The white blood cells are the ones who leave the blood and enter
tissues to fight off pathogens and invaders. They are
not platelets because platelets help the healing of wounds and prevent it from
bleeding by forming blood clots on the wounded area. They are not red blood
cells because they carry oxygen all throughout the body organs. And they are
not capillaries because capillaries are the ones that transports the oxygenated
blood into the arteries.
