National League for Nursing (NLN PAX) Practice Exam 2025 - Free PAX Exam Practice Questions and Study Guide

The correct answer is anaerobic respiration, which occurs when oxygen levels are insufficient for normal aerobic metabolic processes. This type of respiration allows cells, particularly muscle cells during intense exercise or situations where oxygen is scarce, to produce energy without using oxygen. During anaerobic respiration, glucose is partially broken down to yield energy more rapidly than aerobic respiration would allow, but it produces less energy overall.

As muscles continue to exert effort without adequate oxygen, they switch to anaerobic metabolism, which results in the production of ATP (adenosine triphosphate) as well as byproducts such as lactic acid. The accumulation of lactic acid can lead to muscle fatigue and discomfort.

In contrast, aerobic respiration is the process that requires oxygen to convert glucose into energy while producing carbon dioxide and water as byproducts. This process is more efficient in terms of energy yield but cannot occur when oxygen levels are low.

Lactic acid fermentation is a specific type of anaerobic process that occurs in muscle cells, but the broader term, anaerobic respiration, encompasses various pathways, including alcoholic fermentation in yeast.

Oxidative phosphorylation is a part of aerobic respiration that occurs in the mitochondria, where ATP is produced in the presence of oxygen. This process cannot take place when oxygen