Excretion is a vital process that eliminates toxic metabolic wastes from the body to maintain internal stability. Chapter 16 of Class 11 Biology, Excretory Products and Their Elimination, explores how organisms produce and eliminate nitrogenous wastes, the different modes of excretion in various animals, and the structure and functioning of the human excretory system. The chapter explains the process of urine formation, the role of kidneys in osmoregulation and maintaining homeostasis, and examines how hormones regulate kidney function. It also covers common disorders of the excretory system and modern treatment methods like hemodialysis.This chapter is part of the comprehensive NCERT Solutions Class 11 Biology series, which covers all chapters in detail.
The NCERT Solutions for Excretory Products and Their Elimination provided here offer detailed, step-by-step explanations for all textbook questions, helping students strengthen their conceptual understanding, clear doubts effectively, and prepare efficiently for both school exams and competitive tests like NEET.
NCERT Solutions for Class 11 Biology Chapter 16 - All Exercise Questions
Q.
Define Glomerular Filtration Rate (GFR).
Q.
Explain the autoregulatory mechanism of GFR.
Q.
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.
Q.
Give a brief account of the counter current mechanism.
Q.
Describe the role of liver, lungs and skin in excretion.
Q.
Match the items of column I with those of column II:
Q.
What is meant by the term osmoregulation?
Q.
Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic. Why?
Q.
What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Q.
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 Henle’s loop
Q.
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 contains all the constituents as in plasma except _______.
(d) A healthy adult human excretes (on an average) _______ gm of urea/day.
Class 11 Chapter 16 Biology Questions & Answers –Excretory Products and Their Elimination
Class 11 Chapter 16 Biology Questions & Answers –Excretory Products and Their Elimination
Q1. Define Glomerular Filtration Rate (GFR)
Solution: Glomerular Filtration Rate (GFR) is the amount of filtrate formed by the kidneys per minute. It is measured in ml/min. In a healthy person, GFR is approximately 125 ml/min that is equal to 180 litres per day.
Q2. Explain the autoregulatory mechanism of GFR.
Solution: Kidneys maintain a uniform Glomerular Filtration Rate (GFR) with the help of the autoregulatory mechanism. Kidneys have a microscopic structure called juxta glomerular apparatus (JGA) located between an afferent arteriole and distal convoluted tube of the same nephron that is required for this auto-regulation. Whenever there is a fall in glomerular blood flow/glomerular blood pressure/GFR, cells of juxta glomerular apparatus release a hormone called renin which converts angiotensinogen in the blood to angiotensin I and further to angiotensin II.
- Angiotensin II is a strong vasoconstrictor. It increases the glomerular blood pressure and blood flow and thereby, increases the GFR.
- Angiotensin II also activates the release of Aldosterone which causes reabsorption of Na+ and water from the distal parts of the tubule. This also causes an increase in blood pressure and GFR.
Q3. 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.
Solution:(a) True
(b) False
(c) True
(d) True
(e) True
Q4. Give a brief account of the counter current mechanism.
Solution: The transport of substances facilitated by a special arrangement of Henle’s loop of nephron and vasa recta is called counter current mechanism.
When fluid flows in these two tubes which are anti-parallel to each other, it forms a counter current. This helps mammals to produce concentrated urine. There are two counter current systems in human kidneys-
- Henle’s loop consists of ascending and descending limbs. Fluid flows in the two limbs in opposite directions making a counter current system.
- Second counter current system is made by vasa recta. Blood flows in the two limbs of vasa recta in anti-parallel direction.
Henle’s loop and vasa recta are positioned next to each other. Descending limb of Henle’s loop is anti-parallel to ascending limb of vasa recta and ascending limb of Henle’s loop is anti-parallel to descending limb of vasa recta. Counter current system and proximity of the loops help to increase the osmolarity (solute concentration) in inner medullary interstitium i.e. from 300mOsmolL-1 in the cortex to about 1200mOsmolL-1 in the inner medulla. Increased solute concentration in medullary interstitium causes water to come out of collecting duct making the urine concentrated. This system has the ability to concentrate urine upto four times depending upon the need.
Q5. Describe the role of liver, lungs and skin in excretion.
Solution:In addition to kidneys, liver, lungs and skin also play an important role in excretion of waste materials from the body.
Liver: It is the largest gland of the human body. Liver converts toxic ammonia into less toxic urea; thus carry out the detoxification role. It helps in the excretion of bile containing substances like bilirubin, biliverdin which are produced by the decomposition of haemoglobin pigment. Then bilirubin, biliverdin, urea along with other waste like cholesterol, degraded steroid hormones, vitamins and drugs are excreted by the liver. Finally, these substances are thrown out of the body along with digestive wastes.
