Unified Cell Theory
The present unified cell theory states that
In view of this present cell theory the living organisms may be broadly divided into:
The cellular forms may further be classified into:
a) Unicellular organisms with only one cell in their body, for example bacteria. blue-green algae, protozoans, etc. and b) Multicellular organisms having many cells in their body. In such forms the cells organise themselves into tissues, tissues into organs and organs into organ systems. Examples of these are animals ranging from sponges to man and plants ranging from most algae to all flowering plants.
Figure: Some unicellular organisms: (a) Bacterium (Escherichia coli), (b) Blue green alga,(c) Mycoplasma, (d) Amoeba (a protozoan), (e) Chhydomonus (an alga), and (f) Mucor (a fungus)