Chapter 14 — Nutrition, breathing and circulation

Follow food through the body

Human nutrition involves ingestion, digestion, absorption, assimilation and elimination of undigested material. These words describe different stages. Digestion breaks large food molecules into smaller forms that can be absorbed; absorption moves suitable products across the gut wall; assimilation uses the absorbed material in cells. Egestion removes undigested food from the digestive tract. Excretion removes metabolic wastes such as urea by other routes. A question may offer “egestion” and “excretion” together; identify whether the material was never digested or was produced by metabolism.

Digestion begins in the mouth. Chewing physically breaks food into smaller pieces, while saliva contains amylase that begins starch digestion under suitable conditions. The oesophagus moves food toward the stomach; it is not a site of substantial nutrient absorption. In the stomach, acidic gastric juice and enzymes participate in protein digestion. The stomach is not an empty storage bag that contributes no chemistry. Yet the largest share of nutrient absorption occurs in the small intestine, not the stomach. Villi increase the small intestine's effective absorptive surface; they do not make it “longer” by adding external length.

The liver produces bile, which helps emulsify fats; the gallbladder stores and concentrates bile. Bile is not an enzyme that directly cuts fat molecules into smaller chemical units. The pancreas releases digestive enzymes into the small intestine and has an endocrine role involving hormones such as insulin. The two roles belong to the same organ but act through different routes. A four-option item may swap liver, gallbladder and pancreas. Ask whether the stem concerns production, storage, enzyme release or hormonal control.

Carbohydrates, proteins and fats are major nutrient classes. They have different digestive routes and roles. Proteins contribute amino acids for many body structures and functions; carbohydrates and fats can provide energy, with fats also serving other roles. Vitamins and minerals are needed in smaller amounts and have specific functions; water is essential for transport and reactions. “A balanced diet” is a pattern that meets needs across nutrients and energy for an individual. It cannot be reduced to one universally exact menu or to the claim that every vitamin is needed in the same mass.

Breathing is not cellular respiration

Breathing is the movement of air into and out of the lungs. Cellular respiration is a set of reactions in cells that releases usable energy from fuel molecules; oxygen is used in aerobic respiration. One can hold a breath briefly while cells continue to carry out metabolic processes. Inhalation and exhalation are mechanical events; gas exchange occurs across specialised surfaces. A question that calls the movement of the diaphragm “respiration” may be using casual language, so read whether it asks about ventilation or cellular chemistry.

Air travels through the nose or mouth, pharynx, larynx, trachea, branching airways and finally to tiny lung structures where gas exchange occurs. Alveoli provide a large surface and thin exchange barrier. Oxygen diffuses from alveolar air into blood when the relevant partial-pressure gradient favours it; carbon dioxide moves in the opposite direction in the standard lung exchange description. The lung is not a pump that injects oxygen directly into every body cell. Blood transports gases between lungs and tissues.

The diaphragm helps change thoracic volume. During a normal inspiration, it contracts and moves downward, increasing chest volume; pressure relationships cause air to enter. During ordinary expiration at rest, elastic recoil and muscle relaxation help air leave. An MCQ may reverse the direction of diaphragm movement and lung volume. Think in a sequence: diaphragm contracts → chest volume increases → air enters. This is a simplified mechanical account; forced breathing uses additional muscles.

Haemoglobin in red blood cells carries most oxygen in human blood. A smaller amount dissolves in plasma. Carbon dioxide transport uses several forms, prominently bicarbonate in plasma. Do not say that blood plasma carries no gases or that every gas molecule travels attached to haemoglobin. Carbon monoxide can bind haemoglobin strongly, which helps explain its hazard, but an exam preparation guide should not turn that fact into exposure advice. The conceptual test is which blood component principally supports oxygen transport.

Two circuits and a four-chambered pump

The human heart has two atria and two ventricles. The right side receives systemic venous blood and sends it toward the lungs through the pulmonary artery. The left side receives oxygenated blood from the lungs through the pulmonary veins and sends it through the aorta toward the body. Artery and vein names follow direction relative to the heart, not whether blood is oxygen-rich. The pulmonary artery carries blood low in oxygen toward the lungs, while the pulmonary veins carry oxygenated blood back to the heart. This pair is a common exam trap.

