Mitochondrial DNA analysis indicates this organism is closely related to yeast found on Earth. Knowing that the atmospheric oxygen concentration on Mars is extremely low, which of the following best describes ATP production in this cell?

Question

Mitochondrial DNA analysis indicates this organism is closely related to yeast found on Earth. Knowing that the atmospheric oxygen concentration on Mars is extremely low, which of the following best describes ATP production in this cell?

BlackTom AI · Accepted Answer

Yeast-like eukaryotes perform alcoholic fermentation under anoxic conditions: pyruvate is converted to ethanol so NAD+ is regenerated and glycolysis can continue.

Relevant concepts: glycolysis yields 2 ATP and 2 NADH per glucose by substrate-level phosphorylation. Under aerobic conditions NADH is oxidized by the mitochondrial electron transport chain using O2 as the final electron acceptor, yielding many more ATP. In very low-O2 environments, yeast and other facultative anaerobes use fermentation to reoxidize NADH to NAD+, because oxidative phosphorylation is unavailable.

Step-by-step reasoning and biochemical steps:
1. Glycolysis: glucose → 2 pyruvate + 2 ATP (net) + 2 NADH.
2. In alcoholic (ethanol) fermentation (typical of yeast):
   a. Pyruvate → acetaldehyde + CO2 (enzyme: pyruvate decarboxylase).
   b. Acetaldehyde + NADH → ethanol + NAD+ (enzyme: alcohol dehydrogenase).
3. NAD+ regenerated allows glycolysis to continue producing ATP (only 2 ATP per glucose total under fermentation).
Thus the cell, despite having mitochondria-like DNA, will rely on fermentation to maintain NAD+ and produce ATP in a very low-O2 Martian atmosphere.

Why the correct answer is correct: the option “Fermentation producing ethanol and NAD+” exactly matches alcoholic fermentation used by yeast under anaerobic conditions and explains NAD+ regeneration necessary for ATP production via glycolysis.

Why the other options are incorrect:
- “Fermentation producing lactate and NAD+.” describes lactic acid fermentation (typical of animal muscle and some bacteria), not yeast-like organisms that produce ethanol.
- “Anaerobic respiration with O2 as the final electron acceptor.” is contradictory—if O2 is used, respiration is aerobic; plus O2 is scarce on Mars.
- “Anaerobic respiration with H2S as the final electron acceptor.” is biologically unlikely for a eukaryotic yeast-like organism; H2S is typically a reduced product (not the terminal electron acceptor), and sulfate respiration to H2S is a bacterial/archaeal process.

Therefore the correct answer is: Fermentation producing ethanol and NAD+.

Mitochondrial DNA analysis indicates this organism is closely related to yeast found on Earth. Knowing that the atmospheric oxygen concentration on Mars is extremely low, which of the following best describes ATP production in this cell?单项选择题

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