Final answer:
ATP is produced mainly in the mitochondria of a cell, using cellular respiration to convert nutrients into energy. Mitochondria are abundant in cells with high energy demands, such as muscle cells.
Step-by-step explanation:
Adenosine triphosphate (ATP) is produced primarily in the mitochondria, which are referred to as the "powerhouses" or "energy factories" of a cell. The mitochondria use cellular respiration to convert chemical energy from glucose and other nutrients into ATP, which is then used to fuel various cellular activities. Although some ATP is also created in the cytosol of the cell, the majority is synthesized inside the mitochondria. The process of cellular respiration also generates carbon dioxide as a waste product, which we exhale with every breath.
The number of mitochondria present in a cell correlates with the cell's energy requirements. For example, muscle cells have a high concentration of mitochondria because of their substantial energy needs for contraction. Conversely, less active cells, like red blood cells, have none.