With the introduction of electron microscopy, it was made possible to observe internal cell structures. It was discovered (1940) that in some cells (e.g. typical bacteria), the genetic material was not enclosed by a nuclear membrane. In other cells (algae, fungi, protozoa), the nucleus was enclosed in a membrane. This resulted in the division of these organisms into Prokaryotes and Eukaryotes. Bacteria are prokaryotic (absence of nuclear membrane) microbes. Fungi, algae, protozoa, and plant and animal cells are eukaryotic (presence of nuclear membrane) (Fig.1.). A comparison of prokaryotes and eukaryotes is given in Table.
Prokaryotes v/s Eukaryotes
| Character | Prokaryotes | Eukaryotes |
| 1. Nucleus: Nuclear membrane Nucleolus Chromosome Mitotic division Deoxyribonucleoprotein | Absent Absent One (circular) Absent Absent | Present Present More than one (linear) Present Present |
| 2. Cytoplasm: Cytoplasmic streaming Pinocytosis Mitochondria Lysosomes Golgi apparatus Endoplasmic reticulum Chloroplasts Membrane-bound (true) vacuoles Ribosomes Gas vacuoles Mesosomes | Absent Absent Absent Absent Absent Absent Absent Absent 70S, distributed in the cytoplasm Can be present Present | Present Present Present Present Present Present May be present Present 80S arrayed one membrane as in endoplasmic reticulum, 70S in mitochondria and chloroplasts Absent Absent |
| 3. Outer cell structures: Cytoplasmic membranes Cell wall Locomotor organelles Pseudopodia | Generally, sterols absent Peptidoglycan present Simple fibril Absent | Sterols present Peptidoglycan absent Multifibirilled with ‘g + z’ microtubules. Present in some. |
| 4. Examples: | Bacteria, rickettsiae, chlamydiae, actinomycetes. | Fungi, protozoa, algae, plants, animals. |
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