What are dark reactions ?

Dark reaction or biosynthetic pathway is the reaction which is not directly dependent on light but is dependent on the products of light reaction which are ATP and NADPH.  The ATP and NADPH are used to drive the processes leading to the synthesis of food. 
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Name the parts of ATPase enzyme. 


The ATPase enzyme consists of two parts:
i. Fo portion -   which is embedded in the membrane and forms the transmembrane channel tahat carry out the diffusion of proteins across the mebrane. 

ii. F1 portion - which protrudes on the outer surface of the thylakoid membrane on the side that faces the stroma.


 

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How many pigment molecules are involved in photosynthesis ?

Four pigment molecules are involved in photosynthesis. They are :
i. Chlorophyll a,
ii. Chlorophyll b,
iii. Xanthophylls and
iv. Carotenoids 
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What is reaction centre ? Why these are called P700 and P680?

A photosynthetic reaction centre is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. The single chlorophyll a molecule forms the reaction centre. The reaction centre is different in both the photosystems. In PSI the reaction centre chlorophyll a has an absorption peak at 700nm, hence is called P700, while in PSII it has absorption maxima at 680 nm and is called P680.

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Give an experiment to prove that CO2 is necessary for photosynthesis.

To prove that CO2 is necessary for photosynthesis the following experiment can be formed:

1. A potted plant is kept in dark for three days so that the leaves become free from starch.

2. A healthy leaf is selected for experiment.

3. a wide mouth bottle is taken and a little KOH (it absorbs CO2) is added to it. 

4.Half part of the leaf is kept in the bottle with the help of split cork.

5. The apparatus in kept in bright sunlight for few hours.

6. The leaf is plucked and boil in 70% alcohol. It is stained with iodine solution.

Observation : It was observed that the portion of leaf which was out of the bottle turned blue showing the presence of starch. The portion on leaf which was enclosed within the bottle will not show the presence of starch .

Give an experiment to prove that CO2 is necessary for photosynthesis.

 

Conclusion : This shows that CO2 is essential for photosynthesis, because the portion inside the bottle did not get the CO2 as it was absorbed by KOH solution. Thus CO2 is necessary for photosynthesis.

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