Question

Dark reaction of photosynthesis does not need light. Do plants undergo dark reactions at night?

Answer 1

Hint: Plants do photosynthesis at a very slow rate in the night. They need sunlight to make their food. Conversion of sunlight to chemical energy needs electrons, ATP, NADPH etc. they run through a cascade to produce $C{O_2}$, water and energy.

Complete answer:
Photosynthesis is the process of making plant food in the presence of sunlight. This process occurs in the chlorophyll in the plastids. The photosynthesis process is done by absorbing the sunlight and converting it into chemical energy.
The process needs light to occur. It has two photosystems- light reaction and dark reaction. Dark reaction is named so as it does not require light for its working. But it does not mean it occurs in the night as it just needs the products from the light reaction to occur. So both the processes occur in the day time.
Plants do photosynthesis at a good rate on the day only. So the light reaction will produce NADH, ATP which will be used by the dark reaction.
In the dark reaction, carbon dioxide is reduced to carbohydrate. It occurs in three steps- carbon fixation, reduction and regeneration. The Calvin cycle in stroma occurs in the presence of light and the products are used in the dark reaction. This reaction occurs outside the thylakoids. The products are sugar molecules and other organic molecules that are used for the cell to function.

Note: Dark reaction was given by Calvin. This reaction is also called the ${C_3}$ cycle or the reductive pentose phosphate process. The plants carrying out the Calvin cycle are called ${C_3}$ plants. The Calvin cycle occurs in three steps- fixation, reduction and regeneration.