 Now, we talk about briefly the blood groups. What are the blood groups? About 29 different types of blood group systems are found in human beings, but two are very important. One is the ABO system and other is the RH system. Why we have different blood groups? Because our blood cells have different types of antigens on their surface. Antigens are specific proteins which can cause the release of different types of antibodies. One system is ABO blood group system. This is due to two antigens present on the blood cells. One is the antigen A, another is the antigen B. We look at a diagram. On the blood cells in this diagram you can see, there are four blood groups according to the ABO system, O, A, B and AB. If there are two antigens which are involved, antigen A and antigen B, those people who have an O blood group actually do not have any antigen, not A nor B. The other ones who have an A blood group have A antigen present on the surface of their blood cells. As you can see, diagram in the right top. Then those who have only B antigen present on their blood cell surface are called having blood group B. And the last one which have both of these antigens present on their surface of the RBC, A and B, they have blood group AB. Now the second one is the RH. RH is another type of antigen which was actually discovered first in the Rhesus monkey. So these were named as RH. RH is another antigen which is present or absent. So the people who have an RH antigen present on their blood cells are called RH positive and people who do not have it are called RH negative. Now there is a property of these blood groups, these antigens and the blood type according to these antigens, which is very important in blood transfusions because we know that many times blood transfusions are required. In case of a surgery, for example, a person needs a blood transfusion because its blood is lost due to an injury blood good loss. In some diseases like Thalassemia, patient needs consistently blood transfusion. Actually when a person have an antigen A on their blood cells, they produce an antibody B in their blood. Those people who have an antigen B on their blood cell surface, they produce an antibody A. The result is this that if we give wrong blood that is blood group B to the person who have a blood group A, it already have the antibodies present against the B antigen. That is blood group A have anti B antibodies. So if we give wrong blood group, wrong blood to the person, the result will be clumping because antibody B will react with the antigen B on the blood cells and the blood cells will clump together. Due to clumping, the bloods cannot pass through the capillaries and the result will be death of the patient even. So in blood transfusion, this is very important that we do the grouping very correctly. There is one blood group O is called universal donor because it can donate blood to every blood group because O blood group people do not have any antibodies because they do not have any antigen. More precisely the O negative blood group is the universal donor because O negative actually do not have any of three antibodies A, B and R H. They do not have any antigen and they do not have any antibody. Group A B is called a universal acceptor because it have antigen A and antigen B and do not have antibodies for any of these. So A B can accept all the blood types A, B and O. This is about transport system in organisms, different types of organisms and the human blood and its different properties. I hope you understand what we talked about today.