Human Biology and Physiology

(b) more than that in the pulmonary vein.

Pulmonary artery carries deoxygenated blood from the right ventricle at about 25/8 mm Hg, while the pulmonary vein returns blood to the left atrium at a lower pressure. It is far lower than the carotid or aorta (about 120/80 mm Hg), and blood pressure falls along the circuit, so the venae cavae have the lowest.

(d) Emphysema

Cigarette smoking damages alveolar walls and reduces the respiratory surface, causing emphysema (a chronic obstructive disorder). Asthma is mainly an allergic or inflammatory bronchial condition. Acidosis and alkalosis are blood pH disturbances, not smoking-specific disorders.

(c) Relaxin - Inhibin

Relaxin relaxes the pubic symphysis at parturition, and inhibin suppresses FSH; they do not oppose each other. Insulin/glucagon, aldosterone/ANF (Na+ retention vs loss) and parathormone/calcitonin (raise vs lower blood Ca2+) are antagonistic pairs.

(a) Opsin and Retinal

The photopigment rhodopsin (visual purple) of rods consists of the protein opsin bound to retinal, the aldehyde of vitamin A. Retinol is the alcohol form, and transducin is a G-protein in the signalling cascade, not part of the pigment.

(a) Smaller animals have a higher metabolic rate.

Small animals have a larger surface area to volume ratio and a higher metabolic rate per unit mass, so they can supply energy quickly for work against gravity. Option (b) is wrong because their O2 need per gram is higher, and muscle efficiency is not size dependent in the way option (c) claims.

(b) decrease the affinity of hemoglobin with oxygen.

A fall in pH (more H+ or CO2) shifts the oxygen dissociation curve to the right (Bohr effect), lowering Hb affinity for O2 and aiding O2 release to tissues. Acidity actually increases heart rate and brain blood flow, so (a) and (d) are wrong.

(b) Tetanus

When stimuli arrive so rapidly that the muscle cannot relax between them, contractions fuse into a sustained contraction called tetanus. Fatigue is the loss of ability to contract after prolonged activity; tonus is the partial contraction at rest.

(c) Sphincter of Oddi

The sphincter of Oddi guards the opening of the hepatopancreatic duct into the duodenum. The pyloric sphincter lies between stomach and duodenum, the ileocaecal valve between ileum and caecum, and the semilunar valves are in the heart.

(a) parietal cells

Parietal (oxyntic) cells of the gastric glands secrete HCl and intrinsic factor. Peptic (chief) cells secrete pepsinogen, and G cells secrete gastrin; "acidic cells" do not exist.

(b) Hepatic Vein

Urea is synthesised in the liver by the ornithine cycle, so the blood leaving the liver through the hepatic vein carries the most urea. The hepatic portal vein brings blood from the intestine before urea is formed, and the renal vein carries blood after the kidney has removed urea.

(d) Melatonin and Serotonin

Tryptophan is the precursor of serotonin and melatonin. Thyroid hormones are made from tyrosine, while sex steroids and corticoids (cortisol, cortisone) are derived from cholesterol.

(d) Cholecystokinin and secretin

Secretin stimulates bicarbonate-rich pancreatic juice and CCK stimulates enzyme secretion and gall bladder contraction. Insulin, glucagon, angiotensin and epinephrine do not regulate pancreatic juice secretion.

(c) more than that in the blood

Alveolar pO2 is about 104 mm Hg whereas deoxygenated blood arriving has about 40 mm Hg, so O2 diffuses from alveoli into blood. Alveolar pCO2 is only about 40 mm Hg, far lower than pO2, so (a) is wrong.

(d) Photoreceptors in the human eye are depolarized during darkness and become hyperpolarized in response to the light stimulus.

In darkness, photoreceptors have open Na+ channels (dark current) and release neurotransmitter; light closes the channels and causes hyperpolarization. Receptors do produce graded potentials, nociceptors sense pain, and Meissner's corpuscles are touch receptors.

(c) hypersecretion of thyroid gland

Graves' disease is an autoimmune form of hyperthyroidism (exophthalmic goitre) with excess thyroid hormone. Hyposecretion of the thyroid causes cretinism or myxoedema, and adrenal disorders cause Addison's or Cushing's.

(b) Calcium

Ca2+ released from the sarcoplasmic reticulum binds troponin C, moving tropomyosin and unmasking the active sites on actin for myosin heads to form cross-bridges.

(a) Thrombocytes

Thrombocytes (platelets) release clotting factors and form the platelet plug, so low numbers (thrombocytopenia) cause clotting disorders and excessive bleeding. Erythrocytes carry gases and leucocytes defend the body.

(b) Insulin

Insulin, a peptide hormone from pancreatic beta cells, acts mainly on hepatocytes and adipocytes, enhancing glucose uptake and utilisation and lowering blood glucose. Glucagon does the opposite, while gastrin and secretin act on the digestive system.

(d) decreased level of estrogen

Osteoporosis is the age-related loss of bone mass, and the decreased estrogen after menopause is a major cause. Uric acid accumulation causes gout, and fatigue from a neuromuscular immune disorder is myasthenia gravis.

(d) lacking clotting factors

Serum is plasma without fibrinogen and other clotting factors; it still contains antibodies, globulins and albumins.

(c) there is a negative intrapleural pressure pulling at the lung walls

The pleural fluid and the sealed thoracic cavity keep intrapleural pressure slightly below atmospheric, which holds the lungs expanded against the chest wall. Hence some air (residual volume) always stays in the lungs. Option (a) is wrong because intrapulmonary pressure equals atmospheric pressure at rest. Option (d) is wrong because a positive intrapleural pressure would collapse the lungs.

(c) it only stores and releases hormones

The neurohypophysis (posterior pituitary) does not synthesise its hormones. Oxytocin and vasopressin are made in the hypothalamus and only stored and released from here. Option (d) is true of the gland but does not make it 'not true'; the anterior pituitary is also hypothalamus-regulated. Endocrine glands are ductless, so (b) is wrong.

