This example question asks, "Why is anaerobic respiration, also called fermentation, in eukaryotic cells inefficient?" Alright, so for the first one it says, "No metabolic processes are able to continue without oxidation." That's not true. If there's no oxygen available, that's why fermentation happens. Our pyruvate does not go into the mitochondrial matrix; it stays within the cytosol. So, this is not true. Here, ETC or electron transport chain is not able to produce ATP without oxygen as the final electron acceptor. Alright. This one's tricky. The ETC doesn't technically make the ATP. It's the oxidative phosphorylation step that makes the ATP. And we're going to say without oxygen involved, yes, we won't be able to go through stage 4 of food catabolism to make ATP. But this thing is not true because it's not the ETC that's even making the ATP. It's oxidative phosphorylation step where it happens. I know we tack on ETC and oxidative phosphorylation together, but technically it's the oxidative phosphorylation step. Stage, complex 5 or ATP is finally being made through ATP synthase.
Now, here, glycolysis only produces 2 ATP molecules per one glucose molecule. This answers better because here it's telling us why it's inefficient. We're only making 2 ATP molecules per one glucose molecule versus the 20 plus ATP molecules we would have made if we had gone through the ETC and oxidative phosphorylation, stage 4 of food catabolism. So, this is a much better answer. And then overproduction of NAD⁺ causes glycolysis to shut down. No. The production of NAD⁺ is what's allowing us to continue with glycolysis. This is saying the opposite. So, this is not true.
The only answer here that talks about the inefficiency of the absence of oxygen is part C. Under fermentation, we're only making 2 ATP molecules versus the 20 plus ATP molecules we could have made if we went through the mitochondrial matrix through Stage 3 and then Stage 4. So again, C is our final answer.