Double circulation means blood passes through the heart twice in one complete route around the pulmonary and systemic circuits: body → right heart → lungs → left heart → body. The two sides support separation of oxygen-poor and oxygen-rich blood in the normal anatomy. “Twice” does not mean the same drop of blood visits every tissue twice before returning to the lungs. Draw two loops and place the lungs between right and left heart to understand the route. This simple diagram is more useful than memorising the full list of vessel names in isolation.

Arteries carry blood away from the heart and usually have thicker, more elastic walls suited to the pressure they encounter. Veins return blood toward the heart; many contain valves that help prevent backward flow in the relevant parts of the circulation. Capillaries have thin walls allowing exchange with tissues. A pulse reflects pressure waves in arteries, not blood moving through a vein. Blood pressure and pulse rate are different quantities; a value for one cannot be converted to the other without further context.

Blood contains plasma, red blood cells, white blood cells and platelets. Red blood cells mainly transport gases; white blood cells contribute to defence; platelets help clotting. Plasma carries dissolved substances and helps transport many materials. A clotting question should not answer that platelets “make all the blood solid” unaided; clotting is a coordinated process involving other components. Likewise, white blood cells are not one uniform type with only one function. At police-exam level, first know the major component–role map.

A route from food to cell

Suppose a carbohydrate-containing meal is eaten. Digestion can break suitable carbohydrate molecules down; products are absorbed across the small-intestine wall and transported in blood; cells use or store the material according to their needs and regulation. Oxygen taken in by breathing is carried by blood to tissues and supports aerobic release of usable energy from nutrients in cells. Carbon dioxide produced by cells returns in blood to the lungs and is exhaled. This connects digestive, respiratory and circulatory systems without confusing which organ performs each step.

A test item may ask whether “blood produces energy.” The better answer is that cells carry out energy-transforming reactions; blood delivers materials and transports products. Another may say the lungs digest food because both oxygen and nutrients are needed for energy release. That is also a category error. Trace each input from the environment to the cell, name the transport system, then identify the cellular reaction. The route clarifies why multicellular organisms need specialised exchange and circulation.

Worked vessel route

Starting at the right ventricle, trace blood to the pulmonary artery, lungs, pulmonary veins, left atrium, left ventricle, aorta and body tissues. Then systemic veins return blood to the right atrium. If a question begins at a different point, rotate the same loop rather than learning a new sequence. Check each vessel by direction: pulmonary artery leaves the heart, pulmonary veins return. Its oxygen content is a separate property.

For a digestive matching question, place each named structure with its action: mouth—chewing and starting starch digestion; stomach—acidic environment and protein-digestion step; liver—bile production; gallbladder—bile storage; small intestine—major nutrient absorption. Some processes overlap across organs, so the wording “only” is suspect. Choose the main role specified by the question rather than treating a one-word match as a full account of physiology.

Digestive enzymes: distinguish substrate, product and location

An enzyme accelerates a reaction without being consumed as a reactant in that reaction. Digestive enzymes act on particular kinds of food molecules under suitable conditions. Amylase acts on starch; proteases act on proteins; lipases act on fats. A stem may name an enzyme, an organ and a nutrient and ask which association is correct. Identify the substrate first. If the option says amylase digests protein, it is wrong even when it correctly places salivary amylase in the mouth. A partly correct association is not a fully correct answer.

Mechanical breakdown and chemical digestion cooperate. Chewing increases the surface available to digestive action but does not itself convert starch into simple sugar molecules. Emulsification disperses fat into smaller droplets and increases surface for lipase action; it is different from chemically splitting a fat molecule. The stomach's acidic environment supports the action of certain gastric enzymes, whereas conditions in the small intestine are different. There is no single optimum pH for every digestive enzyme. Strongly acidic conditions that suit one stage cannot simply be assumed to improve every stage of digestion.

The small intestine receives secretions from the pancreas and bile from the liver through the biliary system, as well as having its own digestive activities. The usual school-level final products are simple sugars from digestible carbohydrates, amino acids from proteins, and fatty acids with other lipid-digestion products from fats. Much dietary fibre is not digested by human digestive enzymes, though intestinal microbes can act on some components. The presence of fibre does not mean the food supplies no nutrients, and a food's texture alone cannot tell you its chemical composition.

After absorption, many water-soluble nutrients enter blood vessels that drain towards the liver through the hepatic portal circulation. Many absorbed long-chain fat products are packaged and enter intestinal lymphatic vessels before joining the bloodstream. Thus the statement “every absorbed nutrient travels immediately by the same vessel” is too broad. For introductory questions, retain the main distinctions: the small intestine is the major absorptive region, villi and microvilli increase surface area, and absorbed material must then be transported and used or stored. The large intestine absorbs water and electrolytes, but water absorption also occurs in the small intestine.

