The aboye diagram shows the different types of leucocytes.
Identify and name the cells as asked in the following questions.
(a) Name the two types of leucocytes that are phagocytic.
(b) Which among them is the
(i) most abundant
(ii) least in number?
(c) Which among them is involved in
(i) allergic r:eactions
(ii) inflammatory reactions?

You know that there are four blood groups, A, B AB, and O, among human beings. Now, answer the following questions based on that.
(a) What forms the basis for this classification?
(b) Before any transfusion of blood, why should the blood of the donor be matched carefully with that of the recipient?
(c) Why are persons with blood group AB called (universal recipient'?
(d) Name the blood group(s), which
(i) persons with blood group 'O'can receive
(ii) can be donated only to persons with blood group'AB'.

Amit and Mrinal are good friends. Amit,s father had an injury and needed blood transfusion; he is of blood group B. Mrinal is of blood group A and he had arranged for blood donors.
(a) Name the blood groups that will be suitable for transfusion to Amit's father.
(b) Name the antigen and the antibody present in Mrinal's blood.
(c) Why are persons with blood group O known as 'universal donors'?

There are two types of blood groupings - the ABO and Rh groups, which are widely used all over the world.
Answer the following questions regarding Regrouping.
(a) What forms the basis for classifying human individuals as Rh-positive and Rh-negative?
(b) If a foetus is suffering from a condition, called erythroblastosis fetal, identify the Rh group of the
(i) mother
(ii) father
(iii)  foetus.
(c) How can this condition be avoided?

If you injure your finger while cutting vegetables, the blood stops oozing out of the wound in a short time. Blood exhibits coagulation or clotting, a mechanism to prevent excess loss of blood from the body. A clot or coagulum is formed at the site of injury. The following flow chart shows the steps in the mechanism of coagulation. Fill in the blanks A to F.
When blood comes out of the blood vessels from an injury, the platelets release certain factors.
\(\downarrow\) 
These factors stimulate the reactions in the plasma fo form enzyme (A)
\(\downarrow\)
The above enzyme converts (B) in the plasma into (C)
\(\downarrow\)
C converts the inactive (D) into a network of threads, called (E)
\(\downarrow\)
A coagulum or clot is formed when the dead and damaged (F) are trapped in E.

A diagrammatic representation of a standard ECG is given above.
Each of the peaks in the ECG is identified with a Ietter (P, e, R, S, T) which corresponds to a specific electrical activity of the heart.
Answer the following questions.
(a) What doeg f waveirepresent? What happens in the cardiac cycle during this?
(b) When does ventricular contraction start?
(c) What does T wave represent?
(d) How can the heart rate be calculated using ECG?

A schematic plan of double circulation in humans is shown above.
Answer the following questions.
(a) Identify and name the two pathways in the double circulation in human beings.
(b) Arteries are the blood vessels that carry blood from the heart to different parts of the body. Name the two major arteries that carry blood from the heart. Mention the difference in the blood they carry.

A diagrammatic sectional view of the blood vessels, artery and vein, is shown above. Answer the following questions.
(a) Identify the artery and vein. Justify your identification.
(b) Name the three layers in the wall of artery and vein. Which of them causes the difference in the thickness of the walls?