Role of Lungs: Lungs diffuse out a large amount of gaseous waste like CO2 (18 litres/day) as part of normal respiration along with the significant quantity of water.
Role of Skin: Skin contains sweat and sebaceous glands which help in the excretion of many substances. The sweat produced by sweat glands secrete NaCl, small amounts of urea, lactic acid, etc., along with water. Sebaceous glands help in excretion by elimination of certain sterols, hydrocarbons and waxes through sebum.
Q6. Explain micturition.
Solution: Micturition is the process of releasing of urine from urinary bladder. Urine formed by kidney is carried to urinary bladder where it is stored. When urinary bladder is filled with urine, it exerts the pressure on bladder wall. Pressure activates receptors present in bladder wall that send signals to central nervous system (CNS). The CNS sends the signal for the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.
An adult human excretes about 1 to 1.5 litres of urine per day. The urine is light yellow coloured watery fluid which is slightly acidic with a characteristic odour.
Q7. 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
(d) ADH (v) Renal tubule
Solution:
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
Q8. What is meant by the term osmoregulation?
Soluition: Osmoregulation is a process by which organisms maintain homeostasis of water content in their body. It protects body fluids from becoming too dilute or too concentrated. For example, large amount of water goes into the nephrons from blood during the process of glomerular filtration. This water is reabsorbed by medullary interstitium and transferred again to blood in vasa recta thus, maintaining water homeostasis in blood.
Q9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic,
why ?
Solution: Terrestrial animals are generally either ureotelic or uricotelic because it is an adaptation to conserve water. In these animals, water soluble ammonia is converted into less soluble urea and uric acid. These are then filtered by the kidney and excreted out with urine. This requires minimum water; thus the animal conserves water.
Q10. What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Solution: Kidneys have a microscopic structure called juxta glomerular apparatus (JGA) between an afferent arteriole and distal convoluted tubule of the same nephron that is required for the maintenance of uniform Glomerular Filtration Rate (GFR). Whenever there is a fall in GFR, cells of juxta glomerular apparatus release a hormone called renin which travels into the bloodstream of glomerulus where it converts angiotensinogen into angiotensin I. Angiotensin I further gets converted to angiotensin II. Angiotensin helps in constriction of smooth muscle cells of the blood vessel that increases the blood pressure. Increased blood pressure results in an increase in glomerular filtration rate. Angiotensin also stimulates the secretion of aldosterone from adrenal glands. Aldosterone increases the absorption of sodium ions and water which increases blood pressure and brings the GFR back to normal. Thus, juxta glomerular apparatus plays a complex regulatory role in the functioning of the kidney.
Q11. 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.
Solution: (a) Amphioxus
(b) Columns of Bertini
(c) Vasa recta
Q12. 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.
Solution:(a) Ascending limb of Henle’s loop is impermeable to water whereas the descending limb is permeable to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone antidiuretic hormone or vasopressin.
(c) Dialysis fluid contains all the constituents as in plasma except the nitrogenous waste.
(d) A healthy adult human excretes (on an average) 25-30 gm of urea/day.
More Resources of NCERT Solutions for Class 11 Biology
NCERT Solutions for Class 11 Biology Chapter 16 – FAQs
1. What are the main excretory products in humans and how are they formed?
The main excretory products in humans are urea, uric acid, ammonia, carbon dioxide, water, and ions. Urea is formed in the liver through the ornithine cycle (urea cycle) from ammonia, which is produced during amino acid metabolism. Carbon dioxide is produced during cellular respiration, while excess water and ions are regulated by the kidneys.
2. What is the difference between excretion and egestion?
Excretion is the removal of metabolic waste products generated inside the cells during various biochemical reactions (like urea, CO₂, excess water). Egestion is the elimination of undigested food material that was never absorbed into the body cells. Excretion occurs through kidneys, lungs, and skin, while egestion occurs through the anus.
3. How does the kidney maintain homeostasis in the body?
The kidneys maintain homeostasis by: (i) regulating the volume and composition of body fluids, (ii) removing metabolic wastes like urea and uric acid, (iii) maintaining electrolyte balance (Na⁺, K⁺, Ca²⁺, Cl⁻), (iv) regulating blood pH by controlling H⁺ and HCO₃⁻ ions, (v) controlling blood pressure through the renin-angiotensin system, and (vi) producing hormones like erythropoietin and calcitriol.