Explain how living organisms gain and use mass through the process of photosynthesis

Using energy from sunlight, photosynthesizers manufacture food (carbohydrates) from air (carbon dioxide) and water, and dump the waste product (oxygen) back into the air. So they gain mass (energy) which is utilized in many ways (e.g., food storage, procreation, structural support, protection, and much more).

They became more resistant.