Food-energy arithmetic without turning an estimate into a diet plan

An elementary food-energy problem may supply factors of approximately 4 kilocalories per gram for carbohydrate, 4 for protein and 9 for fat. Use the factors stated in the question; these are teaching estimates, not a measurement of every food molecule. Suppose a sample contains 30 g carbohydrate, 8 g protein and 5 g fat. Estimated energy = 30 × 4 + 8 × 4 + 5 × 9 = 120 + 32 + 45 = 197 kilocalories. A common error is adding the three masses and multiplying by one factor, which ignores their different energy values.

If a label gives energy per 100 g, a 40 g portion contains 40/100 of that amount. A hypothetical product supplying 250 kilocalories per 100 g supplies 100 kilocalories per 40 g at the same composition. The calculation does not establish that the portion is suitable for a particular person. Energy is only one feature of a food; protein, fibre, vitamins, minerals and the overall eating pattern also matter. In an exam, separate the numerical scaling question from any claim about nutritional adequacy.

Vitamins are often grouped into fat-soluble A, D, E and K, and water-soluble B-group vitamins and vitamin C. These categories concern chemical behaviour and handling, not whether taking more is automatically beneficial. Minerals such as iron, iodine and calcium have different roles; they are not vitamins. A deficiency association in an examination is a biological relationship, not enough information to diagnose an individual. For example, linking iron with haemoglobin does not mean every case of tiredness proves iron deficiency or that every anaemia has the same cause. Learn the association while retaining the limits of the inference.

Ventilation: volume per breath and volume per minute

Tidal volume is the air moved in or out during an ordinary breath. Breathing frequency counts breaths per minute. A simplified minute-ventilation calculation multiplies the two. With a teaching tidal volume of 500 mL and frequency of 12 breaths per minute, minute ventilation = 500 × 12 = 6,000 mL per minute, or 6 L per minute. These are supplied example values, not fixed normal values for every age, body size or condition. Always attach the time unit to a rate and distinguish millilitres from litres.

Not all inspired air reaches the gas-exchange region in each breath. Air remaining in conducting passages contributes to anatomical dead space. A simplified alveolar-ventilation estimate is (tidal volume − dead-space volume) × frequency. If a problem supplies 500 mL, 150 mL and 12 breaths per minute, the estimate is (500 − 150) × 12 = 4,200 mL per minute. The difference from 6,000 mL is meaningful: total air movement and effective ventilation of exchange regions are different quantities. Use this formula only when the question provides or defines the needed assumptions.

Compare a second hypothetical pattern of 250 mL per breath at 24 breaths per minute with the same 150 mL dead-space assumption. Minute ventilation remains 6 L per minute, but estimated alveolar ventilation becomes (250 − 150) × 24 = 2.4 L per minute. This demonstrates why an equal product of breath size and frequency need not mean equal effective gas exchange. It is an arithmetic illustration, not a suggested breathing routine. The physiological outcome also depends on blood flow, diffusion and the condition of the exchange surfaces.

Diffusion at two sites

At the lungs, the relevant oxygen gradient normally favours movement from alveolar air into blood. At body tissues, the gradient normally favours movement from blood towards cells that use oxygen. Carbon dioxide takes the complementary route from metabolically active tissues into blood and then from blood into alveolar air. The same gas does not have a fixed rule to “always enter blood” regardless of location. Direction depends on the local gradient, and the circulatory system continually carries material between the two exchange sites.

An efficient exchange surface is thin, has substantial area and is supplied in ways that help maintain gradients. Alveoli have these functional features together with capillary supply. Increasing diffusion distance or reducing effective area can impair exchange. These are structure–function principles that also help with plant leaves and small-intestinal villi, although the substances and mechanisms differ. A thin wall supports exchange; it does not mean that every substance can cross without regulation or that an intact barrier has no protective role.

Aerobic respiration converts chemical energy in nutrients into forms cells can use and releases carbon dioxide and water in a simplified net account. ATP serves as a widely used intermediate in cellular energy transfer. Breathing supplies and removes gases, while circulation links exchange surfaces to tissues. If a question asks where ATP-producing metabolic reactions occur, naming the trachea because it conducts air confuses transport with chemical transformation. Mitochondria have major roles in aerobic energy metabolism in many cells, but glycolysis occurs in the cytosol; the complete process is not confined to one organelle.

