Which of the following organelles is primarily involved in the synthesis of ATP?

The mitochondria are often referred to as the "powerhouses" of the cell, primarily because they play a critical role in the synthesis of adenosine triphosphate (ATP), which serves as the main energy currency in cells. They generate ATP through a process known as oxidative phosphorylation, which occurs in the inner mitochondrial membrane. This process utilizes the energy produced from the breakdown of glucose and other nutrients in the presence of oxygen.

Mitochondria contain their own DNA and are involved in metabolic processes, including the citric acid cycle, where acetyl-CoA is oxidized and high-energy electrons are transferred to carriers that feed into the electron transport chain. The resulting proton gradient drives ATP synthase, the enzyme responsible for synthesizing ATP.

The other organelles listed have distinct functions: chloroplasts are primarily involved in photosynthesis, converting light energy into chemical energy (sugar), lysosomes function in digestion and waste processing within the cell, and ribosomes are crucial for protein synthesis, translating messenger RNA into proteins. Hence, the mitochondria's specific role in ATP production makes them the correct answer.