Hint: They are made of two membranes. The outer membrane is responsible for covering the organelle and contains it like skin. The inner membrane folds over repeatedly and creates layered structures called cristae. In this, the fluid contained within it is named a matrix.
Mitochondria are cylindrical or sausage in structure and double membranous organelles which are distributed in the cytoplasm. It is surrounded by two membranes designated as outer and inner membranes. A matrix lies inside the inner membrane. The matrix contains a single circular dsDNA molecule, a few RNA molecules, 70S ribosomes, and the components required for the synthesis of proteins. Mitochondria also are referred to as semi-autonomous cell organelles due to their capability of self-duplication by the presence of DNA.
Mitochondria produce ATP through the process of cellular respiration—specifically, aerobic respiration, which requires oxygen. The acid cycle, or Krebs cycle, takes place within the mitochondria. This cycle involves the oxidation of pyruvate, which comes from glucose, to make the molecule acetyl-CoA. Acetyl-CoA is successively oxidized and ATP is produced.
The acid cycle reduces nicotinamide adenine dinucleotide (NAD+) to NADH. NADH is then utilized in the method of the organic process, which also takes place within the mitochondria. Electrons from NADH travel through protein complexes that are embedded within the inner membrane of the mitochondria. This set of proteins is called an electron transport chain. Energy from the electron transport chain is then wont to transport proteins back across the membrane, which powers ATP synthase to make ATP.
So the correct answer is ‘Mitochondria’.
Note: The amount of mitochondria in a cell depends on how much energy that cell needs to produce. Muscle cells, for instance, have many mitochondria because they have to supply energy to maneuver the body. Red blood cells, which carry oxygen to other cells, have none; they are not got to produce energy.