Which process occurs in the mitochondria of cells?

The correct answer is cellular respiration, which occurs in the mitochondria of cells. This process is essential for converting biochemical energy from nutrients into adenosine triphosphate (ATP), the energy currency of the cell. Mitochondria are often referred to as the "powerhouses" of the cell because they are responsible for producing the majority of a cell's ATP via the processes of glycolysis, the Krebs cycle, and the electron transport chain.

During cellular respiration, glucose and oxygen are used to produce ATP, water, and carbon dioxide. This process involves multiple stages, with the Krebs cycle and electron transport chain specifically occurring within the mitochondria's inner membrane and matrix. This is crucial for aerobic organisms that rely on oxygen to maximize energy production from food sources.

In contrast, other processes listed, such as photosynthesis, occur in chloroplasts (in plants and some algae), fermentation is an anaerobic process that occurs in the cytoplasm of cells without using mitochondria, and protein synthesis happens on ribosomes in the cytoplasm. Each of these processes is important in its own right but operates independently from the key function of mitochondria in energy production through cellular respiration.