It is very condensed compared to gas. The atoms are more compact in water than in gas. Solids are even more compact and are extremely condense compared to gas. Hope this helps!
The process is the difference in atmospherical pressure where air moves from higher to lower pressure area creating winds of various speeds
Ventilation systems are needed in a <span>multicellular organism to actually obtain oxygen and give out carbon dioxide. Without this ventilation system, it would be very difficult for multicellular organisms to survive. It has been also observed that surface diffusion is not enough for a multicellular organism to breath.</span>
