Mammals regularly need to breathe and for this reason water is not a
very convenient environment for them. In a whale, which is a sea mammal, however, this
problem is handled with a breathing system far more efficient than that of many
land-dwelling animals. Whales breathe out one at a time discharging 90% of the
air they use. Thus, they need to breathe only at very long
intervals. At the same time, they have a highly concentrated
substance called "myoglobin" that helps them store oxygen in their muscles.
With the help of these systems, gin-back whale, for instance, can dive as deep
as 500 meters and swim for 40 minutes without breathing at all. The
nostrils of the whale, on the other hand, are placed on its back unlike land-dwelling
mammals so that it can easily breathe.