Past Entrance Papers

Hint

(d) Statements in option (d) are correct as the close proximity between the Henle’s loop and vasa recta as well as the counter-current in them help in maintaining an increasing osmolarity towards the inner medullary interstitium, i.e. from \(300 \mathrm{mosmol} \mathrm{L}^{-1}\) in the cortex (outside) to about \(1200 \mathrm{mOsmol} \mathrm{L}^{-1}\) in the inner medulla(inside).

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(d) Statement in option (d) is correct as a reduction in glomerular filtration rate activates the JG cells to release renin which converts angiotensinogen in blood to angiotensin-I. Other statements are incorrect and can be corrected as Atrial Natriuretic Factor(ANF) causes vasodilation and thereby decreases blood pressure. Angiotensin-II is a powerful vasoconstrictor, it increases the GFR. Counter-current pattern of blood flow is observed in vasa recta.

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(b) Presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine are indicative of diabetes mellitus. In diabetes mellitus, the body produces excess ketones as an indication that it is using an alternative source of energy. It is seen more commonly in type 1 diabetes mellitus.
The presence of glucose indicates Type II diabetes. In some cases, insulin cannot transport blood sugar into the body’s cells effectively. This can also cause blood sugar to be passed out in the urine.

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(a) Adrenal cortex secretes mineralocorticoids, i.e. aldosterone which increases the reabsorption of \(\mathrm{Na}^{+}\) and water from the renal tubule thereby preventing diuresis.

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(c) Podocytes are cells in Bowman’s capsule in the kidneys. They have filtration slits through which the blood is filtered. Protonephridia help in osmoregulation. Nephridia in annelids help in osmoregulation and excretion. Renal calculi are kidney stones that mainly consist of crystallised oxalates.

Hint

(c) Descending limb of Henle’s loop – Reabsorption of water only

PCT – Reabsorption of ions, water organic nutrients

Ascending limb of Henle’s loop – Reabsorption of salts only.
DCT – Conditional reabsorption of sodium ions and water

Hint

(a) Maintaining hyperosmolarity towards the inner medullary interstitium in the kidneys is the factor responsible for the formation of concentrated urine because it provides the concentration gradient necessary for water reabsorption in renal tubules.
Erythropoietin secretion by the juxtaglomerular complex is related to red blood cell production and hydrostatic pressure during glomerular filtration to the amount of filtrate formed by kidneys. High levels of antidiuretic hormone and not low levels produce urine that is more concentrated.

Hint

(b) Statements (C) and (D) are correct. Use of an artificial kidney during haemodialysis may result in reduced RBC production and reduced absorption of calcium ions from the gastrointestinal tract. The former would occur due to the low level of erythropoietin hormone secreted by juxtaglomerular cells. The later would be caused due to the elimination of calcium ions along with phosphate ions during dialysis. Statements (A) and (B) are incorrect because dialysis helps in the removal of nitrogenous waste and potassium ions from the body.

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(b) Ultrafiltration or Glomerular filtration is carried out in the glomerular capillaries found in Malpighian corpuscle. This process is carried out under high pressure.
Henle’s loop continuously absorbs the water from the glomerular filtrate, because of the hyperosmolarity created by the counter-current mechanism. This helps in the concentration of urine and hence, it becomes hypertonic.
Ureters are narrow, tubular structures that convey or transport urine from the kidney to the urinary bladder.
The urinary bladder is a pear-shaped, muscular, sac-like structure that temporarily stores urine.

Hint

(a) Increased level of glucose in the blood which may be caused due to untreated diabetes mellitus results in glycosuria. In this condition, glucose is present in the urine.

Gout is a form of arthritis characterised by severe pain and tenderness in joints. It is caused due to the accumulation of uric acid crystals in joints.

Renal calculi or kidney stones are small masses of crystalline salts within the kidneys. These stones can be of calcium, uric acid, struvite (magnesium ammonium phosphate), etc.
Glomerular nephritis is the inflammation of the filtering unit, i.e. glomerulus of the kidney. It is also known as Bright’s disease. It may cause haematuria (blood in urine) and proteinuria(proteins in the blood).

Hint

(a) Atrial natriuretic factor (ANF) is responsible for lowering of blood pressure and volume. The walls of the atria of the heart release ANF in response to an increase in blood volume and pressure. It opposes regulation by RAAS. It inhibits the release of renin from JGA thereby inhibiting \(\mathrm{NaCl}\) reabsorption by the collecting duct and reduces aldosterone release from adrenal gland.

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(d) Descending limb of loop of Henle is permeable to water but impermeable to electrolytes. Ascending limb of loop of Henle is impermeable to water but permeable to electrolytes.

