Home › GK Questions Asked › Biology › Human Physiology - Respiration, Circulation and Excretion

Human Physiology - Respiration, Circulation and Excretion PYQs – Biology, SSC & Railway

159 Human Physiology - Respiration, Circulation and Excretion (Biology) questions asked in recent SSC and Railway exams, newest first, with exam, date & shift, answers and solutions – page 2 of 2.

📚 159 questionsSSC 49 · Railway 110
12
SSC CHSL Tier-1 2025 – 22 November 2025 Shift 1 · Respiration and excretion in other organisms

Q101. What role do cellular vacuoles play in plant waste management?

  1. (a) They facilitate nutrient absorption
  2. (b) They store waste products
  3. (c) They assist in photosynthesis
  4. (d) They help in water transportation
Answer & solution

Answer: (b) They store waste products

Correct Answer: They store waste products (Option 2)
In plant cells, vacuoles are large, membrane-bound organelles that play a crucial role in waste management. They store metabolic waste products, toxic substances, and by-products that the plant cannot use or needs to isolate from the cytoplasm. This prevents harmful substances from disrupting cellular functions. Plant vacuoles are significantly larger than animal cell vacuoles and can occupy up to 90% of the cell's volume.
Why other options are wrong:
Option 1 - Facilitate nutrient absorption: This is primarily the role of the cell membrane and transport proteins, not vacuoles.
Option 3 - Assist in photosynthesis: Photosynthesis occurs in chloroplasts, not vacuoles.
Option 4 - Help in water transportation: Water transport in plants occurs through xylem vessels, not vacuoles (though vacuoles do maintain cell turgidity).
SSC CHSL Tier-1 2025 – 21 November 2025 Shift 1 · Lymphatic system

Q102. What is the other name of the tissue fluid in human body?

  1. (a) Sweat
  2. (b) Urine
  3. (c) Lymph
  4. (d) Mucus
Answer & solution

Answer: (c) Lymph

Lymph (also called lymphatic fluid) is the other name for tissue fluid (interstitial fluid). When the tissue fluid (fluid surrounding body cells) drains into the lymphatic capillaries, it becomes lymph. Lymph is a clear, yellowish fluid that flows through the lymphatic system and eventually returns to the bloodstream. Why other options are wrong: Option 1 - Sweat: Sweat is produced by sweat glands in the skin as a cooling mechanism; it is not the same as tissue fluid. Option 2 - Urine: Urine is the waste fluid produced by the kidneys; not the same as tissue fluid. Option 4 - Mucus: Mucus is secreted by mucous membranes and glands to protect and lubricate; it is not the other name for tissue fluid.
SSC CHSL Tier-1 2025 – 20 November 2025 Shift 1 · Aerobic and anaerobic respiration

Q103. How many carbon molecules does pyruvate has?

  1. (a) 3
  2. (b) 4
  3. (c) 5
  4. (d) 6
Answer & solution

Answer: (a) 3

Pyruvate (pyruvic acid, chemical formula: CH3COCOO- or C3H4O3) contains 3 carbon atoms. Pyruvate is the end product of glycolysis (breakdown of glucose) and serves as a key metabolic intermediate. It can be converted to acetyl-CoA (entering the Krebs cycle), lactate (during anaerobic respiration), or ethanol (in fermentation). Why other options are wrong: Option 2 (4 carbons): 4-carbon compounds include oxaloacetate and malate in the Krebs cycle. Option 3 (5 carbons): 5-carbon compounds include ribose and ribulose in metabolism. Option 4 (6 carbons): Glucose has 6 carbon atoms; pyruvate is formed when glucose is split into two 3-carbon pyruvate molecules.
SSC CHSL Tier-1 2025 – 20 November 2025 Shift 2 · Heart - structure and functioning

Q104. Why does the human heart has different chambers?

  1. (a) To regulate body temperature
  2. (b) To pump blood to different organs
  3. (c) To prevent the mixing of oxygen-rich blood with carbon dioxide-rich blood
  4. (d) To store blood
Answer & solution

Answer: (c) To prevent the mixing of oxygen-rich blood with carbon dioxide-rich blood

Correct Answer: To prevent the mixing of oxygen-rich blood with carbon dioxide-rich blood
The human heart has four chambers (right atrium, right ventricle, left atrium, left ventricle) primarily to prevent the mixing of oxygenated blood (from lungs) with deoxygenated blood (from body). The right side of the heart handles deoxygenated blood (receives from body, sends to lungs), while the left side handles oxygenated blood (receives from lungs, sends to body). The four-chamber design ensures complete separation for efficient double circulation.
Why other options are wrong:
- To regulate body temperature: This is done by the hypothalamus, skin, and sweating; not the heart chambers.
- To pump blood to different organs: While the heart pumps blood, the different chambers are specifically to separate oxygenated and deoxygenated blood.
- To store blood: The heart does not store blood; it continuously pumps it.
SSC CHSL Tier-1 2025 – 20 November 2025 Shift 2 · Blood vessels, circulation and blood pressure

Q105. Which of the following statement is correct regarding blood vessels?

  1. (a) Arteries are the vessels which carry blood away from the heart to various organs of the body.
  2. (b) Veins collect the blood from heart and spread it to different organs.
  3. (c) Arteries have capillaries to prevent backflow of blood.
  4. (d) The smallest vessels have walls which are one-cell thick and are called veins.
Answer & solution

Answer: (a) Arteries are the vessels which carry blood away from the heart to various organs of the body.

Correct Answer: Arteries are the vessels which carry blood away from the heart to various organs of the body. (Option 1)
Option 1 is correct: Arteries carry oxygenated blood (except pulmonary artery) away from the heart to various organs of the body. They have thick, elastic walls to withstand the high pressure of blood pumped by the heart.
Why others are wrong:
Option 2 - Veins collect the blood from heart and spread it to different organs: Incorrect. Veins carry blood from various organs BACK to the heart, not from the heart to organs.
Option 3 - Arteries have capillaries to prevent backflow of blood: Incorrect. Arteries do not have capillaries for this purpose. Valves (not capillaries) prevent backflow, and they are found in veins and the heart.
Option 4 - The smallest vessels have walls which are one-cell thick and are called veins: Incorrect. The smallest vessels with one-cell thick walls are called capillaries, not veins.
SSC CHSL Tier-1 2025 – 17 November 2025 Shift 1 · Excretory system - kidney and nephron

Q106. Which of the following organ is part of excretory system in human body?
I. A pair of ureters
II. A urethra

  1. (a) Only I
  2. (b) Only II
  3. (c) Both I and II
  4. (d) Neither I nor II
Answer & solution

Answer: (c) Both I and II

The human excretory system (urinary system) consists of: a pair of kidneys, a pair of ureters, the urinary bladder, and the urethra. Both the ureters (I) — which carry urine from kidneys to the bladder — and the urethra (II) — which carries urine from the bladder out of the body — are essential parts of the excretory system. Why other options are wrong: Option 1 (Only I): Incorrect, as the urethra is also part of the excretory system. Option 2 (Only II): Incorrect, as ureters are also part of the excretory system. Option 4 (Neither I nor II): Both are definitely part of the excretory system.
SSC CHSL Tier-1 2025 – 17 November 2025 Shift 3 · Aerobic and anaerobic respiration

Q107. Which type of reactions are driven by the energy provided by ATP?

  1. (a) Neutral reactions
  2. (b) Redox reactions
  3. (c) Endothermic reactions
  4. (d) Exothermic reactions
Answer & solution

Answer: (c) Endothermic reactions

Correct Answer: Endothermic reactions
ATP (Adenosine Triphosphate) provides energy to drive endothermic (endergonic) reactions in biological systems. Endothermic reactions require an input of energy to proceed. When ATP is hydrolysed (ATP -> ADP + Pi), it releases about 30.5 kJ/mol of energy, which is used to power energy-requiring (endothermic/endergonic) cellular processes such as muscle contraction, active transport, and biosynthesis.
Why other options are wrong:
- Neutral reactions: Neither release nor absorb energy; ATP is not required to drive them.
- Redox reactions: ATP is not specifically needed to drive redox reactions (they can be spontaneous).
- Exothermic reactions: These release energy on their own and do not need ATP to drive them.
SSC CHSL Tier-1 2025 – 17 November 2025 Shift 2 · Blood - components and functions

Q108. Carbon dioxide is transported to the lungs from all parts of the body through _____ in humans.

  1. (a) Sweat
  2. (b) Mucus
  3. (c) Blood
  4. (d) Lymph
Answer & solution

Answer: (c) Blood

Correct Answer: Blood (Option 3)
Carbon dioxide (CO2) produced in body cells is transported to the lungs through blood. It is carried in three forms:
1. Dissolved in plasma (about 7%)
2. As bicarbonate ions (HCO3-) in plasma (about 70%) — the major form
3. Combined with haemoglobin as carbaminohaemoglobin (about 23%)
Sweat is produced by sweat glands and does not transport CO2 to the lungs. Mucus lines the respiratory tract but does not transport CO2. Lymph circulates through the lymphatic system but is not a medium for CO2 transport to the lungs.
SSC CHSL Tier-1 2025 – 17 November 2025 Shift 2 · Excretory system - kidney and nephron

Q109. In initial filtrate of kidney, which of the following substance is selectively re-absorbed as the urine flows along the tube in a human kidney?
I. Glucose
II. Amino acids

  1. (a) Only I
  2. (b) Only II
  3. (c) Both I and II
  4. (d) Neither I nor II
Answer & solution

Answer: (c) Both I and II

Correct Answer: Both I and II (Option 3)
In the kidney, the glomerulus filters blood to produce the initial filtrate which contains glucose, amino acids, water, salts, urea, etc. As this filtrate passes through the Proximal Convoluted Tubule (PCT), both glucose (Statement I) and amino acids (Statement II) are completely and selectively reabsorbed back into the bloodstream through active transport.
Under normal conditions, no glucose or amino acids appear in the final urine. Both are essential nutrients that the body conserves.
Option 1 (Only I) is incorrect because amino acids are also fully reabsorbed. Option 2 (Only II) is incorrect because glucose is also fully reabsorbed. Option 4 (Neither) is incorrect as both are reabsorbed.
SSC CHSL Tier-1 2025 – 14 November 2025 Shift 3 · Dialysis and other excretory organs

Q110. What is the primary function of an artificial kidney for humans?

