Stroma

Definition

The stroma is the fluid-filled matrix of a chloroplast, where the Calvin cycle reactions of photosynthesis occur. It contains enzymes, DNA, ribosomes, and is integral to the conversion of carbon dioxide into glucose.

5 Must Know Facts For Your Next Test

1. The stroma surrounds the thylakoid membranes in chloroplasts.
2. It contains enzymes essential for the Calvin cycle or light-independent reactions.
3. The stroma also houses chloroplast DNA and ribosomes, allowing it to produce some proteins independently.
4. ATP and NADPH produced in the thylakoids are used in the stroma during the Calvin cycle.
5. Stromal pH increases when light reactions are active, facilitating enzyme activity for carbon fixation.

Review Questions

• What role does the stroma play in photosynthesis?
• How does the composition of the stroma differ from that of the thylakoid membrane?
• Why is it significant that the stroma contains its own DNA and ribosomes?

Related terms

Thylakoid:

Membrane-bound compartments inside chloroplasts where light-dependent reactions occur.

Calvin Cycle:

A series of biochemical redox reactions occurring in the stroma that convert CO2 into glucose.

Chloroplast: Organelles found in plant cells and eukaryotic algae that conduct photosynthesis.