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(b) From the Bowman’s capsule, a glomerular filtrate enters the proximal convoluted tubule. Absorption of selected materials takes place from the filtrate into the blood of the peritubular capillaries or vasa recta. It is termed tubular reabsorption. Reabsorption involves both passive and active transport across the tubular epithelium. About 65 percent of the glomerular filtrate is normally reabsorbed in the proximal convoluted tubule before reaching the loop of Henle. Glucose, amino acids, vitamins, hormones, sodium, potassium, chlorides, phosphates, bicarbonates, much of water, and some urea from the filtrate are absorbed. Sodium and potassium are reabsorbed by primary active transport.

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(c) Hepatic Vein, because the liver produces urea and other waste materials, and then it pours it all in the right ventricle of the heart for oxygenation. The heart distributes the blood to various parts of the body from here. So the impure blood brought by the Hepatic Vein and other blood vessels gets distributed through the aorta. This will automatically imply that the Renal Artery will contain lesser impure blood than the Hepatic Vein.

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(b) Human urine is usually acidic because hydrogen ions are actively secreted into the filterate. Tubular secretion maintains the \(\mathrm{pH}\) and ionic balance of body fluids in which hydrogen ions are actively secreted into the filtrate and bicarbonate ions are reabsorbed.The correct answer is (b).

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(a) Angiotensinogen is an \(\alpha\)-globulin protein produced by the liver. Renin serves as an enzyme in the conversion of the plasma protein angiotensinogen into angiotensin. This protein stimulates the adrenal cortex to produce aldosterone which acts on the cells of the ascending limb of the loop of Henle and increases the rate of reabsorption of \(\mathrm{Na}^{+}\). Reabsorption of \(\mathrm{Na}^{+}\) brings about the uptake of an osmotically equivalent amount of water. Absorption of sodium and water increases blood volume and pressure.

Hint

(d) About \(65 \%\) of the glomerular filtrate is normally reabsorbed in the proximal convoluted tubule before reaching the loop of Henle. It absorbs glucose, amino acids, vitamins, hormones, \(\mathrm{Na}, \mathrm{K}, \mathrm{Cl}\), phosphates, bicarbonates, water and urea etc. If it is removed, then more concentrated urine with high osmolarity will be produced.

Hint

(a) Aldosterone is a hormone secreted by the outer layer of the adrenal gland (cortex part). Decreased blood volume and interstitial fluid level, resulting in decreased blood pressure, trigger aldosterone secretion. When aldosterone is present in the blood, reabsorption of \(\mathrm{Na}^{+}\)in the filtrate is increased by the epithelial cells of the collecting duct. Retaining \(\mathrm{Na}^{+}\), raises the osmotic pressure of the blood and reduces water loss from the body. When aldosterone is absent, some \(\mathrm{Na}^{+}\)remains in the filtrate and is excreted with the urine.

Hint

(a) In salamander, kidneys (mesonepheric) are the excretory organs and the excretory matter is urea. In Labeo, mesonephric kidney is the excretory organ and excretion is ammonotelic.

Peacock has metanephric kidneys with the excretory matter being uric acid. In housefly, excretion takes place by Malpighian tubules. Excretory waste is uric acid chiefly.

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(a) A-Adrenal gland is correctly mentioned. It is located at the anterior part of the kidney and secretes catecholamines which stimulate glycogen breakdown.

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(c) During glomerular filtration in kidneys, ultrafiltration of blood occurs i.e., almost all the constituents of plasma except proteins pass onto the Bowman’s capsule. Then nearly \(99 \%\) of the filtrate is reabsorbed by renal tubules. Proximal convoluted tubules shows maximum reabsorption and nearly all the essential nutrients and 70-80% of electrolytes and water are reabsorbed by this segment.

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(c) Ammonotelic organisms are those which excrete nitrogenous waste as soluble ammonia. For example, most of aquatic animals such as amphibians, poriferans, fishes, etc. Ureotelic organisms which excrete urea as nitrogenous waste. For example, include cartilaginous fishes, frogs, humans, adult amphibians, etc. Uricotelic organisms are those which excrete nitrogenous waste as uric acid or its salts. For example, mostly include birds, lizard, cockroach, etc. So, the correct answer is ‘Ammonotelic – Aquatic Amphibia, Ureotelic – Frog, Humans, Uricotelic – Pigeon, Lizards, Cockroach’.

Hint

(a) The amount of the filtrate formed by the kidneys per minute is called glomerular filtration rate (GFR). GFR in a healthy individual is approximately \(125 \mathrm{ml} /\) minute, i.e., 180 litres per day.

