Final answer:
Photosynthetic bacteria like cyanobacteria release oxygen into the air through oxygenic photosynthesis, which is vital for other organisms, and played a crucial role in shaping Earth's atmosphere and the evolution of life.
Step-by-step explanation:
Some photosynthetic bacteria are beneficial to other organisms because they release oxygen into the air. An example of such bacteria are cyanobacteria, which are known for their capacity to perform oxygenic photosynthesis. This process uses water as the electron donor and results in the production of glucose and oxygen. The glucose serves as a source of energy or "food" for the bacteria, and the byproduct, oxygen, is essential for other life forms, notably humans, to breathe. Cyanobacteria were also instrumental in the ancient Earth's atmosphere, contributing significantly to its oxygenation and thereby affecting the course of evolution.