(c) proximal convoluted tubule

About 70 percent of filtered Na$^+$ is reabsorbed in the PCT, largely by active transport (Na$^+$/K$^+$ ATPase) with water following. The descending limb of Henle's loop is permeable mainly to water, the DCT reabsorbs only a regulated smaller fraction (aldosterone), and Bowman's capsule only filters.

(b) Rete testis → Efferent ductules → Epididymis → Vas deferens

Sperms leave the seminiferous tubules into the rete testis, pass through the efferent ductules (vasa efferentia) into the epididymis, then to the vas deferens. All other options reverse some step of this sequence.

(a) Fibrous joint

Fibrous joints, such as skull sutures, have bones united by dense fibrous tissue and permit no movement. Cartilaginous joints allow slight movement, and synovial joints (including ball and socket) allow free movement.

(b) Aldosterone

Aldosterone is a mineralocorticoid that regulates Na$^+$ and K$^+$ balance (and water), not sugar metabolism. Cortisone/cortisol (gluconeogenesis), insulin (lowers glucose) and glucagon (raises glucose) all act on sugar metabolism.

(c) Production of body heat

The skeleton makes blood cells (red marrow), stores calcium and phosphate, and supports locomotion with muscles. Body heat is produced mainly by muscle and metabolic activity, not by the skeletal system.

(a) Antidiuretic hormone

ADH (vasopressin) is synthesised in the hypothalamus and stored and released from the posterior pituitary, the 'master gland'. LH, prolactin and MSH are made in the anterior/intermediate pituitary itself.

(b) voluntary motor impulses

The anterior (ventral) horn of the spinal cord contains motor neurons whose axons leave via the ventral root to supply skeletal muscle. Their destruction causes loss of voluntary motor output. Sensory input enters via the dorsal horn.

(b) Premolars

Milk dentition has 20 teeth: incisors, canines and molars (dental formula $\frac{2102}{2102}$). Premolars appear only in the permanent dentition (32 teeth).

(d) hydrogen ions are actively secreted into the filtrate.

The PCT, DCT and collecting duct secrete H$^+$ (and K$^+$) into the filtrate and reabsorb bicarbonate, which acidifies urine to about pH 6. Plasma proteins are not normally excreted.

(a) high density of cones occur, but has no rods.

The fovea centralis in the macula lutea has only cones, giving the sharpest daylight vision. The blind spot, where the optic nerve leaves, has no photoreceptors, and rods are mostly in the periphery.

(b) Emphysema

In emphysema the alveolar walls are damaged (commonly by smoking), so the respiratory surface area is drastically reduced. Pleurisy affects the pleura, pneumonia fills alveoli with fluid by infection, and asthma narrows bronchi.

(d) lipase

Succus entericus (intestinal juice) contains disaccharidases (maltase, etc.), nucleases and nucleosidases, and some lipase is also described in older texts. In the NCERT list the enzyme not included is lipase, which is the key answer. Pancreatic juice supplies the main lipase.

(c) Semilunar valves close down after the blood flows into vessels from ventricles

The first sound (lub) is due to closure of the AV valves at the start of ventricular systole. The second sound (dub) is due to closure of the semilunar valves at the start of ventricular diastole. AV valve opening is silent.

(a) Gliding joint : between carpals

Gliding joints occur between carpals. Skull sutures (frontal-parietal) are fibrous, not cartilaginous. Atlas-axis is the pivot joint, not C3-C4, and the humerus-pectoral girdle joint is ball and socket, not hinge.

(a) regulation of body temperature.

The hypothalamus contains the thermoregulatory centre, along with hunger, thirst and other homeostatic centres. Short-term memory is limbic/hippocampal, locomotor coordination is cerebellar, and decision making is cortical.

(c) Melatonin - pineal gland, regulates the normal rhythm of sleep-wake cycle.

The pineal gland secretes melatonin, which regulates the diurnal rhythm. ANF comes from the atria and lowers blood pressure, oxytocin causes contraction (not mammary growth), and progesterone supports pregnancy and endometrial maintenance.

(b) Urethra

In the male the urethra carries both urine (from the bladder) and semen (via the ejaculatory duct), so it is the shared terminal duct. The vasa efferentia and vas deferens are only reproductive, and the ureter is only urinary.

(b) Reduce both heart rate and cardiac output.

Parasympathetic (vagal) stimulation reduces the rate of SA node firing and conduction, lowering heart rate. Since cardiac output = heart rate $\times$ stroke volume, it also falls. Sympathetic signals do the opposite.

(b) both A and B antigens on RBC but no antibodies in the plasma.

Group AB RBCs carry both A and B antigens, so the plasma has neither anti-A nor anti-B antibodies. With nothing to attack donor cells, an AB person can receive blood of any ABO group (universal recipient). Option (a) is wrong because antigens sit on the RBC surface, not in plasma.

(d) the adrenal medulla, leading to increased secretion of epinephrine and norepinephrine.

In fight-or-flight, the sympathetic system stimulates the adrenal medulla to release adrenaline and noradrenaline. These raise heart rate, blood glucose and alertness. Option (a) is wrong because blood sugar rises, not falls, and (c) is wrong because the renin-angiotensin pathway is activated, not suppressed.

(c) facilitated transport

Fructose is absorbed by facilitated diffusion through carrier proteins (GLUT5), moving down its concentration gradient without using energy. Glucose and amino acids use Na+ co-transport (active), which is why (a) and (b) are tempting but apply to other nutrients. Fructose is too large and polar for simple diffusion.

(b) as bicarbonate ions

About 70% of CO2 is carried as bicarbonate: in RBCs carbonic anhydrase converts CO2 and water to H2CO3, which dissociates to $\mathrm{HCO_3^-}$ and H+. Roughly 20-25% travels as carbamino-haemoglobin and about 7% dissolves in plasma, so (a) and (c) are minor fractions.

