Answer: Mass flow or bulk flow is the movment of substance in big masses or something moving in a big group.
Explanation:
Its kind of like a river or blood flowing through your veins because its a mass of a substance moving in a group.
Respiration releases the energy
Hydra has two main body layers, which makes it "diploblastic". The layers are separated by mesoglea, a gel-like substance. ... The cells making up these two body layers are relatively simple.