The Cell Theory is a fundamental principle in biology that states that all living organisms are composed of cells, that cells are the basic unit of structure and function in living organisms, and that all cells arise from pre-existing cells.

Option 1: Bacteria - Bacteria are single-celled organisms that have their own cellular structure and function. They fit into the Cell Theory.

Option 2: Virus - Viruses are considered acellular because they are not made up of cells. Instead, they are composed of genetic material (DNA or RNA) enclosed in a protein coat. They are unable to perform cellular functions on their own and can only replicate inside host cells. Therefore, viruses do not fit into the Cell Theory.

Option 3: Fungi - Fungi are multicellular organisms composed of eukaryotic cells. Each fungal cell has its own cellular structure and function, conforming to the principles of the Cell Theory.

Option 4: Plants - Plant cells are also eukaryotic cells that make up multicellular organisms. They clearly fit into the Cell Theory.

Therefore, among the given options, the organism that does not fit into the Cell Theory is the virus (Option 2).