Functions of organelles:

(a) Endoplasmic reticulum(ER):

These are continous membrane systems joined to the nuclear membrane on one hand and to the cell membrane on the other. the major functions of E.R. are the following :

(i) It forms the skeletol framework.

(ii) It helps in active transport.


(iii) Metabollic activities i.e. protein synthesis occurs in rough E.R.

(iv) It provides increased surface area for protein synthesis.

(v) It helps in formation of new nuclear membrane(middle lamella) during cell division.

(vi) The smooth ER helps in lipid, glycogen and steroid synthesis.

(b) Chloroplast:

It is the familiar type of plastid containing photosynthetic pigment – the chlorophyll.


Chloroplast is surrounded by two unit membranes. The internal structure shows the colourless ground substance called stroma in which dark reaction occurs and closed flat sac like membrane system called grana where light reaction (photochemical) occurs. The major functions of the chloroplast are given below:

(i) Absorption of light energy by the pigments systems present in thylakoidas.

(ii) Evolution of oxygen through the process of light reaction during photlysis of water.


(iii) Production of NADPH2 and ATP, which are considered as the assimilatory powers of photosynthesis.

(iv) Transfer of CO2, obtained from the air during dark reaction to the 5 carbon sugar called Ribulose 1, 5 diphosphate present in stroma.

(v) Breaking 6- carbons compound into two molecules of P.G.A. from which various types of carbohydrates are formed.

(c) Mitochondria:

It is a highly speciallised organ present in the eukaryotic cells. The functions of the mitochondria are as follows:


(i) Mitochondria are known as the powerhouse of the cell because of the formation and storage of energy-rich compound ATP.

(ii) Mitochondria are concerned with oxidative phosporylation reactions of Kerbs cycle during respiration.

(iii) It is also in volved in the oxidation of proteins and fats.