Final answer:
On average, a single blood donation involves the collection of about 500 milliliters of blood, which constitutes both blood plasma and blood cells. This quantity is a standard unit of blood for donation and represents about 10% of an adult's total blood volume.
Step-by-step explanation:
The average volume of a unit of blood collected during a blood donation procedure is approximately 500 milliliters (mL). This is just about 10% of the total blood volume in the average adult. It's crucial to note that the human body can replenish the fluids lost from donation rather quickly, and red blood cells within a few weeks. The amount of blood in an adult depends on factors like gender, with males typically having 5 to 6 liters and females around 4 to 5 liters. Regardless of gender, a unit of blood for donation consists of both blood plasma and blood cells, with plasma making up about 55% of our total blood volume.