Blood for essential blood!

Blood represents 7 to 8% of total body weight and amounts to between 4 and 6 liters in volume. There are four blood groups: O, A, B, and AB. The Rh factor [+/-] determines whether the group is positive or negative. The O- group is the only one compatible with all others and is therefore called the “universal donor.” Hemoglobin, contained in red blood cells, gives blood its red color and ensures the transport of oxygen (O₂) throughout the body.