The kidneys have built-in mechanisms for the regulation of glomerular filtration rate. One such efficient mechanism is carried out by juxtaglomerular apparatus (JGA). JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. A fall in GFR can activate the JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR comes back to normal.

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(d) Excretion of urea is known as ureotelism and the animals which excrete urea are called ureotelic. Ureotelic animals include Ascaris, earthworm (both are ammonotelic and ureotelic), cartilaginous fishes like sharks and stingrays, semiaquatic amphibians such as frogs and toads, aquatic or semi-aquatic reptiles like turtles, terrapins, and alligators, and man and all other mammals. Urea is less toxic and less soluble in water than ammonia. Hence, it can stay for some time in the body. Amphibian tadpole (e.g., tadpole of frog) excrete ammonia but after metamorphosis frog excretes urea.

Hint

(b) The medulla of the kidney is divided into a number of conical areas, the medulla pyramids or renal pyramids. Peritubular capillaries, loop of Henle, and collecting ducts lie in the medulla (renal pyramids) while convoluted tubules lie in the cortex of the kidney.

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(a) The visceral layer of Bowman’s capsule surrounds the glomerulus and is composed of special type of cells, the podocytes. The podocytes are so called because they possess foot-like processes (projection), the pedicels. The space between pedicels are called slit pores (= filtration slits) through which the glomerular filtrate filters.

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(a) Antidiuretic hormone (ADH) or vasopressin increases the reabsorption of water in the distal convoluted tubule, collecting tubules and collecting ducts of the nephrons of the kidneys. As a result, the reabsorption of water from the glomerular filtrate is increased. When someone drinks lot of water, the requirement of absorption of water decreases, so \(\mathrm{ADH}\) release is suppressed.

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(a) Reptiles, birds, land snails, and insects excrete nitrogenous wastes as uric acid in the form of pellet or paste with a minimum loss of water and are called uricotelic animals.

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(d) In male frogs the sperms are carried through the ureters, hence in male, ureters are called urinogenital ducts.

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(c) Urine formation involves three main processes namely, glomerular filtration, reabsorption, and secretion, that takes place in different parts of the nephron. A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released ( \(1.5\) litres), suggest that nearly 99 percent of the filtrate is reabsorbed by the renal tubules. The descending limb of loop of Henle is permeable to water but almost impermeable to electrolytes. The ascending limb is impermeable to water but allows the transport of electrolytes actively or passively. Conditional reabsorption of \(\mathrm{Na}^{+}\)and water takes place in the distal convoluted tubule. It is also capable of reabsorption of \(\mathrm{HCO}_{3}^{-}\).

Hint

(d) The principle nitrogenous excretory compound in humans is urea. Urea is produced in a series of reactions (urea cycle) which take place in the mitochondrial matrix and cytosol of liver cells. The urea cycle (ornithine cycle) is the series of biochemical reactions that converts ammonia, which is highly toxic, and carbon dioxide to the much less toxic urea during the excretion of metabolic nitrogen derived from the deamination of excess amino acids. The urea is ultimately excreted in solution in urine.

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(c) The adrenal medulla synthesises two hormones adrenaline (epinephrine) and non-adrenaline (non-epinephrine). These hormones are proteinaceous in nature and derived from amino acid tyrosine. Thus, injury to adrenal cortex will not affect the secretion of adrenaline.

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(a) Sensory stretch receptors are responsible for the stretch reflex. If these are removed then autonomic nervous system control will not be there and micturition will continue. Micturition is the expulsion of urine from the urinary bladder.

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(b) Cockroach shows uricotelism. Excretion of uric acid is known as uricotelism and the animals which excrete uric acid are called uricotelic. Animals that live in dry conditions have to conserve water in their bodies. Therefore, they synthesize crystals of uric acid from ammonia. Uric acid crystals are non-toxic and almost insoluble in water. Hence, these can be retained in the body for a considerable time. Uricotelic animals include most insects, (e.g., cockroach), land reptiles (e.g., lizards and snakes), and birds.

Hint

(a) Kangaroo rat is a desert rodent. Its body is covered by hairs. Its urine is more than 20 times concentrated as its plasma. This concentrated waste enables it to live in dry or desert environment where little water is available for him to drink. Most of its water is metabolically produced from the oxidation of carbohydrates, fats, and proteins in the seeds that it eats. The animal remains in cool burrow during daytime and the respiratory moisture condensed in nasal passages.

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(c) A person who is on a long hunger strike and is surviving only on water, will have less urea in his urine. As urea is an organic compound which is a waste product produced during body metabolism.

