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Body Fluids and Circulation

NCERT Class 11 · Biology Based on NCERT Class 11 Biology textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explains the composition and functions of blood and lymph, the mechanisms of blood circulation, and the structure and working of the human heart. It exists in the syllabus to help students understand how essential substances like oxygen and nutrients are transported throughout the body and how waste products are removed. The one big idea a student must walk away with is that the heart, blood vessels, and blood work together in a double circulation system to ensure efficient transport, and that any disruption in this system leads to disorders like hypertension or heart failure.
Key Concepts (23)
Blood
A special connective tissue consisting of a fluid matrix, plasma, and formed elements.
e.g. When you cut your finger, the red liquid that comes out is blood, which contains plasma, RBCs, WBCs, and platelets.
Plasma
A straw coloured, viscous fluid constituting nearly 55 per cent of the blood, containing 90-92 per cent water and 6-8 per cent proteins like fibrinogen, globulins, and albumins.
e.g. The liquid part of blood left after cells are removed is plasma, which helps in clotting and defense.
Serum
Plasma without the clotting factors.
e.g. In a blood test, serum is used to check for antibodies because it lacks clotting proteins.
Erythrocytes (RBCs)
Red blood cells, the most abundant cells in blood, devoid of nucleus in most mammals, biconcave in shape, containing haemoglobin for transport of respiratory gases.
e.g. A healthy adult man has about 5 million RBCs per mm³ of blood, and they live for about 120 days before being destroyed in the spleen.
Leucocytes (WBCs)
Colourless, nucleated blood cells that are relatively lesser in number (6000-8000 per mm³) and are involved in immune responses.
e.g. When you get an infection, your WBC count increases to fight the foreign organisms.
Platelets (Thrombocytes)
Cell fragments produced from megakaryocytes in the bone marrow, involved in coagulation or clotting of blood.
e.g. If you get a small cut, platelets quickly gather at the site to form a clot and stop bleeding.
ABO grouping
Blood grouping based on the presence or absence of two surface antigens (A and B) on RBCs and corresponding antibodies in plasma.
e.g. A person with blood group A has A antigens on RBCs and anti-B antibodies in plasma.
Rh grouping
Blood grouping based on the presence (Rh+ve) or absence (Rh-ve) of the Rh antigen on RBCs, similar to one found in Rhesus monkeys.
e.g. About 80% of humans are Rh positive, meaning they have the Rh antigen on their RBCs.
Erythroblastosis foetalis
A condition in which Rh antibodies from an Rh-ve mother leak into the blood of an Rh+ve foetus, destroying foetal RBCs and causing severe anaemia and jaundice.
e.g. This can happen in the second pregnancy if the first child was Rh+ve and the mother developed antibodies.
Lymph (Tissue Fluid)
A colourless fluid derived from blood, present in the lymphatic system, containing specialised lymphocytes and acting as a carrier for nutrients, hormones, and fats.
e.g. After a fatty meal, lymph in the lacteals of intestinal villi absorbs the fats and transports them.
Sino-atrial node (SAN)
A patch of nodal tissue in the right upper corner of the right atrium that generates the maximum number of action potentials (70-75/min) and initiates the rhythmic contractile activity of the heart, hence called the pacemaker.
e.g. The SAN sets the heart rate; if it fails, an artificial pacemaker is implanted.
Atrio-ventricular node (AVN)
A mass of nodal tissue in the lower left corner of the right atrium close to the atrio-ventricular septum that conducts action potential from the atria to the ventricles.
e.g. The AVN delays the signal slightly so that the atria finish contracting before the ventricles start.
Cardiac cycle
The sequential event in the heart that is cyclically repeated, consisting of systole and diastole of both the atria and ventricles.
e.g. One cardiac cycle lasts 0.8 seconds when the heart beats 72 times per minute.
Stroke volume
The volume of blood pumped out by each ventricle per cardiac cycle, approximately 70 mL.
e.g. If your heart beats 72 times per minute, your stroke volume is about 70 mL per beat.
Cardiac output
The volume of blood pumped out by each ventricle per minute, equal to stroke volume multiplied by heart rate, averaging 5000 mL or 5 litres in a healthy individual.
e.g. An athlete may have a higher cardiac output due to a larger stroke volume or faster heart rate.
Electrocardiogram (ECG)
A graphical representation of the electrical activity of the heart during a cardiac cycle.