(b) the neuromuscular junction

A motor neuron stimulates a muscle fibre at the neuromuscular (motor end plate) synapse, where acetylcholine is released. The impulse then spreads along the sarcolemma and T-tubules to the sarcoplasmic reticulum, which releases Ca2+ for contraction. So (a), (c) and (d) act after the stimulation, not at the site of stimulation.

(d) Rennin

Rennin (in the gastric juice of infants) acts first on milk, curdling the soluble casein into insoluble calcium paracaseinate so that it stays longer for pepsin to act. Pepsin and trypsin then digest proteins, and lipase acts on fats, but these are not the initial step in milk digestion. This follows the standard key.

(d) Retinal is a derivative of Vitamin C.

Retinal is derived from vitamin A, not vitamin C, so this statement is false. The other statements are correct: rhodopsin (opsin plus retinal) is the purplish-red pigment of rods only, retinal absorbs light, and cones have three photopigments for red, green and blue.

(b) Increase in aldosterone levels

Aldosterone from the adrenal cortex acts on the DCT and collecting duct to increase Na+ reabsorption (and water follows). ADH mainly increases water reabsorption, not sodium, and a decrease in aldosterone would reduce sodium reabsorption.

(b) The central gap between myosin filaments in the A-band

The H-zone is the central part of the A-band that has only thick (myosin) filaments, because the thin actin filaments from the two sides do not reach it. It is the region between the ends of actin filaments. Option (c) is wrong because the actin filaments do not extend into the H-zone, and it is not a place without myofibrils.

(a) Glycine, glucose : Small intestine, active absorption

Amino acids (glycine) and glucose are absorbed in the small intestine by active (Na+ co-transport) mechanisms. Fructose is absorbed by facilitated diffusion (and Na+ actively), so (b) is wrong. Fatty acids and glycerol are first incorporated into micelles, and chylomicrons form in the intestinal cells and enter lacteals, so (c) is wrong. Cholesterol and maltose are not absorbed in the large intestine.

(a) Deficiency of iodine in diet

Iodine deficiency in the mother causes low thyroxine in the foetus, which results in cretinism: stunted growth, mental retardation, low IQ and abnormal skin. Low growth hormone alone causes dwarfism without mental retardation, and thyroid cancer or an over-secreting pars distalis is not the cause.

(a) Contraction of both the atria

The P-wave represents atrial depolarisation, which leads to atrial contraction. The QRS complex marks the start of ventricular contraction (the beginning of systole), and the T-wave marks ventricular repolarisation (the end of systole).

(b) Accumulation of uric acid crystals in joints causes their inflammation.

This is gout. Osteoporosis in the elderly is linked with decreased oestrogen, not progesterone. Humans have 12 thoracic vertebrae, not 10. The joint between adjacent vertebrae is a cartilaginous joint, not fibrous.

(c) Fluid filled synovial cavity between two bones : Joint between atlas and axis

A synovial joint has a fluid-filled synovial cavity between the bones, allowing considerable movement. The atlas-axis joint is a pivot joint of this type. The knee is a synovial joint but not "fluid cartilage"; skull sutures are fibrous joints; and the cavity holds synovial fluid, not lymph.

(c) Non-nutrient chemicals produced by the body in trace amount that act as intercellular messenger are known as hormones.

This is the modern definition of a hormone. The adenohypophysis is controlled by hypothalamic hormones through the portal system, not direct neural control. The GI tract, heart, kidney and liver do produce hormones. Releasing and inhibiting hormones come from the hypothalamus, not the pituitary.

(c) Thyroid gland : Thyroxine : Lack of iodine in diet results in goitre

Thyroxine needs iodine, and its deficiency causes a thyroid enlargement (simple goitre). Oxytocin is released from the posterior pituitary, growth hormone from the anterior pituitary, and the corpus luteum secretes progesterone, whereas testosterone comes from the testes.

(c) Cartilaginous and synovial joints

A fall on outstretched hands sends the force through the wrist, elbow and shoulder, which are synovial joints. The shock also travels up to the vertebral column, whose intervertebral discs are cartilaginous joints. Fibrous joints (skull sutures) are not loaded by this blow, so options with fibrous joints are wrong, and 'synaptic' is not a type of joint.

(d) Malleus

The three ear ossicles run malleus, incus, stapes from outside inward. The malleus handle is attached to the tympanic membrane, and the stapes sits against the oval window. The utricle is part of the membranous labyrinth, not an ossicle.

(d) Rete testis → vasa efferentia → epididymis → vas deferens

Sperm formed in the seminiferous tubules pass into the rete testis, leave the testis through the vasa efferentia, are stored and matured in the epididymis, and then travel along the vas deferens. The other options break this order.

(d) The efferent arteriole is wider than the afferent arteriole causing easier outflow of blood from the glomerulus.

This statement is false. The efferent arteriole is narrower than the afferent arteriole, which builds up high hydrostatic pressure in the glomerulus and drives filtration. The large capillary surface area, fenestrations and high pressure all do justify the roughly 180 L/day filtrate.

(c) Residual volume

A spirometer measures only air that moves in and out, giving tidal volume, IRV, ERV and vital capacity. Residual volume stays in the lungs after maximal expiration and cannot be exhaled, so it needs other methods such as helium dilution.

(a) Chronic damage to air sacs or alveoli leading to abnormal reduction in respiratory surface area

Emphysema is a chronic disorder in which alveolar walls are damaged, reducing the respiratory surface. Option (b) describes chronic bronchitis and (c) describes asthma, which are tempting but different. Option (d) is wrong because elasticity is lost, not increased.

