Question

Why is it important in photosynthesis that there is a light and dark reaction, what are the key features of these processes and how do they interact with each other?

Answer 1

Photosynthesis includes both reaction light reaction and dark reaction occurs in chloroplast.

Both reaction is important function in synthesis of food .

Light reaction, occurs in Granada part of chloroplast, required presence of light and end product of this reaction are ATP, NADPH and oxygen. These products ATP and NADPH are utilized in dark reaction for synthesis of food in dark reaction.

Dark reaction also known as calvin cycle synthesize food . This occurs in stroma, do not require light as such directly. But it depends on the product formed in the light reaction.  

Dark reaction although occurs in dark , but it depends on product of light reaction. If light is not present than light reaction will not occur and there will be no NADH and less ATP . As these are required for synthesis of starch so dark reaction will also stop and there will no food form .