Previous year questions: Body Fluids and Circulation
Body Fluids and Circulation36 min readLesson 6 of 6
These ten questions come from the NCERT Exemplar chapter on body fluids and circulation, the only official previous year source available for Class 11 Biology. The set covers the formed elements, blood groups, the conducting system, the cardiac cycle and the ECG. Marks follow the book convention: 1 mark MCQ, 2 marks very short answer, 3 marks short answer and 5 marks long answer. Each heading quotes the Exemplar chapter and question number.
Q1 (NCERT Exemplar, 1 mark; Chapter 18, Multiple Choice 1)
Which of the following cells does not exhibit phagocytic activity?
Answer: Basophils do not show phagocytic activity. Monocytes, neutrophils and macrophages are all phagocytic: neutrophils and monocytes engulf microbes directly, and macrophages are the mature tissue form of monocytes. The question is a reminder that not every white cell is a phagocyte.
Q2 (NCERT Exemplar, 1 mark; Chapter 18, Multiple Choice 2)
One of the common symptoms in people infected with dengue fever is what?
Answer: Dengue commonly causes a significant decrease in the platelet count. Red cell and white cell counts may also change in some infections, but the fall in platelets is the characteristic finding and explains the bleeding tendency in severe dengue.
Q3 (NCERT Exemplar, 1 mark; Chapter 18, Multiple Choice 5)
Which pair of substances is essential for coagulation of blood?
Answer: Calcium ions and platelet factors are the pair essential for coagulation. Heparin is an anticoagulant, and oxalates and citrates work by removing calcium and preventing clotting, so they are the opposite of what the question asks for.
Q4 (NCERT Exemplar, 1 mark; Chapter 18, Multiple Choice 9)
The correct sequence of conduction of the cardiac impulse is what?
Answer: The impulse begins at the sino-atrial node, passes to the atrio-ventricular node, travels down the atrio-ventricular bundle and reaches the ventricular muscle through the Purkinje fibres. The option with this order is correct. The other options put the Purkinje fibres before the AV node or place the AV bundle before the node, which would send the impulse in the wrong direction.
Q5 (NCERT Exemplar, 1 mark; Chapter 18, Multiple Choice 14)
What is the cardiac output of a person with 72 heart beats per minute and a stroke volume of 50 mL?
Answer: Cardiac output is stroke volume multiplied by heart rate, so 50 mL multiplied by 72 beats per minute gives 3600 mL per minute. This is the standard calculation and the answer should be written with the unit.
Q6 (NCERT Exemplar, 2 marks; Chapter 18, Very Short Answer 2)
Complete the missing words: plasma without ___ factors is called serum; ___ and monocytes are phagocytic; eosinophils are associated with ___ reactions; ___ ions play a significant role in clotting; the heart rate can be determined by counting the number of ___ in an ECG.
Answer: Plasma without clotting factors is serum. Neutrophils and monocytes are the phagocytic cells. Eosinophils are associated with allergic reactions. Calcium ions play the significant role in clotting. The heart rate is found by counting the number of QRS complexes or R peaks in the ECG over a fixed time. Each blank maps to a standard fact from the chapter.
Q7 (NCERT Exemplar, 2 marks; Chapter 18, Very Short Answer 5)
Name the disorders described: acute chest pain due to failure of oxygen supply to the heart muscle, and increased systolic pressure.
Answer: Acute chest pain caused by failure of oxygen supply to the heart muscle is angina pectoris, and when the blockage is complete it leads to a heart attack. Increased systolic pressure is hypertension. The two disorders are related because long-standing hypertension accelerates the artery damage that causes coronary disease.
Q8 (NCERT Exemplar, 3 marks; Chapter 18, Short Answer 1)
Why are the walls of the ventricles much thicker than those of the atria?
Answer: The atria only move blood into the ventricles, which lie immediately below them, so a thin muscular wall is enough. The ventricles have to push blood out of the heart and around the body, and the right ventricle sends blood to the lungs while the left ventricle sends it to the whole body. The pressure needed is much higher, especially on the left side, and a thicker muscle can generate that pressure. That is why the ventricular walls are thick and the left ventricular wall is the thickest of all.
Q9 (NCERT Exemplar, 3 marks; Chapter 18, Short Answer 4)
Explain the advantage of the complete partition of the ventricle in birds and mammals, which leads to double circulation.
Answer: In birds and mammals the two ventricles are completely separated by a septum, so oxygenated blood from the left side and deoxygenated blood from the right side never mix. The left ventricle can pump fully oxygenated blood to the body at high pressure while the right ventricle pumps deoxygenated blood to the lungs at a lower pressure. The complete separation gives the tissues a richer oxygen supply and supports the high metabolic rate of warm-blooded animals. It also allows the two circuits to be regulated separately, so the lungs and the body each receive the flow they need.
Q10 (NCERT Exemplar, 5 marks; Chapter 18, Long Answer 2)
Describe the events in the cardiac cycle and explain double circulation.
Answer: One cardiac cycle lasts about 0.8 seconds at 72 beats per minute and has three phases. In atrial systole, lasting about 0.1 second, both atria contract and push the remaining blood into the ventricles. In ventricular systole, lasting about 0.3 second, the ventricles contract, the atrioventricular valves close and blood is pushed into the pulmonary artery and the aorta as the semilunar valves open. In joint diastole, lasting about 0.4 second, all four chambers relax, the semilunar valves close, the atrioventricular valves open and the ventricles fill passively. The closing of the atrioventricular valves gives the first heart sound and the closing of the semilunar valves gives the second. Stroke volume is about 70 mL and cardiac output is about 5 litres per minute.
Double circulation means that blood passes through the heart twice in one complete circuit. In pulmonary circulation the right ventricle pumps deoxygenated blood to the lungs and oxygenated blood returns to the left atrium. In systemic circulation the left ventricle pumps oxygenated blood to the body and deoxygenated blood returns to the right atrium. The two circuits are in series, and because birds and mammals have four completely separated chambers, the oxygenated and deoxygenated blood never mix. This arrangement delivers fully oxygenated blood to the tissues at high pressure and is one reason these animals can maintain a high metabolic rate.
Answer habits for this set
The questions above reward three habits. First, quote the number with its unit whenever a volume, a count or a pressure is asked for: 70 mL, 5 litres per minute, 120 days, 5 to 5.5 million per cubic millimetre. Second, name the vessel or the chamber in every sentence about flow, because an answer that says blood goes to the lungs without naming the right ventricle and the pulmonary artery is incomplete. Third, separate the three levels of description in a cardiac answer: the mechanical events, the electrical events on the ECG and the sounds produced by the valve closures. A table with these three columns is quick to write and easy for the examiner to mark.
The numbers worth remembering
A compact revision list helps on this page. Red cells are about 5 to 5.5 million per cubic millimetre, white cells 6000 to 8000 and platelets 1.5 to 3.5 lakh, and a red cell lives about 120 days. Stroke volume is about 70 mL and cardiac output about 5 litres per minute at rest. One cardiac cycle lasts about 0.8 seconds at 72 beats per minute, divided into 0.1 second of atrial systole, 0.3 second of ventricular systole and 0.4 second of joint diastole. The ECG has three named waves in every normal beat. These values appear again and again in the exemplar items above, so writing them once in a small table and revising that table is more useful than re-reading the whole chapter before the exam. Keep the list beside the diagrams while revising. A quick self-test is to cover the numbers and recall them from the diagrams alone.