Human Immunity and Blood

O negative blood group is known as the universal donor because it lacks both A and B antigens and the Rh factor. This means it can be transfused to patients with any blood type (A, B, AB, or O, regardless of Rh factor) in emergency situations without causing immune reactions.

Blood is the correct answer because haemophilia is a genetic blood disorder where blood does not clot properly due to deficiency of clotting factors (Factor VIII or IX). It is not a disease of bone, liver, or kidney, though these organs may be affected secondarily. The primary defect is in blood coagulation.

Blood plasma is the liquid component of blood in which blood cells (RBCs, WBCs, and platelets) are suspended. It is mostly water and contains proteins, nutrients, hormones, and waste products. Platelets and the various blood cells are the solid components, not the liquid medium.

Hemoglobin is the red pigment in red blood cells that gives blood its characteristic red color. It contains iron and binds oxygen for transport. Plasma is actually pale yellow, platelets are cell fragments, and capillaries are tiny blood vessels - none provide the color.

White blood cells (leukocytes) are the immune system's primary defense against infections and foreign invaders. RBCs carry oxygen, platelets help with clotting, and 'none of the above' is incorrect since WBCs do fight disease.

The ABO blood group system classifies human blood into four main types based on the presence or absence of A and B antigens: Type A has A antigens, Type B has B antigens, Type AB has both, and Type O has neither. This classification is crucial for safe blood transfusion, as mixing incompatible blood types can cause dangerous immune reactions.

H1N1 is a subtype of influenza A virus where H stands for Hemagglutinin (responsible for binding the virus to host cells) and N stands for Neuraminidase (helps release new viral particles from host cells). Option A has the correct spellings of both terms.

In influenza viruses like H1N1, the H refers to hemagglutinin, a surface glycoprotein that helps the virus bind to host cells. The N refers to neuraminidase. Haemoglobin carries oxygen in blood (not viral). Hongkong is a place. Hemoprotein is a general term for iron-containing proteins, not the specific viral protein.

Type O blood is the most common blood type globally, particularly O positive. This is because O is the universal donor for red blood cells and has been evolutionarily favored. Type AB is the rarest blood type. The ABO system categorizes these blood types based on the presence or absence of antigens.

In H1N1 influenza virus, the 'H' stands for hemagglutinin, which is a surface glycoprotein that helps the virus bind to and enter host cells. The 'N' stands for neuraminidase.

Blood group O (especially O negative) is called the universal donor because O red blood cells lack A and B antigens on their surface. This means they can be transfused to almost any patient without triggering an immune reaction. AB is the universal recipient (can receive from all types). A and B can only donate to compatible types.

Erythrocytes are the scientific term for red blood cells, which contain hemoglobin and transport oxygen throughout the body. Thrombocytes are platelets for clotting, and leucocytes are white blood cells for immune defense. The name comes from Greek 'erythros' meaning red.

Hematologists are medical specialists who study blood and blood-forming tissues, including bone marrow. They diagnose and treat blood disorders such as anemia, leukemia, lymphoma, clotting disorders, and other conditions affecting blood cells. Hematology requires understanding of blood components (red cells, white cells, platelets, plasma) and their functions in oxygen transport, immune response, and clotting.