NCERT Exemplar Class 11 Biology Solutions Excretory Products and their Elimination

Multiple Choice Questions
1.The following substances are the excretory products in animals. Choose the least toxic among them.
(a) Urea           (b) Uric acid
(c) Ammonia (d) Carbon dioxide
Solution. (b): Nitrogenous waste substances such as ammonia, urea or uric acid are produced during protein metabolism according to the species. Small amount of nitrogenous waste substances are also produced during the metabolism of nucleic acids. Ammonia is the most toxic, followed by urea and uric acid. The latter is the least toxic.

2.Filtration of the blood takes place at
(a) PCT                       (b) DCT
(c) Collecting ducts (d) Malpighian body.
Solution. (d) : Each nephron has two parts- glomerulus and renal tubule. Glomerulus is a tuft of capillaries formed by afferent arteriole. The renal tubule begins with a double walled cup-like structure called Bowman’s capsule, which encloses glomerulus. Glomerulus along with Bowman’s capsule, is called Malpighian body or renal corpuscle. The tube continues further to form PCT, loop of Henle and DCT. The first step in urine formation is the filtration of blood which is carried out by the Malpighian body.

3.A large quantity of one of the following is removed from our body by lungs.
(a) CO2only           (b) H2Oonly
(c) CO2 and H2O (d) Ammonia
Solution. (a): Human lungs remove about 18 L of CO2 and about 400 mL of water per day.

4.The pH of human urine is approximately
(a) 6.5           (b) 7
(c) 6              (d) 7.5
Solution. (c): Urine is a transparent, light yellow liquid with a slightly acidic pH (avg. pH 6.0). However, the pH  range of urine is normally between 4.5-8.2 depending upon the amount of acidic and basic food in diet.

5.Which one of the following statements is incorrect?
(a) Birds and land snails are uricotelic animals.
(b) Mammals and frogs are ureotelic animals.
(c) Aquatic amphibians and aquatic insects are ammonotelic animals.
(d) Birds and reptiles are ureotelic.
Solution.(d): Animals which excrete uric acid are called uricotelic. Uric acid crystals are non-toxic and almost insoluble in water. Hence, these can be retained in the body for a considerable time and can be excreted with least possible amount of water. Uricotelic animals include most insects, some land crustaceans, land snails, land reptiles and birds. Animals which excrete ammonia are called as ammonotelic e.g., many aquatic animals like protozoans, tailed amphibians, tadpoles, aquatic insects, etc. Animals which excrete urea are called ureotelic e.g., man, frog, etc.

6.Which of the following pairs is wrong?
(a) Uricotelic—–Birds
(b) Ureotelic—–Insects
(c) Ammonotelic—–Tadpole
(d) Ureotelic—–Elephant
Solution.(b): Refer answer 5.

7.Which one of the following statements is incorrect?
(a) The medullary zone of kidney is divided into a few conical masses called medullary pyramids projecting into the calyces.
(b) Inside the kidney the cortical region extends in between the medullary pyramids as renal pelvis.
(c) Glomerulus along with Bowman’s capsule is called the renal corpuscle.
(d) Renal corpuscle, proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) of the nephron are situated in the cortical region of kidney.
Solution.(b): Inside the kidney, the cortical region extends in between the medullary pyramids as renal columns called columns of Bertin.

8.The condition of accumulation of urea in the blood is termed as
(a) Renal calculi (b) Glomerulonephritis
(c) Uremia          (d) Ketonuria.
Solution. (c) : In uremia, concentration of urea goes high in blood because the tubules are not able to remove it from blood.

9.Which one of the following is also known as antidiuretic hormone?
(a) Oxytocin     (b) Vasopressin
(c) Adrenaline (d) Calcitonin
Solution.(b): Antidiuretic hormone (ADH) is also known as vasopressin or pitressin. It is secreted from posterior lobe of pituitary gland.

