Which is the largest of these tissue Organ System cell or organ?

Cells are always the smallest unit in thinking about cells, tissues, organs, organ systems, and the organism. From smallest to largest, the order is:

1. cells, which specialize and make specific types of tissues
2. tissue, made up of specialized cells
3. organs, made up of specialized tissues
4. organ systems, made up of one or more organs that are specialized to do a specific function
5. the entire organism, which includes all of the organ systems.

See question: What is the highest level of organization of these structures cells tissues organs organ system organism