Question

In which specific region of the chloroplast, does Calvin cycle occurs?

• A. Thylakoid membranes
• B. Stroma
• C. Grana
• D. Inner membrane

Hint:

Remember the division of labor in the chloroplast: Light reactions happen {on the membranes} (thylakoids) because they need the membrane-bound protein complexes. The Calvin cycle happens in the {fluid} (stroma) because it involves soluble enzymes. Light provides the energy (ATP/NADPH) from the thylakoids to the stroma, and the stroma uses it to make sugar.

Answer 1

The Correct Option is B

Step 1: Concept Overview:
The question requires identifying the Calvin cycle's location within the chloroplast. Photosynthesis in eukaryotes comprises light-dependent and light-independent (Calvin cycle) reactions, each occurring in a specific chloroplast compartment.
Step 2: Detailed Elaboration:


Light-dependent reactions: Light energy is captured and converted into ATP and NADPH. These reactions occur in the thylakoid membranes, facilitated by pigment-protein complexes (photosystems) and electron transport chains. Thylakoids are often arranged in stacks called grana.
Calvin cycle (Light-independent reactions): ATP and NADPH from the light reactions are used to fix CO₂ and synthesize sugars. This process, involving enzymes like RuBisCO, occurs in the aqueous, fluid-filled space surrounding the thylakoids, known as the stroma.
The chloroplast's inner membrane regulates metabolite transport into and out of the stroma but is not where the Calvin cycle takes place.
Step 3: Conclusion:
The Calvin cycle, a series of enzymatic reactions fixing CO₂, occurs in the chloroplast's stroma.