cell organelles and their functions

cell organelles and their functions

Cell and Cell Organelles

cell organelles and their functions – Shape of the cell : Cells may be spherical, cylindrical, rod shaped, hexagonal or of irregular shape.

– Size of the cell : The size of cell ranges from 0.2u to 0.5u in bacteria to up to 75 mm in the case of Ostrich eggs. But most of the cells are cylinders of 15-30 u in diameter.

– The number of cells in an individual may range from one (Bacteria) to 6 x 10″ (Human beings) to even a large number in animals like whales and elephants.

– The following structures are visible under electron microscope.

i) Cell wall 

ii) Plasmalemnma

iii) Endoplasmic reticulum 

iv) Ribsome 

v) Glgi bodies 

vi) Lysosome 

vii) Spherosomes

viii) Chloroplasts

ix) Mitochondria 

x) Nucleus etc. 


Read Organelle Wikipedia – https://en.wikipedia.org/wiki/Organelle


cell organelles and their functions


Cell wall 


– It is the non-living component of the cell and is secreted by living portion of the cell.

– The main functions of the cell wall is to provide plant cells a definite shape, mechanical support and strength to tissues and orgains.

– A typical cell wall is composed of three different regions

a) Middle lamella, b) Primary wall and c) Secondary wall.


a) Middle Lamella 

– It acts as a comenting layer betwcen the two adjaccnt cells.

– It consists of Ca and Mg pectates.

– Pectic substatances are a mixture of polygalactourons and polysaccharides.


b) Primary Wall 

– It is deposited after the formation of middle lamella.

– It lies between middle lamella and plasmalemma.

– It is composed of hemicellulose (53%), cellulose (30%), pectin (5%), Protein (5%) and lipid (7%).

– It is the principal wall layer of mesistematic cells, chlorophyllous cells and true parenchyma.


e) Secondary Wall

– It is the last to be deposited and lies between primary cell wall and plasma lemma.

– It is innermost layer of cell wall, – It is composed of cellulose, lignin and suberin.


Plasma Lemma 

– The membrane enclosing cytoplasm of a cell is known as plasma lemma or plasma membrane.

– It is composed of lipids and proteins

– Protoplasm consists of cytoplasm and nucleus and is externally bounded by the cell membrane.




– The term protoplasm was coined by Purkinje for the living substance universatly present in all cells.

– It is the living, colloidal, semifluid substance of changing consistencies.


Functions of cell membrane 

– it acts as permeability barrier which controls diffusion of ions.

– It acts as mechanical frame of the cell.

– It acts as vehicle for transport of substances from one organelle to another.



– The living part of the protoplast surrounding the nucleus is known as cytoplasm.

– It is externally bounded by cell meinbrane and internmally by vacuolar membrane.

– It is semipermiable in nature.

– It acts as a medium for transport of the various cellular products & intracellular movements.

– It provides matrix in which the cytoplasmic organelles remain floating.

– The cytoplasmic inclusions are of two types

 a) Living cytoplasmic organelles and ii) nonliving inchisions. (Vacuole)



– They are discoid organelles abbut 5um in diameter and 3um in thickness.

– The term plastid was first used by Schimper (1885).

– There are three different types of plastids are present in the cell.


1) Chromoplasts

– These are coloured plastids containing variously coloured pigments.

– The coloured pigments belonging to carotenoid groups e.g, carotene and xanthophylls.


2) Leucoplasts

– These are coloured plastids originating from protoplstids and may be rod like, spherical or oval in shape.

– They are usually involved in the storage of food. e.g.

amyloplasts —— storage for starch

aleuroplasts —— storage of protein

lipoplast       ——  storage of oil



– They were first discovered by Anatony Von Lecuwenhoek

– They are small green bodies present in cytoplasm.

– The Chloroplasts of higher plants are mainly found in palisade and spongy tissue of leaves.

– They carry out the process of photosynthesis.



– The name mitochondria was given by C. Benda (1897).

– They are often called as bioplasts, chondriosomes, chondriomes etc.

– The are of universal occurrence in every living cell except that of prokaryotes.

– They are granular or rod shaped.

– Their diameter ranges from 0.05 um to 2.0 um and length of 7 um.



– They are known as power house of the cell as they are source of readily availab form of energy to be used in various cellular activities.

– The ATP molecules are formed during aerobic respiration.

– Frotein synthesis takes place in Mitochondria.



– The name ribosome was given by Hagnenan (1958).

– Their presence in plants was reported by Robinson and Brown (1953).

– They are particles of about 200 A° diameters.

– They are composcd of RNA and Protein.



– They provide proper site for binding of mRNA and its translation.

– They help in the process of protein synthesis.


Endoplasmic reticulum

– It was first discovered by Porter (1955

– They are present in all living cells of plants and animals.

– The endoplasmic reticulum arises from the outer membrane of nucleus forming network of tubules.



i) It forms skeletal framework within the cytoplasm

ii) Biosynthesis of fatty acids and phospholipids takes place with the help o endoplasmic Retiuculum.


Golgi Complex

– They were discovered by Camillo Golgi (1898) in the neural tissue.

– They ure variously called as Golgi bodles, Lipochondria and Golgiosome

– They are composed of 2-7 cistenae stacked close to cach other.



i) They participate in cell wall formation.

ii) They give rise to primary lysosomes

iii) They are involved in regulation of fluid balance.

iv) It is supposed to play a role in phospholipid synthesis and lipid absorption.



– These are round dense bodies observed in liver tissues.

– They were named by chirstian de Duve (1955).

– These contain hydrolytic enzymes and as a matter of fact, they act as lytic bodies and hence known as suicide bags of the cell.



ii) They are responsible for intracellular digestion.

ii) Autophagy — during adverse conditions they digest their own cell inclusions.

ii) They perform function of removing the dead cells known as autolysis.



– These are the subcellular filamentous components of eukaryotic cells.

– A single microtuble consists of 13 longitudinal profilaments.

– They are involved in i) Cellular motility ii) Chromosomal movement iii) Intracellular transport of materials and ix) Movement of organanelles within the cell.



– They were discovered by Dangeard (1919)

– These are minute spherical bodies lying free in the cytoplasa.

– They are thought to be involved in fat synthesis and storage and transport of lipids.



– Centrioles are cylindrical structures of about 1200-1500 A° in diameter and 3000- 5000 A° in length. They are always present in pairs

– They are confined to animal cells.

– They are involved in organization of spindle apparatus.

Vacuole : These are nonliving cell inclusions :

– Plant cells have one or more vacuoles of variable size.

– The material contained in the vacuoles called as cell sap.

– Vacuoles are surrounded by unit membrane called as tonoplast.



– It was first discovered by Robert Brown (1831) in an orchid cell.

– It is more or less spherical, tying in the cytoplasm and occupy two-thirds of the cell space.

– It is bounded by two unit membrane of lipoproteinous nature.

– The gap between two unit membrane is called perinuclear space.

– The semifluid substance present inside the nucleus is called as nuclear sap or nucleoplasm.


Chromatin Network

– This forms the skeleton of the nucleus.

– Chromatin threads are the sites of main genetic material which controls all activities of the cell.


Read more – cell division

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