Question

five phase of dark stage reaction

Answer 1

Answer:

Explanation:

Photosynthesis has two main phases:

-The Light Dependent Reactions

-The Calvin Cycle

The light dependent reactions are a series of reactions that occur in the stroma in the chloroplast that produce ATP and NADPH through complex systems of reactions known as Photosystem II and I.

The Calvin Cycle are the light independent reactions (dark reactions is not technically correct because the products of the Light dependent reactions of photosynthesis are what the Calvin Cycle uses to produce glucose and oxygen) The Calvin Cycle is a multi step cycle that basically produces glucose and oxygen. There are three main phases: Carbon Fixation, Reduction, and Regeneration. During Carbon Fixation, Rubisco picks up CO2 and fixes it to make 3-PGA while ATP becomes ADP. During Regeneration, NADPH becomes NADP+ and a Phosphate, and 3-PGA becomes G3P. For everything that I mentioned, there are 6 of them in each Cycle, and 1 G3P leaves the cycle, and 1/2 molecule of Glucose, so 5 G3P molecules keep on going. During Regeneration, 2 Phosphate groups leave, then 3 ATP becomes 3 ADP, and 5 G3P becomes 3 RuBP. This repeats over and over again.

Sometimes, Rubisco picks up an O2 instead of a CO2. That starts something called Photorespiration. Basically in photorespiration, the O2 gets fixed to become 3-PGA, and Phosphoglycolate. Phosphoglycolate is the toxic byproduct of photorespiration, and is the reason that photorespiration can kill a plant. The phosphoglycolate initiates a salvage pathway that loses 3 fixed CO2 molecules, and produces 3 more 3-PGA. Since we now have 9 3-PGA, those become 9-G3P but no glucose is made. After that, there is not enough to regenerate the RuBP, so the cycle can’t work properly.

Some plants have adaptations against photorespiration. They are called C4, or CAM plants. C3 plants have no adaptation against photorespiration. C4 plants seperate the two steps of photosynthesis into two different types of cells. CAM (Crassulacean Acid Metabolism) plants seperate the two steps by day and night, and in that case calling the Calvin Cycle the Dark reactions is actually correct.