The cell theory has three tenets:
- All life forms are composed of cells.
- Cell is the basic unit of life.
- Cells come from pre-existing cells.
The first part of the cell theory clearly states that cells make up all life forms on Earth. There are unicellular life forms (or prokaryotes, like bacteria, etc.) and multicellular life forms (or eukaryotes, such as human beings, animals, plants, etc.). All life forms are organic and are covered under this theory, i.e., all organic life forms are composed of cells. Cells are the basic units, as per the second tenet of the cell theory, and can carry out all the operation necessary to sustain and propagate life (such as, metabolism, reproduction, respiration, etc.). All these self-sufficient units combine together to form higher molecules, thus paving the way for higher organic life forms, like us.
Hope this helps.