e.g. A standard ECG shows P wave, QRS complex, and T wave, each corresponding to specific electrical events.
Pulmonary circulation
The pathway of blood from the right ventricle to the lungs and back to the left atrium via pulmonary veins.
e.g. Deoxygenated blood is pumped from the right ventricle into the pulmonary artery to the lungs for oxygenation.
Systemic circulation
The pathway of blood from the left ventricle to all body tissues and back to the right atrium via veins and vena cava.
e.g. Oxygenated blood from the left ventricle goes through the aorta to supply the entire body.
Hepatic portal system
A unique vascular connection between the digestive tract and liver where the hepatic portal vein carries blood from intestine to the liver before systemic circulation.
e.g. Nutrients absorbed from the small intestine are first taken to the liver for processing via the hepatic portal vein.
Hypertension
High blood pressure, defined as repeated checks showing 140/90 mm Hg or higher, leading to heart diseases and affecting vital organs like brain and kidney.
e.g. A person with a blood pressure reading of 150/95 is considered hypertensive.
Coronary Artery Disease (CAD)
A disease affecting vessels that supply blood to the heart muscle, caused by deposits of calcium, fat, cholesterol, and fibrous tissues, narrowing the lumen of arteries.
e.g. Atherosclerosis is a common form of CAD that can lead to heart attacks.
Angina
A symptom of acute chest pain that appears when not enough oxygen is reaching the heart muscle, also called angina pectoris.
e.g. A person with angina may feel chest pain while climbing stairs due to reduced blood flow to the heart.
Heart failure
The state of heart when it is not pumping blood effectively enough to meet the needs of the body, sometimes called congestive heart failure.
e.g. Heart failure is not the same as cardiac arrest; it means the heart is weak but still beating.
Formulas & Equations (6)
Cardiac Output = Stroke Volume × Heart Rate
Reads as: Cardiac output equals stroke volume multiplied by heart rate
Variables: Cardiac Output (mL/min or L/min), Stroke Volume (mL/beat, approx 70 mL), Heart Rate (beats/min, approx 72)
Use when: Calculating the volume of blood pumped by each ventricle per minute
⚠ Students often forget that cardiac output is per ventricle, not total blood pumped by the whole heart.
Stroke Volume ≈ 70 mL
Reads as: Stroke volume is approximately 70 millilitres
Variables: Stroke Volume (mL)
Use when: Describing the volume of blood ejected per beat in a healthy individual
⚠ Students sometimes confuse stroke volume with cardiac output.
Heart Rate ≈ 72 beats/min
Reads as: Heart rate is approximately 72 beats per minute
Variables: Heart Rate (beats per minute)
Use when: Describing the normal resting heart rate
⚠ Students may think the heart rate is fixed, but it can vary with activity.
Duration of one cardiac cycle = 60 / Heart Rate = 60 / 72 ≈ 0.8 seconds
Reads as: Duration of one cardiac cycle equals 60 divided by heart rate, which is approximately 0.8 seconds
Variables: Duration (seconds), Heart Rate (beats per minute)
Use when: Calculating the time for one complete cardiac cycle
⚠ Students often forget to convert minutes to seconds.
Normal Blood Pressure = 120/80 mm Hg
Reads as: Normal blood pressure is 120 over 80 millimetres of mercury
Variables: Systolic pressure (120 mm Hg), Diastolic pressure (80 mm Hg)
Use when: Describing normal blood pressure values
⚠ Students sometimes think the numbers are in different units or confuse systolic and diastolic.
Hypertension threshold = 140/90 mm Hg or higher
Reads as: Hypertension is defined as 140 over 90 millimetres of mercury or higher
Variables: Systolic pressure (140 mm Hg), Diastolic pressure (90 mm Hg)
Use when: Identifying high blood pressure
⚠ Students may think a single high reading indicates hypertension; it requires repeated checks.
How It Works
Coagulation of Blood (Clotting)
  1. Step 1: Injury or trauma stimulates platelets to release certain factors.
  2. Step 2: These factors activate a cascade of enzymic reactions involving inactive plasma factors, forming an enzyme complex called thrombokinase.
  3. Step 3: Thrombokinase converts inactive prothrombin (in plasma) into active thrombin, with the help of calcium ions.
  4. Step 4: Thrombin converts inactive fibrinogen (in plasma) into fibrin threads.
  5. Step 5: Fibrin forms a network that traps dead and damaged formed elements, creating a clot (coagulum).
💡 Students often forget that calcium ions are essential for clotting and that both platelet factors and tissue factors can initiate the cascade.
Cardiac Cycle
