Which chloroplast compartment surrounds the thylakoid membranes?

Which chloroplast compartment surrounds the thylakoid membranes?

• A. Stroma
• B. Nucleus
• C. Cytosol
• D. Matrix

Answer: (A)

The surrounding fluid of the thylakoid membranes is the stroma. After light-dependent reactions occur on the thylakoid membranes, the stroma houses the enzymes of the Calvin cycle that convert CO2 into sugars. The thylakoid lumen is the internal space inside the thylakoid membranes, where protons accumulate during photosynthesis, but that lumen is distinct from the stroma. The nucleus and cytosol are parts of the cell outside the chloroplast, and the matrix refers to the inside of mitochondria, not chloroplasts, so they don’t surround the thylakoids.

The surrounding fluid of the thylakoid membranes is the stroma. After light-dependent reactions occur on the thylakoid membranes, the stroma houses the enzymes of the Calvin cycle that convert CO2 into sugars. The thylakoid lumen is the internal space inside the thylakoid membranes, where protons accumulate during photosynthesis, but that lumen is distinct from the stroma. The nucleus and cytosol are parts of the cell outside the chloroplast, and the matrix refers to the inside of mitochondria, not chloroplasts, so they don’t surround the thylakoids.