10.Match the terms given in column I with their physiological processes given in column II and choose the correct answer.
Column 1                                                   Column II
A. Proximal convoluted tubule        (i) Formation of concentrated urine
B. Distal convoluted tubule              (ii) Filtration of blood
C. Henle’s loop                                      (iii) Reabsorption of 70-80% of electrolytes
D. Counter-current  mechanism    (iv) Ionic balance
E. Renal corpuscle                                (v) Maintenance of concentration gradient in medulla
(a) A-(iii), B-(v), C-(iv), D-(ii), E-(i)
(b) A-(iii), B-(iv), C-{i), D-(v), E-(ii)
(c) A-(i), B-(iii), C-(ii), D-(v), E-(iv)
(d) A-(iii), B-(i), C-(iv), D-(v), E-(ii)

11.Match’the abnormal conditions given inColumn A with their explanations given in  Column B and choose the correct option.
Column A                               Column B
A. Glycosuria                         (i) Accumulation of uric acid in joints
B. Renal calculi                    (ii) Inflammation in glomeruli
C. Glomerular nephritis  (iii) Mass of crystallised salts within the kidney
D. Gout                                    (iv)Presence of glucose in urine Presence of glucose in urine
(a) A-(i),    B-(iii), C-(ii), D-(iv)
(b) A-(iii), B-(ii),  C-(iv), D-(i)
(c) A-(iv),  B-(iii), C-(ii), D-(i)
(d) A-(iv), B-(ii),  C-(iii), D-(i)

12.We can produce concentrated/ dilute urine. This is facilitated by a special mechanism. Identify the mechanism.
(a) Reabsorption from PCT
(b) Reabsorption from collecting duct
(c) Reabsorption/ Secretion in DCT
(d) Counter current mechanism in Henle’s loop/ Vasa recta
Solution.(d) : The counter current mechanism helps to concentrate the filtrate which occurs in loop of Henle and vasa recta in the medulla region of the kidney. This gradient is mainly caused by NaCl and urea. It helps in easy absorption of water from the filtrate present in the collecting duct so that the concentration of the filtrate (urine) is increased. Therefore,hypertonic urine is produced in human beings.

13. Dialysing unit (artificial kidney) contains a fluid which is almost same as plasma except that it has ‘
(a) High glucose (b) High urea
(c) No urea (d) High uric acid.
Solution. (c) : Artificial kidney, called dialysing unit, is a machine that is used to filter the blood . of a person whose kidneys are damaged. The process is called haemodialysis. Dialysing unit has a cellophane tube suspended in a salt-water solution of the same composition as the normal blood plasma, except that no urea is present. Blood of the patient is pumped from one of the arteries into the cellophane tube. Pores of the cellophane tube allow urea, uric acid, creatinine, excess salts and excessH+ ions to diffuse from the blood into the surrounding solution. The blood thus purified is then pumped into a vein of the patient.



Very Short Answer Type Questions
1.Where does the selective reabsorption of Glomerular filtrate take place?
Solution.Selective reabsorption of glomerular tubular filtrate takes place in proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.

2.What is the excretory product from kidneys of reptiles?
Solution. The excretory product from kidneys of reptiles is uric acid

3.What is the composition of sweat produced by sweat glands?
Solution. Composition of sweat is water, NaCl small amounts of urea, lactic acid etc.

4.Identify the glands that perform the excretory function in prawns.
Solution. Adrenal glands or green glands perform the excretory function in prawns.

5.What is the excretory structure in Amoeba?
Solution. Contractile vacuole performs the function of excretion as well as osmoregulation in Amoeba.

6.The following abbreviations are used in the context of excretory functions, what do they stand for?
(a) ANF (b) ADH
(c) GFR (d) DCT
Solution.(a) Atrial Natriuretic Factor
(b) Antidiuretic Hormone
(c) Glomerular Filtration Rate
(d) Distal Convoluted Tubule

7.Differentiate glycosuria from ketonuria.
Solution.Presence of glucose in urine is called glycosuria while presence of ketone bodies in urine is called ketonuria.

8.What is the role of sebaceous glands?
Solution.‘Sebaceous glands eliminate certain substances like sterols, hydrocarbons and waxes through sebum. This secretion provides a protective, oily covering for the skin.

9.Name two actively transported substances in glomerular filtrate.
Solution. Two actively transported substances in glomerular filtrate are glucose and amino acids.

10.Mention any two metabolic disorders, which can be diagnosed by analysis of urine.
Solution.Diabetes mellitus and phenylketonuria are two metabolic disorders that can be diagnosed by analysis of urine. In diabetes mellitus, large amounts of glucose and ketones. are secreted in the urine i.e., glucosuria and ketonuria respectively. Phenylketonuria can be diagnosed by examining urine for the presence of ketone phenylpyruvate (ketonuria).

11.What are the main processes of urine formation?
Solution. Glomerular filtration, selective reab-sorption and secretion are the main processes of urine formation.

12.Sort the following into actively or passively transported substances during reabsorption of GFR. glucose, aminoacids, nitrogenous wastes, Na+, water
Solution.Actively transported : Glucose, amino acids and Na+.Passively transported : Nitrogenous wastes and water.