(c) Fast glycolytic fibres

Fast glycolytic (white) fibres have few mitochondria and little myoglobin and depend on anaerobic glycolysis, so lactic acid builds up quickly and they fatigue first. Slow oxidative (red) fibres use aerobic respiration and resist fatigue for long periods.

(c) The sino-atrial node has a higher inherent rate of depolarisation.

Many conducting tissues are auto-excitable, but the SA node depolarises fastest (about 70-75 per minute), so it reaches threshold first and sets the pace for the whole heart. Option (b) is wrong because other parts are also auto-excitable, only slower.

(c) Increased production of T-lymphocytes

Thymosin from the thymus promotes differentiation and maturation of T-lymphocytes, supporting cell-mediated immunity. It does not inhibit antibodies. The thymus degenerates with age, so thymosin output falls in older people.

(b) pressure

The Pacinian corpuscle is a mechanoreceptor in the dermis with concentric layers around a nerve ending. It senses rapid changes in pressure and vibration, not temperature, light or gravity.

(d) Pancreas and gall bladder

Cholecystokinin (CCK), secreted by the duodenal mucosa in response to fats and proteins, stimulates the pancreas to release pancreatic juice and the gall bladder to release bile.

(c) (i), (ii) and (iv)

Glucose filtered 162 g and reabsorbed 162 g, so it is completely reabsorbed. Urea 54 g filtered with 24 g reabsorbed is partial reabsorption. Creatinine appears in urine (1.7 g) at more than the filtered 1.6 g with nothing reabsorbed, so it is secreted. Statement (iii) is wrong: proteins are mostly reabsorbed (1.9 of 2 g), not secreted.

(c) It allows ventricles to receive all the blood from the atria.

The AV nodal delay of about 0.1 s lets the atria finish contracting and empty fully into the ventricles before ventricular systole begins. Atria do not need rest for this purpose, and the delay has nothing to do with venous return.

(c) Descending limb of loop of Henle is impermeable to water.

This is false: the descending limb is permeable to water and nearly impermeable to electrolytes, so water leaves and the filtrate becomes concentrated. The ascending limb is the one impermeable to water. The DCT regulates Na+ and K+, and the loop of Henle helps produce concentrated urine.

(b) Marasmus is caused by a calorie deficiency while Kwashiorkor is caused by protein deficiency.

Marasmus arises from overall energy (calorie) deficiency in infants, with severe wasting, while kwashiorkor arises from protein deficiency with relatively adequate calories, producing oedema and a swollen belly. Vitamin B and D deficiencies cause other disorders, so (a) is wrong, and (c) and (d) misstate the causes.

(c) Inflammation of bronchioles; Decreased respiratory surface

Asthma is inflammation of the bronchi and bronchioles with difficulty in breathing, while emphysema is damage to alveolar walls that decreases the respiratory surface. The order in the question is asthma first, then emphysema.

(c) a-iii, b-i, c-ii

The tricuspid valve lies between right atrium and right ventricle, the bicuspid (mitral) valve between left atrium and left ventricle, and the semilunar valves guard the pulmonary artery and aorta exits (here, right ventricle to pulmonary artery).

(b) a-iii, b-i, c-iv, d-ii

Tidal volume is 500-550 mL, IRV 2500-3000 mL, ERV 1000-1100 mL and residual volume 1100-1200 mL.

(c) ligaments attached to the ciliary body

The lens is held in position by suspensory ligaments (zonules of Zinn) attached to the ciliary body. The ciliary muscles change its curvature for accommodation, but the lens is not attached to the iris.

(c) Epinephrine

Epinephrine (adrenaline) is derived from the amino acid tyrosine. Estradiol and estriol are steroids from cholesterol, and ecdysone is an insect steroid hormone.

(a) Estrogen and Parathyroid hormone

Estrogen maintains bone density, and its fall after menopause leads to osteoporosis. Parathyroid hormone raises blood calcium by mobilising it from bone, so excess causes bone loss. Aldosterone, progesterone and prolactin are not the main bone regulators.

(b) Limbic system : consists of fibre tracts that interconnect different regions of brain; controls movement.

This pairing is wrong. The limbic system, with the hypothalamus, controls emotions, motivation, memory and behaviour such as sexual behaviour, not movement. The other three pairings are correct.

(d) a-iv, b-i, c-ii, d-iii

Glycosuria is glucose in urine, gout is uric acid accumulation in joints, renal calculi are masses of crystallised salts in the kidney, and glomerular nephritis is inflammation of the glomeruli.

(b) a-iv, b-i, c-ii, d-iii

Ultrafiltration occurs in the Malpighian corpuscle, urine is concentrated in Henle's loop, the ureter transports urine, and the urinary bladder stores it. The proximal convoluted tubule, though listed, is not the answer to any item.

(d) Parietal cells

Parietal (oxyntic) cells secrete HCl and intrinsic factor. Intrinsic factor is needed to absorb vitamin B$_{12}$ in the ileum, and B$_{12}$ is required for maturation of red blood cells, so these cells help erythropoiesis indirectly. Chief cells secrete pepsinogen, and goblet and mucous cells secrete protective mucus, so none of them affects RBC formation.

(d) a-ii, b-iii, c-i

Fibrinogen is the plasma protein that is converted to fibrin in blood clotting. Globulins include the antibodies (gamma globulins) and so serve in defence. Albumin is the most abundant plasma protein and maintains osmotic balance.

(b) Silicosis

Silicosis is caused by inhaling silica dust, as in mining, quarrying and stone cutting, so it is an occupational lung disorder with fibrosis. Emphysema is mainly caused by smoking and is not job-specific. Botulism is food poisoning, and anthrax (the word "Anthracis" here is a distractor) is an infectious disease.

(c) binds to troponin to remove the masking of active sites on actin for myosin.

