The rapid depolarization phase
of myocardial contractile cells is due to the Na+ ions. Sodium ions are essential
for regulation of blood and body fluids, communication of nerve impulses, heart
activity, and metabolic purposes. Physiologically, it survives as an ion in the
body. Sodium is needed by
animals but is not needed by plants. The human prerequisite for sodium<span> must be less
than 500 mg per day. </span>
It is a perfect example of a natural selection.
(I'm not sure if this is the exact answer that you are looking for.)
The skeleton of an embryo is made up of cartilage and collagen
Hope this helps :3
They are further classified into: fish, amphibians, birds, reptiles and mammals.
I hope I've helped : )
