Pre AP Biology -CELLS 7.2 Fermentation- MCQ Exam Style Questions -New Syllabus 2025-2026
Pre AP Biology -CELLS 7.2 Fermentation- MCQ Exam Style Questions – New Syllabus 2025-2026
Pre AP Biology -CELLS 7.2 Fermentation- MCQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.
▶️ Answer/Explanation
The correct option is a.
Facultative anaerobes can survive and grow in both the presence and absence of oxygen.
Under aerobic conditions, they perform aerobic respiration, which generates more ATP per glucose molecule.
This higher energy yield supports faster cell division and greater biomass accumulation.
In anaerobic conditions, they switch to less efficient processes like fermentation, yielding less ATP.
Thus, growth is typically slower and less abundant without oxygen.
Overall, the culture in aerobic conditions would exhibit greater growth compared to the anaerobic one.
▶️ Answer/Explanation
The correct option is A.
In the Electron Transport Chain (ETC), electrons are passed along proteins to oxygen, the final electron acceptor.
This movement provides energy to pump $H^+$ ions across the membrane, creating an electrochemical gradient.
Oxygen gas ($O_2$) is essential here to accept electrons and form water ($H_2O$).
ATP synthase then uses the flow of $H^+$ ions back across the membrane to power the phosphorylation of ADP.
This process adds a phosphate group to $ADP$ to synthesize $ATP$.
Options B, C, and D are incorrect as they misidentify the substrates or the role of water and $CO_2$.
▶️ Answer/Explanation
The correct answer is C. $\text{H}^+$ ions.
During cellular respiration, the electron transport chain pumps $\text{H}^+$ ions into the intermembrane space.
This creates a high electrochemical gradient (proton-motive force) relative to the mitochondrial matrix.
$\text{H}^+$ ions flow back into the matrix through the $\text{F}_0$ subunit of the ATP synthase enzyme.
This flow (chemiosmosis) triggers the rotation of the enzyme’s central shaft and the $\text{F}_1$ catalytic unit.
The mechanical energy from this “spinning” converts $\text{ADP} + \text{P}_i$ into $\text{ATP}$.
This entire process is fundamentally known as oxidative phosphorylation.
▶️ Answer/Explanation
The correct answer is A. $\text{NAD}^+$.
In glycolysis, $\text{NAD}^+$ is reduced to $\text{NADH}$ as glucose is broken down.
Without oxygen, the electron transport chain cannot oxidize $\text{NADH}$ back to $\text{NAD}^+$.
Fermentation steps in to oxidize $\text{NADH}$, converting it back into $\text{NAD}^+$.
This regenerated $\text{NAD}^+$ is essential for the glyceraldehyde-3-phosphate dehydrogenase reaction in glycolysis.
By recycling this carrier, the cell can continue to produce a net of $2$ $\text{ATP}$ molecules per glucose.
Without this regeneration, glycolysis would stop due to a lack of available electron acceptors.
▶️ Answer/Explanation
The correct answer is B. anaerobic.
The term anaerobic literally means “without air” or “without oxygen.”
Fermentation is a metabolic process that extracts energy from carbohydrates.
This process occurs in the absence of $O_2$ (free oxygen).
In contrast, aerobic processes require oxygen to proceed.
During fermentation, $NADH$ is oxidized back to $NAD^+$ to keep glycolysis running.
Common products of this anaerobic pathway include lactic acid or ethanol and $CO_2$.
▶️ Answer/Explanation
The correct option is C. fermentation.
In the absence of oxygen ($\text{O}_2$), the cell cannot perform aerobic respiration.
Glycolysis produces $2$ molecules of pyruvate and $2$ molecules of $\text{NADH}$.
Without oxygen, the Krebs cycle and electron transport chain ($ETC$) cannot operate.
Fermentation occurs to regenerate $\text{NAD}^+$ from $\text{NADH}$.
This regeneration allows glycolysis to continue producing a small amount of $\text{ATP}$.
In animals, this typically results in lactic acid; in yeast, it results in ethanol and $\text{CO}_2$.