  1. Step 1: All four chambers are in joint diastole (relaxed). Tricuspid and bicuspid valves are open; semilunar valves are closed. Blood flows from veins into atria and then into ventricles.
  2. Step 2: SAN generates an action potential, causing atrial systole (contraction). This pushes about 30% more blood into the ventricles.
  3. Step 3: The action potential reaches the AVN, then the AV bundle (bundle of His), and spreads through Purkinje fibres to the ventricular musculature.
  4. Step 4: Ventricular systole begins. Atria undergo diastole. Ventricular pressure rises, closing tricuspid and bicuspid valves (first heart sound 'lub').
  5. Step 5: Ventricular pressure further increases, forcing open semilunar valves. Blood is pumped into the pulmonary artery (right ventricle) and aorta (left ventricle).
  6. Step 6: Ventricles relax (ventricular diastole). Ventricular pressure falls, closing semilunar valves (second heart sound 'dub').
  7. Step 7: As ventricular pressure declines further, tricuspid and bicuspid valves open. Blood flows from atria into ventricles. Joint diastole resumes.
  8. Step 8: SAN generates a new action potential, and the cycle repeats.
💡 Students often confuse the sequence of valve openings and closures. Remember: AV valves close at the start of ventricular systole; semilunar valves close at the start of ventricular diastole.
Formation of Lymph (Tissue Fluid)
  1. Step 1: As blood passes through capillaries in tissues, some water and small water-soluble substances move out into the spaces between cells.
  2. Step 2: Larger proteins and most formed elements remain in the blood vessels.
  3. Step 3: This fluid released out is called interstitial fluid or tissue fluid, with mineral distribution similar to plasma.
  4. Step 4: An elaborate network of lymphatic vessels collects this fluid.
  5. Step 5: The fluid in the lymphatic system is called lymph, which is drained back to the major veins.
💡 Students often think lymph is identical to blood; it lacks larger proteins and has fewer formed elements, but contains specialised lymphocytes.
Double Circulation in Humans
  1. Step 1: Pulmonary circulation: Deoxygenated blood from the right ventricle is pumped into the pulmonary artery, goes to the lungs for oxygenation, and returns via pulmonary veins to the left atrium.
  2. Step 2: Systemic circulation: Oxygenated blood from the left ventricle is pumped into the aorta, distributed to all body tissues via arteries, arterioles, and capillaries, and deoxygenated blood is collected by venules, veins, and vena cava, returning to the right atrium.
💡 Students often mix up which side of the heart handles oxygenated vs deoxygenated blood. Right side handles deoxygenated; left side handles oxygenated.
Regulation of Cardiac Activity
  1. Step 1: The heart is myogenic, meaning its normal activities are auto-regulated by specialised nodal tissue (SAN, AVN).
  2. Step 2: A neural centre in the medulla oblongata moderates cardiac function through the autonomic nervous system (ANS).
  3. Step 3: Sympathetic nerves increase heart rate, strength of ventricular contraction, and cardiac output.
  4. Step 4: Parasympathetic nerves decrease heart rate, speed of conduction, and cardiac output.
  5. Step 5: Adrenal medullary hormones (e.g., adrenaline) can also increase cardiac output.
💡 Students often forget that the heart is myogenic (self-excitable) and that neural and hormonal factors only moderate, not initiate, the heartbeat.
Exam Traps — Don't Make These Mistakes
⚠ Confusing Serum and Plasma
✗ Serum is the same as plasma.
→ Serum is plasma without the clotting factors, so they are not identical.
✓ Serum is plasma from which clotting factors have been removed.
⚠ Mixing up Universal Donor and Universal Recipient
✗ AB group individuals are universal donors because they can donate to anyone.
→ AB group individuals are universal recipients (can receive from anyone), not universal donors. O group individuals are universal donors.
✓ Group O individuals are universal donors because their RBCs lack A and B antigens. Group AB individuals are universal recipients because their plasma lacks anti-A and anti-B antibodies.
⚠ Thinking Heart Failure Means Heart Stops
✗ Heart failure is when the heart stops beating.
→ Heart failure means the heart is not pumping effectively, but it is still beating. Cardiac arrest is when the heart stops.
✓ Heart failure is a condition where the heart does not pump blood effectively enough to meet the body's needs; it is not the same as cardiac arrest.
⚠ Confusing Systole and Diastole
✗ Systole is relaxation and diastole is contraction.
→ Systole is contraction, diastole is relaxation.
✓ Systole refers to contraction of the heart chambers, while diastole refers to relaxation.
