The phylum Cnidaria contains some of Earth
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Gas Exchange in Animals
Before we get into how Cnidarians go about gas exchange, let's take a moment to review why this gas exchange is so important. Think about human gas exchange for a minute: you breathe in oxygen and breathe out carbon dioxide. You do this because you need oxygen for many cellular processes, and carbon dioxide is a waste product so you need to expel this gas.
Well, other animals need to do the same thing in order to drive their cellular processes. Some do it through lungs like us, others through their gills like fish and sharks. Others exchange gas through means such as passive exchange through their skin like frogs. And while they don't necessarily breathe gases in and out the same way we do, it's still an important process for all animals in order to remain happy and healthy.
Gas Exchange in Cnidarians
Cnidarians don't have lungs, and even though they live in aquatic environments they don't have gills either. So they have to exchange 'good' and 'bad' gases a little bit differently. Instead of breathing, gas exchange in Cnidarians occurs through direct diffusion. This is the process by which particles move from a place where the particle concentration is high to a place where the concentration of those particles is low. Amazingly, diffusion occurs inside your body as well, and is the mode of transport for many molecules across your cell membranes.
In diffusion, particles will naturally move from an area of high concentration to an area of low concentration.
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But diffusion is not an active process, meaning that the gases and nutrients that move from one location to the other are not pumped by the animal. Instead, they flow naturally based on the differences in concentration. And in Cnidarians, the diffusion of gases occurs in the gastrovascular cavity which is called the coelenteron.
During this process, oxygen in the surrounding environment diffuses through the 'skin' of the Cnidarian, moving from the outside of the animal to the inside. Waste gas also moves this way, but in the opposite direction. Here, waste gas diffuses from the inside of the animal to the outside environment. And voila: Cnidarian 'breathing'!
Lesson Summary
The phylum Cnidaria is home to some 10,000 fascinating creatures including jellies, corals, and hydras just to name a few. And because these are animals like you and me, they need to exchange 'good' and 'bad' gases in order to drive cellular processes. But unlike us, they don't 'breathe' gases through their mouth.
Instead, they exchange gases through their bodies through a process called direct diffusion. This is a passive mode of transport that moves particles from an area of high concentration to an area of low concentration. During Cnidarian gas exchange, oxygen from the surrounding environment diffuses into the animal through the coelentreron or gastrovascular cavity, while carbon dioxide is expelled out as a waste product.
