The primary waste product of photosynthesis is oxygen (O₂). During the light- dependent reactions of photosynthesis, water molecules are split (photolysis), releasing oxygen as a byproduct that the plant does not use and thus expels into the atmosphere. This oxygen is considered a waste product of photosynthesis because it is produced as a result of the process but is not needed by the plant itself; however, it is essential for the survival of most other living organisms that rely on oxygen for respiration

. While oxygen is the main waste product, there are other byproducts related to respiration processes in plants, such as carbon dioxide released during stomatal, dark, root, and rhizosphere respiration. These are less directly linked to photosynthesis but are part of the overall metabolic activities of plants

. In summary:

• Waste product of photosynthesis: Oxygen (O₂)
• Source: Produced during the splitting of water molecules in the light-dependent reactions
• Role: Released into the atmosphere; critical for aerobic life but considered waste from the plant’s perspective