Ca$^{2+}$ released from the sarcoplasmic reticulum binds to troponin C. This shifts tropomyosin and exposes the myosin-binding sites on actin, so cross-bridges can form. Myosin head detachment needs fresh ATP, and Ca$^{2+}$ does not prevent cross-bridge formation, so (a) and (d) are wrong. Myosin ATPase activity is a property of the myosin head, and Ca$^{2+}$ acts on troponin, not on myosin.

(d) Free ribosomes and RER

Nissl bodies (Nissl granules) are the granular masses in the cell body and dendrites of neurons. They are clusters of ribosomes and rough endoplasmic reticulum and are the site of protein synthesis in the neuron. They are not made of SER, and they are not just nucleic acids.

(b) Thecodont, Diphyodont, Heterodont

In humans the teeth are set in sockets of the jaw bone (thecodont). Two sets appear, milk teeth and then permanent teeth (diphyodont). There are four kinds of teeth, incisors, canines, premolars and molars (heterodont). Pleurodont (teeth fused to the side of the jaw) and homodont (all teeth alike) do not describe humans.

(c) (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)

Crypts of Lieberkühn are glands in the small intestine. Glisson's capsule is the connective tissue sheath covering the liver. The islets of Langerhans are the endocrine part of the pancreas. Brunner's glands are mucus-secreting glands in the duodenal submucosa.

(b) Hypothalamus

The hypothalamus contains the thermoregulatory centre, which senses blood temperature and triggers sweating, vasodilation or shivering. The medulla controls respiration, heart rate and blood pressure. The cerebrum handles higher functions, and the corpus callosum only connects the two hemispheres.

(b) Muscular dystrophy

Muscular dystrophy (for example Duchenne, which is X-linked recessive) is a genetic disorder with progressive degeneration of skeletal muscle. Myasthenia gravis is autoimmune, tetany is caused by low Ca$^{2+}$, and botulism is caused by a bacterial toxin, so none of them is inherited.

(a) (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)

The P wave is atrial depolarisation, the QRS complex is ventricular depolarisation, and the T wave is ventricular repolarisation. Atrial repolarisation is hidden by the QRS complex, so it does not appear as its own wave. A reduced T wave points to coronary ischemia.

(b) Binding to DNA and forming a gene-hormone complex.

Steroid hormones are lipid soluble, so they cross the plasma membrane and bind to intracellular receptors. The hormone-receptor complex then binds to DNA and regulates gene expression. Water-soluble peptide hormones act through membrane receptors and second messengers such as cAMP, which is why (c) is wrong for steroids.

(b) Seminiferous tubules $\rightarrow$ Rete testis $\rightarrow$ Vasa efferentia $\rightarrow$ Epididymis $\rightarrow$ Vas deferens $\rightarrow$ Ejaculatory duct $\rightarrow$ Urethra $\rightarrow$ Urethral meatus

Sperms form in the seminiferous tubules and pass to the rete testis, then through the vasa efferentia into the epididymis. From there they go through the vas deferens, which joins the seminal vesicle duct to form the ejaculatory duct, then into the urethra and out at the urethral meatus. The other options skip steps or place the epididymis before the vasa efferentia.

(b) inflammation of bronchi and bronchioles.

Wheezing with difficulty in breathing is the feature of asthma, which is inflammation of the bronchi and bronchioles in response to allergens and pollutants. Fibrosis with damage of alveolar walls is emphysema, and reduced surfactant is respiratory distress syndrome of newborns. A benign growth in the nasal cavity is a nasal polyp.

(c) 100 beats per minute

Stroke volume = EDV $-$ ESV $= 100 - 50 = 50$ mL. Cardiac output = stroke volume $\times$ heart rate, so heart rate $= 5000/50 = 100$ beats per minute.

(b) Maintaining hyperosmolarity towards inner medullary interstitium in the kidneys.

The counter-current mechanism of the loop of Henle and vasa recta keeps the medullary interstitium increasingly hyperosmolar. When ADH is present, water leaves the collecting duct by osmosis to this gradient and concentrated urine forms. Low ADH gives dilute urine, erythropoietin is about RBC production, and hydrostatic pressure drives filtration but does not concentrate urine.

(a) 1500 mL

Expiratory capacity (EC) = tidal volume + expiratory reserve volume $= 500 + 1000 = 1500$ mL. Residual volume is not part of EC, so the 1200 mL is a distractor. Adding it would give functional residual capacity plus TV, which is not asked.

(d) GLUT IV

GLUT IV is the insulin-dependent glucose transporter found in skeletal muscle, heart and adipose tissue. Insulin moves it to the cell surface. GLUT I, II and III work without insulin: for example GLUT II is in liver, pancreatic beta cells and kidney, and GLUT III is in neurons.

(c) (iii) and (iv) are correct

Haemodialysis removes nitrogenous wastes and excess K$^{+}$, so (i) and (ii) are wrong. But the artificial kidney cannot replace the endocrine functions of the kidney. Less erythropoietin means reduced RBC production, and less active vitamin D (calcitriol) means reduced calcium absorption from the gut.

(d) Cornea consists of dense matrix of collagen and is the most sensitive portion of the eye.

The cornea is the transparent, avascular front part of the fibrous coat, made of dense collagen matrix, and it is rich in pain nerve endings. It is not made of elastin, and it is not vascularised (so (c) is wrong). The external covering of the eyeball is the sclera, which is also proteinaceous.

(c) (a)-(v), (b)-(iv), (c)-(i), (d)-(ii)

Insulin deficiency causes diabetes mellitus, thyroxin deficiency causes goitre, and a shortage of corticoids causes Addison's disease. Growth hormone excess in adults causes acromegaly (iii), but the printed option (c) pairs it with (ii). Diabetes insipidus is caused by lack of ADH. Option (c) is the only one with the first three pairs right, and option (d) wrongly pairs insulin with diabetes insipidus, so (c) is the intended key (the last pair appears to be a typo in the source).

(d) There are seven pairs of vertebrosternal, three pairs of vertebrochondral and two pairs of vertebral ribs.

