What term is given to specialized cells that perform a specific function in an organism?

The term that refers to specialized cells performing a specific function in an organism is "tissue cells." These cells are organized to work together to perform particular tasks essential for the organism's health and survival. For instance, nerve cells, muscle cells, and blood cells are all specialized types of cells that contribute to the overall functioning of tissues, which in turn form organs and systems within an organism.

In general biology, specialized cells differentiate from common stem cells to take on distinct roles—such as conducting impulses, contracting for movement, or transporting oxygen—highlighting their importance in the structure and function of living beings.

The other options refer to different biological concepts. "Organ systems" are groups of organs that work together for a common purpose, "organelles" are specialized structures within cells that perform specific functions, and "protoplasm" is the gel-like substance within a cell that contains organelles and is essential for cellular processes, but it does not refer to a type of specialized cell.