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: Understanding the Concept:
The question asks to identify the location of the Calvin cycle within the chloroplast. Photosynthesis in eukaryotes is divided into two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). Each stage occurs in a specific compartment of the chloroplast.
Step 2: Detailed Explanation:


Light-dependent reactions: This stage involves capturing light energy and using it to produce ATP and NADPH. These reactions are carried out by pigment-protein complexes (photosystems) and electron transport chains that are embedded in the thylakoid membranes. The thylakoids are often stacked into structures called grana.
Calvin cycle (Light-independent reactions): This stage uses the ATP and NADPH produced during the light reactions to fix atmospheric carbon dioxide (CO₂) and synthesize sugars. This process is catalyzed by a series of enzymes, such as RuBisCO, which are soluble and located in the aqueous, fluid-filled space surrounding the thylakoids. This space is called the stroma.
The inner membrane of the chloroplast regulates the passage of metabolites into and out of the stroma but is not the site of the Calvin cycle itself.
Step 3: Final Answer:
The Calvin cycle, being a series of enzyme-catalyzed reactions that fix CO₂, takes place in the stroma of the chloroplast.