Which organelle is commonly known as the "powerhouse of the cell"?

The term "powerhouse of the cell" refers specifically to mitochondria because they are responsible for generating adenosine triphosphate (ATP), the primary energy currency of the cell. This process occurs through cellular respiration, where mitochondria convert nutrients, particularly glucose, into usable energy. Mitochondria have their own DNA, which enables them to produce some of the proteins necessary for this energy production, and they play a vital role in metabolic activities, including the regulation of the cellular metabolism and the control of the cell cycle.

Chloroplasts, while also energy-related as they carry out photosynthesis, are primarily found in plants and some algae, converting sunlight into chemical energy. The nucleus serves as the control center of the cell, housing genetic material and regulating gene expression. The endoplasmic reticulum is involved in protein and lipid synthesis and transportation, but does not produce energy directly. Thus, the distinct role of mitochondria in generating ATP justifies their designation as the cell's "powerhouse."