⚠ Misidentifying the Pacemaker
✗ The AVN is the pacemaker of the heart.
→ The SAN generates the maximum number of action potentials (70-75/min) and sets the pace, so it is the pacemaker. The AVN conducts the signal but does not set the pace.
✓ The sino-atrial node (SAN) is the pacemaker of the heart because it generates the highest frequency of action potentials and initiates the heartbeat.
⚠ Forgetting Calcium Ions in Clotting
✗ Only thrombokinase and thrombin are needed for clotting.
→ Calcium ions play a very important role in the conversion of prothrombin to thrombin.
✓ Calcium ions are essential for the conversion of prothrombin to thrombin during blood coagulation.
Compare & Contrast
Composition and function
Blood
Lymph
Blood contains plasma, RBCs, WBCs, and platelets, and is primarily for transport of gases, nutrients, and wastes. Lymph is a colourless fluid with fewer proteins, contains specialised lymphocytes, and is involved in immune responses and absorption of fats.
Pathway of blood
Open Circulatory System
Closed Circulatory System
In open circulation (arthropods, molluscs), blood pumped by the heart passes into open spaces called sinuses. In closed circulation (annelids, chordates), blood is always circulated through a closed network of blood vessels, allowing more precise regulation.
Pathway and function
Pulmonary Circulation
Systemic Circulation
Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium. Systemic circulation carries oxygenated blood from the left ventricle to all body tissues and returns deoxygenated blood to the right atrium.
Phase of cardiac cycle
Systole
Diastole
Systole is the contraction phase of the heart chambers, forcing blood out. Diastole is the relaxation phase, allowing chambers to fill with blood.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 SA-I (2 marks), 1 SA-II (3 marks), 1 LA (5 marks) — total approximately 11-12 marks
Most asked: Composition and functions of blood (plasma and formed elements) · ABO and Rh blood grouping and donor compatibility · Structure of the human heart and its chambers · Cardiac cycle and its phases · ECG waves (P, QRS, T) and their significance · Double circulation (pulmonary and systemic) · Disorders of circulatory system (hypertension, CAD, angina, heart failure)
Don't skip: Describe the cardiac cycle with a diagram.; Explain ABO and Rh blood grouping and their clinical significance.; Draw a labelled diagram of the human heart and explain double circulation.; Explain the events of blood coagulation.
One-Line Revision (read aloud before the exam)
  1. Blood is a special connective tissue with a fluid matrix called plasma and formed elements (RBCs, WBCs, platelets).
  2. Plasma is 90-92% water and contains proteins like fibrinogen (clotting), globulins (defense), and albumins (osmotic balance).
  3. Serum is plasma without clotting factors.
  4. RBCs are biconcave, lack a nucleus, contain haemoglobin, and live about 120 days before being destroyed in the spleen.
  5. WBCs are nucleated, colourless, and include granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
  6. Platelets are cell fragments from megakaryocytes involved in blood clotting.
  7. ABO grouping is based on A and B antigens on RBCs and corresponding antibodies in plasma; O is universal donor, AB is universal recipient.
  8. Rh incompatibility between an Rh-ve mother and Rh+ve foetus can cause erythroblastosis foetalis.
  9. Lymph is a colourless fluid derived from blood, containing lymphocytes, and helps in immune responses and fat absorption.
  10. The sino-atrial node (SAN) is the pacemaker of the heart, generating 70-75 action potentials per minute.
  11. The cardiac cycle consists of atrial systole, ventricular systole, and joint diastole, lasting 0.8 seconds at 72 beats per minute.
  12. Stroke volume is about 70 mL per beat, and cardiac output is about 5 litres per minute.
  13. ECG shows P wave (atrial depolarisation), QRS complex (ventricular depolarisation), and T wave (ventricular repolarisation).
  14. Double circulation includes pulmonary circulation (right ventricle to lungs to left atrium) and systemic circulation (left ventricle to body to right atrium).
  15. The heart is myogenic, but its activity is moderated by the autonomic nervous system and adrenal medullary hormones.
  16. Hypertension is blood pressure of 140/90 mm Hg or higher.
  17. Coronary Artery Disease (CAD) involves narrowing of arteries due to deposits of calcium, fat, and cholesterol.
  18. Angina is chest pain due to inadequate oxygen supply to the heart muscle.
  19. Heart failure is when the heart pumps ineffectively, not the same as cardiac arrest.

