Answer:
The concentration gradient is the driving force.
Explanation:
Passive transport of substance occurs when they are moved from the region of their higher concentration to that of their lower concentration. The concentration gradient is the difference in the concentration of substances between two regions or across the membrane. The concentration gradient of substances drives their passive movement. The passive movement of substances does not use metabolic energy. Simple diffusion and facilitated diffusion are two examples of this transport.
In general, echinoderms typically respire by simple diffusion, using gills or specialized projections, like tube feet or pockets, to circulate water and oxygen through their bodies. Many echinoderms also use a simple hemal system, a series of pockets and tubes that serves almost like a net of veins and arteries.
