Final answer:
Oceanic phytoplankton, especially Prochlorococcus, produce oxygen through photosynthesis, which humans need to breathe. They also convert sunlight into chemical energy, vital for life on Earth. The recirculation of nutrients through ocean upwelling is crucial for this process.
Step-by-step explanation:
The substance necessary for human life that is produced by ocean organisms which photosynthesize is oxygen. Phytoplankton, microscopic photosynthetic organisms found in the surface waters of oceans, are vital in this process. In particular, Prochlorococcus, a tiny marine organism discovered in 1986, is considered one of the most abundant photosynthetic organisms on Earth and plays a significant role in the global oxygen and carbon cycles by producing a substantial amount of the world's oxygen.
Photosynthesis carried out by these oceanic organisms not only produces oxygen but also converts light energy from the Sun into chemical energy, in the form of organic compounds like glucose (C6H12O6). This transformative process sustains nearly all life forms on the planet by providing the essential elements for energy and respiration. Moreover, ocean upwelling ensures the recirculation of nutrients necessary to support the ongoing process of photosynthesis in aquatic ecosystems.