Of the 12 pairs of ribs, the first 7 are true ribs (vertebrosternal) joined directly to the sternum. The 8th, 9th and 10th are vertebrochondral (false ribs) joined through cartilage to the 7th rib. The 11th and 12th are floating (vertebral) ribs with no ventral attachment, so (a), (b) and (c) are wrong.

(c) Higher $\mathrm{H^+}$ conc. in alveoli favours the formation of oxyhaemoglobin.

This is the wrong statement. Alveoli have high $p\mathrm{O_2}$, low $p\mathrm{CO_2}$, lower $\mathrm{H^+}$ (higher pH) and lower temperature, and these favour oxyhaemoglobin formation. A high $\mathrm{H^+}$ concentration shifts the curve right (Bohr effect) and favours dissociation of oxygen, as in tissues.

(a) (i) and (ii)

Inspiration occurs when the diaphragm and external intercostal muscles contract. This increases thoracic volume and pulmonary volume, so intra-pulmonary pressure falls below atmospheric pressure and air flows in. Statements (iii) and (iv) describe the opposite, so they are wrong.

(c) Ileum is a highly coiled part.

The small intestine has three parts, the duodenum, jejunum and the long, highly coiled ileum. The ileum opens into the large intestine, not the small intestine. Serosa is the outermost layer of the alimentary canal. The vermiform appendix arises from the caecum.

(c) Ketonuria and Glycosuria

In diabetes mellitus, insulin deficiency or resistance raises blood glucose above the renal threshold, so glucose appears in urine (glycosuria). Fat breakdown also produces ketone bodies in urine (ketonuria). Uremia and renal calculi are kidney problems, not specific indicators of diabetes.

(b) trypsinogen into trypsin

Enterokinase from the intestinal mucosa activates inactive trypsinogen from the pancreas into trypsin. Trypsin then activates other pancreatic zymogens. Pepsinogen is converted to pepsin by HCl, and caseinogen is converted to casein by rennin.

(c) (a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)

The organ of Corti lies on the basilar membrane. The cochlea is the coiled part of the labyrinth. The Eustachian tube connects the middle ear with the pharynx. The stapes is attached to the oval window.

(b) Reabsorption of $\mathrm{Na^+}$ and water from renal tubules due to aldosterone

Diuresis is increased urine output. Aldosterone increases $\mathrm{Na^+}$ and water reabsorption, which reduces urine volume. Undersecretion of ADH causes more water loss, not more reabsorption, so (a) is wrong. ANF causes vasodilation, not vasoconstriction. Reduced renin lowers aldosterone and promotes diuresis.

(d) (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)

The placenta secretes hCG. The zona pellucida is a layer of the ovum. The bulbo-urethral glands lubricate the penis. Leydig cells secrete androgens.

(c) Depolarisation of ventricles

The P wave is atrial depolarisation, the QRS complex is ventricular depolarisation (and contraction begins), and the T wave is ventricular repolarisation. Atrial repolarisation is hidden within the QRS complex.

(a) (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

Eosinophils release histaminase and destructive enzymes in allergic reactions. Basophils release granules containing histamine. Neutrophils are phagocytes. Lymphocytes mediate the immune response.

(c) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)

ADH deficiency from the pituitary causes diabetes insipidus. Thyroid hyperactivity gives Grave's disease. Adrenal cortex hypofunction gives Addison's disease. Insulin deficiency in the pancreas gives diabetes mellitus.

(a) Glucocorticoids stimulate gluconeogenesis.

Cortisol promotes gluconeogenesis, lipolysis and proteolysis. Glucagon causes hyperglycaemia, not hypoglycaemia. Insulin is hypoglycaemic and acts mainly on hepatocytes and adipocytes, not pancreatic cells.

(d) (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Floating ribs (11th and 12th) do not connect with the sternum. The acromion articulates with the clavicle. The scapula is a flat triangular bone located between the second and seventh ribs. The glenoid cavity of the scapula receives the head of the humerus.

(c) Both Statement I and Statement II are correct

Fatty acids and glycerol are insoluble in water, so they are not absorbed directly into blood. They are packed into micelles, re-esterified in the intestinal mucosa and coated with protein to form chylomicrons. Chylomicrons enter the lacteals (lymph capillaries of villi) and reach the blood through the lymphatic vessels, so both statements hold.

(b) Digestion of disaccharides

Salivary amylase acts on starch (complex carbohydrates) giving maltose, and saliva lubricates the mouth and has lysozyme to control bacteria. Disaccharides are digested later by intestinal enzymes (maltase, sucrase, lactase), not by saliva.

(a) (A) is correct but (R) is not correct

Osteoporosis means decreased bone mass and higher fracture risk, so A is correct. Its common cause is decreased estrogen levels (as after menopause), not increased, so R is false.

(b) Statement I is incorrect but Statement II is correct

A blood clot (coagulum) is a network of fibrin threads in which blood cells are trapped; thrombin is the enzyme that converts fibrinogen to fibrin, not the threads. The spleen stores RBCs and destroys old ones, hence is called the graveyard of erythrocytes.

(d) 5 ml

Oxygenated arterial blood carries about 20 ml O$_2$ per 100 ml, while mixed venous blood returns with about 15 ml. So every 100 ml of oxygenated blood delivers about $20-15=5$ ml of O$_2$ to tissues under normal conditions.

(c) Arthritis – Inflammed joints

Arthritis is inflammation of joints. Myasthenia gravis is autoimmune (not genetic), muscular dystrophy is a genetic disorder (not autoimmune), and tetany is rapid muscle spasm due to low Ca$^{2+}$, not high.

(b) Provides surface for diffusion of O$_2$ and CO$_2$

The conducting part (nostrils to terminal bronchioles) warms, humidifies and filters air. Gas exchange occurs only in the respiratory part, the alveoli.

