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Body Fluids and Circulation – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 15. Notes, key terms, important questions with answers and MCQs.

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Chapter overview

Blood and lymph transport materials. The human heart pumps blood through a double circulation, and its activity is recorded by an ECG.

Blood

  • Plasma (≈ 55%) and formed elements: RBCs (haemoglobin), WBCs (neutrophils most common, lymphocytes for immunity), platelets (clotting).
  • ABO blood groups; O is the universal donor, AB the universal recipient; Rh incompatibility can cause erythroblastosis foetalis.
  • Clotting: thrombokinase → prothrombin to thrombin → fibrinogen to fibrin; needs Ca²⁺.

Heart and circulation

  • Four-chambered heart; SA node is the pacemaker; impulse via AV node, bundle of His, Purkinje fibres.
  • Cardiac cycle ≈ 0.8 s; stroke volume ≈ 70 mL; cardiac output ≈ 5 L/min.
  • ECG: P wave (atrial depolarisation), QRS (ventricular depolarisation), T wave (ventricular repolarisation); disorders include hypertension, coronary artery disease, angina, heart failure.

Key terms

Pacemaker
SA node that starts each heartbeat
Double circulation
blood passes twice through the heart in one complete circuit
Lymph
colourless fluid formed from tissue fluid, containing lymphocytes; returns fluid to blood and carries fats

Formulas

  • Cardiac output = stroke volume × heart rate

Important questions with answers

What is the function of the lymphatic system?2 marks

It returns excess tissue fluid to the blood, carries absorbed fats from the intestine (lacteals), and helps immunity through lymphocytes and lymph nodes.

Why is the wall of the left ventricle thicker than that of the right ventricle?3 marks

The left ventricle pumps blood to the whole body (systemic circulation) against high resistance, while the right ventricle pumps only to the nearby lungs. So the left needs a thicker, stronger muscular wall.

Describe the cardiac cycle with the events of each phase and explain the heart sounds.5 marks

One cycle lasts about 0.8 s at 72 beats/min. Joint diastole: all chambers relax; blood fills the atria and flows into the ventricles through open AV valves. Atrial systole (about 0.1 s): atria contract and push about 30% more blood into the ventricles. Ventricular systole (about 0.3 s): ventricles contract, AV valves close (first sound "lub"), pressure rises, semilunar valves open and blood is pumped into the pulmonary artery and aorta. Ventricular diastole: ventricles relax, semilunar valves close (second sound "dub") to prevent backflow, and the cycle repeats. Stroke volume is about 70 mL, so cardiac output is about 5 L/min.

Quick revision

  • SA node = pacemaker.
  • O = universal donor.
  • QRS = ventricular depolarisation.

Exam tips

  • Normal BP is about 120/80 mm Hg.
  • Remember the pathway of an impulse: SA node → atria → AV node → bundle of His → bundle branches → Purkinje fibres → ventricles.

Practice MCQs

  1. Pacemaker of the heart is the

    1. AV node
    2. bundle of His
    3. SA node
    4. Purkinje fibres
    Show answer

    Answer: (c) SA node. SA node.

  2. Universal donor blood group is

    1. A
    2. O
    3. AB
    4. B
    Show answer

    Answer: (b) O. No A or B antigens.

  3. The QRS complex in an ECG shows

    1. atrial depolarisation
    2. atrial repolarisation
    3. ventricular repolarisation
    4. ventricular depolarisation
    Show answer

    Answer: (d) ventricular depolarisation. Ventricles contract.

  4. Most abundant WBCs are

    1. lymphocytes
    2. eosinophils
    3. neutrophils
    4. basophils
    Show answer

    Answer: (c) neutrophils. 60–65%.

  5. The valve between the left atrium and left ventricle is

    1. tricuspid
    2. semilunar
    3. bicuspid (mitral)
    4. pulmonary
    Show answer

    Answer: (c) bicuspid (mitral). Two flaps.

  6. With stroke volume 70 mL and heart rate 72/min, cardiac output is about

    1. 3.5 L/min
    2. 7 L/min
    3. 5 L/min
    4. 10 L/min
    Show answer

    Answer: (c) 5 L/min. 5040 mL.

  7. Which ion is essential for blood clotting

    1. Na⁺
    2. K⁺
    3. Cl⁻
    4. Ca²⁺
    Show answer

    Answer: (d) Ca²⁺. Calcium.

  8. Erythroblastosis foetalis can occur when

    1. mother Rh⁺, foetus Rh⁻
    2. mother Rh⁻, foetus Rh⁺ (second pregnancy)
    3. both Rh⁻
    4. both Rh⁺
    Show answer

    Answer: (b) mother Rh⁻, foetus Rh⁺ (second pregnancy). Maternal anti-Rh antibodies.

All chapters of Class 11 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.