NCERT Solutions for Class 11 Biology Chapter 16 Excretory Products and Their Elimination (original) (raw)

Last Updated : 18 May, 2023

**NCERT Solutions for class 11 Biology Chapter-16: Excretory Products and their Elimination: The chapter on **Excretory Products and their Elimination is important for students approaching the board exams. This article introduces NCERT solutions designed to help students explain the concepts of further learning and how to write to get good grades on exams. The solutions are presented in very simple language for ease of understanding.

NCERT CBSE Chapter 16 **Excretory Products and their Elimination of Class 11 Biology discusses the concept of excretion and explains the excretory functions of the skin, liver, large intestine, lungs, and kidneys. It also describes the other organs of the urinary system and several urinary system disorders. Revise the basic concepts of **Excretory Products and their Elimination for quick revision and class notes.

Q1: Define Glomerular Filtration Rate (GFR).

**Answer:

Glomerular filtration rate (GFR) represents the flow of plasma from the glomerulus into Bowman’s space over a specified period and is the chief measure of kidney function. GFR in a healthy individual is approximately 125 ml/minute, i.e.,180 litres per day.

Q2: Explain the autoregulatory mechanism of GFR.

**Answer:

Autoregulation is a fundamental component of renal function. The kidneys have built-in mechanisms for the regulation of glomerular filtration rate. It is mediated by juxtaglomerular apparatus. Juxtaglomerular apparatus 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 activates the Juxtaglomerular cells. It leads to the release of renin, which stimulates the glomerular blood flow and thereby the GFR returns back to normal.

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

Answer:

• a)True.
• b)False. ADH facilitates water reabsorption from nephrons, thereby preventing diuresis and producing hypertonic urine.
• c)True.
• d)True.
• e)True.

Q4: Give a brief account of the counter-current mechanism.

**Answer:

The mechanism used by the kidneys to concentrate urine is called the counter current mechanism.

• The Henle’s loop and vasa recta play a significant role in this. The flow of filtrate in the two limbs of Henle’s loop is in opposite directions and thus forms a counter current. The flow of blood through the two limbs of vasa recta is also in a counter current pattern.
• The 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 mOsmolL–1 in the cortex to about 1200 mOsmolL–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 portion 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.
• The above described transport of substances facilitated by the special arrangement of Henle’s loop and vasa recta is called the counter-current mechanism.

Q5: Describe the role of the liver, lungs, and skin in excretion.

**Answer:

• **Liver: The liver is the principal organ for the excretion of cholesterol, bile pigments (bilirubin and biliverdin), inactivated products or steroid hormones, drugs, and excess vitamins. These substances are carried by the bile to the intestine and are eliminated with feces.
• **Lungs: Lungs help in the elimination of CO2 produced in the body. Some moisture and some volatile materials are also lost during expiration.
• **Skin: Skin excretes salt, urea, water, amino acids, traces of lactic acid, CO2, etc. through sweat glands. Skin also excretes wax, sterols, fatty acids, and certain hydrocarbons through sebaceous glands.

Q6: Explain micturition.

**Answer:

The process of emptying urine from the storage organ, the urinary bladder is called Micturition.

Urine formed by the nephrons is ultimately carried to the urinary bladder where it is stored. The bladder normally accommodates up to 300-400 ml in adults. When the bladder is distended it sends signals to the brain, which is perceived as the 'full bladder' sensation. This 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. The process of release of urine is called micturition and the neural mechanisms causing it is called the micturition reflex.

Q7: Match the items of column I with those of column II:

**Answer:

Q8: What is meant by the term osmoregulation?

**Answer:

The process of regulating water potential in order to keep fluid and electrolyte balance within a cell or organism relative to the surrounding is known as Osmoregulation. An example employed by organisms is excretion, such as getting rid of metabolic wastes and other substances toxic to the body when they are in large amounts.

Q9: Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?

**Answer:

Terrestrial animals are generally either ureotelic or uricotelic because:

• Ammonia produced by metabolism is converted into urea in the liver of terrestrial animals and released into the blood which is filtered and excreted out by the kidneys.
• Ammonia is highly toxic in nature. Therefore, it needs to be converted into a less toxic form such as urea or uric acid.

Q10: What is the significance of the juxta glomerular apparatus (JGA) in kidney function?

**Answer:

The juxtaglomerular apparatus functions to maintain blood pressure and acts as a quality control mechanism to ensure proper glomerular flow rate and efficient sodium reabsorption.

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 Henle’s loop.

**Answer:

• a) **Amphioxus is an example of a chordate that has flame cells as excretory structures.
• b) The cortical portions projecting between the medullary pyramids in the human kidney are the **columns of Bertini.
• c) A loop of the capillary that runs parallel to Henle’s loop is known as the **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 the hormone __________.
• (c) Dialysis fluid contain all the constituents as in plasma except _________
• (d) A healthy adult human excretes (on average) ____ gm of urea/day.

**Answer:

• (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 the hormone Antidiuretic Hormone (ADH).
• (c) Dialysis fluid contain all the constituents as in plasma except nitrogenous waste.
• (d) A healthy adult human excretes (on average) 25-30 gm of urea/day.