Question

Mitochondria are sites of
A. Oxidative phosphorylation
B. Photolysis
C. Phosphorylation
D. Starch synthesis

Answer 1

Hint: The aerobic respiration of a cell takes place in the mitochondria. It consists of the Krebs cycle and the electron transport chain. Mitochondria is responsible for the production of energy in the form of ATP. The ATP gets generated through the electron transport chain, which consists of oxygen at its end step.

Complete answer:
Mitochondria are sites of oxidative phosphorylation.
The electron transport chain consists of various molecules that are present in the compartments of mitochondria. Through a series of redox reactions, electrons are transported from one member of the chain to another.
$NADH$ and $FAD{H_2}$ act as electron carriers. They carry electrons from the previous stages of respiration to molecules near the beginning of the transport chain. After this, they get converted into $NA{D^ + }$ and $FAD$ , which can be re-utilised in the respiration process.
Electrons move down the chain and release energy, thereby moving to a lower energy level. Some of the energy is utilised to pump ${H^ + }$ ions into the intermembrane spaces.
Oxygen is present at the end of the chain. Electrons cause the conversion of oxygen to water.
${H^ + }$ Ions flow into the matrix and cause the synthesis of ATP with the help of an enzyme ATP synthase.

The correct answer is – A. Oxidative phosphorylation.

Note:
A proton gradient is created by the ${H^ + }$ ions. This gradient causes the synthesis of ATP in a process known as chemiosmosis.
Oxidative phosphorylation is a combination of the electron transport chain and chemiosmosis. Chemiosmosis accounts for the production of the majority of the ATP .
This process occurs in the membranes (compartments) of mitochondria, whereas, the Krebs cycle occurs in the matrix.