The correct answer is option 2: mitochondria.

Mitochondria are the site of cellular respiration in animal cells. Cellular respiration is the process by which cells convert nutrients into energy in the form of ATP (adenosine triphosphate). This process takes place in the mitochondria, which are often referred to as the "powerhouses" of the cell.

Option 1, ribosomes, are responsible for protein synthesis and are not directly involved in cellular respiration. Option 3, endoplasmic reticulum, is responsible for the synthesis and transport of proteins, lipids, and other important molecules, but it is not the site of cellular respiration. Option 4, lysosomes, are involved in the digestion of cellular waste and are not directly involved in cellular respiration.

Therefore, the correct answer is option 2: mitochondria.