What is the difference between oxygenic and anoxygenic photosynthesis?

What is the difference between oxygenic and anoxygenic photosynthesis?

• A. Oxygenic uses water as electron donor and releases O2; anoxygenic uses other donors and releases little or no O2.
• B. Anoxygenic uses water as electron donor and releases O2.
• C. Oxygenic uses carbon dioxide as the electron donor.
• D. Anoxygenic releases oxygen as a major byproduct.

Answer: (A)

The main concept is that the source of electrons driving the light reactions determines whether oxygen is released. In oxygenic photosynthesis, water is split to donate electrons, and this water-splitting releases molecular oxygen as a byproduct. In anoxygenic photosynthesis, organisms use other reduced compounds—such as hydrogen sulfide, hydrogen, or organic molecules—as electron donors, so water is not split and little or no oxygen is produced. This is why the described difference emphasizes water as the electron donor with O2 release for oxygenic photosynthesis, and alternative donors with little or no O2 for anoxygenic photosynthesis. The other statements fail because they either misstate the electron donor (using CO2 as an electron donor) or misstate the oxygen outcome (anoxygenic releasing O2, or oxygenic not using water).

The main concept is that the source of electrons driving the light reactions determines whether oxygen is released. In oxygenic photosynthesis, water is split to donate electrons, and this water-splitting releases molecular oxygen as a byproduct. In anoxygenic photosynthesis, organisms use other reduced compounds—such as hydrogen sulfide, hydrogen, or organic molecules—as electron donors, so water is not split and little or no oxygen is produced. This is why the described difference emphasizes water as the electron donor with O2 release for oxygenic photosynthesis, and alternative donors with little or no O2 for anoxygenic photosynthesis. The other statements fail because they either misstate the electron donor (using CO2 as an electron donor) or misstate the oxygen outcome (anoxygenic releasing O2, or oxygenic not using water).