13.Complete the following:
(a) Urinary excretion = Tubular reabsorption +Tubular secretion ________
(b) Dialysis fluid = Plasma ________
Solution.(a) The equation given in the question is incorrect. The correct equation is as follows: Urinary excretion = Glomerular filtration – Tubular reabsorption + Tubular secretion.
(b) Dialysis fluid = Plasma – Nitrogenous wastes.

14.Mention the substances that exit from the tubules in order to maintain a concentration gradient in the medullary interstitium.
Solution. NaCl and urea are the two substances that exit from the tubules in order to maintain concentration gradient in the medullary interstitium.

15.Fill in the blanks appropriately.
Organ Excretory wastes
(a) Kidneys ______________
(b) Lungs ______________
(c) Liver ______________
(d) Skin ______________
Solution.(a) Urea, water, nitrogen, creatinine, amino acids, vitamins, hormones, chlorides, phosphate, potassium, sodium, calcium, magnesium, lead etc.
(b) CO2and water.
(c) Bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs.
(d) Water, NaCl, urea, lactic acid, sterols, waxes and hydrocarbons.

Short Answer Type Questions
1.Show the structure of a renal corpuscle with the help of a diagram.
Solution. The structural diagram of a renal corpuscle is as follows:

2.What is the role played by renin-angiotensin in the regulation of kidney function?
Solution. A fall in glomerular blood flow or glomerular blood pressure or GFR can activate the juxtaglomerular (JG) cells to release renin which converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II, being a powerful vasoconstrictor, increases the glomerular blood pressure and thereby GFR. Angiotensin II also activates the adrenal cortex to release aldosterone. This hormone causes reabsorption of Na+ and water from the distal parts of the tubule. This also leads to an increase in blood pressure and GFR. This whole mechanism is known as the renin-angiotensin mechanism.

3.Aquatic animals generally are ammonotelic in nature whereas terrestrial forms are not. Comment.
Solution. Aquatic animals like bony fishes, aquatic amphibians and aquatic insects exerete ammonia i.e,, they are ammonotelic in nature. This is because ammonia is highly toxic and is readily soluble in water. It is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions. Excretion of nitrogenous wastes in the form of urea requires a lot of water. Terrestrial animals cannot afford to lose so much of water, thus they convert ammonia into urea or uric acid which are less toxic and can be stored in body for longer.
Terrestrial amphibians and mammals mainly exerete urea and are called ureotelic animals while reptiles, birds, land snails excrete uric acid and are called uricotelic animals. Urea and uric acid are less soluble in water and can be excreted with lesser loss of water. Thus, terrestrial adaptation necessitated the production of urea and uric acid for conservation of water.

4.The composition of glomerular filtrate and urine is not same. Comment.
Solution.Glomerular filtrate contains all the contents of blood plasma except proteins. About 180 litres of glomerular filtrate is produced per day. Then, mainly in PCT and DCT reabsorption of various contents of the filtrate like, water, glucose, nutrients, ions etc. occurs. As a result, now the composition of urine is quite different from that of the glomerular filtrate. Some ions are also added to this fluid by tubules i.e., tubular secretion to maintain ionic and acid-base balance of body fluids. Thus, the composition of glomerular filtrate and urine is not same.

5.What is the procedure advised for the correction of extreme renal failure? Give a brief account of it.
Solution. Kidney transplantation is the ultimate procedure advised for the correction of extreme renal failure. A functioning kidney is transplanted from a donor, preferably a close relative to minimise its chances of rejection by the immune system of the recipient. Modern clinical procedures have increased the success rate of such a complicated technique.

6.How have the terrestrial organisms adapted themselves for conservation of water?
Solution.Refer answer 3.

7.Label the parts in the following diagram.

8.Explain, why a haemodialysing unit called artificial kidney?
Solution. A haemodialysing unit is called artificial kidney because it performs the same function as that of the kidney i.e., with its help, the blood is cleared of the nitrogenous wastes without losing plasma proteins. Haemodialysing is done to those patients whose kidneys are malfunctioning leading to accumulation of urea in the blood.

9.Comment upon the hormonal regulation of selective reabsorption.
Solution. An excessive loss of fluid from the body can activate the osmoreceptors present in the body which further stimulate the hypothalamus to release antidiuretic  hormone (ADH) from the neurohypophysis. ADH facilitates water reabsorption from the latter parts of the tubule. An increase in body fluid volume can switch off the osmoreceptors and suppress the ADH release to complete the feedback.
Angiotensin II also activates the adrenal cortex to release aldosterone. This hormone causes reabsorption of Na+ and water from the distal parts of the tubule.

