Pre AP Biology -CELLS 7.1 Cellular Respiration- MCQ Exam Style Questions -New Syllabus

Pre AP Biology -CELLS 7.1 Cellular Respiration- MCQ Exam Style Questions – New Syllabus 2025-2026

Pre AP Biology -CELLS 7.1 Cellular Respiration- MCQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.

Pre AP Biology – MCQ Exam Style Questions- All Topics

Question

Phosphofructokinase ($\text{PFK}$) is regulated by a number of metabolites. In addition to those mentioned in the text, which one of the following would also make sense?

a. Pyruvate could function as an activator of $\text{PFK}$.

b. Glucose could function as an inhibitor of $\text{PFK}$.

c. $\text{ADP}$ could function as an activator of $\text{PFK}$.

d. Acetyl-$\text{CoA}$ could act as an activator of $\text{PFK}$.

▶️ Answer/Explanation

Detailed solution

The correct option is c.
$\text{PFK}$ is a key rate-limiting enzyme in glycolysis that senses the energy status of the cell.
High levels of $\text{ADP}$ indicate that the cell is low on energy ($\text{ATP}$).
Therefore, $\text{ADP}$ acts as an allosteric activator to speed up glycolysis.
Conversely, $\text{ATP}$ and Citrate act as inhibitors when energy is abundant.
Pyruvate and Acetyl-$\text{CoA}$ are downstream products; high levels usually signal to slow down, not activate, the earlier steps.
Glucose is the starting substrate and typically does not directly inhibit this specific control point.

Question

In cellular respiration, which of the following does the term uncoupled refer to, specifically?

a. The two parts of glycolysis are running independently of each other.

b. Respiratory electron transport is operating, but chemiosmosis is inhibited.

c. Respiratory electron transport is operating, but proton pumping is inhibited.

d. Oxidative phosphorylation is occurring, but the proton-motive force remains high.

▶️ Answer/Explanation

Detailed solution

The correct option is b.

In normal oxidative phosphorylation, electron transport is coupled to $ATP$ synthesis via a proton gradient.
Uncoupling occurs when the inner mitochondrial membrane becomes leaky to protons ($H^+$).
This allows the Electron Transport Chain (ETC) to continue operating and consuming oxygen.
However, the protons bypass ATP synthase, meaning chemiosmosis is effectively inhibited.
As a result, the energy from the electron gradient is released as heat rather than being captured as $ATP$.
Therefore, respiration continues at a high rate, but $ATP$ production is disconnected from the process.

Question

The breakdown of fats releases fatty acids. In what form do the carbon molecules enter the respiratory pathway?

a. as $\text{NADH}$

b. as $\text{acetyl-CoA}$

c. as glucose

d. as pyruvate

▶️ Answer/Explanation

Detailed solution

The correct option is b. as $\text{acetyl-CoA}$.
Fatty acids undergo a process called $\beta$-oxidation within the mitochondria.
During this process, long-chain fatty acids are broken down into $2$-carbon units.
These $2$-carbon units are converted into $\text{acetyl-CoA}$ molecules.
The resulting $\text{acetyl-CoA}$ then enters the Krebs cycle (citric acid cycle).
This allows the energy stored in fats to be harvested via the aerobic respiratory pathway.
Unlike glycerol, fatty acids do not convert to glucose or pyruvate before entering the cycle.

Pre AP Biology -CELLS 7.1 Cellular Respiration- MCQ Exam Style Questions -New Syllabus