Final answer:
During photosynthesis, water is split and oxygen is produced as a byproduct. This oxygen is then released into the atmosphere.
Step-by-step explanation:
In photosynthesis, oxygen is produced as a byproduct when water is split. This process occurs in the thylakoid membranes of chloroplasts, specifically in the light-dependent reactions. During photosynthesis, water molecules are broken down into oxygen (O₂) and hydrogen ions (H⁺) by a process called photolysis. The oxygen that is released then diffuses out of the plant and into the atmosphere, where it can be used by aerobic organisms for respiration.