In 1968, German scientists Theodore Schwann who was a zoologist and Matthias Scheilden who was botanist proposed cell theory when they werestudying tissues. They proposed spontaneous generation as the method for cell origination but spontaneous generation later proven and called as abiogenesis.
Cell theory states as follows:
· All living organisms are composed of cells. They may be unicellular or multicellular.
· Cell is the basic unit of life.
According to Rudolf Virchow “omnis cellulae e cellulae” means all cells arises from pre- existing cells.
Modern version of cell theory:
· Energy flows occur within cells.
· Cell contains hereditary information (DNA) which is passed on from cell to cell during cell division.
· All cells have same basic chemical composition and metabolic activities.
· Cell is the fundamental unit of structure and function in living being.
· All basic chemical and physiological functions are carried out inside the cells.
· Cell activity depends on the activities of sub cellular structure within cells.
Major events in studying cells are compiled in such ray diagram:
Plant cell and animal cells structure differs in many aspects. The main difference is the presence and absence of cell wall.
Prokaryotes are primitive organisms as their name suggest where all cell oragnelles are not well developed while eukaryotes are developed organisms with well defined cell organelles
Organisms are composed of cells which have some special structures that help them to perform some special functions. These structures are known as cell organelles. Such organelles are nucleus, ER, golgi body, lysosome, chloroplast, mitochondria.