Which of the following structures is primarily involved in cell metabolism and energy production?

The mitochondria are often referred to as the "powerhouses" of the cell due to their critical role in energy production through the process of cellular respiration. Within the mitochondria, glucose and other nutrients are converted into ATP (adenosine triphosphate), which is the primary energy currency of the cell. This process involves various biochemical pathways, including the Krebs cycle and the electron transport chain, which take place within the inner membranes of the mitochondria.

In contrast to the mitochondria, the nucleus primarily serves as the control center of the cell, housing DNA and regulating gene expression. Ribosomes are responsible for protein synthesis, translating messenger RNA into polypeptide chains, and while they contribute to cell function, they are not directly involved in energy metabolism. The endoplasmic reticulum has two forms (rough and smooth) and is mainly involved in the synthesis, folding, modification, and transport of proteins and lipids rather than energy production.

Therefore, the involvement of mitochondria in converting energy from nutrients into usable forms for the cell firmly establishes them as the central hub for cell metabolism and energy production.