how are blood types determined?

A. marker mocules marked on red blood cells
B. Marker mocules marked on white blood cells
C. Plasma fibrin's precense
D. Blood available for transfusion

The correct answer is A. marker molecules marked on red blood cells. Blood types are determined by the presence or absence of specific marker molecules known as antigens on the surface of red blood cells. These antigens can include a variety of proteins and carbohydrates. The most well-known blood type systems are ABO and Rh.

In the ABO system, there are four main blood types: A, B, AB, and O. Each type is determined by the presence or absence of two antigens: A and B. A person with type A blood has the A antigen on their red blood cells, type B has the B antigen, type AB has both antigens, and type O has neither.

Rh factor is another important marker molecule. Rh positive (Rh+) blood has the Rh antigen on the red blood cell surface, while Rh negative (Rh-) blood does not. This factor is particularly relevant in pregnancy, as Rh- mothers carrying an Rh+ baby can develop antibodies against the Rh antigen, potentially causing complications in subsequent pregnancies.

To determine blood types, a sample of blood is taken and tested in a laboratory. The blood cells are mixed with specific antibodies that will cause a reaction if the corresponding antigens are present. Based on the reactions observed, the blood type can be identified.