Question

Why ATP is needed for dark reaction?

Answer 1

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Dark reactions make use of these organic energy molecules (ATP and NADPH). This reaction cycle is also called Calvin Benison Cycle, and it occurs in the stroma. ATP provides the energy while NADPH provides the electrons required to fix the CO2(carbon dioxide) into carbohydrates. So this two reactions are important for a photosynthesis

Answer 2

ATP is needed for dark reaction to fix Carbon-di-oxide.

Explanation:

Dark reaction is also known as Calvin Benson cycle. In this reaction the sunlight is not needed. The ATP is formed in first step of the photosynthesis and used in the body for the energy so the inorganic $CO_{2}$ needs to be transformed into the carbohydrate.  

This process takes place in the stroma in the leaf. ATP and NADPH added with the $CO_{2}$ and water forms carbohydrate as end product. So the ATP is necessary in the dark reaction.