MCQs — 10 Questions with Answers

Q1. What is the percentage composition of water in blood plasma?

  • A. 50-60%
  • B. 70-80%
  • C. 90-92% ✓
  • D. 95-98%

Answer: C — Plasma is 90-92% water, which makes it a fluid medium for transporting dissolved substances.

Q2. Which of the following statements about RBCs is INCORRECT?

  • A. RBCs are biconcave in shape
  • B. RBCs contain haemoglobin for oxygen transport
  • C. RBCs have a nucleus in most mammals ✓
  • D. RBCs are produced in red bone marrow

Answer: C — RBCs are devoid of nucleus in most mammals;

Q3. A person with blood group O can donate blood to which of the following groups?

  • A. Only group O
  • B. Groups A, B, and O only
  • C. Groups A, B, AB, and O ✓
  • D. Only group AB

Answer: C — Group O has no antigens, so it does not trigger immune response in any recipient; hence it is the universal donor for all groups.

Q4. What is the normal haemoglobin level in a healthy adult measured as?

  • A. 8-10 g per 100 ml blood
  • B. 12-16 g per 100 ml blood ✓
  • C. 18-20 g per 100 ml blood
  • D. 5-8 g per 100 ml blood

Answer: B — A healthy individual has 12-16 grams of haemoglobin in every 100 ml of blood, which is the standard clinical reference.

Q5. The spleen is called the 'graveyard of RBCs' because it is responsible for:

  • A. Producing new RBCs
  • B. Storing RBCs temporarily
  • C. Destroying old RBCs after their 120-day lifespan ✓
  • D. Filtering pathogens from blood only

Answer: C — The spleen destroys old RBCs that have completed their 120-day lifespan, hence the name 'graveyard of RBCs'.

Q6. Which statement about WBCs is correct? Assertion (A): Neutrophils are the most abundant WBCs at 60-65% of total WBCs. Reason (R): Neutrophils are phagocytic cells that destroy foreign organisms.

  • A. Both A and R are correct and R is the correct explanation of A
  • B. Both A and R are correct but R is not the correct explanation of A ✓
  • C. A is correct but R is incorrect
  • D. Both A and R are incorrect

Answer: B — Both statements are true: neutrophils are abundant (60-65%) AND they are phagocytic, but abundance is not due to their phagocytic nature alone—it is their role in primary defence.

