Which of the following components would NOT be found in the cytoplasm of a cell?

The nucleus is correctly identified as a component that would not be found in the cytoplasm of a cell. The nucleus is a membrane-bound organelle that houses the cell's genetic material (DNA) and is responsible for directing cellular activities, including growth, metabolism, and reproduction. It is enclosed by a nuclear envelope, which separates it from the cytoplasm, the gel-like substance that fills the cell.

In contrast, mitochondria, ribosomes, and the endoplasmic reticulum are all components that exist within the cytoplasm. Mitochondria are known as the powerhouses of the cell, where energy production occurs. Ribosomes are the sites of protein synthesis, and the endoplasmic reticulum is involved in the synthesis of proteins and lipids as well as processing and transporting these molecules. Thus, they play essential roles within the cytoplasm, while the nucleus functions independently, making it distinct from the cytoplasmic components.