Which of the following would be classified as an organelle?

An organelle is a specialized subunit within a cell that has a specific function. The mitochondrion is a well-known organelle that plays a crucial role in energy production through ATP synthesis during cellular respiration. It is often referred to as the powerhouse of the cell because it generates the energy required for various cellular processes.

While ribosomes and the nucleus are also key components of the cell, they are classified differently. Ribosomes, for example, are not considered organelles in the same way that mitochondria are; rather, they are ribonucleoprotein complexes involved in protein synthesis. The nucleus, on the other hand, is indeed classified as an organelle as it houses the cell's genetic material and controls cellular activities.

Option D suggests that all listed choices fall under the category of organelles, which is also accurate. Consequently, the choice that solely identifies mitochondrion overlooks the broader classification of the nucleus and ribosomes. Understanding this distinction helps clarify the varied functionalities and classifications of cell components within cellular biology.