Diffusion allows the exchange of substances; the entry of oxygen, proteins, etc into the cell and the removal of waste substances.
There are several organ systems in the body. One of them would be the respiratory system. There are many more including the heart, digestive, and the skeletal.
Can u please add a little more? I don't know anymore.
Normally a 10× drop for each trophic level, so I'd say 2,000 kilocal.
True millions of different species live on coral reefs