Structure of cell

Structure of cell

Cell wall

In plant cell there is a rigid cell wall which is non living and freely permeable. It is made up of cellulose or chitin. It provide shape and rigidity to the cell.
Cell wall of bacteria is made up of peptidoglycan.

Cell membrane

It is also known as plasma membrane which form the outer covering of animal cell. It plant cell it is found within cell wall. It is thin, elastic, living, double layer, permeable membrane. It is made up of phospholipid molecules.
Function : It regulates movement of molecules inside and outside of the cell.

Protoplasm

The whole fluid present inside inside plasma membrane is protoplasm. The name protoplasm is given by Purkenje in 1839. Protoplasm is made up of various chemical substances like water, ions, salt and organic molecule. It is the living part of cell.
Protoplasm is divided into two parts :
i.   Cytoplasm : The fluid found outside the nuclear membrane.
ii. Nucleoplasm : The fluid found inside the nuclear membrane.
»   99% of protoplasm is made up of oxygen (76%), carbon (10.5%) hydrogen (10%) and nitrogen (2.5%).
»   80% of protoplasm is water.
»   The ratio of inorganic and organic compound found in protoplasm is 81:19.

Golgi bodies

Discovered by scientist Camilo Golgi. Golgi bodies are made up of group of tubes, vesicles and vacuoles. In plant it is more in number and here it is known as dictyosomes.
Function : It work as storage, processing and packaging of material. It also involved in the synthesis of cell wall, plasma membrane and lysosomes.
» It help in the synthesis of carbohydrate from simple sugar which combine with protein made by ribosome forming glycoprotein.

Endoplasmic reticulum

Membranous network of tubules like structure found in cytoplasm is called endoplasmic reticulum. It is attached with the nucleus on one side and on other side it is joined with plasma membrane.
Function: Endoplasmic reticulum helps in the distribution of material. It forms supporting framework of cell.

Ribosome

Discovered by Palade. Small granules like structure found attached to the endoplasmic reticulum or in free state. It is made up of ribonucleic acid (RNA).
Function: Take part in protein synthesis.

Lysosome

Discovered by De Duve. These are sac like structure bounded by single membrane and contain hydrolytic enzyme.
Function : It helps in intracellular digestion. The enzyme found in lysosome may digest the entire cell. So it is also known as suicidal bag.
Lysosome is not found in Red blood corpuscles of mammal.

Centrosome

Discovered by Boveri. It is only found in animal cell taking part in cell division. It is not bounded by membrane consist of two centriole.
Function : Help in the formation of spindle fibre between pole during cell division.

Plastid

Only found in plant cell. It is of three type :
(a) Chloroplasts : These ate green pigment found in green plant involve in photosynthesis. So, it is known as 'Kitchen of the cell’ Chloroplast is bounded by two unit membrane having grana and stroma. Grana are membrane bounded sac present like structure found in stacks containing chlorophyll molecule. Stroma is the matrix present inside the chloroplast which contain photosynthetic enzymes and starch grain. Granum is the site of light reaction during photosynthesis while storm is the site of dark reaction.
Function : Chloroplast provides green colour to plant & take part in photosynthesis.

(b) Chromoplast: provides various colours to the plant like flower, fruit etc.
» Chromoplasts are of different kind.
» Lycopene : In tomato it provide red colour.
» Carotine: Provide yellow or orange colour in plant.
» Betanin : Found in sugar beet.

(c) Leucoplast:It is colourless. It stores the food in the form of starch, fat & protein.
» Leucoplast is found in root and underground stem.

Vacuole

It is fluid filled single membrane bounded, dead organelles of cell. In plant cell it is larger in size but in animal it is smaller in size.
Function : It helps in osmoregulation. It stores toxic metabolic waste.

Nucleus

The nucleus is a spherical, centrally located is a major structure found in the cell. In plant cell it is shifted towards periphery. It is bounded by double layered nuclear membrane having pore. Within nucleoplasm nucleolus and chromatin material is present. Nucleolus is rich in protein and RNA. Chromatin material is thin thread like structure forming network. This is made up of genetic substance DNA (deoxyribo nucleic acid) and histone protein. During cell division chromatin breaks into pieces and form chromosome.
Function: It controls all the activity of cells. So it is also known as 'control room' of cell. Chromatin transmits hereditary characters from parents to their offspring.
» Other than nucleus DNA is also found in mitochondria and chloroplast.

Difference between Plant and Animal cells

Plant cell	Animal Cell
Plant cells are larger in size	Animal cells are generally smaller in size
Plastid present	Plastid absent
Cell wall present, made up of cellulose and chitin	Cell wall absent
Centrosome absent	Centrosome present
Vacuoles are larger in size	Vacuoles are smaller in size

»   Cell becomes turgid because of endosmosis
»   The process of imbibition involves both diffusion and capillary action.
»   A cell increases in volume when it is placed in hypotonic solution.