May 24, 2017

Let's see why.

#### Explanation:

We have to break this question down to understand how ${\text{O}}_{2}$ limits the TCA cycle .

First things first, we need to understand what area of biology this question concerns. Well, this question asks you about cellular respiration, particularly, about the Krebs cycle and the electron transport chain (ETC) .

So again, how is ${\text{O}}_{2}$ important in all of this? Remember, ${\text{O}}_{2}$ acts as the final electron acceptor in the electron transport chain. This means if we are limited with our supply of ${\text{O}}_{2}$ molecules, the rate of oxidative phosphorylation decreases.

If the rate of oxidative phosphorylation decreases, we get a buildup of $\text{NADH}$ and ${\text{FADH}}_{2}$ molecules which are produced from the Krebs cycle.

Increased levels of $\text{NADH}$ will inhibit the Krebs cycle. If we are not provided with enough oxygen, then our cells can't undergo aerobic respiration. The tissues will have to resort to producing $\text{ATP}$ molecules via lactic acid fermentation .

![https://d2jmvrsizmvf4x.cloudfront.net/qkpFXwgjQ5KlwFqDwjbj_LACTIC_ACID_FERMENTATION.jpg)