All living things
to their environment

An environment includes living things such as plants, animals, people, and even the tiniest of microbes. The living portions of the environment are called the biotic parts. The nonliving portions, such as rocks, sunlight, and air, are called the abiotic parts.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

after a the power stroke, adp is released, but the cross-bridge formed is still in place. atp then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.