Organisms that have ventilation systems will draw in air (or water) that is rich in oxygen and will draw out air that has carbon dioxide. This is essential for a multicellular organism to thrive because carbon dioxide is harmful for an organism since carbon dioxide (CO2) is a waste product. Such is the system that contain veins, capillaries and arteries. On the other hand, organisms that don’t have ventilation system, can survive without it because they are single-celled and the path for the nutrients and needed oxygen is so short that they can efficiently exchange gases at the surface.