This happens when a detection is accomplished through heuristics. There is no such thing as a heuristic virus. As a technical concept, everything in malware detection is done via heuristics.
Photosynthesis is the process in which plants (also autotrphoic protists and some bacteria) use light energy, from the Sun, to make sugars and organic food molecules from CO2 and water (H2O). This process is essential for the formation of not only energy, but also for the formation of glucose for purposes of structure.
Quick Answer. Plants produce oxygen as a byproduct of photosynthesis, the process that plants and other organisms use to create usable energy. Photosynthesis consists of carbon dioxide and water reacting in the presence of energy from sunlight, which produces glucose and oxygen.