Plasma is the watery, yellow liquid part of blood. It is secured by taking a sample of blood and spinning it in a centrifuge until the blood cells and solid components are separated out to the bottom of the blood container. The plasma may then be drawn off the sample. Blood makes up about 8% of the human body weight, so for a 175 pound man, that would be 14 pounds. Plasma makes up about 55% of the blood by weight, so 55% of 14 pounds would be 7.7 pounds.
Plasma contains all kinds of dissolved electrolytes, fibrinogen, and is a major carrier of carbon dioxide. Plasma is composed of water by about 92%, so proper hydration is of key importance in maintaining nutrient and waste product transaction. Plasma has many applications and uses, from surgical procedures to healing traumas suffered by burn victims.