(d) (b), (d) and (e) only

PTH raises blood Ca$^{2+}$ by stimulating bone resorption, increasing renal tubular reabsorption and increasing Ca$^{2+}$ absorption from food. So decreasing blood Ca$^{2+}$ (b), decreasing absorption (d) and increasing carbohydrate metabolism (e) are not its effects.

(b) Impulse transmission across a chemical synapse is always faster than that across an electrical synapse.

Transmission at a chemical synapse is slower because of neurotransmitter release, diffusion and receptor binding. Electrical synapses, with closely placed membranes and direct current flow, are faster.

(a) Blood moves freely from atrium to the ventricle during joint diastole.

In joint diastole all chambers relax, the AV valves are open and blood flows passively from atria into ventricles. The SA node (not AVN) initiates atrial contraction, semilunar valves close when ventricular pressure falls, and AV valves open as ventricular pressure drops below atrial pressure.

(a) Both Statement I and Statement II are true.

The vas deferens receives a duct from the seminal vesicle and opens into the urethra as the ejaculatory duct. The cervical canal together with the vagina forms the birth canal.

(b) A-II, B-IV, C-I, D-III

Cartilaginous joints lie between adjacent vertebrae, the ball and socket joint is between humerus and pectoral girdle, fibrous joints are the sutures between flat skull bones, and the saddle joint is between carpal and metacarpal of the thumb.

(a) A-IV, B-III, C-II, D-I

CCK is secreted by the intestine and acts on the pancreas; GIP inhibits gastric secretion/motility (gastric gland); ANF is secreted by the heart; ADH acts on the kidney.

(a) A-III, B-I, C-IV, D-II

The fovea has the greatest visual acuity, the iris is the coloured portion regulating pupil diameter, the blind spot is where the optic nerve leaves and photoreceptors are absent, and the sclera is the outer dense connective tissue layer.

(d) IRV + ERV + TV

Vital capacity is the maximum air that can be exhaled after a maximum inspiration: $VC = IRV + ERV + TV$. Residual volume is not included, since it stays in the lungs.

(a) A-III, B-I, C-IV, D-II

The P-wave is atrial depolarisation, the Q-wave marks the beginning of ventricular systole, the QRS complex is ventricular depolarisation, and the T-wave is ventricular repolarisation.

(b) Ileo-caecal valve

The ileo-caecal valve at the junction of ileum and caecum prevents backflow of material from the caecum. The sphincter of Oddi guards the hepatopancreatic duct, the gastro-oesophageal sphincter the stomach entrance, and the pyloric sphincter the stomach exit.

(c) A-III, B-I, C-IV, D-II

Peptic (chief) cells secrete pepsinogen, goblet cells secrete mucus, oxyntic (parietal) cells secrete HCl and intrinsic factor for vitamin B12 absorption, and hepatic cells secrete bile.

(c) A is true but R is false

Nephrons are cortical or juxta-medullary by position, so A is true. The reasoning is reversed: juxta-medullary nephrons have long loops of Henle that run deep into the medulla, while cortical nephrons have short loops.

(a) Limbic system and hypothalamus

The limbic system, together with the hypothalamus, controls sexual behaviour, emotional expression (excitement, pleasure, rage, fear) and motivation. Corpora quadrigemina handle visual and auditory reflexes. The brain stem, epithalamus, corpus callosum and thalamus do not regulate these emotional behaviours.

(c) C and D only

Thyroid hormones regulate BMR, support RBC formation and maintain water and electrolyte balance (A, B, E). The sleep-wake rhythm is controlled by melatonin from the pineal gland (C). Immune system development is linked to thymosin from the thymus (D). So C and D are not under thyroid control.

(b) B, C and D only

ADH promotes water reabsorption and so prevents diuresis (B), and it causes vasoconstriction, which raises blood pressure (D). ANF causes vasodilation (C). A is wrong because loss of body fluid activates (not switches off) osmoreceptors. E is wrong because ADH helps restore blood volume and does not decrease GFR.

(b) B and C only

The sarcoplasmic reticulum stores Ca$^{2+}$ (B). Striations arise from the arrangement of actin and myosin (C). A is wrong because the connective tissue layer around bundles is fascia and the bundle itself is the fascicle. D is wrong because the functional unit of contraction is the sarcomere, between two Z lines. The M line is only the middle of the A band.

(c) B and C only

Basophils secrete histamine, serotonin and heparin and take part in inflammatory responses (B, C). A is wrong because neutrophils are the most abundant WBCs. D is wrong because the kidney-shaped nucleus belongs to monocytes. E is wrong because basophils are granulocytes.

(c) Both Statement I and Statement II are false

The descending limb of the loop of Henle is permeable to water and almost impermeable to electrolytes, so Statement I is reversed. The PCT is lined by simple cuboidal brush-border epithelium, not columnar, so Statement II is also false.

(a) A is false but R is true

FSH acts on ovarian follicles in females but on Sertoli cells in males. Leydig (interstitial) cells are acted on by LH. So A is false. R is true, since growing follicles secrete estrogen and interstitial cells secrete androgens.

(c) High $p\mathrm{O_2}$ and Lesser $\mathrm{H^+}$ concentration

In alveoli, high $p\mathrm{O_2}$, low $p\mathrm{CO_2}$, low H$^+$ (higher pH) and lower temperature favour binding of O$_2$ to haemoglobin. Options with high temperature, high $p\mathrm{CO_2}$ or high H$^+$ shift the curve right and favour release of oxygen, as in tissues.

(b) A-II, B-IV, C-I, D-III

Expiratory capacity = TV + ERV. Functional residual capacity = ERV + RV. Vital capacity = ERV + TV + IRV. Inspiratory capacity = TV + IRV. This matches A-II, B-IV, C-I, D-III.

(b) E-C-A-D-B

The impulse starts at the SA node, passes to the AV node, then the AV bundle (bundle of His), then the left and right bundle branches, and finally the Purkinje fibres in the ventricular walls.

(b) Uterine fundus

The Fallopian tube has the infundibulum (with fimbriae), ampulla and isthmus. The fundus is a part of the uterus, not of the tube.

(a) A-III, B-I, C-IV, D-II

Fibrous joints (skull sutures) allow no movement. Cartilaginous joints (between adjacent vertebrae) allow limited movement. Hinge joints (knee) help locomotion. Ball and socket joints (humerus with pectoral girdle) allow rotational movement.

(a) Glucagon

Glucagon is a peptide (protein) hormone. Cortisol, testosterone and progesterone are steroid hormones derived from cholesterol.

(c) A-III, B-IV, C-II, D-I

The pons connects different regions of the brain. The hypothalamus has neurosecretory cells. The medulla controls respiration and gastric secretions. The cerebellum has a convoluted surface giving extra space for neurons and regulates posture and balance.

(c) A-III, B-II, C-IV, D-I

The P wave is atrial depolarisation. The QRS complex is ventricular depolarisation. The T wave is ventricular repolarisation. The T-P gap is the period when the heart muscles are electrically silent.

(a) A-III, B-IV, C-I, D-II

Exophthalmic goitre is hyperthyroidism with protruding eyeballs. Acromegaly is excess growth hormone in adults. Cushing's syndrome is excess cortisol, with moon face and hyperglycaemia. Cretinism is hypothyroidism in childhood with stunted growth.

(d) Loop of Henle of juxta medullary nephron runs deep into medulla.

Juxtamedullary nephrons have long loops of Henle extending deep into the medulla. They are fewer than cortical nephrons (a is wrong). Their corpuscles lie in the inner cortex near the medulla, not in the outer medulla (c is wrong). Columns of Bertini are extensions of the cortex between pyramids and are not the location of these nephrons (b is wrong).

(d) Statement I is correct but Statement II is incorrect

The corpus callosum connects the two cerebral hemispheres. The brain stem consists of the midbrain, pons and medulla oblongata, not the cerebrum, so Statement II is wrong.

(d) A-III, B-I, C-IV, D-II

The heart secretes atrial natriuretic factor (ANF), which lowers blood pressure. The kidney (juxtaglomerular cells) secretes erythropoietin, the gastrointestinal tract secretes secretin and other peptides, and the adrenal cortex secretes aldosterone.

(b) B, C and D Only

Adrenaline and noradrenaline (adrenal medulla) raise heart rate and strength of contraction, cause piloerection and are hyperglycemic (stimulate glycogenolysis). They cause pupillary dilation, not constriction, so A is wrong.

(b) It will be digested in Gastro-Intestinal (GI) tract

Insulin is a protein (polypeptide) hormone. Given orally it would be broken down by proteolytic enzymes such as pepsin and trypsin in the GI tract before absorption, so it must be injected. Bioavailability would be decreased, not increased, so (d) is wrong.

(b) Anti-diuretic hormone (ADH)

ADH (vasopressin) and oxytocin are synthesized by neurosecretory cells of the hypothalamus and stored and released from the posterior pituitary. LH, FSH and ACTH are made in the anterior pituitary under the control of hypothalamic releasing hormones.

(a) A-IV, B-II, C-I, D-III

Progesterone is secreted by the corpus luteum. Relaxin comes from the ovary. MSH is secreted by the pars intermedia of the pituitary, and catecholamines (adrenaline and noradrenaline) from the adrenal medulla.

(c) Myasthenia gravis

Myasthenia gravis is an autoimmune disorder in which antibodies attack acetylcholine receptors at the neuromuscular junction, causing fatigue, weakness and paralysis of skeletal muscle. Muscular dystrophy is genetic, and arthritis and gout affect joints.

(a) High $p\mathrm{O_2}$, low $p\mathrm{CO_2}$, less $\mathrm{H^+}$, lower temperature

At the alveoli, these conditions shift the oxygen dissociation curve to the left and favour binding of $\mathrm{O_2}$ to haemoglobin. The opposite conditions (low $p\mathrm{O_2}$, high $p\mathrm{CO_2}$, more $\mathrm{H^+}$, higher temperature, as in tissues) favour release of $\mathrm{O_2}$.

(b) Junction of hepato-pancreatic duct and duodenum

The sphincter of Oddi guards the opening of the common hepato-pancreatic duct into the duodenum, regulating the flow of bile and pancreatic juice. The ileo-caecal valve and the gastro-oesophageal (cardiac) sphincter are different structures.

(a) $p\mathrm{O_2}=104$ and $p\mathrm{CO_2}=40$

Alveolar air has $p\mathrm{O_2}\approx104$ mm Hg and $p\mathrm{CO_2}\approx40$ mm Hg. Option (b) is deoxygenated blood and tissues, and (d) is atmospheric air ($159$ and $0.3$). Option (c) is not the standard NCERT value.

(b) Intestinal juice

Succus entericus is the intestinal juice secreted by the glands of the small intestine (crypts of Lieberkuhn and Brunner's glands), containing enzymes such as maltase, lactase and peptidases. Pancreatic juice and gastric juice are separate secretions, and chyme is partly digested food.

(d) Absence of antibodies, anti-A and anti-B, in plasma

AB blood has both A and B antigens on the RBCs but no anti-A or anti-B antibodies in the plasma. Hence it can receive blood from any ABO group without agglutination, making AB a universal recipient.

(d) Juxtaglomerular cells of the kidney

Low oxygen levels stimulate the juxtaglomerular cells of the kidney to release erythropoietin, which stimulates erythropoiesis in bone marrow. Bone marrow is the target, not the source.

(d) (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

The scapula is a triangular flat bone, and the cranial bones are joined by fibrous (suture) joints. The sternum is a flat bone, and the vertebral column has cartilaginous joints between vertebrae.