(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

(c) Assertion is true but Reason is false

Structure of Human Heart
i) The heart is made of specialized type of muscle called the cardiac muscle.
ii) The heart is enclosed in a double walled sac called pericardium. It contains lubricating pericardial fluid which reduces friction during heart beat and protects it from mechanical injuries.
iii) The human heart is four chambered. The two upper thin walled chambers of the heart are called auricle or atria (sing: atrium) and two lower thick walled chambers are called ventricles.
iv) The right atrium receives deoxygenated blood from different parts of the body through the main veins superior vena cava, inferior vena cava and coronary sinus.
v) From the left atrium arises Pulmonary vein which brings oxygenated blood from the lungs to heart.
vi) From the right ventricle arises the pulmonary artery which takes deoxygenated blood from heart to lungs.
vii) The left ventricle gives rise to aorta.
viii) The heart contains three types of valves.
a) Tricuspid valve auricle and right ventricle.
b) Bicuspid or mitral valve is located between the left auricle and left ventricle.
c) Semilunar valves are located at the base of pulmonary artery and aorta.

Blood Groups
(i) The concept of blood grouping was discovered by Karl Landsteiner. He identified blood groups A, B and O. AB blood group was recognized by Decastello and Steini.
(ii) Human blood contains certain specific substances called agglutinogens or antigens (Ag) and agglutinins or antibodies (Ab). Antigens are found on the membrane surface of RBC. Antibodies are present in blood plasma. Based on the presence or absence of antigen and antibodies human blood group is classified into four groups called A, B, AB, and O. An individual has one of the four blood groups.
(iii) 'A' group individuals: Antigen 'A' is present on the surface of RBC and antibody b (anti-b) is present in the plasma.
(iv) 'B' group individuals: Antigen 'B' is present on the surface of RBC and antibody an (anti-a) is present in the plasma.
(v) 'AB' group individuals: Antigens A and B are present on the surface of RBC and antibodies are absent in the plasma.
(vi) 'O' group individuals: No antigen A or B are absent on the surface of RBC. However, the plasma contains both antibodies 'a' and 'b' (anti a and b).
Blood donation :
(i) In blood transfusion one must consider the antigen and antibody compatibility (matching) between the donor and the person receiving blood (recipient). When an individual receives a mismatched blood group from the donor agglutination (clumping) of blood occurs in the body which leads to death.

The heart contains pericardial fluid to reduce friction during heart beat and protect it from mechanical injury.

Functions of Lymph:
a) Supplies nutrients and oxygen to those parts where blood cannot reach.
b) It drains away excess tissue fluid and metabolites and returns proteins to the blood from tissue spaces.
c) The lymph also carries absorbed fats from small intestine to the blood.
d) The lymphatic capillaries of intestinal villi (lacteals) absorb digested fats.
e) Lymphocytes in the lymph defend the body from infections.