Biology Class 11 NCERT Solutions: Chapter 19 Excretory Products and Their Elimination Part 1 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q: 1. Define Glomerular Filtration Rate (GFR)


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

Q: 2. Explain the auto regulatory mechanism of GFR.


The mechanism by which the kidney regulates the glomerular filtration rate is auto regulative. 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 flow and glomerular filtration rate. When there is a fall in the glomerular filtration rate, it activates the juxtaglomerular cells to release renin. This stimulates the glomerular blood flow, thereby bringing the GFR back to normal. Renin brings the GFR back to normal by the activation of the renin-angiotensin mechanism.

The Glomerular Filtration Rate

Q: 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 Bowmans capsule.

(D) Henles loop plays an important role in concentrating the urine.

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


(A) True

(B) False

(C) True

(D) True

(E) True

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


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 U-shaped part of the nephron. Blood flows 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 flows 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.

Q_4_Vasa Rectae and Henle՚s Loop

The osmolality increases from in the cortex to 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 and urea.

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


Liver, lungs, and skin also play an important role in the process of excretion.

The Human Excretory System

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 then 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.

Q: 6. Explain micturition.


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 reflex action. This reflex 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 of urine per day

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