NCERT Class 11-Biology: Chapter – 18 Body Fluids and Circulation Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 10:

Explain the consequences of a situation in which blood does not coagulate.


If blood clotting does not take place excessive bleeding would take place which might lead to death.

Question 11:

What is the significance of time gap in the passage of action potential from sino-atrial node to the ventricle?


Time gap in the passage of action potential from sino-atrial node to the ventricle allows ventricles to relax. This causes ventricular pressure to fall leading to the closure of semilunar valves which prevents the backflow of blood into the ventricles.

Question 12:

How will you interpret an electrocardiogram (ECG) in which time taken in QRS complex is higher.


In an ECG, QRS complex represents ventricular depolarization. Normal duration of QRS complex is less than or equal to 0.10 seconds. If QRS complex is longer than 0.10 seconds and the wave is enlarged it indicates the person is having Myocardial Infarction or Heart Attack.

Short Answer Type Questions

Question 1:

The walls of ventricles are much thicker than atria. Explain.


1. The walls of ventricles are much thicker than atria because, ventricles have to exert more pressure as it pumps out blood to all organs of the body. Atria receives blood so they have less load to take, hence thinner walls.

2. Right ventricle receives oxygenated blood from the lungs than pumps this blood to the left ventricle.

3. In turn left ventricle pumps oxygenated blood to all parts of the body.

Question 2:

Differentiate between

a. Blood and Lymph

b. Basophils and Eosinophils

c. Tricuspid and bicuspid valve



Blood and Lymph
(i) RBCs are present(i) RBCs are absent
(ii) Blood flows through blood vessels.(ii) Lymph flows through lymphatic system only


Basophils and Eosinophils
(i) Have 3-lobed nucleus and less number of coarse(i) Have beloved nucleus and coarse
(ii) Blood flows through blood vessels. granules(ii) Lymph flows through lymphatic system only granules
(iii) They comprise of the blood volume.(iii) They comprise of the blood volume.


Basophils and Eosinophils
(i) Present between right auricle and right ventricle(i) Present between left auricle and right ventricle
(ii) Has three flaps(ii) Has two flaps
(iii) Also, known as right atrioventricular valve(iii) Also, known as mitral valve

Question 3:

Briefly describe the followings:

a. Anaemia

b. Angina Pectoris

c. Atherosclerosis

d. Hypertension

e. Heart failure

f. Erythroblastosis foetalis


a. Anaemia: It is a disorder that occurs due to decreased number of RBC՚s or lesser amount of haemoglobin than the normal value. It might be caused due to excessive loss of blood, destruction of RBC՚s etc.

b. Angina Pectoris: It is caused when adequate oxygen does not reach the heart muscles leading to chest pain and discomfort.

c. Atherosclerosis: It is the condition in which build-up of cholesterol, fats takes place in the wall of the artery. This cause՚s decreased size of the lumen hence decreased flow of blood towards the heart takes place. It is also known as Coronary Artery Disease.

d. Hypertension: It is the condition in which there is a constant increase in the normal blood pressure, which is 120/80 mm Hg. It affects all the vital organs like heart, kidney and brain etc. Blood pressure equal to or above 140/90 mm Hg is considered hypertension. It may be caused due to stress, high sodium intake or heart related problems.

e. Heart failure: It is the condition in which heart is unable to pump enough blood to meet the body՚s requirement. it՚s main symptom is congestion of the lungs. It may occur due to weakening of the heart muscles or due to any other defects.

f. Erythroblastosis foetal is: In this condition there is a destruction of foetal RBC՚s due to an incompatibility between the mother and foetus՚s Rh factor or Rhesus Monkey factor. This may lead to death or severe Anaemia of the foetus

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