Q7. If a person has 4.2 million RBCs per mm³ of blood, this person likely has:

  • A. Normal RBC count
  • B. Polycythemia (too many RBCs)
  • C. Anaemia (too few RBCs) ✓
  • D. No abnormality as this is average for some populations

Answer: C — Normal RBC count is 5-5.5 million per mm³; a count of 4.2 million is below normal, indicating anaemia or oxygen-carrying capacity reduction.

Q8. Why does Rh incompatibility cause problems only in the second pregnancy of an Rh-negative mother carrying an Rh-positive foetus, not the first?

  • A. The placenta prevents foetal blood from mixing with maternal blood in the first pregnancy only
  • B. The mother's antibodies are produced after exposure to Rh antigen during delivery of the first child ✓
  • C. Rh antigen is expressed only from the second pregnancy onwards
  • D. The Rh-positive foetus develops immunity in the second pregnancy

Answer: B — In the first pregnancy, the placenta separates bloods; during first delivery, the mother is exposed to foetal Rh+ve blood and forms anti-Rh antibodies that attack the second Rh+ve foetus.

Q9. Which of the following is NOT a function of plasma proteins? Assertion: Fibrinogen aids in blood clotting, globulins in defence, and albumins in osmotic balance. Reason: Plasma proteins also directly carry oxygen and carbon dioxide.

  • A. Both statements are correct
  • B. Assertion is correct, Reason is incorrect ✓
  • C. Both statements are incorrect
  • D. Assertion is incorrect, Reason is correct

Answer: B — Plasma proteins (fibrinogen, globulins, albumins) do NOT directly transport O₂ and CO₂; haemoglobin in RBCs does that, not plasma proteins.

Q10. Calculate: If the normal WBC count is 8000 per mm³ and neutrophils constitute 60% of total WBCs, how many neutrophils are present per mm³?

  • A. 3200 per mm³
  • B. 4800 per mm³ ✓
  • C. 5600 per mm³
  • D. 6400 per mm³

Answer: B — Neutrophils = 60% of 8000 = 0.60 × 8000 = 4800 per mm³; this calculation applies the percentage formula to blood cell counts.

Flashcards

What is blood? Define it with its two main components.

Blood is a special connective tissue consisting of a fluid matrix (plasma) and formed elements (RBCs, WBCs, and platelets).

What percentage of blood is plasma, and what is its main component?

Plasma constitutes 55% of blood and is 90-92% water.

Name the three main proteins found in plasma and their functions.

Fibrinogen (clotting), globulins (defence), and albumins (osmotic balance) are the major plasma proteins.

What is the normal count of RBCs in a healthy adult male?

A healthy adult male has 5 to 5.5 million RBCs per mm³ of blood.

Why are RBCs called 'red blood cells' and what do they contain?

RBCs are called red blood cells because they contain haemoglobin, a red-coloured iron-containing protein that transports oxygen.

What is the lifespan of an RBC and where are old RBCs destroyed?

RBCs have an average lifespan of 120 days and are destroyed in the spleen, which is called the graveyard of RBCs.

Which blood group is the universal donor and why?

O blood group is the universal donor because it has no A or B antigens on RBCs, so it cannot trigger immune rejection.

What is Rh incompatibility and when does it become dangerous in pregnancy?

Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive foetus; it causes problems in the second pregnancy due to maternal antibodies.

Name the two main categories of WBCs and give one example of each.

The two main categories are granulocytes (e.g. neutrophils) and agranulocytes (e.g. lymphocytes).

What is the difference between plasma and serum?

Plasma is blood fluid with clotting factors present, while serum is plasma without the clotting factors.

Important Board Questions

Define blood and mention its two main components with their percentage composition in blood. [2 marks]

State that blood is a connective tissue; mention plasma (55%) and formed elements (45%) with brief function of each.

