The elephant is a creature of epic proportions — and yet, it owes its enormity to more than 1,000 trillion microscopic cells. And on the epically small end of things, there are likely millions of unicellular species, yet there are very few we can see with the naked eye. Why is that? Why don’t we get unicellular elephants? Or blue whales? Or brown bears?
Red blood cells
how the body makes red blood cells, which contain hemoglobin and carry oxygen throughout the body. Anemia occurs when there are too few red blood cells or not enough hemoglobin.
White blood cell
Observe the process of a type of white blood cell, known as a macrophage, engulfing bacteria.