NCERT Solutions for Class 11 Biology Chapter 19: Excretory Products and their Elimination

1. Define Glomerular Filtration Rate (GFR).

Ans. 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 ml/minute, i.e., 180 litres per day.

2. Explain the autoregulatory mechanism of GFR.

Ans. The kidneys have autoregulatory or built-in mechanisms for the regulation of glomerular filtration rate (GFR). One such efficient mechanism is carried out by juxtaglomerular apparatus (JGA). Juxtaglomerular apparatus is a microscopic structure formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact.

It has important role in regulating the renal blood flow and glomerular filtration rate. When there is a fall in the glomerular filtration rate, it activates the juxtaglomerular cells to release rennin (an enzyme that is produced by the granular cells of afferent arteriole at the JGA). Renin brings the GFR back to normal by the
activation of the renin-angiotensin mechanism. It enzymatically converts angiotensinogen (made by the liver) into angiotensin I.

3. Indicate whether the following statements are true or false :

(a) Micturition is carried out by a reflex.

(b) ADH helps in water elimination, making the urine hypotonic.

(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.

(d) Henle’s loop plays an important role in concentrating the urine.

(e) Glucose is actively reabsorbed in the proximal convoluted tubule.

Ans. (a) True.
Micturition is the act of passing urine. The wall of urinary bladder is stimulated by the
stretch receptors located in it and the urine is passed by reflex action.

(b) False.
ADH or anti diuretic hormone is produced by the hypothalamus and secreted by the posterior pituitary gland. ADH increases the re-absorption of water in the collecting ducts and reduces the rate of formation of
urine.

(d) True.
The counter current multiplication in the loop of Henle is responsible for concentrating the urine.

(e) True.
Glucose and sodium are absorbed by the proximal convoluted tubule and returned to the blood by active transport.

4. Give a brief account of the counter current mechanism.

Ans. The counter-current mechanism is used to concentrate urine in the kidneys by the nephrons of the human excretory system. The removal of water makes the urine/ filtrate more concentrated. The Henle’s loop and vasa recta play a significant role in facilitating the countercurrent mechanism in kidney.

(a) Counter-current is formed by the flow of filtrate in the two limbs of Henle's loop, which is in opposite directions.

(b) The flow of blood in two limbs of vasa recta is also in a counter current pattern.

(d) NaCI is returned to the interstitium by the ascending portion of vasa recta.

(e) The small amount of urea enters the thin segment of the ascending limb of Henle's loop.

(f) This small amount of urea is transported back to the interstitium by the collecting tubule. It is facilitated by the special arrangement of Henle's loop and vasa recta that we call the counter current mechanism.

Significance: The counter-current mecha-nism helps to maintain a concentration gradient in the medullary interstitium. This leads to the easy passage of water from the collecting tubule thereby concentrating the filtrate (urine). This mechanism helps to maintain a concentration gradient.

5. Describe the role of liver, lungs and skin in excretion.

Ans. Role of liver, lungs and skin in excretion:

(a) Liver: It is large digestive gland and the part of digestive system. It secretes bile and helps in excretion metabolic products like cholesterol and other waste products through it. It converts ammonia into urea for the excretion. It converts the decomposed haemoglobin pigment into the bile pigments called bilirubin and biliverdin.

(b) Lung: It helps in excretion of carbon dioxide from the body by the process of exhalation.

(c) Skin: It consists of many tiny pores like sweat glands and sebaceous glands. The waste products are separated and excreted through the sweat glands as sweat. The sebaceous glands secrete an oily product known as sebum.

6. Explain micturition.

Ans. Micturition is the process by which the urine from the urinary bladder is excreted. The urine accumulates; the muscular walls of the bladder expand due to excitation of stretch receptors located in it. The walls stimulate the sensory nerves in the urinary bladder, setting up a reflex action. This reflex action stimulates the urge to pass out urine. This information is integrated in the spine and relayed to parasympathetic neurons and somatic motor neurons. This allows external sphincter to open and urine to flow out known as micturition.

7. Match the items of column I with those of column II :

Column I	Column II
(a) Ammonotelism	(i) Birds
(b) Bowman’s capsule	(ii) Water reabsorption
(c) Micturition	(iii) Bony fish
(d) Uricotelism	(iv) Urinary bladder
(e) ADH	(v) Renal tubule

Ans. The correct match is as follows:

Column I	Column II
(a) Ammonotelism	(iii) Bony fish
(b) Bowman’s capsule	(v) Renal tubule
(c) Micturition	(iv) Urinary bladder
(d) Uricotelism	(i) Birds
(e) ADH	(ii) Water reabsorption

8. What is meant by the term osmoregulation?

Ans. The process of maintaining an internal balance between water and dissolved materials by the kidneys is called osmoregulation. It is a homeostatic mechanism that regulates the optimum concentration of water and salts in the tissues and body fluids. The kidneys are the main osmoregulatory organs in human body.

They function to filter blood and maintain the dissolved ion concentrations of body fluids.

9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?

Ans. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic.

Because ammonia is highly toxic in nature and water soluble and cannot be completely eliminated from the body. Therefore, it needs to be converted into less toxic forms such as urea or uric acid. It also helps in conserving water in body by the terrestrial animals.

10. What is the significance of juxta glomerular apparatus (JGA) in kidney function?

Ans. Juxta Glomerular Apparatus (JGA) is a special structure which consists of the cells of glomerulus, distal tubule and afferent and efferent arterioles. It is located in a special region of nephron where the afferent arteriole and the distal convoluted tubule are connected to each other. It plays a major role in the regulation of glomerular Filtration Rate (GFR). When the GFR falls, it activates the juxta glomerular cells to release renin enzyme which further stimulates the glomerular blood flow. This brings back the glomerular filtration rate to the normal level.

11. Name the following:

(a) A chordate animal having flame cells as excretory structures

(b) Cortical portions projecting between the medullary pyramids in the human kidney

(c) A loop of capillary running parallel to the Henle’s loop.

Ans. (a) Amphioxus has flame cells: Flame cells are a type of excretory cells that also play role in osmoregulation.

(b) Columns of Bertini: These are the cortical portions projecting between the medullary pyramids in the human kidney. They represent the cortical tissues present within the medulla.

(c) Vasa rectae: It is a loop of capillary that runs parallel to Henle’s loop. Vasa rectae, along with Henle’s loop, helps in maintaining a concentration gradient in the medullary interstitium.

12. Fill in the gaps :

(a) Ascending limb of Henle’s loop is _______ to water whereas the descending limb is _______ to it.

(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone _______.

(c) Dialysis fluid contain all the constituents as in plasma except _______.

(d) A healthy adult human excretes (on an average) _______ gm of urea/day.
Ans. (a) impermeable, permeable

(b) ADH (anti-diuretic hormone)

(d) 25-30