A student is arrested for drunk driving after flunking a breath test for alcohol. In court, the student swears he was not drinking and argues that his car’s exhaust system was leaking carbon monoxide (CO) into the passenger compartment. This placed him in an anaerobic environment and his body switched over to the fermentation pathway, resulting in a buildup of alcohol in his bloodstream. The judge having completed Biology 160 in undergraduate studies says his story is ________.

The story told by the student arrested for drunk driving -in the opinion of the judge who understands biology- is not plausible, humans do not produce alcohol in a fermentation pathway.

Explanation:

Options for this question are:

Plausible as long as he was not exposed to CO too long, which would have resulted in suffocation.
Plausibles if his blood glucose levels were also very low.
Not plausible, humans do not produce alcohol in a fermentation pathway.
Not plausible, because only CO₂ build up would have that effect.

In humans, cellular respiration involves the use of oxygen to produce energy, through the oxidative phosphorylation that occurs in the mitochondria.

Under conditions where cells obtain little oxygen -as in athletes exposed to rigorous and prolonged exercise - an anaerobic pathway is activated to produce ATP, which is faster but less efficient than the aerobic pathway, where lactic acid is produced.

Alcoholic fermentation is restricted to a few anaerobic organisms - such as yeasts - capable of producing ethanol from a sugar, such as glucose or sucrose.

What makes the student's story implausible, by claiming that his body produced alcohol by staying within a carbon monoxide-laden environment, is the fact that humans do not produce alcohol when exposed to low oxygen environments, but rather lactic acid.