Question

In mitochondria, protons accumulate in the
A. Outer membrane
B. Inter membrane space
C. Inner membrane
D. Matrix

Answer 1

Hint: Mitochondria is the essential cell organelle present in almost all of the cells. It is responsible for the production of energy in the cell thus called a powerhouse of the cell. Mitochondria is usually not visible under the microscope, to make it visible it is stained with specific dies.
Mitochondria is a sausage-shaped cell organelle whose number in a cell depends upon the physiological activity of the cells. It is the busiest and active organelle in a cell as it continuously produces energy-rich compounds called ATP.

Complete answer:
Mitochondria are covered by a double unit membrane called the outer and inner membrane. Both these membranes are composed of phospholipids and cholesterol. The outer membrane has more phospholipids and cholesterol than the inner membrane. The outer membrane and the inner membrane divides the lumen of mitochondria distinctly into two aqueous compartments known as outer and inner compartments. The inner compartment is called a matrix.
The two membranes of Mitochondria have their specific enzymes associated with mitochondrial functions. During respiratory processes, the terminal oxidation of NADH and FADH occurs in the inner mitochondrial membrane. The process is called an electron transport system (ETS).
All the reduced proton acceptors like NADH and FADH move to the inner mitochondrial membrane. Here they undergo ETS and release their protons into intermembrane space (outer compartment) and get reoxidized along with the synthesis of ATP.
The inner membrane is studded with pinhead particles called oxysomes which are concerned with oxidative phosphorylation (formation of ATP).

Thus the correct answer is option B.

Note:
During every step of ETS, oxidation and reduction of electron carriers occur and energy is released. It is the energy of this oxidation-reduction coupling mechanism that is utilized for creating a proton gradient in the intermembrane space. This gradient is responsible for the synthesis of ATP.
The protons that are accumulated in the intermembrane space are ultimately accepted by the oxygen. Thus oxygen is the final proton acceptor during ETS.