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(d) Angiotensinogen is a plasma protein produced and secreted by the liver cells Renin is secreted from juxtaglomerular cells and acts enzymatically on angiotensinogen to release 10 amino acid contaning peptide angiotensin-I. Macula densa is actually a plaque in the wall at the end of thick ascending limb of nephrons.

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(a) Bowman’s glands (olfactory glands) occur below the olfactory epithelia. Their ducts open on the olfactory epithelial surface. These glands secrete watery mucus to protect and keep the epithelium moist.

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(c) Some animals have dual behaviour of excretion eg. earthworm. It excretes ammonia (hence called ammonotelic) when enough water is available but excretes urea (ureotelic) in dry conditions.

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(c) Walls of glomerular capillaries and Bowman’s capsule are very thin and are semipermeable due to the presence of pores in the former and slit-pores in the latter. They allow water and small molecules in the blood to pass through them. Fluid containing these materials is forced out of the glomerular capillaries into the Bowman’s capsule by the high pressure of the blood in the glomerular capillaries. This pressure is about \(70 \mathrm{~mm} \mathrm{Hg}\) in man. The fluid tends to move in the reverse direction due to (i) the osmotic pressure of plasma proteins in the glomerular capillaries, and (ii) hydrostatic pressure of the fluid in the urinary tubule. These pressures in man are about \(30 \mathrm{~mm}\). Hg. and \(20 \mathrm{~mm}\). Hg. respectively. The net force moving the fluid from the glomerular capillaries, called the filtration pressure, is \(70-(30+20)\) or \(20 \mathrm{mmHg}\).

Hint

(d) Under fasting conditions which are associated with high rate of fatty acid oxidation, the liver produces a large amount of ketone bodies viz. acetoacetate, \(\beta\)-hydroxybutyrate, and acetone. The normal level of ketone blood level is \(0.2 \mathrm{mmol} / \mathrm{L}\). Presence of excess ketone bodies in urine is termed as ketonuria.

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(c) The animals which excrete mainly uric acid are uricotelic and this phenomenon is called uricotelism. Uric acid is excreted by terrestrial reptiles (lizard, snakes, etc) birds, and insects to conserve water in their body. Frog and mammals excrete urea and so
they are called as ureotelic animals and this phenomenon is known as ureotelism.

Hint

(d) Reabsorption is a process by which useful constituents of glomerular filtrate are returned into the blood streams. It occurs in convoluted tubules (proximal convoluted tubule) as well as loop of Henle. Basically loop of Henle, in association with vasa rectae, plays an important role in the counter-current mechanism (the process which makes urine hypertonic, i.e., more concentrated). Therefore, if Henle’s loop was absent from mammalian nephron the urine will be more dilute.

Hint

(b) Terrestial animals have limited access to water. Hence they have to secrete hypertonic urine and conserve water. Choices (c) and (d) are characteristics of marine animals who need to overcome the problem of preventing entry of salts and loss of water. Choice (a) is characteristic of freshwater animals.

Hint

(a) Hydra being a coelenterate, has blind sac body plan. It has only one mouth which serves as the opening for ingestion and waste elimination besides diffusion across the body wall.
The fluid is excreted through a break in the body wall created as a result of a strong contraction when the gut is distended with fluid. A normal hydra, therefore, must remove excess fluid by contracting and expelling it through its mouth.

Hint

(b) Concentration of urine depends upon the length of Henle’s loop. The loop of Henle is the hairpin-shaped section of a kidney tubule situated between the proximal and distal tubules in the nephron. It consists of a thin descending limb which is permeable to water and a thick ascending limb which is impermeable to water complex movements of ions and water across the walls of the loop enable it to function as a countercurrent multiplier, resulting in the production of concentrated urine in the collecting duct.

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(d) Enteronephridia is concerned with excretion of nitrogenous waste. In annelids, the nephridia are the excretory organs. In earthworm, three types of nephridia are found (a) septal (b) pharyngeal, and (c) integumentary. The septal nephridia do not discharge
the excretory fluid to the exterior. Instead, these pour it into the intestine. Hence, these are also called enteronephric nephridia.

Hint

(b) Length of Henle’s loop determined the concentration of urine. Urine is concentrated through counter current mechanism which involves (a) the loop of Henle (b) the vasa recta (c) nearby collecting tubules and ducts, (d) the interstitial fluid.

Hint

(b) Sweat glands are coiled tubular glands situated in the dermis and connected to
a sweat duct that opens as a pore on the surface of the skin. These secrete sweat which contains \(0.1-0.4 \%\) of sodium chloride, sodium acetate, and urea. Sweating occurs when the body temperature increases. As sweat evaporates from the skin surface, energy is lost from the body as latent heat of vaporation and in this way
sweat reduces body temperature.

