What is the term for a subunit within a cell that performs a specialized function?

The term for a subunit within a cell that performs a specialized function is "organelle." Organelles are distinct structures within a cell that carry out specific tasks vital for the cellular operations. For example, mitochondria generate energy, ribosomes synthesize proteins, and the endoplasmic reticulum is involved in the synthesis and processing of biomolecules. Each organelle contributes to the overall function and health of the cell, reflecting the complex and highly organized nature of cellular life.

In contrast, "tissue" refers to a group of cells that work together to perform a specific function in an organism, while "organ" signifies a structure made up of different tissues collaborating on broader tasks. The "cell membrane" is a protective barrier that encases the cell and regulates what enters and exits, but it is not classified as a subunit within the cell carrying out a specialized internal function. Thus, the correct answer effectively captures the essence of cellular organization and the roles of its components.