What are the roles of NADPH and ATP during the chemical stage of photosynthesis?

Answer 1

Photosynthesis is split into two separate phases: the light dependent reactions and the light independent reactions (also called the Calvin cycle or the "dark" reactions). ATP and NADPH have different roles in each of the reactions, so let's look at the two separately.

In the light dependent reactions, the plant cell is harvesting energy from light and turning it into chemical energy. The forms of chemical energy made are NADPH and ATP (from their low energy forms of NADP⁺ and ADP). So basically the cell takes the light energy and turns it into usable energy in the forms of these two molecules. That is simple enough. But where do these molecules go afterwards? The purpose of creating this energy is actually to power the light independent reactions. So these two molecules are sent over to the second phase of photosynthesis.

In the light independent reactions, the plant cell is using the chemical energy made from the light dependent reactions and using it to make food. This would be like the energy from your oven necessary to cook something for you to eat. Instead of heat energy, the plant uses chemical energy. So the plant takes the NADPH and the ATP from the light dependent reactions and uses the energy to create the sugar Glucose. This can be stored by the plant and turned into energy for cell processes as needed. So what happens to the NADPH and ATP after they "lose energy"? The light independent reactions turn NADPH back into NADP⁺ and ATP back into ADP.

In case you are wondering, NADP⁺ and ADP don't just disappear. They travel back to the light dependent reactions to be turned back into NADPH and ATP again. So they are recycled back and forth.

So in summary, there are two main roles of NADPH and ATP: (1) they tie the light dependent reactions and the light independent reactions together and (2) they act as sources of energy to take the energy from the sun to the light independent reactions to make the plants food.

I hope this helps! I highly encourage you to look up a picture of Photosynthesis on Google so you can see the connection between these two! Let me know if you need any further clarification.