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

Please read in the explanation section.

Explanation:

At the time of photosynthesis, daylight is used by the plants to transform water and dioxide into the aldohexose and gas. Three types of reactions can occur inside of the stroma in three conditions. Those are briefly given below:

Requirement (a)

Bright Sunlight: In the bright daylight, usually high energy sugars are produced. The Calvin cycle occurs within the stroma. ATP and NADPH, which were produced during photosynthesis, are used in this Calvin cycle. Using this Calvin cycle,  the products ATP and NADPH are used to transform the molecules of carbonic acid gas into high-energy sugars. These sugars are used later in the further cellular processes.

Here, photosynthesis changes sunlight into chemical energy. Here, spiling water has done to release O2 and to makes CO2 into sugar.

Requirement (b)

Darkness: As well as the bright sunlight stage, In the dark, the Calvin cycle continuously happens within the stroma. At this stage, sugar also produced. During the Calvin cycle, the products ATP and NADPH are used to transform the molecules of CO2 into high-energy sugars. We can say that the same reactions like bright sunlight occurs in the darkened stage.

In this stage, ATP gives the energy, and NADPH provides the electrons. To fix the CO2 into carbohydrates, energy and electrons are required.

Requirement (c)

Extended darkness period: Here, decrease condition found. There will be a decrease in the rate of products ATP and NADPH if the plants are present within the dark period for a long time. During the dark period, the Calvin cycle can't be continued. This happens because the production rate of ATP and NADP reduced because of the lack of sunlight.

As the Calvin cycle stops here, no significant chemical reaction found in this stage.