What are specialized structures in a cell that perform specific jobs called?

Specialized structures within a cell that perform distinct, specific functions are termed organelles. Each organelle has a unique role that contributes to the overall operation and maintenance of the cell. For example, mitochondria are known as the powerhouses of the cell because they generate energy, while ribosomes are responsible for protein synthesis.

The term "cells" refers to the basic unit of life, which can contain many organelles but is not specific to the structures themselves. "Tissues" refer to groups of similar cells that work together to perform a particular function, and "organs" are composed of different types of tissues working together for broader biological functions in the organism. In this context, organelles are the correct choice, as they directly denote those specialized structures responsible for carrying out the individual tasks necessary for cellular function.