Which organelle is known as the powerhouse of the cell?

• A. Ribosome
• B. Golgi apparatus
• C. Nucleus
• D. Mitochondria

Answer: (D)

Mitochondria are known as the powerhouse of the cell because they are primarily responsible for producing adenosine triphosphate (ATP), the energy currency of the cell. Through a process called oxidative phosphorylation that occurs during cellular respiration, mitochondria convert the energy stored in food molecules into ATP. This process involves several critical steps, including the Krebs cycle and the electron transport chain, which take place within the mitochondria's inner membrane and matrix.

The unique double-membrane structure of mitochondria also supports their function, as it provides compartments that facilitate various processes necessary for ATP production. Furthermore, mitochondria contain their own DNA and ribosomes, which allows them to produce some of the proteins needed for their function independently of the cell’s nuclear DNA.

The other organelles listed do not share this primary function. Ribosomes are involved in protein synthesis, the Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles, and the nucleus serves as the control center of the cell, housing the genetic material and coordinating activities like growth and reproduction.