Different kinds of cell found in the human body
Cell Shape : Cells are of variable shapes and sizes. Their shape is according
to the function. Generally cells are spherical but they may be elongated (nerve
cell), branched (pigmented), discoidal (RBC), spindle-shaped (muscle cell) etc.
Cell Size : Size of cell is variable depending upon the type of organism.
Some are microscopic while some are visible with naked eyes. Their size may
vary from 0.2 mm to 18 cm.
• Size of a typical cell in a multicellular organism ranges from 20-30 mm
The largest cell is ostrich egg (15 cm in diameter with shell & 8 cm in
diameter without cell).
• The longest cell is nerve cell (upto 1 m or more).
• Smallest cells so far known are PPLOs e.g., mycoplasma (0.1 mm in
• Human egg is 0.1 mm in diameter.
Components of Cell
There is an occurrence of division of labour within a cell as they all got certain
specific components called ‘Cell organelles’. Each of them perform a specific
The three basic components of all the cells are :
Cell Membrane :
(a)Cell membrane is also called as plasma membrane or plasma lemma.
(b)It is the limiting boundary of each cell which separates the cytoplasm from its surroundings.
(c)It is found in both plant as well as animal cells.
(d)It is the outermost covering of a cell in case of animals and lies below the cell wall in case of plants.
(e)It is made up of proteins and lipids where proteins are sandwiched. between bilayer of lipids.
(f)Plasma membrane is selectively permeable in nature. It allows or permits the entry and exit of some materials in and out of the cell.
(g)Singer and Nicholson gave the fluid mosaic model of plasma membrane. According to them, it consists of a protein layer sandwiched between two layers of lipids. It is in quasifluid state.
It is 75A thick.
(h)It is flexible and can be folded, broken and reunited.
Functions of Plasma Membrane :
(a)It regulates the movement of molecules inside and outside the cell.
(b)It helps in maintaining the distinct composition of the cell.
(ii)Transportation of molecules across the Plasma Membrane :
This can be done by following ways :