Long Answer Type Questions
1.Explain the mechanism of formation of concentrated urine in mammals.
Solution. The Henle’s loop and vasa recta play a significant role in producing a concentrated urine in mammals. A counter current is formed by the movement of the filtrate in the two limbs of Henle’s loop in opposite directions. The flow of blood through the two limbs of vasa recta is also in a counter current’ pattern. An increased osmolarity towards the inner medullary interstitium is maintained by the proximity between the Henle’s loop and vasa recta, as well as the counter current in them i.e., from 300 m Osmol L -1 in the cortex to about 1200 m Osmol L -1 in the inner medulla. This gradient is mainly caused by NaCl and urea. NaCl is transported by the ascending limb of Henle’s loop which is exchanged with the descending limb of vasa recta. NaCl is returned to the interstitium by the ascending limb of vasa recta. Similarly, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule. This special arrangement of Henle’s loop and vasa recta that facilitates the transport of substances is called counter current mechanism. This mechanism helps to maintain a concentration gradient in the medullary interstitium. Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine).

2.Draw a labelled diagram showing reabsorption and secretion of major substances at different partsof the nephron.
Solution. Reabsorption and secretion of major substances at different parts of the nephron can be represented in a diagram as follows. Arrows indicate direction of movement of materials.

3.Explain briefly, micturition and disorders of the excretory system.
Solution. Micturition : The process of release of urine from urinary bladder is called micturition. A signal is initiated by the stretching of the urinary bladder as it gets filled with urine. In response, the stretch receptors on. the walls of the bladder send signals to the CNS. The CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.
Disorders of excretory system :
(i) Uremia – Accumulation of urea in blood is called uremia. Malfunctioning of kidneys can lead to uremia, which is highly harmful and may lead to kidney failure.
(ii)Renal calculi : Stone or insoluble mass of crystallised salts formed within the kidney are called renal calculi. They are commonly composed of calcium oxalate. They can cause pain if they cause obstruction and prevent urine flow in the ureter or kidney, or by direct irritation of the bladder.
(iii)Glomerulonephritis : It is inflammation of glomeruli of kidney.
can be represented in a diagram as follows. Arrows indicate direction of movement of materials.
Proximal convoluted tubule Distal convoluted tubule

4.How does tubular secretion help in maintaining ionic and acid-base balance in body fluids?
Solution.The cells of the renal tubule also excrete additional wastes from the blood stream into the filtrate by the process of tubular secretion. Creatinine, hippuric acid, pigments, drugs like pencillin are actively secreted into the PCT. Urea enters the thin segment of the ascending limb of loop of Henle by diffusion. Potassium, hydrogen ions, ammonia, HCO3 ions are secreted into the DCT by active transport.
Thus, tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid base balance of body fluids.

5.The glomerular filtrate in the loop of Henle gets concentrated in the descending limb and then gets diluted in the ascending limb. Explain.
Solution. As the filtrate flows in the desending limb, its water is reabsorbed due to increasing osmolality of intestitial fluid. The electrolytes are not reabsorbed here. Thus, the filtrate becomes concentrated as it moves down.’ The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the intestinal fluid.

6.Describe the structure of a human kidney with the help of a labelled diagram.
Solution.Humans have of a pair of kidneys which are reddish brown, bean shaped structures situated between the levels of last thoracic and third lumbar vertebrae close to the dorsal inner wall of the abdominal cavity. Each kidney of an adult human measures 10-12 cm in length, 5-7 cm in width, 2-3 cm in thickness with an average weight of 120-170 gm. There is present a notch called hilum towards the centre of the inner concave surface of the kidney. Through the hilum, ureter, blood vessels and nerves enter. Inner to the hilum, is a broad funnel shaped space called the renal pelvis with projections called calyces. The layer on the outside of the kidney is a tough capsule. Inside the kidney, there are two zones, an outer cortex and an inner medulla. The medulla is divided into a few conical masses called medullary pyramids projecting into the calyces. The cortex extends in between the medullary pyramids as renal columns called columns of Bertin. The medullary pyramids are connected with minor calyces (sine, calyx) which in turn lead into major calyces. A human kidney possesses two to three major calyces. Major calyces open into renal pelvis which in turn leads to ureter. A kidney has about ten lakh nephrons. A longitudinal section of a human kidney in diagrammatic view is as follows: