Prokaryotic Photosynthesis: Videos & Practice Problems

The main difference between prokaryotic and eukaryotic photosynthesis lies in the cellular structures involved. Prokaryotes lack membrane-bound organelles, including chloroplasts. Therefore, in prokaryotes, the light reactions occur in the plasma membrane, and the Calvin cycle takes place in the cytoplasm. In contrast, eukaryotic photosynthesis occurs within chloroplasts, with light reactions happening in the thylakoid membranes and the Calvin cycle in the stroma. This structural difference is crucial for understanding how photosynthesis is adapted to different cellular architectures.

Oxygenic photosynthesis uses water (H₂O) as the primary electron donor, resulting in the production of oxygen gas (O₂). It employs chlorophyll a as the primary pigment in both photosystem I and II. In contrast, anoxygenic photosynthesis does not produce oxygen because it uses alternative electron donors like hydrogen sulfide (H₂S). Organisms performing anoxygenic photosynthesis use bacteriochlorophylls and only one photosystem, either photosystem I or II, but not both. These differences highlight the diversity in photosynthetic mechanisms among microorganisms.

In prokaryotic photosynthesis, the light reactions occur in the plasma membrane or cytoplasmic membrane. The Calvin cycle, on the other hand, takes place in the cytoplasm. This is different from eukaryotic photosynthesis, where the light reactions occur in the thylakoid membranes of chloroplasts, and the Calvin cycle occurs in the stroma of the chloroplasts. Understanding these locations is essential for grasping how prokaryotic cells adapt to their lack of membrane-bound organelles.

Anoxygenic photosynthesis does not produce oxygen gas because it uses electron donors other than water (H₂O). Common alternative electron donors include hydrogen sulfide (H₂S). Since water is not used, oxygen gas (O₂) is not generated as a byproduct. Instead, other molecules, often containing sulfur, are produced. This process also involves bacteriochlorophylls and only one photosystem, either photosystem I or II, but not both. This distinction is crucial for understanding the metabolic diversity among photosynthetic microorganisms.

Organisms that perform oxygenic photosynthesis include cyanobacteria, algae, and plants. These organisms use water (H₂O) as the primary electron donor, resulting in the production of oxygen gas (O₂). They utilize chlorophyll a as the primary pigment in both photosystem I and II. Cyanobacteria are a classic example of prokaryotes that perform oxygenic photosynthesis, while algae and plants are eukaryotic examples. Understanding these organisms helps in studying the ecological and evolutionary significance of oxygenic photosynthesis.