Heart chambers, valves and pressure

Blood travels from an atrium into the corresponding ventricle and then into an artery leaving the heart. The tricuspid valve is between the right atrium and right ventricle; the mitral or bicuspid valve is between the left atrium and left ventricle. Semilunar valves guard the outflow into the pulmonary trunk and aorta. Valve movements respond to pressure differences and help maintain one-way flow. A valve does not actively pump blood by itself. The contraction of cardiac muscle generates the pressure changes that move blood through the circulation.

The left ventricle has a thicker muscular wall than the right because it normally drives the systemic circulation against a greater pressure requirement. This does not mean it sends out a permanently larger volume with every beat in a stable circulation; the two sides must maintain approximately matched average outputs. If one side continually pumped far more than the other, blood would accumulate somewhere in the circuit. Distinguish pressure generation from the volume pumped. The same amount of fluid can require different pressures depending on the resistance of the pathway.

Cardiac output is the volume pumped by one ventricle per unit time. In a simple calculation, output = heart rate × stroke volume. Given 70 beats per minute and 70 mL per beat, output is 4,900 mL per minute, or 4.9 L per minute. Do not double this merely because the heart has two ventricles: the circuits are connected in sequence. A hypothetical change to 100 beats per minute and 80 mL per beat gives 8 L per minute. Those numbers illustrate the formula and do not specify a clinical target.

Systole refers to a contraction phase and diastole to a relaxation phase of the relevant chambers. The usual systolic and diastolic arterial-pressure readings are pressures, commonly expressed in millimetres of mercury; heart rate is a frequency expressed in beats per minute. A pulse can help estimate heart rate in ordinary circumstances but is not itself a blood-pressure reading. Stems often place these quantities next to one another to encourage a unit error. Read the unit before interpreting the number.

Retrieval practice with reasons

Item 1: An organ produces bile, while another stores it. The production organ is the liver and the storage organ is the gallbladder. Item 2: A food example contains 10 g protein and 6 g fat, with energy factors 4 and 9 kilocalories per gram. Its contribution from those two components is 40 + 54 = 94 kilocalories; any other components would need separate information. Item 3: Blood leaving the right ventricle next enters the pulmonary outflow towards the lungs, not the aorta.

Item 4: A sample breathing pattern is 400 mL per breath at 15 breaths per minute. Minute ventilation is 6 L per minute. If the stated dead space is 150 mL, the simplified alveolar estimate is 3.75 L per minute. Item 5: At 75 beats per minute and 60 mL per beat, cardiac output is 4.5 L per minute. For both calculations, cancel the per-breath or per-beat unit explicitly and retain the per-minute unit. This makes a mistaken multiplication by the number of lungs or ventricles easier to detect.

Recall and review

Distinguish digestion, absorption, assimilation, egestion and excretion. Explain bile production versus bile storage. Trace air to the alveoli and state the difference between breathing and cellular respiration. Follow the pulmonary and systemic blood routes; identify why a pulmonary artery can carry oxygen-poor blood. Finally, link food absorption and oxygen transport to cellular energy release without assigning that reaction to blood itself. Attempt the chapter practice set, then use the explanations to revisit any uncertain concepts.

Figure 14. Original chapter diagram.

Practice 31 questions

Choose one answer for each item. The answer key and explanations follow this chapter set.

1. Which blood component, made of small cell fragments, clumps at a wound site and helps to stop bleeding?

A. Red blood cells B. White blood cells C. Platelets (thrombocytes) D. Plasma proteins

2. Deficiency of which mineral can reduce haemoglobin synthesis and cause iron-deficiency anaemia?

A. Iron B. Iodine C. Calcium D. Sodium

3. Which vitamin is essential for the normal clotting of blood?

A. Vitamin A B. Vitamin C C. Vitamin D D. Vitamin K

4. Arrange the following in the correct order in which inhaled air passes through them:
(A) Bronchi (B) Trachea (C) Alveoli (D) Larynx (E) Bronchioles

A. D, B, A, E, C B. B, D, A, E, C C. D, B, E, A, C D. D, A, B, E, C

5. Arrange the following in the order in which a drop of blood returning from the body passes through them:
(A) Left atrium
(B) Right ventricle
(C) Lungs
(D) Right atrium
(E) Left ventricle

A. D, A, C, B, E B. B, D, C, E, A C. D, B, A, C, E D. D, B, C, A, E

6. Assertion (A): The pulmonary artery carries deoxygenated blood. Reason (R): It carries blood away from the right ventricle to the lungs, where that blood is oxygenated. Choose the correct option.

