The answer is mollusks and annelids.
Coelom<span>ates are animals which body cavity (coelom) is filled with fluid. Fluid surrounds organs, protects them and allows their free movement and growth. All vertebrates and some invertebrates, such as mollusks, annelids, and arthropods, are coelomates.</span>
They use it to convert into C6H12O6 ( glucose) through photosynthesis. Then other living things consume the plant/ algae and use it to go through cellular respiration and make ATP. The energy travels up the food chain as other animals eat the herbivore/omnivore.
I would say the scientific method?