Whales, like humans, breathe to take in oxygen, which they use to generate the energy needed to think and to move. But when a whale sounds (dives) it can’t breathe while it’s underwater. So how does it generate enough energy to stay under for so long (the record is nearly 2 hours!). You might think that a whale, being as big as it is, could just take a very big breath and hold it. But, in fact, whales have rather small lungs for their size. Besides, most of the oxygen the whale breathes in just before it dives is used very quickly.
So the whale has to rely on oxygen it stored before it sounded, oxygen attached to proteins in the blood (hemoglobin) and muscle (myoglobin). We have these proteins too, but in smaller amounts. Whales also conserve energy while they are underwater, by slowing their heartbeat and by pumping blood to only a few organs (brain, heart and muscles). Humans have this “diving reflex” also, although it’s not as well developed. If a whale gets low on oxygen, it can generate a small amount of energy without using oxygen, but this process creates lactic acid – the substance that makes your legs “burn” if you run too far or too fast. Whales, however, don’t seem to mind the “burn” as much as we do. So the whale’s secret to staying under water for a long time is to store up a lot of oxygen before it dives and then use as little of it as possible while it’s submerged.