NCERT Solutions for Class 11 Biology Chapter 16 Excretory Products and their Elimination

NCERT
SOLUTIONS
CLASS - 11th

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Class : 11th
Subject : Biology
Chapter : 19
Chapter Name : Excretory Products And Their Elimination

Q1 De ne Glomerular Filtration Rate (GFR).

Answer. Glomerular ltration rate is the amount of glomerular ltrate formed in all the nephrons
of both the kidneys per minute. In a healthy individual, it is about 125 ml/minute. Glomerular
ltrate contains glucose, amino acids, sodium, potassium, urea, uric acid, ketone bodies, and large
amounts of water.

Q2 Explain the autoregulatory mechanism of GFR.

Answer. The mechanism by which the kidney regulates the glomerular ltration rate is
autoregulative. It is carried out by the juxtaglomerular apparatus. Juxtaglomerular apparatus is a
microscopic structure located between the vascular pole of the renal corpuscle and the returning
distal convoluted tubule of the same nephron.
It plays a role in regulating the renal blood ow and glomerular ltration rate. When there is a fall
in the glomerular ltration rate, it activates the juxtaglomerular cells to release renin. This
stimulates the glomerular blood ow, thereby bringing the GFR back to normal. Renin brings the
GFR back to normal by the activation of the renin- angiotensin mechanism.

Q3 Indicate whether the following statements are true or false:
(a) Micturition is carried out by a re ex.
(b) ADH helps in water elimination, making the urine hypotonic.
(c) Protein-free uid is ltered 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.

Answer. (a) True
(b) False
(c) True
(d) True
(e) True

Q4 Give a brief account of the counter current mechanism.

Answer. The counter current mechanism operating inside the kidney is the main adaptation for
the conservation of water. There are two counter current mechanisms inside the kidneys. They are
Henle's loop and vasa rectae. Henle's loop is a IJ- shaped part of the nephron. Blood ows in the
two limbs of the tube in opposite directions and this gives rise to counter currents. The Vasa recta
is an efferent arteriole, which forms a capillary network around the tubules inside the renal
medulla. It runs parallel to Henley's loop and is U-shaped. Blood ows in opposite directions in
the two limbs of vasa recta. As a result, blood entering the renal medulla in the descending limb
comes in close contact with the outgoing blood in the ascending limb.

The osmolarity increases from 300 mOsmol/L in the cortex to 1200 mOsmol/L in the inner medulla
by counter current mechanism. It helps in maintaining the concentration gradient, which in turn
helps in easy movement of water from collecting tubules. The gradient is a result of the movement
of NaCl and urea.

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

Answer. Liver, lungs, and skin also play an important role in the process of excretion. Role of the
liver: Liver is the largest gland in vertebrates. It helps in the excretion of cholesterol, steroid
hormones, vitamins, drugs, and other waste materials through bile. Urea is formed in the liver by
the ornithine cycle. Ammonia — a toxic substance — is quickly changed into urea in the liver and
thence eliminated from the body. Liver also changes the decomposed haemoglobin pigment into
bile pigments called bilirubin and biliverdin.
Role of the lungs:
Lungs help in the removing waste materials such as carbon dioxide from the body. Role of the
skin:
Skin has many glands which help in excreting waste products through pores. It has two types of

glands — sweat and sebaceous glands.
Sweat glands are highly vascular and tubular glands that separate the waste products from the
blood and excrete them in the form of sweat. Sweat excretes excess salt and water from the body.
Sebaceous glands are branched glands that secrete an oily secretion called sebum.

Q6 Explain micturition.

Answer. Micturition is the process by which the urine from the urinary bladder is excreted. As the
urine accumulates, the muscular walls of the bladder expand. The walls stimulate the sensory
nerves in the bladder, setting up a re ex action. This re ex stimulates the urge to pass out urine.
To discharge urine, the urethral sphincter relaxes and the smooth muscles of the bladder contract.
This forces the urine out from the bladder. An adult human excretes about 1 — 1.5 litres of urine
per day.

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

Answer.

Q8 What is meant by the term osmoregulation?

Answer. Osmoregulation is a homeostatic mechanism that regulates the optimum temperature of
water and salts in the tissues and body uids. It maintains the internal environment of the body by
water and ionic concentration.

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

Answer. Terrestrial animals are either ureotelic or uricotelic, and not ammonotelic. This is because
of the following two main reasons:
(a) Ammonia is highly toxic in nature. Therefore, it needs to be converted into a less toxic form
such as urea or uric acid.
(b) Terrestrial animals need to conserve water. Since ammonia is soluble in water, it cannot be
eliminated continuously. Hence, it is converted into urea or uric acid. These forms are less toxic
and also insoluble in water. This helps terrestrial animals conserve water.

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Q10 What is the signi cance of juxtaglomerular apparatus (JGA) in kidney function?

Answer. Juxtaglomerular apparatus (JGA) is a complex structure made up of a few cells of
glomerulus, distal tubule, and afferent and efferent arterioles. It is located in a specialised region
of a nephron, wherein the afferent arteriole and the distal convoluted tubule (DLT) come in direct
contact with each other. The juxtaglomerular apparatus contains specialised cells of the afferent
arteriole known as juxtaglomerular cells. These cells contain the enzyme renin that can sense
blood pressure. When glomerular blood ow (or glomerular blood pressure or glomerular ltration
rate) decreases, it activates juxtaglomerular cells to release renin.
Renin converts the angiotensinogen in blood into angiotensin I and further into angiotensin II.
Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and
ltration rate. Angiotensin II also stimulates the adrenal cortex of the adrenal gland to produce
aldosterone. Aldosterone increases the rate of absorption of sodium ions and water from the distal
convoluted tubule and the collecting duct. This also leads to an increase in blood pressure and
glomerular ltration rate. This mechanism, known as renin-angiotensin mechanism, ultimately
leads to an increased blood pressure.

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Q11 Name the following:
(a) A chordate animal having ame 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.

Answer. (a) Amphioxus is an example of a chordate that has ame cells as excretory structures.
Flame cell is a type of excretory and osmoregulatory system.
(b) The cortical portions projecting between the medullary pyramids in the human kidney are the
columns of Bertini. They represent the cortical tissues present within the medulla.
(c) A loop of capillary that runs parallel to Henle's loop is known as vasa rectae. Vasa rectae, along
with Henle's loop, helps in maintaining a concentration gradient in the medullary interstitium.

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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 uid contains all the constituents as in plasma except_____.
(d) A healthy adult human excretes (on an average) gm ______ of urea/day.

Answer. (a) Ascending limb of Henle's loop is impermeable to water, whereas the descending
permeable limb is to it.
(b) Reabsorption of water from distal parts of the tubules is facilitated by the hormone
vasopressin.
(c) Dialysis uid contains all the constituents as in plasma, except the nitrogenous wastes.
(d) A healthy adult human excretes (on an average) 25-30 gm of urea/day.

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