  1. (a) To produce urine
  2. (b) To remove nitrogenous waste products from the blood
  3. (c) To filter glucose from the blood
  4. (d) To increase blood pressure
Answer & solution

Answer: (b) To remove nitrogenous waste products from the blood

Correct Answer: To remove nitrogenous waste products from the blood
An artificial kidney (dialysis machine/ haemodialyser ) performs the primary function of removing nitrogenous waste products (such as urea, creatinine, and excess salts) from the blood when the natural kidneys fail to do so. This process is called haemodialysis . The blood is passed through a semi-permeable membrane that filters out waste products.
Why other options are wrong:
- To produce urine: Urine production is a result of kidney function; an artificial kidney does not produce urine itself.
- To filter glucose from the blood: Glucose is normally reabsorbed by natural kidneys; artificial kidney focuses on waste removal.
- To increase blood pressure: Kidneys regulate blood pressure, but that is not the primary function of the artificial kidney/dialysis.
SSC CHSL Tier-1 2025 – 14 November 2025 Shift 2 · Blood vessels, circulation and blood pressure

Q111. Why do arteries have thick, elastic walls in human body?

  1. (a) To accommodate high blood pressure
  2. (b) To prevent blood clotting
  3. (c) To facilitate nutrient exchange
  4. (d) To store oxygen
Answer & solution

Answer: (a) To accommodate high blood pressure

Arteries carry oxygenated blood directly from the heart under high pressure. Their thick, muscular, and elastic walls allow them to withstand and accommodate this high blood pressure without bursting. The elasticity also helps maintain steady blood flow. Why others are wrong: - To prevent blood clotting: This is not the function of thick walls; blood clotting is managed by platelets and clotting factors. - To facilitate nutrient exchange: This is the function of capillaries (thin walls allow exchange), not arteries. - To store oxygen: Arteries transport oxygen-rich blood; they do not store oxygen.
SSC CHSL Tier-1 2025 – 13 November 2025 Shift 3 · Human respiratory system

Q112. How is air initially filtered when it is taken into the human body?

  1. (a) By fine hair in the nostrils
  2. (b) By tonsils in the throat
  3. (c) By rings of cartilage
  4. (d) By the lungs
Answer & solution

Answer: (a) By fine hair in the nostrils

When air enters the body, it is first filtered by fine hair (vibrissae/nasal hair) present in the nostrils. These hairs trap large dust particles, pollutants, and foreign particles before they reach the lungs. Tonsils help fight infections in the throat but do not filter air physically. Rings of cartilage provide structural support to the trachea. The lungs perform gas exchange, not initial filtration.
SSC CHSL Tier-1 2025 – 13 November 2025 Shift 1 · Blood vessels, circulation and blood pressure

Q113. In humans, what is the value of normal systolic and diastolic blood pressure respectively?

  1. (a) 75 mm Hg and 60 mm Hg respectively
  2. (b) 80 mm Hg and 70 mm Hg respectively
  3. (c) 100 mm Hg and 95 mm Hg respectively
  4. (d) 120 mm Hg and 80 mm Hg respectively
Answer & solution

Answer: (d) 120 mm Hg and 80 mm Hg respectively

Correct Answer: 120 mm Hg and 80 mm Hg respectively
The normal blood pressure in healthy adults is 120/80 mm Hg:
- Systolic pressure (120 mm Hg): The pressure in arteries when the heart beats and pumps blood out.
- Diastolic pressure (80 mm Hg): The pressure in arteries when the heart is at rest between beats.
This is commonly expressed as '120 over 80.' Blood pressure above 130/80 mm Hg is classified as hypertension (high blood pressure).
Why other options are wrong:
- 75/60 mm Hg: Too low; this would indicate hypotension (low blood pressure).
- 80/70 mm Hg: Below normal range.
- 100/95 mm Hg: The diastolic value (95) is too high and abnormal.
SSC CHSL Tier-1 2025 – 13 November 2025 Shift 2 · Aerobic and anaerobic respiration

Q114. What is the process called when organisms acquire oxygen from outside the body to break down food sources?

  1. (a) Respiration
  2. (b) Digestion
  3. (c) Photosynthesis
  4. (d) Fermentation
Answer & solution

Answer: (a) Respiration

Respiration (specifically aerobic respiration) is the process in which organisms take in oxygen from outside the body to break down glucose (food) and release energy. The overall equation is: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP) Why others are wrong: - Digestion: The mechanical and chemical breakdown of food in the digestive system; does not involve oxygen directly for energy release. - Photosynthesis: A process in green plants that uses sunlight to convert CO ₂ and water into glucose; opposite in nature. - Fermentation: An anaerobic process (without oxygen) that breaks down food into simpler compounds like alcohol or lactic acid.
SSC CHSL Tier-1 2025 – 12 November 2025 Shift 3 · Blood - components and functions

Q115. Which of the following statement is correct regarding haemoglobin in humans?
I. In humans it is the respiratory pigment
II. It has very low affinity for oxygen

  1. (a) Only I
  2. (b) Only II
  3. (c) Both I and II
  4. (d) Neither I nor II
Answer & solution

Answer: (a) Only I

Correct Answer: Only I
Statement I is correct: Haemoglobin is the respiratory pigment in humans. It is a red- coloured , iron-containing protein found in red blood cells (RBCs) that carries oxygen from the lungs to the body tissues.
Statement II is incorrect: Haemoglobin has HIGH affinity for oxygen (not low). This high affinity allows it to pick up oxygen efficiently in the lungs. However, it releases oxygen at the tissue level due to lower partial pressure of oxygen. (Carbon monoxide has even higher affinity for haemoglobin , which is why CO poisoning is dangerous.)
Why 'Only II' is wrong: Statement II is false; haemoglobin has high, not low, affinity for oxygen.
Why 'Both I and II' is wrong: Statement II is incorrect.
Why 'Neither' is wrong: Statement I is correct.
SSC CGL Tier-1 2025 – 17 September 2025 Shift 1 · Aerobic and anaerobic respiration

Q116. . Read the following statements about aerobic respiration:
1. Glycolysis occurs in the mitochondria.
2. Kreb's cycle occurs in the mitochondrial matrix.
3. The final electron acceptor in aerobic respiration is oxygen.
Which of the above statements arecorrect?

  1. (a) Only 1 and 2 are correct
  2. (b) Only 2 and 3 are correct
  3. (c) Only 1 and 3 are correct
  4. (d) 1, 2 and 3 all are correct
Answer & solution

Answer: (b) Only 2 and 3 are correct

Glycolysis takes place in the cytoplasm, not in mitochondria — Statement 1 is incorrect.
Kreb's cycle occurs in the mitochondrial matrix — Statement 2 is correct.
In aerobic respiration, oxygen acts as the final electron acceptor in the electron transport chain — Statement 3 is correct.
Hence only 2 and 3 are correct.
SSC CGL Tier-1 2025 – 15 September 2025 Shift 2 · Heart - structure and functioning

Q117. Which of the following is the correct sequence of blood flow through heart chambers?

  1. (a) Right atrium → Right ventricle → Left atrium → Left ventricle
  2. (b) Left atrium → Left ventricle → Right atrium → Right ventricle
  3. (c) Right ventricle → Right atrium → Left ventricle → Left atrium
  4. (d) Left ventricle → Left atrium → Right ventricle → Right atrium
Answer & solution

Answer: (a) Right atrium → Right ventricle → Left atrium → Left ventricle

Deoxygenated blood enters Right atrium → Right ventricle → pulmonary circulation → Left atrium (oxygenated) → Left ventricle → systemic circulation.
Hence sequence: Right atrium → Right ventricle → Left atrium → Left ventricle.
SSC CGL Tier-1 2025 – 12 September 2025 Shift 1 · Aerobic and anaerobic respiration

Q118. Which pathway in cellular respiration generates the most ATP?

  1. (a) Glycolysis
  2. (b) Krebs cycle
  3. (c) Electron transport chain
  4. (d) Fermentation
Answer & solution

Answer: (c) Electron transport chain

Glycolysis: 2 ATP; Krebs cycle: 2 ATP; ETC (Oxidative Phosphorylation): about 32–34 ATP.
The Electron Transport Chain produces by far the most ATP.
Hence, the answer is Electron transport chain.
RRB NTPC UG CBT-1 2024-25 – 29 August 2025 Shift 3 · Blood - components and functions

Q119. What is the name of the glycoprotein produced in the liver that plays a crucial role in blood clotting?

  1. (a) Selectin
  2. (b) Mucins
  3. (c) Fibrinogen
  4. (d) Cadherin
Answer & solution

Answer: (c) Fibrinogen

RRB NTPC UG CBT-1 2024-25 – 28 August 2025 Shift 3 · Human respiratory system

Q120. The exchange of gases at the alveoli and tissues occurs by which process?

  1. (a) Osmosis
  2. (b) Decantation
  3. (c) Diffusion
  4. (d) Filtration
Answer & solution

Answer: (c) Diffusion

RRB NTPC UG CBT-1 2024-25 – 18 August 2025 Shift 2 · Blood vessels, circulation and blood pressure

Q121. In humans, which blood vessels carry oxygen-rich blood away from the heart to all the body parts?

  1. (a) Arteries
  2. (b) Capillaries
  3. (c) Venules
  4. (d) Veins
Answer & solution

Answer: (a) Arteries

RRB NTPC UG CBT-1 2024-25 – 8 August 2025 Shift 3 · Disorders of the respiratory, circulatory and excretory systems

Q122. In which chronic disease do the inner walls of the lungs' air sacs, called alveoli, become damaged, causing them to eventually burst?

