Q6TYU - Campbell Biology

Question

Question: When electrons flow along the electron transport chain of mitochondria, which of the following changes occurs?

1. The pH of the matrix increases.
2. ATP synthase pumps protons by active transport.
3. The electrons gain free energy.
4. NAD⁺ is oxidized

Step-by-Step Solution

Answer

1. The option “The pH of the matrix increases” is true.
2. The option “ATP synthase pumps protons by active transport” is false.
3. The option “The electrons gain free energy” is false.
4. The option “NAD⁺ is oxidized” is false.

Step 1: Reactions of mitochondria

Mitochondria are the organelles in which significant metabolic reactions such as the electron transport chain occurs. The primary energy molecules, such as ATP, are created in the mitochondria. 

Step 2: Explanation of option ‘(A)’

The pH of the mitochondrial matrix increases due to the influx of hydrogen ions into the matrix. It happens with the help of the ATP synthase. This process is known as the chemiosmosis process.

 

Thus, a change in pH occurs due to the electron transport chain occurring with the ATP synthesis.

Therefore, the given statement is true.

Step 3: Explanation of option ‘(B)’

Hydrogen ions have to transport to the intermembrane space. These hydrogen ions pump back into the matrix to carry out ATP synthesis via the proton pump. 

 

Thus, electron transport moves the hydrogen, and it does not activate the proton pump directly.

Therefore, the given statement is false.

Step 4: Explanation of option ‘(C)’

The electron generated from the electron transport chain will possess the energy to move the hydrogen ions.

 

Thus, the fate of the electron is to move the hydrogen ions in the oxidative phosphorylation mechanism.

Therefore, the given statement is false.

Step 5: Explanation of option ‘(D)’

NAD⁺ oxidation does not occur during the release of the electron from the electron transport chain. NAD⁺ is a determining factor in the glycolysis process. 

 

Thus, NAD⁺ oxidation is not the process that involves the electron from the electron transport chain.

Therefore, the given statement is false.