What are the exceptions to cell theory

Cell theory explains the basic characteristics of cells, but there are some exceptions. These exceptions include viruses, coenocytic organisms, mitochondria, chloroplasts, red blood cells (RBCs), and sieve tube cells.

1. Viruses- Viruses are not considered cells because they don’t have the structures or processes that cells do. They are non-cellular and exist somewhere between living and non-living things.
2. Coenocytic Organisms- These organisms have many nuclei inside one large cell instead of one nucleus per cell. This goes against the idea that each cell has a single nucleus. Examples are some fungi like Rhizopus and algae like Vaucheria.
3. Mitochondria and Chloroplasts- These tiny parts inside cells have their own DNA and can reproduce by themselves. Because of this, they don’t completely follow the rule that all cells come from existing cells.
4. Red Blood Cells (RBCs)- Mature red blood cells in mammals do not have a nucleus or other cell parts that are usually important. Even so, they are still considered living cells because they carry out their job of transporting oxygen.
5. Sieve Tube Cells- These special plant cells don’t have a nucleus when mature, which makes them another exception to the cell theory.