  1. (a) Cystic fibrosis
  2. (b) Arrhythmias
  3. (c) Dyspepsia
  4. (d) Emphysema
Answer & solution

Answer: (d) Emphysema

SSC Selection Post 2025 (Phase XIII) – 2 August 2025 Shift 1 · Blood - components and functions

Q123. Which blood cells help in fighting infections in the human body?

  1. (a) Red blood cells
  2. (b) White blood cells
  3. (c) Platelets
  4. (d) Plasma
Answer & solution

Answer: (b) White blood cells

Correct Answer: Option 2 – White blood cells
White blood cells (WBCs / leukocytes) are the body's primary immune defense. They identify, attack, and destroy pathogens such as bacteria, viruses, fungi, and parasites. Types of WBCs include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Option 1 (Red blood cells): RBCs (erythrocytes) carry oxygen from the lungs to body tissues; they do not fight infections.
Option 3 (Platelets): Thrombocytes help in blood clotting and wound healing; not involved in fighting infections.
Option 4 (Plasma): The liquid component of blood that transports cells, nutrients, hormones, and waste products; not directly involved in fighting infections (though it carries antibodies).
RRB NTPC GL CBT-1 2024-25 – 24 June 2025 Shift 2 · Heart - structure and functioning

Q124. Within the cardiac conduction system, which structure is recognised as the primary pacemaker responsible for initiating each heartbeat?

  1. (a) Bundle of His
  2. (b) Purkinje fibers
  3. (c) Sinoatrial (SA) node
  4. (d) Atrioventricular (AV) node
Answer & solution

Answer: (c) Sinoatrial (SA) node

RRB NTPC GL CBT-1 2024-25 – 23 June 2025 Shift 3 · Human respiratory system

Q125. The efficiency of gas exchange in the alveoli is primarily attributed to which structural characteristic?

  1. (a) Abundance of mucus-secreting cells
  2. (b) A robust elastic network to maintain alveolar shape
  3. (c) Large surface area combined with a thin alveolar-capillary barrier
  4. (d) Thick epithelial lining to protect from pathogens
Answer & solution

Answer: (c) Large surface area combined with a thin alveolar-capillary barrier

RRB NTPC GL CBT-1 2024-25 – 18 June 2025 Shift 3 · Heart - structure and functioning

Q126. Cardiomyocytes rely heavily on which mechanism to maintain their membrane potential and ensure proper contraction?

  1. (a) Passive diffusion through gap junctions only
  2. (b) A combination of voltage-gated ion channels and active ion pumps
  3. (c) Facilitated diffusion of nutrients exclusively
  4. (d) Endocytosis of extracellular fluid
Answer & solution

Answer: (b) A combination of voltage-gated ion channels and active ion pumps

RRB NTPC GL CBT-1 2024-25 – 18 June 2025 Shift 1 · Excretory system - kidney and nephron

Q127. In renal physiology, which segment of the nephron is most critical for generating the osmotic gradient that concentrates urine?

  1. (a) Loop of Henle
  2. (b) Proximal convoluted tubule
  3. (c) Collecting duct
  4. (d) Distal convoluted tubule
Answer & solution

Answer: (a) Loop of Henle

RRB NTPC GL CBT-1 2024-25 – 11 June 2025 Shift 1 · Aerobic and anaerobic respiration

Q128. In glycolysis, which enzyme catalyses the rate-limiting phosphorylation of fructose-6-phosphate?

  1. (a) Pyruvate kinase
  2. (b) Phosphofructokinase-1 (PFK-1)
  3. (c) Hexokinase
  4. (d) Glyceraldehyde-3-phosphate dehydrogenase
Answer & solution

Answer: (b) Phosphofructokinase-1 (PFK-1)

RRB Technician Grade III 2024-25 – 30 December 2024 Shift 1 · Blood - components and functions

Q129. Which of the following is NOT a function of blood?

  1. (a) Helps in the synthesis of starch
  2. (b) Transports waste materials
  3. (c) Transports hormones
  4. (d) Transports gases
Answer & solution

Answer: (a) Helps in the synthesis of starch

Correct Answer: Option 1 — Helps in the synthesis of starch
Starch is made only by green plants during photosynthesis, where the glucose produced in the chloroplast is stored in the form of starch. Human blood takes no part in making starch, so this is not a function of blood.
Blood is a fluid connective tissue made of a liquid matrix called plasma together with RBCs, WBCs and platelets. It transports oxygen and carbon dioxide, digested food, hormones and nitrogenous wastes, helps in clotting (platelets), defends the body against germs (WBCs) and helps to regulate body temperature.
❌ Why the other options are incorrect
✗ Transports waste materials — true; blood carries urea, uric acid and CO₂ to the kidneys and lungs for removal.
✗ Transports hormones — true; endocrine glands pour hormones straight into the blood, which delivers them to the target organs.
✗ Transports gases — true; haemoglobin in the RBCs carries oxygen, while CO₂ travels mostly dissolved in the plasma.
📌 SSC & Railway Exam Facts
• Blood is the only fluid connective tissue; plasma forms about 55% of blood.
• Haemoglobin is an iron-containing red pigment; its shortage causes anaemia.
• Platelets (thrombocytes) help in blood clotting; vitamin K is needed for clotting.
• Blood groups A, B, AB and O were discovered by Karl Landsteiner; O⁻ is the universal donor and AB⁺ the universal recipient.
• The human heart has four chambers; arteries carry blood away from the heart and veins bring it back.
RRB Technician Grade III 2024-25 – 30 December 2024 Shift 2 · Excretory system - kidney and nephron

Q130. Which of the following substances is NOT selectively reabsorbed as the urine flows along the tubules?

  1. (a) Amino acids
  2. (b) Urea
  3. (c) Salts
  4. (d) Glucose
Answer & solution

Answer: (b) Urea

Correct Answer: Option 2 — Urea
Urine is formed in the nephron, the functional unit of the kidney, in three steps. In glomerular filtration, blood is filtered under pressure in the Bowman's capsule, and the filtrate contains water, glucose, amino acids, salts and urea. In selective reabsorption, the useful substances are taken back into the blood as the filtrate flows along the tubule. In tubular secretion, extra ions are added to the urine.
Urea is the nitrogenous waste produced in the liver from the breakdown of excess amino acids. Because the whole purpose of excretion is to throw urea out of the body, it is not reabsorbed and stays in the filtrate to become urine. Glucose, amino acids, salts and most of the water are selectively reabsorbed, which is why normal urine contains no glucose or protein.
❌ Why the other options are incorrect
✗ Amino acids — fully reabsorbed in the proximal convoluted tubule; they are the building blocks of proteins and too valuable to lose.
✗ Salts — reabsorbed according to the body's need, to keep osmoregulation and ionic balance.
✗ Glucose — completely reabsorbed in a healthy person; glucose in urine (glycosuria) indicates diabetes mellitus.
📌 SSC & Railway Exam Facts
• A human kidney has about 1 million (10 lakh) nephrons.
• Normal urine is about 95% water, 2.5% urea and 2.5% other salts/wastes.
• Excretory path — kidney → ureter → urinary bladder → urethra.
• The amount of water reabsorbed is controlled by the hormone ADH (vasopressin) from the pituitary.
• Haemodialysis is the artificial kidney technique used in kidney failure.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 1 · Aerobic and anaerobic respiration

Q131. What is the energy currency for most cellular processes?

  1. (a) ATP
  2. (b) DNA
  3. (c) RNA
  4. (d) NAD
Answer & solution

Answer: (a) ATP

Correct Answer: Option 1 — ATP
ATP (Adenosine Triphosphate) is called the energy currency of the cell. It is manufactured mainly in the mitochondria during cellular respiration, when glucose is oxidised step by step and the energy released is locked up in the high-energy phosphate bonds of ATP.
Whenever a cell needs energy, the terminal phosphate bond of ATP is broken by water (hydrolysis) to give ADP + inorganic phosphate, releasing about 30.5 kJ/mol of usable energy. This energy drives muscle contraction, protein synthesis, nerve impulse conduction and active transport across membranes.
❌ Why the other options are incorrect
✗ DNA — Deoxyribonucleic acid is the hereditary material of the cell; it stores and transmits genetic information and controls protein synthesis, but it is not an energy carrier.
✗ RNA — Ribonucleic acid carries the genetic message (mRNA) and takes part in protein synthesis (tRNA, rRNA); it does not supply energy for cell work.
✗ NAD — Nicotinamide adenine dinucleotide is only a hydrogen / electron carrier (coenzyme); it hands electrons to the electron transport chain, where ATP is finally produced.
📌 SSC & Railway Exam Facts
• ATP was discovered by Karl Lohmann (1929); the idea of ATP as energy currency is linked with Fritz Lipmann.
• Mitochondrion is the powerhouse of the cell; ATP is synthesised on its inner folds called cristae.
• Aerobic respiration of one glucose molecule yields 38 ATP (net 36 in eukaryotes), while anaerobic respiration yields only 2 ATP.
• In plants, ATP is also produced in the chloroplast during the light reaction of photosynthesis.
• GTP is another high-energy compound, used in protein synthesis and in the Krebs cycle.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 2 · Blood vessels, circulation and blood pressure

Q132. Which of the following statements is/are correct related to transportation?
(i) Arteries are the vessels which carry blood away from the heart to various organs of the body.
(ii) The arteries have thin and elastic walls.
(iii) Veins have valves that ensure that blood flows only in one direction.

  1. (a) (i), (ii) and (iii)
  2. (b) Only (i) and (ii)
  3. (c) Only (i) and (iii)
  4. (d) Only (i)
Answer & solution

Answer: (c) Only (i) and (iii)

Correct Answer: Option 3 — Only (i) and (iii)
Checking each statement against NCERT:
• (i) is correct — Arteries carry blood away from the heart to the organs. (The only exception is the pulmonary artery, which carries deoxygenated blood to the lungs.)
• (ii) is incorrect — arteries have thick, strong and elastic walls, not thin walls. Blood leaves the heart under high pressure, and thick elastic walls are needed to withstand and smooth out that pressure.
• (iii) is correct — Veins have valves along their length. Blood in veins flows at low pressure, often against gravity, so the valves prevent backflow and keep the flow unidirectional.
Hence only (i) and (iii) are correct.
❌ Why the other options are incorrect
✗ (i), (ii) and (iii) — includes (ii), which wrongly describes arterial walls as thin.
✗ Only (i) and (ii) — again accepts the false statement (ii) and wrongly leaves out the true statement (iii).
✗ Only (i) — too narrow; statement (iii) about valves in veins is also correct.
📌 SSC & Railway Exam Facts
• Artery — thick elastic walls, no valves, carries blood away from the heart, deep-seated.
• Vein — thin walls, valves present, carries blood towards the heart, superficial.
• Capillaries are just one cell thick, so gases and nutrients can be exchanged with tissues.
• The human heart has four chambers; double circulation means blood passes through the heart twice in one full cycle.
• Pulmonary artery carries deoxygenated blood and pulmonary vein carries oxygenated blood — the classic exceptions.
RRB Technician Grade III 2024-25 – 29 December 2024 Shift 3 · Aerobic and anaerobic respiration

Q133. Select the INCORRECT pair.

  1. (a) Ethanol – 2 carbon molecules
  2. (b) Pyruvate – 3 carbon molecules
  3. (c) Lactic acid – 4 carbon molecules
  4. (d) Glucose – 6 carbon molecules
Answer & solution

Answer: (c) Lactic acid – 4 carbon molecules

Correct Answer: Option 3 — Lactic acid – 4 carbon molecules
Lactic acid contains 3 carbon atoms (C₃H₆O₃), not 4, so this pair is incorrect. Lactic acid is formed in our muscles during anaerobic respiration, when the oxygen supply falls short during heavy exercise; its accumulation causes muscle cramps.
Respiration begins with glycolysis in the cytoplasm, where one molecule of glucose (6 carbon) is broken into two molecules of pyruvate (3 carbon). Pyruvate then has three possible fates — in yeast it gives ethanol (2 carbon) + CO₂ (fermentation), in muscle it gives lactic acid (3 carbon), and in the presence of oxygen it is broken down in the mitochondria into CO₂ + H₂O, releasing the maximum energy.
❌ Why the other options are incorrect
✗ Ethanol – 2 carbon molecules — a correct pair; ethanol (C₂H₅OH) is produced along with CO₂ during fermentation in yeast.
✗ Pyruvate – 3 carbon molecules — a correct pair; pyruvate is the end product of glycolysis.
✗ Glucose – 6 carbon molecules — a correct pair; glucose (C₆H₁₂O₆) is the starting substrate of respiration.
📌 SSC & Railway Exam Facts
• Glycolysis takes place in the cytoplasm; aerobic breakdown takes place in the mitochondria.
• The mitochondrion is the powerhouse of the cell; energy is stored as ATP.
• Aerobic respiration yields 38 ATP per glucose molecule, anaerobic respiration only 2 ATP.
• Yeast is used in brewing and baking because of alcoholic fermentation.
• Cramps after running are caused by the build-up of lactic acid in the muscles.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Aerobic and anaerobic respiration

Q134. Which of the following gases present in the atmosphere is used by terrestrial organisms for respiration?

  1. (a) Neon
  2. (b) Hydrogen
  3. (c) Oxygen
  4. (d) Nitrogen
Answer & solution

Answer: (c) Oxygen

Correct Answer: Option 3 — Oxygen
Terrestrial organisms take oxygen from the atmospheric air for aerobic respiration. Inside the cell, oxygen completes the breakdown of glucose in the mitochondria, releasing carbon dioxide, water and a large amount of energy stored as ATP.
Air contains about 21% oxygen, which is far more than the amount dissolved in water, so land animals get oxygen easily and can afford a high rate of respiration. Aquatic organisms, which depend on dissolved oxygen, must breathe much faster. The overall equation is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
❌ Why the other options are incorrect
✗ Neon — a chemically inert noble gas present in traces; it takes part in no biological reaction and is used in glow signs.
✗ Hydrogen — almost absent from the atmosphere as free gas; it is highly inflammable and is not used in breathing.
✗ Nitrogen — makes up about 78% of air, but animals cannot use it directly; only nitrogen-fixing bacteria such as *Rhizobium* can fix it.
📌 SSC & Railway Exam Facts
• Composition of air: N₂ ≈ 78%, O₂ ≈ 21%, Ar ≈ 0.93%, CO₂ ≈ 0.04%.
• Oxygen was discovered by Carl Wilhelm Scheele and Joseph Priestley.
• Haemoglobin in RBCs carries oxygen as oxyhaemoglobin.
• Aerobic respiration gives 38 ATP per glucose; anaerobic gives only 2 ATP.
• Breakdown of glucose to pyruvate (glycolysis) occurs in the cytoplasm.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 1 · Aerobic and anaerobic respiration

Q135. Which of the following statements is/are correct related to respiration?
(i) Pyruvate is converted into ethanol and carbon dioxide in yeast during fermentation.
(ii) The break-down of pyruvate using oxygen takes place in chloroplast.
(iii) In muscle cells, pyruvate is converted into lactic acid.

  1. (a) Only (i) and (ii)
  2. (b) Only (i) and (iii)
  3. (c) Only (i)
  4. (d) (i), (ii) and (iii)
Answer & solution

Answer: (b) Only (i) and (iii)

Correct Answer: Option 2 — Only (i) and (iii)
Respiration always begins with glycolysis in the cytoplasm, where one glucose molecule is broken into two molecules of the 3-carbon compound pyruvate. What happens to pyruvate next depends on the availability of oxygen.
(i) is correct — in yeast, in the absence of oxygen, pyruvate is converted into ethanol + CO₂; this anaerobic process is fermentation and is used in brewing and baking.
(ii) is wrong — the oxygen-using (aerobic) break-down of pyruvate into CO₂ and water occurs in the mitochondria, not in the chloroplast. The chloroplast is the site of photosynthesis.
(iii) is correct — in our muscle cells during sudden activity, the lack of oxygen turns pyruvate into lactic acid, which causes cramps.
❌ Why the other options are incorrect
✗ Only (i) and (ii) — statement (ii) wrongly places aerobic breakdown in the chloroplast.
✗ Only (i) — it leaves out (iii), which is a correct statement about muscle cells.
✗ (i), (ii) and (iii) — cannot be right because (ii) itself is false.
📌 SSC & Railway Exam Facts
• Glycolysis = cytoplasm; Krebs cycle = mitochondrial matrix.
• Mitochondrion is the powerhouse of the cell; the energy currency is ATP.
• Aerobic respiration gives 38 ATP; fermentation gives only 2 ATP.
• Lack of oxygen in muscles builds up oxygen debt, relieved by deep breathing.
• Yeast is used in bread making, beer and wine because of fermentation.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 2 · Heart - structure and functioning

Q136. Which of the following organisms have three-chambered hearts?

  1. (a) Fishes
  2. (b) Mammals
  3. (c) Birds
  4. (d) Amphibians
Answer & solution

Answer: (d) Amphibians

Correct Answer: Option 4 — Amphibians
Amphibians (frogs, toads, salamanders) and most reptiles have a three-chambered heart — two atria and a single undivided ventricle. Oxygenated blood returning from the lungs and skin enters the left atrium, while deoxygenated blood from the body enters the right atrium. Both empty into the one ventricle, so the two streams mix to some extent before being pumped out.
This mixing means the body tissues receive blood of mixed oxygen content. Such animals are cold-blooded (poikilothermic) — their body temperature changes with the surroundings — so their oxygen demand is lower and mixed blood is sufficient for them.
❌ Why the other options are incorrect
✗ Fishes — have a two-chambered heart (one atrium, one ventricle) with single circulation; blood passes through the heart only once per complete circuit.
✗ Mammals — have a four-chambered heart with complete separation of oxygenated and deoxygenated blood, needed for their high energy requirement.
✗ Birds — also have a four-chambered heart; being warm-blooded (homeothermic) they need highly efficient oxygen supply.
📌 SSC & Railway Exam Facts
• Heart chambers: Fish – 2, Amphibians & most Reptiles – 3, Crocodile, Birds & Mammals – 4.
• The crocodile is the only reptile with a four-chambered heart.
• Double circulation (blood passes twice through the heart in one cycle) occurs in birds and mammals.
• The frog also performs cutaneous respiration (breathing through moist skin) while in water.
• The human heart's valves prevent backflow — the tricuspid on the right and the bicuspid (mitral) on the left.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 3 · Excretory system - kidney and nephron

Q137. What is the filtration unit of the kidney?

  1. (a) Seminiferous tubule
  2. (b) Nephron
  3. (c) Neuron
  4. (d) Sperm
Answer & solution

Answer: (b) Nephron

Correct Answer: Option 2 — Nephron
The nephron is the basic structural and functional filtration unit of the kidney. Each human kidney contains about one million nephrons. A nephron consists of a cup-shaped Bowman's capsule enclosing a ball of capillaries called the glomerulus, followed by a long tubule that ends in the collecting duct.
Urine formation occurs in three steps: glomerular filtration, in which blood entering under high pressure is filtered so that water, glucose, salts, amino acids and urea pass into the capsule; selective reabsorption, in which useful substances such as glucose, amino acids, salts and most water are taken back into the blood; and secretion, in which extra wastes are added to the tubule. What remains is urine.
❌ Why the other options are incorrect
✗ Seminiferous tubule — the coiled tubule inside the testis where sperms are produced; it has no excretory role.
✗ Neuron — the structural and functional unit of the nervous system, which conducts electrical impulses; it does not filter blood.
✗ Sperm — the male gamete, a single reproductive cell with a head, middle piece and tail; it is not a unit of any organ.
📌 SSC & Railway Exam Facts
• The excretory system: two kidneys, two ureters, urinary bladder and urethra.
• The main nitrogenous waste in humans is urea, made in the liver from ammonia.
• Haemodialysis (artificial kidney) is used when the kidneys fail.
• Glomerulus + Bowman's capsule = Malpighian body/corpuscle.
• An adult human produces about 1 to 1.8 litres of urine per day.
RRB Technician Grade III 2024-25 – 28 December 2024 Shift 3 · Aerobic and anaerobic respiration

Q138. Where is glucose converted into pyruvate?

  1. (a) Golgi-complex
  2. (b) Ribosome
  3. (c) Mitochondria
  4. (d) Cytoplasm
Answer & solution

Answer: (d) Cytoplasm

Correct Answer: Option 4 — Cytoplasm
The breakdown of the six-carbon sugar glucose into two molecules of the three-carbon compound pyruvate (pyruvic acid) is called glycolysis, and it takes place in the cytoplasm of the cell. This very first step is common to both aerobic and anaerobic respiration and does not require oxygen.
What happens to the pyruvate next depends on oxygen. In the presence of oxygen it enters the mitochondria and is completely broken down into CO₂ and water, releasing a large amount of energy. In the absence of oxygen, pyruvate is converted into ethanol and CO₂ in yeast (fermentation) or into lactic acid in our muscle cells, which causes cramps after heavy exercise.
❌ Why the other options are incorrect
✗ Golgi-complex — it packages, modifies and dispatches materials made by the endoplasmic reticulum and forms lysosomes; it plays no part in glycolysis.
✗ Ribosome — the site of protein synthesis, made of RNA and protein; it does not break down glucose.
✗ Mitochondria — the site of the later stages of aerobic respiration (Krebs cycle and electron transport), which act on pyruvate after glycolysis, not on glucose.
📌 SSC & Railway Exam Facts
• Glycolysis — in the cytoplasm; Krebs cycle — in the mitochondrial matrix.
• Aerobic respiration yields 38 ATP per glucose; anaerobic yields only 2 ATP.
• Mitochondria is the powerhouse of the cell; ATP is the energy currency.
• Mitochondria have their own DNA and ribosomes and can make some of their own proteins.
• Lactic acid accumulation in muscles causes cramps; yeast fermentation is used in bread and alcohol making.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 1 · Respiration and excretion in other organisms

Q139. In plants, some waste products are stored as resins and gums especially in the:

  1. (a) cellular vacuoles
  2. (b) old xylem
  3. (c) tissues with dead cells
  4. (d) leaves
Answer & solution

Answer: (b) old xylem

Correct Answer: Option 2 — old xylem
Plants have no specialised excretory organ, so they handle waste in several simple ways. Gaseous wastes such as oxygen (from photosynthesis) and carbon dioxide (from respiration) leave through the stomata; excess water is removed by transpiration.
Solid and semi-solid wastes are simply stored rather than thrown out. Many of them collect in the cellular vacuoles, some are stored in leaves that later fall off, and other wastes are stored as resins and gums, especially in old xylem — the xylem that has already become non-functional for conduction. Plants also excrete some waste into the surrounding soil.
❌ Why the other options are incorrect
✗ cellular vacuoles — they do store many plant wastes, but the specific storage form of resins and gums named in NCERT is old xylem, not the vacuole.
✗ tissues with dead cells — a vague description; resins and gums are stored in a definite tissue, the old (secondary) xylem.
✗ leaves — leaves store wastes that are removed when the leaf falls (abscission), but resins and gums are not stored there.
📌 SSC & Railway Exam Facts
• Plants remove gaseous wastes through stomata and lenticels.
• Resins and gums are typical waste products of the old xylem (heartwood).
• Latex, rubber, tannins and alkaloids are also plant waste/secondary products.
• Excess water is lost as vapour by transpiration, and in liquid form by guttation.
• In humans the excretory unit is the nephron; plants have no such organ.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Heart - structure and functioning

Q140. Where does the oxygen-rich blood from the lungs come into the heart?

  1. (a) the pulmonary arteries
  2. (b) the pulmonary veins
  3. (c) the left ventricle
  4. (d) the left atrium
Answer & solution

Answer: (d) the left atrium

Correct Answer: Option 4 — the left atrium
Oxygen-rich (oxygenated) blood from the lungs enters the heart at the left atrium, the thin-walled upper chamber on the left side. It is brought there by the pulmonary veins. The left atrium relaxes while it is collecting this blood, then contracts so that the blood passes down into the left ventricle.
The left ventricle has the thickest muscular wall of all four chambers, because it must pump the oxygenated blood with great force into the aorta and onward to the whole body. The right atrium meanwhile receives deoxygenated blood from the body through the vena cava, and the right ventricle sends it to the lungs through the pulmonary artery.
❌ Why the other options are incorrect
✗ the pulmonary arteries — they carry deoxygenated blood away from the right ventricle to the lungs; they are not a chamber of the heart.
✗ the pulmonary veins — they are the vessels that bring oxygen-rich blood from the lungs, but the blood "comes into" the heart at a chamber, the left atrium.
✗ the left ventricle — blood reaches it only after the left atrium contracts; it is the pumping chamber, not the receiving chamber.
📌 SSC & Railway Exam Facts
• The human heart has four chambers — two atria (upper) and two ventricles (lower).
• Pulmonary artery is the only artery carrying deoxygenated blood; pulmonary vein the only vein carrying oxygenated blood.
• Double circulation — blood passes through the heart twice in one complete cycle.
• The left ventricle wall is the thickest; valves prevent backflow of blood.
• Normal human heartbeat is about 72 times per minute; blood pressure about 120/80 mm Hg.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Aerobic and anaerobic respiration

Q141. Which of the following statements is/are correct related to respiration?
(i) Pyruvate is converted into ethanol and carbon dioxide in yeast during fermentation.
(ii) The break-down of pyruvate using oxygen takes place in chloroplast.
(iii) In muscle cells, pyruvate is converted into lactic acid.

  1. (a) (i), (ii) and (iii)
  2. (b) Only (i) and (ii)
  3. (c) Only (i) and (iii)
  4. (d) Only (i)
Answer & solution

Answer: (c) Only (i) and (iii)

Correct Answer: Option 3 — Only (i) and (iii)
Respiration begins in the cytoplasm, where glucose (6C) is broken into two molecules of pyruvate (3C) — this step is glycolysis. What happens to the pyruvate next depends on the availability of oxygen.
In the absence of oxygen (anaerobic respiration), pyruvate is converted in yeast into ethanol and carbon dioxide; this is fermentation, so statement (i) is correct. In our muscle cells during vigorous exercise, the sudden lack of oxygen makes pyruvate turn into lactic acid, which causes cramps; statement (iii) is also correct. In the presence of oxygen (aerobic respiration) pyruvate is broken into carbon dioxide and water inside the mitochondria, not the chloroplast — so statement (ii) is wrong.
❌ Why the other options are incorrect
✗ (i), (ii) and (iii) — wrongly accepts (ii); the aerobic break-down of pyruvate occurs in the mitochondria.
✗ Only (i) and (ii) — again includes the false statement (ii) and leaves out the true statement (iii).
✗ Only (i) — too narrow; statement (iii) about lactic acid in muscle cells is perfectly correct.
📌 SSC & Railway Exam Facts
• Glycolysis occurs in the cytoplasm; further aerobic break-down in the mitochondria.
• Aerobic respiration releases much more energy than anaerobic respiration.
• Chloroplast is the site of photosynthesis, not of respiration.
• Muscle cramps are caused by the accumulation of lactic acid.
• Energy released in respiration is stored as ATP; CO₂ + H₂O + energy are the products of aerobic respiration.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 2 · Heart - structure and functioning

Q142. Amphibians have a ______ chambered heart.

  1. (a) Four
  2. (b) One
  3. (c) Two
  4. (d) Three
Answer & solution

Answer: (d) Three

Correct Answer: Option 4 — Three
Amphibians such as the frog, toad and salamander have a three-chambered heart — two atria and a single ventricle. Oxygenated blood from the lungs and skin enters the left atrium and deoxygenated blood from the body enters the right atrium, but because there is only one ventricle the two kinds of blood mix to some extent before being pumped out.
This mixing is tolerable for amphibians and many reptiles because they are cold-blooded (poikilothermic) — they do not use energy to keep their body temperature constant, so their oxygen demand is lower. Birds and mammals, being warm-blooded, need a four-chambered heart that keeps oxygenated and deoxygenated blood completely separate.
❌ Why the other options are incorrect
✗ Four — a four-chambered heart is found in birds, mammals and crocodiles, which need fully separated blood streams.
✗ One — a single-chambered heart does not occur in vertebrates; fishes have two chambers, not one.
✗ Two — two chambers (one atrium + one ventricle) are found in fishes, which pump only deoxygenated blood to the gills — single circulation.
📌 SSC & Railway Exam Facts
• Fish — 2 chambers; Amphibians and most reptiles — 3; Crocodile, birds and mammals — 4.
• Fishes show single circulation; birds and mammals show double circulation.
• Crocodile is the only reptile with a four-chambered heart.
• Cold-blooded — fish, amphibians, reptiles; warm-blooded — birds and mammals.
• In humans, the left ventricle wall is thickest as it pumps blood to the whole body through the aorta.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Heart - structure and functioning

Q143. Which organ of the human body pumps blood?

  1. (a) Heart
  2. (b) Stomach
  3. (c) Liver
  4. (d) Pancreas
Answer & solution

Answer: (a) Heart

Correct Answer: Option 1 — Heart
The heart is a muscular pumping organ roughly the size of our fist, made of cardiac muscle. It has four chambers — two upper atria and two lower ventricles — and the partition between them prevents oxygenated and deoxygenated blood from mixing.
Deoxygenated blood from the body enters the right atrium, passes to the right ventricle and is pumped to the lungs. Oxygenated blood returns to the left atrium, moves into the left ventricle, and is pumped out through the aorta to the whole body. Because blood passes through the heart twice in one cycle, humans have double circulation.
❌ Why the other options are incorrect
✗ Stomach — a digestive organ; it churns food and secretes HCl and pepsin, it does not pump blood.
✗ Liver — the largest gland of the body; it secretes bile and detoxifies substances.
✗ Pancreas — a mixed gland; it secretes pancreatic juice and the hormones insulin and glucagon.
📌 SSC & Railway Exam Facts
• The left ventricle has the thickest wall because it pumps blood to the whole body.
• Normal human heartbeat is about 72 times per minute; blood pressure is about 120/80 mm Hg.
• William Harvey discovered the circulation of blood.
• Valves in the heart ensure one-way flow of blood.
• The study of the heart is cardiology; the heart is covered by the pericardium.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Excretory system - kidney and nephron

Q144. Which of the following is INCORRECTLY matched related to the excretory system of humans?

  1. (a) Ureter - a pair
  2. (b) Kidney - a pair
  3. (c) Urethra - a pair
  4. (d) Urinary bladder - unpaired
Answer & solution

Answer: (c) Urethra - a pair

Correct Answer: Option 3 — Urethra - a pair
The human excretory system consists of a pair of kidneys, a pair of ureters, one urinary bladder and one urethra. So the urethra is single (unpaired), and calling it "a pair" is the incorrect match.
The bean-shaped kidneys filter the blood through about one million nephrons each, forming urine. The two ureters carry this urine down to the urinary bladder, where it is stored. From the bladder, urine is finally passed out of the body through the single urethra, whose opening is guarded by a sphincter muscle that gives voluntary control over urination.
❌ Why the other options are incorrect
✗ Ureter - a pair — correct; one ureter arises from each kidney and opens into the bladder.
✗ Kidney - a pair — correct; two bean-shaped kidneys lie on either side of the backbone in the abdomen.
✗ Urinary bladder - unpaired — correct; there is only one muscular bladder storing urine.
📌 SSC & Railway Exam Facts
• The nephron is the structural and functional unit of the kidney.
• Filtration happens in the Bowman's capsule + glomerulus (Malpighian body).
• An adult produces about 1–1.8 litres of urine a day; urine is about 95% water.
• The main nitrogenous waste in human urine is urea, made in the liver.
• Haemodialysis is the artificial kidney treatment for kidney failure.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Aerobic and anaerobic respiration

Q145. Accumulation of which substance in our muscles during sudden activity causes cramps?

  1. (a) Lactic acid
  2. (b) Glucose
  3. (c) Sucrose
  4. (d) Pyruvic acid
Answer & solution

Answer: (a) Lactic acid

Correct Answer: Option 1 — Lactic acid
During sudden vigorous exercise the oxygen supply to the muscles falls short of the demand. The muscle cells then switch from aerobic respiration to anaerobic respiration, in which pyruvate is converted into lactic acid and only a little energy is released.
This lactic acid accumulates in the muscle fibres and irritates them, producing the painful cramps we feel. When we rest and breathe deeply, the extra oxygen taken in — the oxygen debt — oxidises the lactic acid, and the cramp is relieved.
❌ Why the other options are incorrect
✗ Glucose — the starting fuel of respiration, broken down in the cytoplasm; its accumulation does not cause cramps.
✗ Sucrose — a disaccharide (table sugar) of glucose + fructose; it is a transport sugar in plants, not a muscle waste.
✗ Pyruvic acid — the 3-carbon intermediate formed in glycolysis; it is quickly converted to lactic acid, so it is not what builds up.
📌 SSC & Railway Exam Facts
• Glycolysis occurs in the cytoplasm; aerobic breakdown of pyruvate occurs in the mitochondria.
• In yeast, anaerobic respiration gives ethanol + CO₂ — this is fermentation.
• Aerobic respiration yields 38 ATP per glucose; anaerobic gives only 2 ATP.
• The energy currency of the cell is ATP (adenosine triphosphate).
• Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
RRB Technician Grade III 2024-25 – 27 December 2024 Shift 3 · Blood - components and functions

Q146. Which of the following is/are NOT present in the plasma?

  1. (a) Proteins
  2. (b) Hormones
  3. (c) Salts
  4. (d) Undigested food
Answer & solution

Answer: (d) Undigested food

Correct Answer: Option 4 — Undigested food
Plasma is the liquid matrix of blood — a pale yellow fluid that makes up about 55% of the blood volume and is about 90–92% water. Dissolved in it are plasma proteins (albumin, globulin, fibrinogen), hormones, mineral salts, digested food such as glucose and amino acids, and wastes such as urea and carbon dioxide.
Undigested food never enters the blood at all. Only food that has been completely digested into small soluble molecules can be absorbed through the villi of the small intestine into the blood. Undigested material passes on into the large intestine and is thrown out of the body as faeces (egestion).
❌ Why the other options are incorrect
✗ Proteins — plasma proteins like fibrinogen (clotting), albumin (osmotic balance) and globulin (immunity) are always present.
✗ Hormones — endocrine glands pour hormones directly into the blood, which carries them to their target organs.
✗ Salts — sodium, potassium, calcium and bicarbonate ions are dissolved in plasma and maintain its pH and balance.
📌 SSC & Railway Exam Facts
• Blood = plasma (55%) + formed elements (45%); serum is plasma without fibrinogen.
• Villi in the small intestine absorb digested food into the blood.
• Plasma carries CO₂ mostly as bicarbonate and urea to the kidneys.
• Fibrinogen + platelets bring about blood clotting.
• The pH of human blood is about 7.4, slightly alkaline.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 1 · Respiration and excretion in other organisms

Q147. Which of the following is/are correct with regard to the technique of plants to get rid of waste material?
A. Plants get rid of excess water by transpiration.
B. Waste products may be stored in leaves that fall off.
C. Waste products are stored as resins and gums, especially in old xylem.

  1. (a) Both A and B
  2. (b) A, B and C
  3. (c) Both A and C
  4. (d) Both B and C
Answer & solution

Answer: (b) A, B and C

Correct Answer: Option 2 — A, B and C
Plants have no special excretory organs, so they get rid of waste by several simple methods — and all three statements are correct.
• A — correct. Plants remove excess water as water vapour through the stomata of leaves by transpiration.
• B — correct. Many waste products are stored in leaves; when these leaves become old and fall off, the wastes are thrown out of the plant body along with them.
• C — correct. Plants also store wastes as resins and gums, especially in old xylem, which is no longer used for conduction. Lac, rubber and gums are such products.
In addition, plants release oxygen as a by-product of photosynthesis and carbon dioxide during respiration, and excrete some wastes into the soil through roots.
❌ Why the other options are incorrect
✗ Both A and B — leaves out C, but storage of wastes as resins and gums in old xylem is an NCERT-stated method.
✗ Both A and C — leaves out B, but shedding of waste-laden leaves is a genuine method of plant excretion.
✗ Both B and C — leaves out A, but removal of excess water by transpiration is also correct.
📌 SSC & Railway Exam Facts
• Plant excretory products include resins, gums, latex, tannins, rubber and alkaloids.
• Opium comes from poppy latex, quinine from cinchona bark, rubber from the latex of *Hevea*.
• Plants can afford to keep wastes because many of their tissues are dead (e.g. old xylem).
• In humans, excretion is done by the kidney, lungs, skin and liver; the nephron is the functional unit of the kidney.
• Plants lose water in liquid form by guttation through hydathodes.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 2 · Excretory system - kidney and nephron

Q148. Which of the following statements is/are INCORRECT related to excretion in human being?
(i) In human beings, kidney is located in the thoracic region.
(ii) Urine is stored in the urinary bladder.
(iii) CO₂ is removed from the blood into the lungs.

  1. (a) Only (i)
  2. (b) Only (i) and (ii)
  3. (c) (i), (ii) and (iii)
  4. (d) Only (i) and (iii)
Answer & solution

Answer: (a) Only (i)

Correct Answer: Option 1 — Only (i)
Excretion is the removal of harmful nitrogenous wastes produced by metabolism. Checking each statement:
• (i) is INCORRECT — the two kidneys lie in the abdominal region, on either side of the backbone, just below the diaphragm. The thoracic (chest) cavity contains the heart and lungs, not the kidneys.
• (ii) is correct — urine made by the kidneys flows through the ureters and is stored in the urinary bladder until it is passed out through the urethra.
• (iii) is correct — carbon dioxide is an excretory product of respiration and is removed from the blood into the alveoli of the lungs and breathed out.
Since only statement (i) is wrong, the answer is Only (i).
❌ Why the other options are incorrect
✗ Only (i) and (ii) — statement (ii) is perfectly true; the bladder is indeed the storage organ for urine.
✗ (i), (ii) and (iii) — it wrongly marks all three as incorrect, although (ii) and (iii) are true.
✗ Only (i) and (iii) — statement (iii) is true, because the lungs really do excrete CO₂.
📌 SSC & Railway Exam Facts
• The human excretory system = 2 kidneys + 2 ureters + 1 urinary bladder + 1 urethra.
• The structural and functional unit of the kidney is the nephron; each kidney has about one million nephrons.
• Filtration occurs in the glomerulus inside the Bowman's capsule, together called the Malpighian body.
• Humans are ureotelic — the main nitrogenous waste is urea, made in the liver.
• In kidney failure, blood is cleaned by dialysis using an artificial kidney.
RRB Technician Grade III 2024-25 – 26 December 2024 Shift 3 · Human respiratory system

Q149. Which of the following statements is/are correct related to respiration?
(i) In alveoli, exchange of gases takes place.
(ii) The walls of alveoli contain an extensive network of blood vessel.
(iii) In human beings, the respiratory pigments is haemoglobin.

  1. (a) (i), (ii) and (iii)
  2. (b) Only (i)
  3. (c) Only (i) and (iii)
  4. (d) Only (i) and (ii)
Answer & solution

Answer: (a) (i), (ii) and (iii)

Correct Answer: Option 1 — (i), (ii) and (iii)
All three statements agree with NCERT:
• (i) is correct — the alveoli are the balloon-like air sacs at the end of the smallest bronchioles, and they are the actual site of gaseous exchange in the lungs. O₂ diffuses from alveolar air into the blood and CO₂ diffuses out.
• (ii) is correct — the wall of each alveolus is only one cell thick and is wrapped in an extensive network of blood capillaries, so the two gases have a very short distance to diffuse.
• (iii) is correct — the respiratory pigment of human beings is haemoglobin, a red, iron-containing protein present in the red blood cells; it has a very high affinity for oxygen.
❌ Why the other options are incorrect
✗ Only (i) — it leaves out (ii) and (iii), though both are true.
✗ Only (i) and (iii) — it wrongly rejects (ii); alveolar walls really are richly supplied with capillaries.
✗ Only (i) and (ii) — it wrongly rejects (iii); haemoglobin is indeed the human respiratory pigment.
📌 SSC & Railway Exam Facts
• Path of air: nostrils → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
• Each pair of lungs has about 300 million alveoli, giving a surface area of nearly 80 m².
• Haemoglobin carries O₂ as oxyhaemoglobin; CO₂ is mostly carried as bicarbonate in plasma, because it is more soluble in water.
• Carbon monoxide (CO) binds haemoglobin about 200–250 times more strongly than oxygen, causing suffocation.
• The diaphragm and the intercostal muscles bring about breathing; the rate of breathing in an adult at rest is about 12–20 per minute.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Human respiratory system

Q150. In human beings, air is taken into the body through the nostrils and from here the air passes through the throat and into the lungs. Which of the following ensures that the air-passage does NOT collapse in the throat?

  1. (a) Rings of cartilage
  2. (b) Size of mouth cavity
  3. (c) Nostrils large hairs
  4. (d) Nostrils large pores
Answer & solution

Answer: (a) Rings of cartilage

Correct Answer: Option 1 — Rings of cartilage
Air drawn in through the nostrils passes into the nasal cavity, then the pharynx (throat) and the larynx (voice box), and finally enters the trachea (wind pipe). The wall of the trachea is supported by C-shaped rings of cartilage. These rings act like a stiff scaffolding and keep the air passage permanently open, so the tube does not collapse when the pressure inside falls or when the food pipe lying behind it bulges during swallowing.
Beyond this the trachea divides into two bronchi, which branch repeatedly into bronchioles ending in balloon-like alveoli, where the actual exchange of gases with the blood takes place.
❌ Why the other options are incorrect
✗ Size of mouth cavity — the buccal cavity only takes part in chewing and swallowing food; it gives no structural support to the respiratory tract.
✗ Nostrils large hairs — hairs in the nostrils, along with mucus, only filter dust and germs from incoming air; they cannot hold the throat open.
✗ Nostrils large pores — wide nasal openings merely allow air to enter; they play no mechanical role in preventing the trachea from collapsing.
📌 SSC & Railway Exam Facts
• The nasal cavity warms, moistens and filters air before it reaches the lungs.
• The epiglottis covers the glottis during swallowing so that food does not slip into the wind pipe.
• Gas exchange occurs across the thin walls of the alveoli; human lungs contain roughly 300 million (30 crore) alveoli.
• The right lung has 3 lobes and the left lung 2 lobes; both are covered by a double membrane, the pleura.
• Breathing movements are produced by the diaphragm and the intercostal muscles; the respiratory pigment is haemoglobin.
RRB Technician Grade III 2024-25 – 24 December 2024 Shift 1 · Aerobic and anaerobic respiration

Q151. If glucose :: six-carbon molecule, then pyruvate :: ________.

  1. (a) four-carbon molecule
  2. (b) three-carbon molecule
  3. (c) five-carbon molecule
  4. (d) two-carbon molecule
Answer & solution

Answer: (b) three-carbon molecule

Correct Answer: Option 2 — three-carbon molecule
The first step of respiration is glycolysis, which takes place in the cytoplasm of every cell. Here one molecule of glucose, a six-carbon (C₆) molecule, is broken down into two molecules of pyruvate (pyruvic acid), each of which is a three-carbon (C₃) molecule. A small amount of energy is released as ATP at this stage, and glycolysis is common to both aerobic and anaerobic respiration.
The fate of pyruvate then depends on the availability of oxygen — in mitochondria with oxygen it is completely oxidised to CO₂ and H₂O, releasing a large amount of energy.
❌ Why the other options are incorrect
✗ four-carbon molecule — no four-carbon compound is formed from glucose at this step; oxaloacetic acid (4-C) belongs to the much later Krebs cycle.
✗ five-carbon molecule — glycolysis produces no 5-carbon product; α-ketoglutaric acid (5-C) is again a Krebs cycle intermediate.
✗ two-carbon molecule — ethanol and acetyl CoA are 2-carbon, but they are formed from pyruvate afterwards, not directly from glucose.
📌 SSC & Railway Exam Facts
• Glycolysis occurs in the cytoplasm; the rest of aerobic respiration occurs in the mitochondria.
• In yeast, pyruvate changes to ethanol + CO₂ — this fermentation is used in baking and brewing.
• In our muscles during vigorous exercise, pyruvate forms lactic acid (3-C), causing cramps.
• Complete aerobic respiration of one glucose molecule yields about 38 ATP; anaerobic respiration yields only 2 ATP.
• ATP is called the energy currency of the cell; the term was given by Lipmann.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 1 · Aerobic and anaerobic respiration

Q152. Sometimes, when there is a lack of oxygen in our muscle cells, the pyruvate by anaerobic respiration is converted into:

  1. (a) acetic acid
  2. (b) methyl alcohol
  3. (c) ethyl alcohol
  4. (d) lactic acid
Answer & solution

Answer: (d) lactic acid

Correct Answer: Option 4 — lactic acid
Respiration begins in the cytoplasm with glycolysis, in which one molecule of glucose (6 C) is broken down into two molecules of pyruvate (3 C). What happens next depends on the supply of oxygen.
During vigorous exercise, the demand for energy in our muscle cells rises faster than oxygen can be supplied. In this lack of oxygen, pyruvate is converted into lactic acid (3 C) by anaerobic respiration, releasing only a little energy. The accumulation of lactic acid in the muscles causes cramps and muscular pain, which are relieved by rest, massage and a hot-water bath, as the extra oxygen then oxidises the lactic acid.
❌ Why the other options are incorrect
✗ acetic acid — the acid of vinegar, produced by Acetobacter bacteria; it is not the product of anaerobic respiration in muscles.
✗ methyl alcohol — methanol, a poisonous industrial alcohol that causes blindness and death; it is not formed in the body.
✗ ethyl alcohol — formed with CO₂ during anaerobic respiration in yeast (fermentation), not in human muscle cells.
📌 SSC & Railway Exam Facts
• Glycolysis occurs in the cytoplasm; the Krebs cycle occurs in the mitochondria.
• Aerobic respiration gives CO₂ + H₂O + much energy (38 ATP); anaerobic gives little energy (2 ATP).
• Yeast → ethanol + CO₂; muscle cells → lactic acid; green plants → CO₂ + H₂O.
• ATP is the energy currency of the cell; mitochondria are the powerhouse.
• The breakdown of glucose into pyruvate is common to all three pathways of respiration.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Blood vessels, circulation and blood pressure

Q153. Which of the following statement(s) is/are correctly related to transportation?
(i) Arteries are the vessels which carry blood away from the heart to various parts of the body.
(ii) Arteries have thin and elastic walls.
(iii) Veins have valves which ensure that blood flows only in one direction.

  1. (a) Only (i)
  2. (b) (i), (ii) and (iii)
  3. (c) Only (i) and (iii)
  4. (d) Only (i) and (ii)
Answer & solution

Answer: (c) Only (i) and (iii)

Correct Answer: Option 3 — Only (i) and (iii)
Arteries are the thick vessels that carry blood away from the heart to the organs of the body. Blood leaves the heart in spurts and at high pressure, so arterial walls are thick, strong, muscular and elastic — never thin. Statement B is therefore wrong.
Veins collect blood from the organs and bring it back to the heart. Here the blood is no longer under high pressure, so veins have thin walls and are fitted with valves that permit blood to flow in one direction only and stop it from flowing backwards. Statement C is correct, and statement A is correct by the very definition of an artery.
Hence only A and C are correctly related to transportation.
❌ Why the other options are incorrect
✗ Only (i) — it rejects statement C, but the one-way valves of veins are a standard textbook fact.
✗ (i), (ii) and (iii) — it accepts B, yet arteries have thick elastic walls; thin walls belong to veins and capillaries.
✗ Only (i) and (ii) — it again accepts the false statement (ii) and drops the correct statement (iii).
📌 SSC & Railway Exam Facts
• The pulmonary artery is the only artery carrying deoxygenated blood; the pulmonary vein is the only vein carrying oxygenated blood.
• Blood circulation was discovered by William Harvey.
• The human heart has four chambers — two atria and two ventricles; the left ventricle has the thickest wall.
• Normal blood pressure is about 120/80 mm Hg, measured with a sphygmomanometer.
• Humans show double circulation — blood passes through the heart twice in one complete round.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Excretory system - kidney and nephron

Q154. The term _______ refers to the densely packed kidney filtration unit.

  1. (a) Nephron
  2. (b) Neurone
  3. (c) Capillary
  4. (d) Glomerulus
Answer & solution

Answer: (a) Nephron

Correct Answer: Option 1 — Nephron
The nephron is the structural and functional unit of the kidney. Each human kidney contains about one million nephrons packed closely together, which is exactly what the phrase "densely packed kidney filtration unit" describes.
A nephron has two parts — the Malpighian body (a cluster of capillaries called the glomerulus enclosed in the cup-shaped Bowman's capsule) and a long renal tubule. Urine formation takes place in three steps: glomerular filtration of blood under pressure, selective reabsorption of glucose, amino acids, salts and most water in the tubule, and tubular secretion of extra wastes. The fluid that finally leaves is urine, which passes through the ureter to the urinary bladder.
❌ Why the other options are incorrect
✗ Neurone — the structural and functional unit of the nervous system, made of dendrites, cell body, axon and nerve endings; it conducts impulses, it does not filter blood.
✗ Capillary — the thinnest blood vessel, one cell thick, where exchange of gases and nutrients with tissues happens; it is only a part of the nephron's blood supply.
✗ Glomerulus — this is the tuft of capillaries inside the Bowman's capsule that does the filtering, but it is a part of the nephron, not the complete filtration unit.
📌 SSC & Railway Exam Facts
• Excretory system — 2 kidneys, 2 ureters, 1 urinary bladder, 1 urethra.
• Kidneys are bean-shaped, placed near the backbone; the right kidney is slightly lower than the left.
• An adult produces about 1–1.8 litres of urine per day; urine is about 95% water and contains urea.
• Urea is made in the liver from ammonia and removed by the kidneys — humans are ureotelic.
• Kidney failure is treated by haemodialysis, using an artificial kidney.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 2 · Blood - components and functions

Q155. Which of the following transports food, carbon dioxide and nitrogenous wastes in dissolved form?

  1. (a) Blood platelets
  2. (b) Plasma
  3. (c) Red blood corpuscles
  4. (d) Lymph
Answer & solution

Answer: (b) Plasma

Correct Answer: Option 2 — Plasma
Plasma is the straw-coloured liquid matrix of blood and makes up about 55 per cent of its volume. It is roughly 90–92 per cent water, the rest being proteins (albumin, globulin, fibrinogen), salts, glucose, hormones and vitamins.
Because it is a solvent, plasma transports food (digested nutrients), carbon dioxide and nitrogenous wastes such as urea in dissolved form. It also carries hormones, distributes heat evenly through the body and helps maintain blood pressure and pH. Blood is therefore called a fluid connective tissue — cells floating in a liquid matrix.
❌ Why the other options are incorrect
✗ Blood platelets (thrombocytes) — tiny cell fragments that plug a cut and start blood clotting, so that pressure in the system is not lost; they transport nothing.
✗ Red blood corpuscles (RBCs) — contain the pigment haemoglobin and specialise in carrying oxygen; in mammals they are biconcave and lack a nucleus.
✗ Lymph — a colourless fluid formed from leaked plasma; it carries lymphocytes and digested fats and drains tissue fluid back into blood, but it is not the main transport medium of blood.
📌 SSC & Railway Exam Facts
• Blood = Plasma (55%) + Formed elements (45%) — RBC, WBC and platelets.
• RBC lifespan ~120 days; they are made in the bone marrow and destroyed in the spleen (the graveyard of RBCs).
• WBCs are the body's soldiers; they fight infection.
• Blood groups A, B, AB, O were discovered by Karl Landsteiner; O⁻ is the universal donor, AB⁺ the universal recipient.
• Deficiency of haemoglobin causes anaemia; iron is its central metal atom.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · Blood - components and functions

Q156. In a situation where we are injured and start bleeding, the bleeding could lead to a loss of pressure that could reduce the efficiency of the pumping system. To avoid this, which cells mainly help to clot blood at the injury point?

  1. (a) Red blood corpuscles
  2. (b) Lymph
  3. (c) White blood corpuscles
  4. (d) Blood platelets
Answer & solution

Answer: (d) Blood platelets

Correct Answer: Option 4 — Blood platelets
Blood platelets, also called thrombocytes, are tiny, colourless, nucleus-free fragments of large bone-marrow cells. They circulate all over the body and, the moment a vessel is cut, they collect at the injury site and release clotting factors.
These factors convert the soluble plasma protein fibrinogen into insoluble threads of fibrin, which form a mesh over the wound and trap blood cells — this is the clot. The clot seals the leak, so the blood pressure needed by the pumping system is not lost and germs are kept out. Vitamin K and calcium are essential for this process.
❌ Why the other options are incorrect
✗ Red blood corpuscles — they carry oxygen with the help of haemoglobin; they may get trapped in the fibrin mesh but play no active part in clotting.
✗ Lymph — a colourless tissue fluid that carries lymphocytes and digested fats and returns fluid to the blood; it is not a clotting agent.
✗ White blood corpuscles — the defence cells of the body; they engulf germs and make antibodies, protecting against infection, not against bleeding.
📌 SSC & Railway Exam Facts
• Normal platelet count — about 1.5 to 4.5 lakh per cubic millimetre of blood.
• Dengue fever causes a sharp fall in the platelet count.
• Haemophilia is a genetic disease in which blood does not clot; it is a sex-linked disorder.
• Vitamin K is the anti-haemorrhagic vitamin; heparin is a natural anticoagulant.
• RBC ≈ 5 million/mm³, WBC ≈ 5,000–10,000/mm³; the WBC : RBC ratio is about 1 : 600.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · Blood - components and functions

Q157. Which of the following pigments is present in the red blood corpuscles of human beings?

  1. (a) Xanthophyll
  2. (b) Haemoglobin
  3. (c) Chlorophyll
  4. (d) Melanin
Answer & solution

Answer: (b) Haemoglobin

Correct Answer: Option 2 — Haemoglobin
Haemoglobin is the red respiratory pigment packed inside the red blood corpuscles (RBCs). It is a conjugated protein made of the protein globin and the iron-containing pigment haem, so iron is its central metal atom — and that is what gives blood its red colour.
Haemoglobin has a very high affinity for oxygen. In the lungs it combines with oxygen to form oxyhaemoglobin, and in the tissues, where oxygen pressure is low, it releases the oxygen. It also carries a small share of carbon dioxide back as carbaminohaemoglobin. Mammalian RBCs are biconcave and lack a nucleus, which makes room for more haemoglobin.
❌ Why the other options are incorrect
✗ Xanthophyll — a yellow plant pigment of the carotenoid group; it gives autumn leaves their yellow colour and is not found in blood.
✗ Chlorophyll — the green plant pigment of the chloroplast that traps sunlight for photosynthesis; its central metal atom is magnesium.
✗ Melanin — the brown-black pigment of the skin, hair and eyes; it protects the skin from ultraviolet rays but has no role in oxygen transport.
📌 SSC & Railway Exam Facts
• Normal haemoglobin — about 14–16 g/dL in men and 12–14 g/dL in women.
• Deficiency of haemoglobin causes anaemia; iron and folic acid help correct it.
• Carbon monoxide binds haemoglobin about 200–250 times more strongly than oxygen, causing suffocation.
• RBCs are formed in the bone marrow and destroyed in the spleen, the graveyard of RBCs.
• Chlorophyll centre — magnesium; haemoglobin centre — iron; a classic PYQ pairing.
RRB Technician Grade III 2024-25 – 23 December 2024 Shift 3 · Excretory system - kidney and nephron

Q158. Which of the following is INCORRECTLY matched related to the excretory system of humans?

  1. (a) Urinary bladder – unpaired
  2. (b) Ureter – a pair
  3. (c) Urethra – a pair
  4. (d) Kidney – a pair
Answer & solution

Answer: (c) Urethra – a pair

Correct Answer: Option 3 — Urethra – a pair
The urethra is a single, unpaired tube, not a pair. It is the final passage of the excretory system, carrying urine from the urinary bladder to the outside of the body. In the male it is longer (about 20 cm) and also carries semen; in the female it is short (about 4 cm) and carries urine only. So this pair is incorrectly matched.
The complete human excretory system is: a pair of kidneys, a pair of ureters, one urinary bladder and one urethra.
❌ Why the other options are incorrect
✗ Urinary bladder – unpaired — correctly matched; there is only one muscular bladder, which stores urine until it is voluntarily released by the urethral sphincter.
✗ Ureter – a pair — correctly matched; two ureters, one from each kidney, carry urine down into the bladder.
✗ Kidney – a pair — correctly matched; two bean-shaped kidneys lie on either side of the backbone, the right one slightly lower because of the liver.
📌 SSC & Railway Exam Facts
• The nephron is the structural and functional unit of the kidney; each kidney has about one million of them.
• Urine formation has three steps — glomerular filtration, selective reabsorption and tubular secretion.
• Urea is formed in the liver and excreted by the kidneys; humans are ureotelic.
• An adult passes about 1–1.8 litres of urine a day; urine is roughly 95% water.
• Kidney failure is treated by haemodialysis with an artificial kidney, or by a kidney transplant.
RRB Technician Grade III 2024-25 – 20 December 2024 Shift 3 · Excretory system - kidney and nephron

Q159. Which of the following connects the kidney with the urinary bladder?

  1. (a) Ureter
  2. (b) Pelvis
  3. (c) Urethra
  4. (d) Penis
Answer & solution

Answer: (a) Ureter

Correct Answer: Option 1 — Ureter
The human excretory system consists of two kidneys, two ureters, one urinary bladder and one urethra. Urine produced by the nephrons (the functional units of the kidney) is collected in the renal pelvis and is then carried away by a long muscular tube called the ureter.
Each ureter runs from the hilum of the kidney down to the urinary bladder, pushing urine along by peristalsis. The bladder stores the urine until it is expelled through the urethra during micturition.
❌ Why the other options are incorrect
✗ Pelvis (renal pelvis) — the funnel-shaped cavity inside the kidney itself that collects urine from the collecting ducts; it does not connect two organs.
✗ Urethra — the tube that carries urine from the urinary bladder to the outside of the body, not from the kidney.
✗ Penis — a male reproductive organ through which the urethra passes in males; it is not a link between kidney and bladder.
📌 SSC & Railway Exam Facts
• The nephron is the structural and functional unit of the kidney; each kidney has about 1 million nephrons.
• Filtration takes place in the glomerulus inside the Bowman's capsule — together called the Malpighian body.
• Urea is made in the liver from ammonia and is removed by the kidneys; human urine is about 95% water.
• An artificial kidney works on the principle of dialysis; the kidney is located in the abdominal cavity on either side of the backbone.
• Skin, lungs and liver are also excretory organs; in plants, excess water is removed by transpiration and guttation.
12

More Biology chapters

Reproduction177 questionsEcology and Environment168 questionsTissues142 questionsControl and Coordination138 questionsCell - Structure and Function133 questionsNutrition and Digestion99 questionsDiseases, Immunity and Health87 questionsHeredity and Evolution76 questionsPlant Physiology and Morphology76 questionsBiotechnology and Applied Biology69 questionsDiversity and Classification of Living Organisms68 questionsBiology Miscellaneous11 questionsHuman Body - General Facts10 questionsMicroorganisms4 questions
📥 PDF of this paper (all subjects, English & Hindi): All previous year papers PDF · ▶ Attempt previous year papers as free online tests · 🏆 Free live mock tests · 📰 Daily current affairs quiz