A. Both A and R are true and R explains A B. Both A and R are true but R does not explain A C. A is true but R is false D. A is false but R is true

7. Which instrument is used to measure blood pressure?

A. Stethoscope B. Electrocardiograph C. Sphygmomanometer D. Spirometer

8. Match List-I (Blood vessel) with List-II (Function):
List-I: (a) Vena cava (b) Pulmonary vein (c) Aorta (d) Pulmonary artery
List-II: (i) Carries blood from the right ventricle to the lungs (ii) Brings deoxygenated blood from the body to the right atrium (iii) Carries oxygenated blood from the left ventricle to the body (iv) Brings oxygenated blood from the lungs to the left atrium

A. a-iv, b-ii, c-iii, d-i B. a-ii, b-iv, c-i, d-iii C. a-i, b-iv, c-iii, d-ii D. a-ii, b-iv, c-iii, d-i

9. In a simplified ABO-only red-cell compatibility model that sets aside Rh and other antigens, consider: 1. Group A red cells have antigen A and plasma anti-B. 2. Group O plasma contains anti-A and anti-B. 3. Group B red cells are ABO-compatible with recipients of group B or AB. 4. Group AB red cells are ABO-compatible with recipients of any ABO group. Which are correct?

A. 1, 3 and 4 only B. 2 and 4 only C. 1, 2 and 3 only D. 1, 2, 3 and 4

10. In a typical resting adult comparison, exhaled air contains approximately what percentage of carbon dioxide?

A. 0.4% B. 4% C. 16% D. 21%

11. Plasma, the pale-yellow liquid part of blood, forms approximately what percentage of total blood volume?

A. 45% B. 55% C. 70% D. 90%

12. Who discovered the ABO blood group system in 1900–01 and later received the Nobel Prize for it?

A. William Harvey B. Robert Koch C. Alexander Fleming D. Karl Landsteiner

13. The plasma of a person with which blood group contains both anti-A and anti-B antibodies?

A. A B. B C. AB D. O

14. The sinoatrial (SA) node, the natural pacemaker of the human heart, is located in the:

A. Left atrium B. Right atrium C. Right ventricle D. Left ventricle

15. Which large veins bring deoxygenated blood from the body into the right atrium of the heart?

A. Right and left pulmonary veins B. Jugular and femoral veins C. Superior and inferior vena cava D. Hepatic portal veins

16. Which valve guards the opening between the left atrium and the left ventricle of the human heart?

A. Tricuspid valve B. Pulmonary semilunar valve C. Bicuspid (mitral) valve D. Aortic semilunar valve

17. Which cancer of blood-forming tissues involves abnormal development of white-blood-cell precursors?

A. Leukaemia B. Anaemia C. Haemophilia D. Arteriosclerosis

18. Exchange of oxygen and carbon dioxide between the alveoli and the blood capillaries takes place by:

A. Osmosis B. Active transport C. Diffusion D. Phagocytosis

19. In a blood pressure reading of 120/80 mm Hg, the lower figure (80) represents which pressure?

A. Diastolic pressure B. Systolic pressure C. Pulse pressure D. Venous pressure

20. Consider the ABO system alone. I: Group AB red cells are compatible with recipients of every ABO group. II: Group AB plasma contains neither anti-A nor anti-B antibodies. Which statement(s) is/are correct?

A. Only I B. Only II C. Both I and II D. Neither I nor II

21. Consider the following statements:
Statement I: The pulmonary semilunar valve guards the opening between the left atrium and the left ventricle.
Statement II: The tricuspid valve lies between the right atrium and the right ventricle.
Which of the above is/are correct?

A. Only I B. Only II C. Both I and II D. Neither I nor II

22. Which of the following blood vessels does NOT carry oxygenated blood?

A. Pulmonary artery B. Aorta C. Pulmonary vein D. Renal artery

23. The bacterium Helicobacter pylori, discovered by Barry Marshall and Robin Warren, is chiefly associated with which disorder?