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(b) Ureotelic animals include Ascaris, earthworm, cartilaginous fishes, semiaquatic amphibians aquatic or semiaquatic reptiles like turtles and alligators.

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(a) Growth hormone, released by the anterior lobe of the pituitary which brings about body growth by synthesis and deposition of proteins in tissues. Renin secreted by special cells in kidneys regulates blood pressure. Aldosterone reduces \(\mathrm{Na}^{+}\) elimination by helping active reabsorption from the nephric filtrate.

Hint

(c) A nephron is a unit of structure and function in a kidney. A kidney contains about a million nephrons, each approximately \(3 \mathrm{~cm}\) long.

A nephron is a long tubule differentiated into four regions having different anatomical features and physiological role: Bowman’s capsule, proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). The latter opens into one of the collecting ducts. Nephridia are the excretory organs of annelids.

Hint

(b) In ureotelic animals urea is formed from ammonia by Ornithine cycle.
\(\mathrm{CO}_{2}+2 \mathrm{NH}_{3} \rightarrow \mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}+\mathrm{H}_{2} \mathrm{O}\)
                ammonia            Urea

Hint

(b) A nephron is a unit of structure and function in a kidney. A kidney contains about a million nephrons, each approximately 3 cm. long. A nephron is a long tubule differentiated into four regions having different anatomical features and physiological role proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). The latter opens into one of the collecting ducts. Nephridia are the excretory organs of annelids.

Hint

(c) Individual cells have no role to play in this process. Excess water in the blood affects the osmoreceptors present in hypothalamus and volume receptors present in the left atrium, ventricles, and pulmonary veins. This causes \(\mathrm{ADH}\) release so that body hydration is regulated by the removal of excess water by the kidney.

Hint

(b) Uric acid is the least soluble nitrogenous waste and \(1 \mathrm{~g}\) of it needs only \(10 \mathrm{~mL}\) of water to be expelled out of the body.
Another advantage of it is that it is least toxic among all nitrogenous wastes and can be retained in the body for longer period, so it is of greater advantage to animals which have limited access to water like birds and lizards.

Hint

(a) From the option given glomerulus do not belong to uriniferous tubule. Each nephron is about \(6 \mathrm{~cm}\) long and is divided into two parts: Bowman’s capsule and nephric or uriniferous tubule. Glomerulus is a group of about 50 capillaries. Its capillary wall has numerous minute pores, so the permeability of glomerular membrane increases 100-500 times as high as that of the usual capillary. While Henle’s loop, DCT, and collecting tubules are part of the uriniferous tubule.

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(b) If the kidney fails to reabsorb water the concentration of urine will be low and
urination will be more frequent, a condition called polyuria as a result, the
tissues of the body will be dehydrated and shrink.

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(a) Glucose is taken back from the glomerular filtrate by the proximal convoluted tubule by active transport.

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(b) Ammonia is highly soluble in water, so in aquatic animals \(e. g\) ., tadpole of frog, the nitrogenous waste products are excreted in the form of ammonia. In terrestrial animals \(e . g\)., adult frog, these wastes are excreted in the form of urea.

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(d) The cells lining the proximal convoluted tubule are well adapted for the reabsorption of materials from the filtrate. They have abundant mitochondria and bear numerous microvilli on the free side thus giving brush border appearance. The cells reabsorb entire glucose, amino acids, most of the inorganic ions, much of the water as well as some urea from the filtrate.

Hint

(b) Nephron is the excretory unit of the human excretory system. Each nephron has a Bowman’s Capsule, a Proximal Convoluted Tubule (PCT), Loop of Henle (Descending & Ascending limbs), and Distal Convoluted Tubule (DCT) which then enter into collecting duct.

Hint

(c) Brush border cells are found mainly in the following organs: The small intestine tract: This is where absorption takes place.

The microvilli that constitute the brush border have enzymes for this final part of digestion anchored into their apical plasma membrane as integral membrane proteins.

They are known to secrete large amounts of protein-rich material and are thought to secrete the enzyme peptidase, which breaks peptide molecules into amino acids suitable for assimilation by the body. In humans, the granules are found to contain carbohydrates, proteins, and radioactive zinc.

Hint

(c) From Bowman’s capsule, glomerular filtrate enters the proximal convoluted tubule. Most of the useful substances like Glucose, Amino Acids, inorganic ions \(\left(\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Cl}^{-}\right.\)etc), and most of the important buffer bicarbonates are reabsorbed in Proximal Convoluted Tubule. Cells are specially adaptive for absorption having numerous microvilli & mitochondria (to provide energy for active absorption).