SHORT COMING OF CELL THEORY / EXCEPTIONS OF CELL THEORY
(i) Viruses can be considered as exception to cell theory. They are made of proteins and ones of nucleic acid i.e.
DNA or RNA. They are inert except when in a living cell. They are incapable of self regulation, self reproduction and independent existance, so they lack protoplasm, the essential part of the cell.
(ii) Bacteria & Blue green algae, which are prokaryotes lack well organised nucleus, nuclear membrane, nucleolus and nucleoplasm. Chromatin is in direct contact with cytoplasm.
(iii) Protozoans are not cellular, they are acellular. i.e. there body is not divisible into cells.
(iv) Coenocytic hyphae of Rhizopus (fungus) and algae like Vaucheria are multinucleate and aseptate. RBCs lose nuclei and many organelles but still keep living.