Explain the ABO blood grouping system with reference to antigens, antibodies, and transfusion compatibility. Why is group O considered a universal donor? [5 marks]

Create a table showing A, B, AB, O groups with their antigens and antibodies; explain that O has no antigens so no immune rejection occurs in any recipient; define universal donor accordingly.

What is erythroblastosis foetalis? Explain the mechanism of its occurrence in the second pregnancy of an Rh-negative mother carrying an Rh-positive foetus, and how it can be prevented. [6 marks]

Define the disease; explain that 1st pregnancy is safe (placenta separates bloods), but during delivery maternal blood contacts foetal Rh+ve blood → mother forms anti-Rh antibodies → 2nd pregnancy: these antibodies cross placenta and destroy foetal RBCs; prevention: give anti-Rh antibodies after 1st delivery to prevent maternal sensitization.

Assertion-Reason Questions for Body Fluids and Circulation

Q1. Assertion (A):

Group O individuals can donate blood to persons with any blood group.

Reason (R):

Group O RBCs lack both A and B antigens, so they will not trigger immune response in any recipient.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true, and the reason correctly explains why O group is the universal donor. The absence of A and B antigens prevents agglutination with any recipient's antibodies.

Q2. Assertion (A):

Neutrophils are the most abundant white blood cells in human blood.

Reason (R):

Neutrophils constitute 60-65% of total WBC count and are primarily involved in destroying pathogens through phagocytosis.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — The assertion is true (neutrophils are most abundant), and the reason is also factually correct, but the reason does not explain WHY they are most abundant. The abundance relates to their critical role in immediate defense, not just their phagocytic function.

Q3. Assertion (A):

RBCs in mammals lack a nucleus at maturity.

Reason (R):

Loss of nucleus in RBCs provides more space for haemoglobin and increases oxygen-carrying capacity.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both assertion and reason are true. Mammalian mature RBCs are enucleated (lack nucleus), and this adaptation allows more haemoglobin molecules to fit in the cell, increasing oxygen transport efficiency.

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Case-Based Questions (CBQ) for Body Fluids and Circulation

Case Study:

A 32-year-old woman in her second pregnancy visited a hospital with complaints of nausea and fatigue. During routine blood tests, her blood group was determined as Rh negative (Rh−ve). Her medical records showed that her first child, born 3 years ago, was healthy with no complications. However, the current pregnancy shows elevated levels of anti-Rh antibodies in her blood serum. The attending physician expressed concern about the foetus and recommended close monitoring throughout the pregnancy.

Q1. Why were anti-Rh antibodies present in the mother's blood?

  • A. She was born with these antibodies as part of her natural immunity
  • B. These antibodies were formed after exposure to Rh positive blood during first delivery ✓
  • C. The current Rh positive foetus is triggering antibody production during pregnancy
  • D. Antibodies were transferred from a previous blood transfusion

Answer: B

Q2. What is the primary risk to the current Rh positive foetus due to elevated maternal anti-Rh antibodies?

  • A. Destruction of foetal RBCs leading to anaemia and jaundice (erythroblastosis foetalis) ✓
  • B. Prevention of nutrient transport across the placenta
  • C. Increased clotting of foetal blood leading to thrombosis
  • D. Rejection of foetus by maternal immune system causing abortion

Answer: A

Q3. Why was the first child of this Rh negative mother born healthy despite carrying Rh positive blood?

  • A. Foetal blood does not circulate before delivery, so no antigen exposure occurs
  • B. The placenta provides complete separation between maternal and foetal blood during pregnancy ✓
  • C. The first foetus had Rh negative blood like the mother
  • D. Maternal antibodies are not produced until after the second pregnancy

Answer: B

Q4. What preventive measure should have been taken immediately after the first delivery to prevent complications in the second pregnancy?

  • A. Administer anti-Rh antibodies (RhoGAM) to the mother within 72 hours of delivery ✓
  • B. Perform immediate blood transfusion to the newborn
  • C. Give anti-A and anti-B antibodies to the mother
  • D. Ensure the second child is also Rh negative through genetic counselling

Answer: A

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