Explain the processes that take place in the stroma including the reactants going in and the product from these processes in (a) bright sunlight and in (b) darkness. (c) what happens over an extended period of darkness of many days?

In daylight calvin cycle occurs, in darkness Calvin cycle occurs along with conversion of CO2 into sugar and in extended darkness Calvin cycle stops

Explanation:

During daylight, Calvin cycle takes place within the stoma. In this process, energy obtained from sun is converted and stored into bio molecules namely ATP and NADPH.  

During darkness, Calvin cycle takes place but the energy of biomolecules i.e ATP and NADPH is used to convert carbon dioxide into sugar. Prolonged exposure to darkness causes reduction in production of energy molecules. Also, the Calvin cycle stops in extreme darkness for a long period of time.

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