Body of livings are composed of many tiny structures i.e. cell. Cell is considered as a structural, functional and biological unit of life .Cell is also known as building block of life.
Study of cell is called “Cytology”.
The cell was discovered by “Robert Hook” in 1665.
 |
| Cells in Onion peel |
Cell theory
Schwann & Schleiden proposed "Cell theory" in 1839 . According to this theory-
1. All living things are made up of one or more cells.
2.Cells are the basic living units within organisms and the chemical reactions of of life take place within the cell.
3.All cells arises from pre-existing cells.
Cells are of two types i.e. Prokaryotic cell and Eukaryotic Cell.
Prokaryotic cell
This cell is seen as bacteria and blue green algae.
Prokaryotic cells do not have developed nucleus. There are no nuclear membrane and nucleolus. Cell membrane is found . Circular DNA is found and in direct contact of cytoplasm. Mitochondria ,chloroplast are absent in these cells. Ribosomes are of 50 S & 30 S type in prokaryotic cells.
Single chromosome is found and is circular in nature. Prokaryotic cell shows binary fission.
 |
| Bacteria :A prokaryotic cell |
Eukaryotic Cell
Eukaryotic cells contain true nucleus with double membranous nuclear membrane. Nucleolus is present in nucleoplasm. Well developed, membrane bounded cell-orgenelles like mitochondria ,chloroplast (algae& plants) endoplasmic reticulum etc ,are found in eukaryotic cell. DNA is associated with histones proteins to form chromosomes . Chromosomes are found inside nucleus. Eukaryotic cells show Mitosis & Meiosis cell divisions.
Ex- Plant cell & animal cell.
 |
| A typical Plant Cell |
Differences between Plant cell and animal cell
Properties
|
Plant Cell
|
Animal Cell
|
Cell
wall
|
Cell wall of cellulose is present .
|
Absent
|
Chloroplast
|
Present
|
Absent
|
Vacuoles
|
Larger than animal cells.
|
Absent
or tiny.
|
Centrosomes
|
Absent
|
Present
|
Lysosomes
|
Absent
|
Present
|
