Final answer:
Reactive oxygen species (ROS) are oxygen cells that can be released by normal metabolism as well as pollution, smoking, radiation, and stress. They can have both beneficial and harmful effects on cellular functions.
Step-by-step explanation:
Reactive oxygen species (ROS) such as peroxides and free radicals are oxygen cells that are released by normal metabolism as well as pollution, smoking, radiation, and stress. Examples of ROS include the hydroxyl radical OH, H2O2, and superoxide (O2). Some ROS are important for certain cellular functions, such as cell signaling processes and immune responses against foreign substances. However, excessive production of ROS can lead to cellular damage and even cell death.