Which of the following is required for photosynthesis to take place?

a. sugar

b. oxygen

c. ATP

d. water

the answer is A.

For photosynthesis to take place, the sugar called ribulose is needed. It is used during the light independent reactions or Calvin cycle of photosynthesis.

During the first phase of the Calvin cycle called the carboxylation phase, a carbon dioxide molecule is added onto a ribulose sugar to form a 6-carbon intermediate which because of its instability immediately disintegrates to form two identical molecules of a 3-carbon molecule known as 3PGA (3-phosphoglycerate).

3PGA is then converted to a G3P (glyceraldehyde-3 - phosphate), a 3-carbon sugar that is then used to make glucose, starch, sucrose and plant cellulose