Re: How does the paramecium breathe?

Natasha:

Creatures like Paramecium are much different from familiar animals (like mammals) in one crucial way: they are very small. So small, in fact, that dissolved gases like oxygen can simply diffuse ("soak") all the way into the Paramecium cell, without any "pumping" action at all. This is ture of bacteria, ciliates, etc. and even small animals like worms. It is only when animals get bigger (the size of a small insect) that "breathing" is necessary. (In insects, they use simple air pipes built all along the side of their body instead of lungs; in aquatic insects which don't have access to as much oxygen as land insects do, they actually have gills, which they vibrate to increase the absorption of oxygen). It is interesting to realize that our own breathing process is actually not very effecient; the lungs of birds do a much better job of removing oxygen from the air!

By the way, you may have seen the contractile vacuole in Paramecium, beating like a heart, but it is just a water pump used to dispose of excess fluid, preventing them from swelling up too much.

Your question reminds me of some other neat facts:

Animals that get big enough need to have a oxygen-carrying protein in their blood: in mammals, its red hemoglobin (containing iron) and with horse shoe crabs its a blue, copper-containing protein (yes, they have blue blood!) I just found out that a hemoglobin-like protein has been found in bacteria. Yet they are much much smaller than Paramecium, and don't need to breath or have blood. It turns out that this hemoglobin-like protein is used as an oxygen sensor, helping this oxygen-using bacteria to find the best sources of oxygen (like an air bubble).

Cheers,
Dean Jacobson, protistologist