Biology · Photosynthesis in Higher Plants · NEET
No. The name 'dark reaction' only means light is not directly needed. It does NOT mean it happens at night. In fact it usually runs in daytime, right after the light reaction, because it needs the fresh ATP and NADPH made by the light reaction. NCERT even calls this name misleading, so it prefers 'biosynthetic phase'. For NEET, remember: dark reaction = light-independent, not night-time.
The light reaction takes place in the thylakoid membranes (the grana), because the pigments, photosystems and electron chain sit there. The dark reaction (Calvin cycle) takes place in the stroma, the fluid around the grana, because RuBisCO and the Calvin cycle enzymes are there. NEET trap: many students swap these two, so link 'membrane = light' and 'fluid stroma = sugar'.
The light reaction makes two products that the dark reaction needs: ATP (energy) and NADPH (reducing power / hydrogen). These carry the captured light energy into the stroma. The dark reaction uses ATP and NADPH to fix CO2 and build sugar. Oxygen is also released by the light reaction, but O2 is a waste product and is NOT used by the dark reaction.
The light reaction is called the photochemical phase because 'photo' means light and it uses light to drive chemistry (splitting water and exciting electrons). The dark reaction is called the biosynthetic phase because 'biosynthetic' means building molecules; here CO2 is built up into carbohydrate. NCERT uses these exact terms, so learn both name pairs for NEET.
No. The dark reaction does not directly need light OR chlorophyll. Chlorophyll is only needed in the light reaction to trap light. The dark reaction only needs CO2, ATP and NADPH (plus water and the enzyme RuBisCO). This exact point was tested in NEET 2024, so it is high-yield.
Which of the following are required for the dark reaction of photosynthesis? A. Light B. Chlorophyll C. CO2 D. ATP E. NADPH Choose the correct answer from the options given below:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The light reaction needs light, occurs in the thylakoid membrane, splits water, and makes ATP, NADPH and O2. The dark reaction does not directly need light, occurs in the stroma, and uses ATP and NADPH to fix CO2 into sugar.
The light reaction produces oxygen. Oxygen comes from the splitting of water (photolysis) on the inner side of the thylakoid membrane. The dark reaction does not release oxygen.
The Calvin cycle is the dark reaction (biosynthetic phase). It fixes CO2 in the stroma using ATP and NADPH from the light reaction.
Because it wrongly suggests the reaction happens in darkness. It actually runs mostly in the day, right after the light reaction, and only means 'light is not directly required'. NCERT prefers the term 'biosynthetic phase'.
Yes, in daylight they run together and are linked. The light reaction keeps supplying fresh ATP and NADPH, and the dark reaction keeps using them to build sugar.
