Study of cell


Cell is the basic structural and functional unit of life.
»   The word 'cell' was first coined by British scientist Robert Hook in the year 1665.
»   Study of cell is called cytology.
»   The smallest cell is Mycoplasma gallisepticum.
»   The longest cell in human body is Neuron.
»   The biggest cell is egg of Ostrich.
»   Schilden and Schwan established cell theory in the year 1838-39

Main features of the cell theory
1. All organism are composed of cell.
2. Body of every organism is made of cell.
3. Each cell arises from pre-existing cell.
4. Every organism starts its life from single cell.

Types of Cell

1. Prokaryotic cell
These are primitive cell having three basic structure f typical cell but lack nuclear membrane. Nuclear material is present in a region of cytoplasm called nucleoid. Other membrane bound organelles are absent such as mitochondria, lysosome, golgi bodies etc. Ex.-Virus, bacteria and cynobacteria are Prokaryotes.
»   Number of Mitochondria in bacterial cell is zero.
»   The smallest known prokaryotic organism is Mycoplasma.

2. Eukaryotic cell
These are complete cell which contain membrane bound organelles and nucleus. Unicellular and multicellular plant and animal have Eukaryotic cell.
»   The biggest single called organism is Acetabularia.
»   Nucleus contain chromatin made up of DNA and histone protein.
»   Nucleolus is present inside nucleus.

Difference between Prokaryotes and Eukaryotes Cell

Prokaryotes Eukaryotes
Size of cell is generally small Size of cell is generally large
Cell division takes place by fission or budding Cell division takes place by mitosis and meiosis
Membrane bound cell organelles are absent Cell organelles present
Nucleus absent Nucleus present
It contain single chromosome which is circular in shape It contains more than one chromosome