Answer:
D
Explanation:
proteins make up every thing
Counter current involves blood in the capillaries flowing in the opposite direction to the flow of water flowing over them. Gases diffuse faster from one area to another when the concentration difference between the two areas is at its greatest, as compared to when the concentration difference is low.
Bony fish belong to Class Osteichthyes, while cartilaginous fish belong to Class Chondrichthyes. Bony fish have a bony skeleton, while cartilaginous fish have one composed mostly of cartilage. Bony fish have body coverings of scales, while cartilaginous fish are covered with dendritical projections (think shark skin).
Bony fish are found in fresh and salt water; cartilaginous fish are found only in salt water. Bony fish have gills covered by an operculum; cartilaginous fish have gill slits. Bony have no eyelids; the cartilaginous fish do. Bony fish have an air-filled swim bladder; cartilaginous fish have an oil-filled liver to keep them bouyant. Hope this helps! Whew!
blood flows at a high pressure, so if the arteries are thin and less muscular, the arteries can explode due to the pressure. so it needs thick and muscular properties so that it can withstand the increasing pressure of the flow of blood.
im not sure why it needs to be elastic. Hope it helped :)
