Circulatory System — Biology

Q.1

WBCS Prelims 2022

Which metal is present in haemoglobin?

A. Iron

B. Zinc

C. Magnesium

D. Copper

Explanation

Why Correct: Iron forms the heme group in hemoglobin, binding oxygen in red blood cells.
Distractor Analysis: Zinc is a cofactor in carbonic anhydrase and many other enzymes. Magnesium is central to chlorophyll in plants and many human enzymes. Copper is present in cytochrome c oxidase and ceruloplasmin.
Takeaway: Hemoglobin has four heme groups, each with one iron atom that can bind one O2 molecule.

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Q.2

WBCS Prelims 2020

Which can bind O2 molecules?

A. Red blood cells

B. White blood cells

C. Vitamin B12

D. Vitamin E

Explanation

Why Correct: Red blood cells contain hemoglobin, an iron-containing protein that specifically binds oxygen molecules in the lungs and transports them to tissues throughout the body.
Distractor Analysis: White blood cells function in immune defense against pathogens and do not transport oxygen. Vitamin B12 (cobalamin) is essential for DNA synthesis and red blood cell formation but does not bind oxygen. Vitamin E (tocopherol) acts as an antioxidant protecting cell membranes from oxidative damage.
Takeaway: Each hemoglobin molecule can bind up to four oxygen molecules, with binding affinity increasing cooperatively as each oxygen binds.

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Q.3

WBCS Prelims 2019

ECG records

A. rate of heart beats

B. potential difference

C. ventricular concentration

D. volume of blood pumped

Explanation

Why Correct: An electrocardiogram (ECG) records the electrical potential differences generated by the heart's depolarization and repolarization during each cardiac cycle.
Distractor Analysis: Heart rate can be derived from ECG intervals but is not the direct recording. Ventricular concentration is not a standard physiological measurement. Volume of blood pumped per beat (stroke volume) requires echocardiography or other imaging, not ECG.
Takeaway: The P wave represents atrial depolarization, QRS complex represents ventricular depolarization, and T wave represents ventricular repolarization.

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Q.4

WBCS Prelims 2018

Life span of red blood cells is ________days.

A. 60

B. 120

C. 180

D. 240

Explanation

Why Correct: Human red blood cells (erythrocytes) have an average lifespan of about 120 days before being removed by macrophages in the spleen and liver.
Distractor Analysis: 60 days approximates the lifespan of platelets (thrombocytes). 180 days does not correspond to the standard lifespan of any primary human blood cell type. 240 days does not correspond to the standard lifespan of any primary human blood cell type.
Takeaway: White blood cells (leukocytes) exhibit varied lifespans from hours to years, with neutrophils surviving only 6-8 hours in circulation.

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Q.5

WBCS Prelims 2018

Amounts of O2 normally carried by 100 ml of pure human blood, is

A. 40 ml

B. 10 ml

C. 20 ml

D. 30 ml

Explanation

Why Correct: 100 ml of arterial blood carries approximately 20 ml of oxygen when fully saturated, with hemoglobin binding about 1.34 ml O2 per gram and blood containing around 15 g hemoglobin per 100 ml.
Distractor Analysis: 40 ml would require physiologically impossible hemoglobin levels or oxygen solubility. 10 ml represents venous blood oxygen content after tissue delivery. 30 ml exceeds normal arterial oxygen-carrying capacity.
Takeaway: Venous blood typically carries 12-15 ml O2 per 100 ml, creating an arteriovenous oxygen difference of 4-8 ml used clinically to assess tissue oxygen extraction.

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Q.6

WBCS Prelims 2012

Normal human blood is

A. Acidic

B. Alkaline

C. Neutral

D. Variable

Explanation

Why Correct: Blood pH above 7.0 is alkaline, and the normal range of 7.35–7.45 falls within the alkaline side of the pH scale.
Distractor Analysis: Acidic pH is below 7.0, like gastric juice at pH 1.5–3.5. Neutral pH is exactly 7.0, like pure water. Variable describes fluids whose pH changes, like urine which ranges from 4.5 to 8.0.
Takeaway: The body maintains blood pH within a narrow range (7.35–7.45) through bicarbonate buffering; deviations cause acidosis (7.45).

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Q.7

WBCS Prelims 2010

Cardiac muscles do not undergo fatigue, because

A. Interconnection of cells by intercalated disc

B. Having numerous mitochondria

C. Having more actins

D. Having more myosin

Explanation

Why Correct: Cardiac muscle cells contain abundant mitochondria that continuously produce ATP through aerobic respiration, preventing lactic acid buildup and fatigue.
Distractor Analysis: Intercalated discs enable rapid electrical conduction between cardiac cells but do not prevent fatigue. Both actin and myosin filaments are present in cardiac muscle, but their relative quantities do not determine fatigue resistance.
Takeaway: Cardiac muscle relies exclusively on aerobic respiration, unlike skeletal muscle which can use anaerobic glycolysis leading to lactic acid accumulation and fatigue.

