Light and Dark Reactions in Chloroplasts — NEET Biology
✅ Asked in NEET 2025NEET 2025: The light-dependent reactions of photosynthesis in plants occur in:
NEET 2025: The light-dependent reactions of photosynthesis in plants occur in:
NEET 2025: Calvin cycle operates in:
In photosynthesis, the light-independent reactions take place at: (NEET 2015 / AIPMT 2015)
Answer & NCERT explanation
Correct answer: A — Grana
Light-dependent reactions occur in grana, the stacked thylakoid membranes inside chloroplasts. According to NCERT, photosystems I and II are embedded in thylakoid membranes where light energy is captured and converted to chemical energy (ATP and NADPH). Stroma is where light-independent Calvin cycle occurs, cytoplasm lacks photosynthetic machinery, and matrix refers to mitochondrial compartment.
Read more NCERT concept on the PYQ
You have studied the structure of chloroplast in Chapter 8. Within the chloroplast there is membranous system consisting of grana, the stroma lamellae, and the matrix stroma. There is a clear division of labour within the chloroplast. The membrane system is responsible for trapping the light energy and also for the synthesis of ATP and NADPH. In stroma, enzymatic reactions synthesise sugar, which in turn forms starch. The former set of reactions, since they are directly light driven are called light reactions (photochemical reactions). The latter are not directly light driven but are dependent on the products of light reactions (ATP and NADPH). Hence, to distinguish the latter they are called, by convention, as dark reactions (carbon reactions). However, this should not be construed to mean that they occur in darkness or that they are not light-dependent.
NTA tests whether students understand that light reactions occur in the thylakoid membrane (grana and stroma lamellae) and produce ATP and NADPH, while dark reactions occur in the stroma and synthesize sugars using those products. The biggest trap is misinterpreting 'dark reactions' as reactions that happen only in darkness or don't need light—this is completely wrong. Dark reactions are light-dependent indirectly because they need ATP and NADPH from light reactions to proceed. Remember: light reactions = membrane system = light-driven; dark reactions = stroma = not directly light-driven but totally dependent on light reaction products.
What does NCERT say about You have studied structure?
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