A. Typhoid B. Cholera C. Cirrhosis of the liver D. Peptic ulcer

24. Match List-I (Vitamin) with List-II (Chemical name):
List-I: (a) Vitamin A (b) Vitamin B1 (c) Vitamin D (d) Vitamin K
List-II: (i) Retinol (ii) Calciferol (iii) Thiamine (iv) Phylloquinone

A. a-iii, b-i, c-ii, d-iv B. a-i, b-iii, c-ii, d-iv C. a-i, b-iii, c-iv, d-ii D. a-ii, b-iii, c-i, d-iv

25. A meal provides 50 g of carbohydrate, 20 g of protein and 10 g of fat. Taking 4 kcal per gram for carbohydrate and protein and 9 kcal per gram for fat, what is the total energy of the meal?

A. 320 kcal B. 350 kcal C. 370 kcal D. 410 kcal

26. Which organ stores and concentrates bile made by the liver before its release into the small intestine?

A. Pancreas B. Gallbladder C. Spleen D. Appendix

27. The term "vitamine" was coined in 1912 by which biochemist?

A. Casimir Funk B. Frederick Gowland Hopkins C. Christiaan Eijkman D. Elmer McCollum

28. Pellagra, marked by dermatitis, diarrhoea and dementia, is caused by deficiency of which vitamin?

A. Thiamine (B1) B. Niacin (B3) C. Riboflavin (B2) D. Cobalamin (B12)

29. The vermiform appendix is attached to which part of the intestine?

A. Duodenum B. Caecum C. Rectum D. Stomach

30. Which is the longest part of the human small intestine, joining the large intestine?

A. Duodenum B. Jejunum C. Caecum D. Ileum

31. Which pair of salivary glands lies beneath the tongue?

A. Parotid glands B. Submandibular glands C. Sublingual glands D. Lacrimal glands

Answers and explanations

1. C. Platelets (thrombocytes) are small cell fragments that clump at a wound and trigger clotting. Red cells carry oxygen with haemoglobin, and white cells defend the body against infection.

2. A. Iron is required to build haemoglobin in red blood cells. Too little available iron can cause iron-deficiency anaemia. Anaemia has several other possible causes, so this item names the subtype rather than implying all anaemia comes from iron deficiency.

3. D. Vitamin K (phylloquinone) is needed for the blood-clotting process, and its deficiency causes delayed clotting and easy bleeding. Green leafy vegetables are a good source, and gut bacteria also make some of it.

4. A. Air passes from nostrils and pharynx to the larynx (voice box), then the trachea (windpipe), the two bronchi, the finer bronchioles and finally the alveoli, where gas exchange occurs. So the order is D, B, A, E, C.

5. D. Blood from the body enters the right atrium, goes to the right ventricle, is pumped to the lungs via the pulmonary artery, returns through the pulmonary vein to the left atrium and then reaches the left ventricle: D, B, C, A, E.

6. A. Both are true and R explains A. Blood leaving the right ventricle in the pulmonary artery has returned from the body and has not yet passed through lung gas exchange; it is therefore deoxygenated relative to systemic arterial blood. It is an artery because it carries blood away from the heart.

7. C. Blood pressure is measured in mm Hg with a sphygmomanometer. A stethoscope is used to listen to heart and pulse sounds, an electrocardiograph records the electrical activity of the heart, and a spirometer measures lung volumes.

8. D. The vena cava returns deoxygenated blood to the right atrium (a-ii); the pulmonary vein brings oxygenated blood to the left atrium (b-iv); the aorta leaves the left ventricle for the body (c-iii); the pulmonary artery runs from the right ventricle to the lungs (d-i).

9. C. In the stated ABO-only red-cell model, 1, 2 and 3 are correct. AB red cells have both A and B antigens and are not compatible with every ABO recipient, so 4 is false. Actual transfusion decisions also require Rh typing, antibody screening and compatibility testing; the simplified table is an exam model only.

10. B. A standard school approximation is about 4% CO₂ in exhaled air, compared with roughly 0.04% in ordinary inhaled air. Real values vary with breathing pattern and sampling. The question asks for order of magnitude, not a fixed clinical measurement.

11. B. Plasma makes up about 55% of blood volume, and the formed elements (RBCs, WBCs and platelets) about 45%. The 90% figure is the water content of plasma itself, a common trap.

12. D. Austrian scientist Karl Landsteiner discovered the ABO blood groups (1900–01) and won the 1930 Nobel Prize; he later co-discovered the Rh factor. William Harvey described blood circulation, Koch identified the TB bacterium and Fleming discovered penicillin.