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Q.8

WBCS Prelims 2008

Amount of blood pumped by an adult heart per hour is about

A. 150 litre

B. 200 litre

C. 300 litre

D. 340 litre

Explanation

Why Correct: An adult heart pumps approximately 5 liters per minute at rest, which equals 300 liters per hour (5 × 60).
Distractor Analysis: 150 liters per hour corresponds to 2.5 liters per minute, which is below normal resting cardiac output. 200 liters per hour equals 3.33 liters per minute, still below typical resting output. 340 liters per hour would require 5.67 liters per minute, slightly above average resting cardiac output.
Takeaway: Cardiac output is calculated as stroke volume × heart rate, with typical resting values of 70 ml stroke volume and 70 beats per minute.

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Q.9

WBCS Prelims 2008

The instrument used for measuring blood pressure is called

A. Barometer

B. Sphygmomanometer

C. Tonometer

D. None of the above

Explanation

Why Correct: Sphygmomanometers measure blood pressure using an inflatable cuff and pressure gauge, detecting systolic and diastolic pressures.
Distractor Analysis: Barometers measure atmospheric pressure. Tonometers measure intraocular pressure in the eye.
Takeaway: Blood pressure readings follow systolic/diastolic format (e.g., 120/80 mmHg), where systolic represents ventricular contraction and diastolic represents ventricular relaxation.

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Q.10

WBCS Prelims 2005

Which one of the following blood-group-bearing persons is called a universal donor?

A. A

B. B

C. AB

D. O

Explanation

Why Correct: Blood type O negative lacks A, B, and Rh antigens, allowing safe transfusion to all blood types without triggering immune reactions.
Distractor Analysis: Type A contains A antigens, type B contains B antigens, and type AB contains both A and B antigens, all of which can cause incompatibility reactions in recipients lacking those antigens.
Takeaway: Type AB positive individuals are universal plasma donors because their plasma lacks anti-A and anti-B antibodies.

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Q.11

WBCS Prelims 2005

The amount of blood in the blood circulatory system of a man is

A. one litre

B. two litres

C. five litres

D. ten litres

Explanation

Why Correct: An average adult male has approximately 5 liters of blood, which constitutes about 7-8% of total body weight.
Distractor Analysis: One liter is the typical blood volume of a newborn infant. Two liters represents the plasma component only, not total blood volume. Ten liters would require a body weight of over 140 kg, which is far above average.
Takeaway: Blood constitutes 7-8% of body weight in adults, with females having slightly less (4-5 liters) than males.

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Q.12

WBCS Prelims 2005

Antibodies are synthesized by

A. Bone marrow

B. Plasma and Lymph

C. Liver

D. Kidney

Explanation

Why Correct: Plasma cells, derived from B-lymphocytes, produce and secrete antibodies into plasma and lymph fluids.
Distractor Analysis: Bone marrow produces B-lymphocyte precursors but not mature antibody-secreting cells. Liver synthesizes plasma proteins like albumin and clotting factors, not immunoglobulins. Kidney filters blood and maintains electrolyte balance, with no role in antibody production.
Takeaway: Each antibody molecule consists of two heavy chains and two light chains, with variable regions that bind specific antigens.

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Q.13

WBCS Prelims 2003

Universal donor in blood transfusion refers to

A. Blood Group A

B. Blood Group B

C. Blood Group AB

D. Blood Group O

Explanation

Why Correct: Blood group O lacks both A and B antigens on red blood cells, allowing safe transfusion to recipients of any ABO blood type.
Distractor Analysis: Blood group A contains A antigens and anti-B antibodies. Blood group B contains B antigens and anti-A antibodies. Blood group AB contains both A and B antigens and no anti-A or anti-B antibodies, making it the universal recipient.
Takeaway: For Rh factor, Rh-negative blood (e.g., O-) serves as universal donor for Rh-negative recipients, while Rh-positive blood cannot be given to Rh-negative individuals.

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Q.14

WBCS Prelims 2000

A red blood cell lives for about

A. One week

B. One month

C. Four months

D. One year

Explanation

Why Correct: Human red blood cells (erythrocytes) have an average lifespan of 120 days, which is approximately four months.
Distractor Analysis: One week is far too short for red blood cell lifespan. One month is the typical lifespan of platelets, not red blood cells. One year is too long; red blood cells are continuously replaced every four months.
Takeaway: White blood cells have highly variable lifespans—neutrophils live 6-8 hours, lymphocytes can live years, while red blood cells consistently last 120 days.

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