Final answer:
Oxygenic photosynthesis is the process by which certain bacteria use water as the electron donor, releasing oxygen as a byproduct.
Step-by-step explanation:
The type of photosynthesis performed by bacteria that utilizes water (H2O) as the electron donor is known as oxygenic photosynthesis. This process is in contrast to anoxygenic photosynthesis, where compounds other than water serve as electron donors, and therefore, oxygen is not produced as a byproduct. During oxygenic photosynthesis, the splitting of water molecules releases oxygen, thus contributing to the oxygenation of Earth's atmosphere over geological timescales.