Yeah, so the plants turn carbon dioxide and water into cellulose and water mostly, herbivores digest the cellulose into protein and carbohydrates we can eat, we eat them and turn that protein and carbohydrates into our bodies and energy using oxygen, back into carbon dioxide and water and expel it. It's the carbon cycle.

Yes, the mass has been increasing: meteors bombarding the earth daily

It can't really be said there is a net-gain in mass (in fact most websites seem to estimate a net loss).

https://physics.stackexchange.com/questions/297622/is-the-earth-gaining-or-losing-mass-over-time

also plants make their food out of pretty much the definition of nothing, massless particles that makes its way up the food chain

I don't know what you mean by «massless particles», but plants do not make food out of "the definition of nothing". Photosynthesis is a chemical process and like any other chemical process due to the law of conservation of mass (disregarding mass-energy equivalence), the mass of the reagents is the same as the mass of the products. The sugars produced during photosynthesis weren't just produced with light as input. Light is the energy source that fuels the reaction in the light dependent of phase of photosynthesis, which has water as input, whose products (besides oxygen molecules which are a "useless" byproduct of the reaction) are used to produce the sugars in the non-light dependent phase which also takes carbon dioxide as input (there are obviously more substances involved in the reaction but they are "reused" between the two phases).

So, the mass of the "food" of the plant is in reality obtained from water and carbon dioxide, not out of "nothingness".

Plants make their food from matter that's already here on Earth. They take CO2 and water and use the sun's energy to turn them into sugar. They don't just get it from nothing.

Ah that's what you meant. I thought sperms got confused as food