During the daytime, plants produce energy in the form of ATP and NADPH (light reactions)...during the night, these energy forms go to the dark reactions (Calvin Cycle) to fuel the production of organic molecules from CO2 collected during the day...some of these organic molecules will be stored (starch) and some will be used for plant structural growth (cellulose), and some for other organic molecules (lipids, proteins, etc).
The energy harvested via the light reaction is stored by forming a chemical called ATP (adenosine triphosphate), a compound used by cells for energy storage. This chemical is made of the nucleotide adenine bonded to a ribose sugar, and that is bonded to three phosphate groups. This molecule is very similar to the building blocks for our DNA.
The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn't directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Actually, notice that the first product of photosynthesis is a three-carbon compound called glyceraldehyde 3-phosphate. Almost immediately, two of these join to form a glucose molecule.
and to answer ur desert plant question....
There is yet another strategy to cope with very hot, dry, desert weather and conserve water. Some plants (for example, cacti and pineapple) that live in extremely hot, dry areas like deserts, can only safely open their stomates at night when the weather is cool. Thus, there is no chance for them to get the CO2 needed for the dark reaction during the daytime. At night when they can open their stomates and take in CO2, these plants incorporate the CO2 into various organic compounds to store it. In the daytime, when the light reaction is occurring and ATP is available (but the stomates must remain closed), they take the CO2 from these organic compounds and put it into the Calvin cycle. These plants are called CAM plants, which stands for crassulacean acid metabolism after the plant family, Crassulaceae (which includes the garden plant Sedum) where this process was first discovered.
dark period=Calvin Cycle
Calvin Cycle= The Calvin cycle or Calvin-Benson cycle or Dark Reaction is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms
The second of the two major steps of photosynthesis (the other being the light reactions). The cycle fixes CO2 and produces carbohydrates
so do plants sleep at night? Nope!