Question

Mitochondrial inner membrane encloses____________.

• A. aqueous humor
• B. matrix
• C. cytosol
• D. mucus

Hint:

Remember the division of labor inside a mitochondrion based on its anatomy:

• Mitochondrial Matrix: Site of Link Reaction and Krebs Cycle.

• Inner Mitochondrial Membrane (Cristae): Site of Electron Transport Chain (ETC) and Oxysomes ($F_0-F_1$ complexes) for ATP synthesis.

Answer 1

The Correct Option is B

Step 1: Recall mitochondrial structure.
A mitochondrion has two membranes, an outer one and a folded inner one, which create two compartments.
Step 2: Name the two compartments.
Between the two membranes lies the intermembrane space, and the inner membrane encloses a central space.
Step 3: Identify the central space.
The fluid filled core surrounded by the inner membrane is the matrix, a gel-like proteinaceous fluid.
Step 4: Recall what the matrix holds.
The matrix contains mitochondrial DNA, $70S$ ribosomes, and the enzymes of the Krebs cycle, confirming it is the inner compartment.
Step 5: Reject the wrong options.
Aqueous humor belongs to the eye, cytosol surrounds the mitochondrion from outside, and mucus is a body secretion, so none of these sit inside the inner membrane.
Step 6: Conclude.
The inner mitochondrial membrane encloses the matrix.
\[ \boxed{\text{matrix}} \]