Answer:
Photosynthesis provides most of the oxygen that humans and animals breathe. Chlorophyll uses sunlight energy to transform the carbon dioxide and water into oxygen and carbon-based compounds such as glucose, a sugar that helps plants grow.
For macrophytes, photosynthesis in reproductive structures decreases the energy and carbon costs of reproduction to the rest of the plan, which might be more important for iteroparous rather than semelparous organisms.
Hope that helps. x