Photosynthesis :- Chloroplast and functions

 

Q. 2: Describe ultra – structure of chloroplast.  

     Write a note a Grana of chloroplast:               

                Draw a well – labelled diagram of chloroplast:

1)  Chloroplast is found in plant cells only.

2) Chloroplast is considered as site of photosynthesis.

3) It is a double membranous structure and the membranes are made up of lipids and proteins i.e. lipoproteins in nature.

4) The membranes are also called as peristomium.

5) Outer and inner membranes are smooth and continuous in nature.

6) Outer and inner membranes are separated by space called as inter membranous space or periplastidal space which is filled up with watery fluid called as peristomium fluid.

7) Functionally, these two membranes are selectively permeable and allow entry and exit of certain substances only.

8) Chloroplast shows two structural components which are as follows:

A) Grana:          

i)  It is made up to thylakoids or lamellae arranged similar to stack of coins.

ii) Each granum shows presence of 8 – 12 thylakoids.  Each thylakoid is made up of 225 to 230 quantosomes.

iii) Each quantosomes shows presence of 4 photosynthetic pigments namely chl–a chl–b, carotenoids and xanthophyll.

iv) Due to presence of quantosomes appearance is granular, hence the name grana.

v)  Grana is responsible for absorption of light and its conversion into ATP.

vi) Grana acts as site for light reaction or photochemical phase.

B) Stroma:

i)  It is homogenous matrix or ground substance.

ii) It shows presence of its own DNA called as ct DNA or plastidome (Plastids), RNA, ribosomes, ions, enzymes etc.

iii) DNA can synthesize different types of enzymes required for various biochemical reactions.

iv) It acts as site for enzyme dependent reactions of photosynthesis (biochemical phase or dark reaction or light independent phase). 

9) Due to presence of DNA, chloroplast becomes semiautonomous structure but it cannot duplicate itself.

 

 

 Q.3: Give various functions of chloroplast    

OR             

       Give different functions of grana and stroma of the chloroplast.

Ans.: A) Grana:

1.  Different photosynthetic pigments absorb solar energy and chl-a converts it into ATP i.e. biologically usable form of energy.

2. Photolysis of water i.e. splitting of water molecule in the presence of light and chlorophyll into its components is carried out in grana.

It releases molecular oxygen.

        2H2O2H2 +O2­

3) Assimilatory power of photosynthesis i.e. ATP and NADPH2 are synthesized in grana.

4) Grana serves as a site for light reaction.

B. Stroma:

1) It is a site of CO2 fixation and its reduction into stored food i.e.; glucose.

2) It brings about synthesis of different types of enzymes required for CO2 fixation.

3) It acts as a site for dark reaction or biochemical phase.