fermentation, and it's a response to oxygen-limited situations such as high-intensity exercise. This leads to the correct option being B. lactic acid threshold.

Step-by-step explanation:

The shift in metabolism that breaks down pyruvic acid to lactic acid during conditions when oxygen is limited or absent is known as lactic acid fermentation. This process is crucial for generating ATP when aerobic respiration cannot occur due to a lack of oxygen. For example, during intense exercise, muscles may require energy more rapidly than oxygen can be supplied, leading to lactic acid formation from pyruvic acid.

The enzyme NAD* is recycled during this process from NADH, which is essential for glycolysis to continue. The lactic acid generated can lead to muscle fatigue as it accumulates, but it is also transported to the liver where it can be converted back to pyruvate or glucose through the Cori Cycle, particularly after exercise. In this context, the correct option for the shift in metabolism that breaks down pyruvic acid to lactic acid is B. lactic acid threshold.