13. D. Within the basic ABO system, group O red cells have neither A nor B antigen, while group O plasma contains both anti-A and anti-B antibodies. Group A plasma has anti-B, group B has anti-A, and group AB has neither. This does not by itself establish clinical transfusion compatibility; Rh and other antigens matter.

14. B. The sinoatrial node is in the right atrium and normally initiates electrical impulses that pace the heart. The atrioventricular node then conducts with a short delay toward the ventricles. Resting heart rate varies between people and circumstances, so a single 70–72-per-minute number is not a defining fact.

15. C. Deoxygenated blood enters the right atrium through the superior and inferior vena cava. The pulmonary veins carry oxygenated blood from the lungs to the left atrium, and the hepatic portal vein carries blood to the liver.

16. C. The bicuspid or mitral valve lies between the left atrium and left ventricle, while the tricuspid valve lies between the right atrium and right ventricle. Semilunar valves guard the exits into the pulmonary artery and the aorta.

17. A. Leukaemia is a cancer of blood-forming tissues involving abnormal white-blood-cell lineages. A patient’s measured white-cell count can be high, normal or low depending on the type and stage, so an increase in total white-cell number is not required for the diagnosis. Anaemia, haemophilia and arteriosclerosis describe different disorders.

18. C. Gases move across the thin alveolar and capillary walls by simple diffusion, from higher to lower partial pressure, without any energy expenditure. Osmosis refers to movement of water, and active transport requires energy.

19. A. The lower number is the diastolic pressure, recorded when the heart relaxes between beats. The higher number (120) is the systolic pressure, recorded when the heart contracts and pushes blood out.

20. B. Only II is correct. AB red cells bear both A and B antigens, so they are not suitable for every ABO recipient. AB plasma lacks anti-A and anti-B antibodies. Real component transfusion also considers Rh and other antigens and uses compatibility testing; this question isolates ABO logic.

21. B. Only Statement II is correct. The tricuspid valve guards the right atrium-right ventricle opening. Between the left atrium and left ventricle lies the bicuspid (mitral) valve; the semilunar valves sit at the exits of the ventricles.

22. A. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The pulmonary vein brings oxygenated blood from the lungs to the left atrium, and the aorta and its branches, such as the renal artery, carry oxygenated blood to the body.

23. D. H. pylori infection is a major cause of peptic ulcers of the stomach and duodenum; Marshall and Warren won the 2005 Nobel Prize for this. Typhoid is caused by Salmonella typhi and cholera by Vibrio cholerae; cirrhosis is chronic liver scarring.

24. B. Vitamin A is retinol (a-i), vitamin B1 is thiamine (b-iii), vitamin D is calciferol (c-ii) and vitamin K is phylloquinone (d-iv). Their deficiencies cause night blindness, beriberi, rickets and delayed clotting respectively.

25. C. Energy = (50 x 4) + (20 x 4) + (10 x 9) = 200 + 80 + 90 = 370 kcal. Fat gives more than double the energy per gram of carbohydrate or protein, which is why its share is large despite the small mass.

26. B. The liver produces bile. The gallbladder stores and concentrates it and releases it into the duodenum when needed for fat digestion. The pancreas makes digestive enzymes and hormones, while the spleen and appendix are not bile-storage organs.

27. A. Casimir Funk coined "vitamine" (vital amine) in 1912. Hopkins and Eijkman shared the 1929 Nobel Prize for work on accessory food factors and beriberi, and McCollum is credited with identifying vitamin A.

28. B. Pellagra is classically associated with niacin (vitamin B3) deficiency. Thiamine deficiency is associated with beriberi. Vitamin B12 deficiency can cause megaloblastic anaemia; pernicious anaemia is a particular B12-deficiency condition caused by impaired absorption, commonly due to lack of intrinsic factor. The answer to this question remains B3.

29. B. The appendix arises from the caecum, at the beginning of the large intestine near the ileocaecal junction. It is rich in lymphoid tissue and may have immune-related roles, so calling it simply functionless or “vestigial” is an outdated oversimplification. Duodenum, rectum and stomach are not its attachment site.

30. D. The small intestine runs duodenum (shortest, C-shaped around the pancreas), jejunum and ileum; the ileum is the longest part and opens into the caecum of the large intestine. The caecum itself is part of the large intestine.

31. C. Humans have three pairs of salivary glands: parotid (largest, near the ear), submandibular (under the jaw) and sublingual (under the tongue). Lacrimal glands secrete tears, not saliva.