NCERT MOST IMPORTANT QUESTIONS CLASS – 11 | BIOLOGY IMPORTANT QUESTIONS | CHAPTER -19 | EXCRETORY PRODUCTS AND THEIR ELIMINATION | EDUGROWN |

In This Post we are  providing Chapter-19 EXCRETORY PRODUCTS AND THEIR ELIMINATION NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS  can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.

NCERT MOST IMPORTANT QUESTIONS ON EXCRETORY PRODUCTS AND THEIR ELIMINATION

Question 1.
State the importance of counter-current systems in renal functioning.

Answer:
Vasa rectal is responsible for the concentration of urine. The vase rectal is in the form of loops. Therefore, the blood flows in the opposite directions in two limbs of each vasa Fecta; the blood entering its descending limb comes into close contact with the outgoing blood in the ascending limb. This is called a Counter-Current System. The two limbs of the loops of Henle form another Counter-Current System.

Importance: The counter-current system significantly contributes to concentrating urine in mammals.

Question 2.
Describe the hormonal feedback circuits in controlling renal functions.

Answer:
Two important hormonal control of the kidney function by negative feedback circuits can be identified:
1. Control by Antidiuretic Hormone ADH: ADH produced in the hypothalamus of the brain and released into the blood from the pituitary gland, enhances fluid retention by making the kidneys reabsorb more water. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood.

The osmoreceptors cells also promote thirst. Drinking reduces the osmolarity of the blood which inhibits the secretion of ADB, thereby completing the feedback circuit.

2. Control by Juxtaglomerular Apparatus (JGH): It operates a multihormonal Renin-Angiotensin-Aldosterone System (RAAS). JGA responds to decrease the blood pressure and release enzyme renin into the blood. In the blood, the enzyme initiates chemical reactions that convert a plasma protein called angiotensinogen to a peptide called angiotensin II which works as a hormone.

Angiotensin II increases blood pressure and stimulates the adrenal gland to release aldosterone, a hormone. This leads to an increase in blood volume and pressure completing the feed¬back circuit by supporting the release of renin.

Still another hormone, a peptide called Atrial Natriuretic Factor ANF), opposes the regulation by RAAS.

Thus, ADH, the RAAS, and ANF provide an elaborate system of checks and balance that regulate the kidney functioning to control body fluid, osmolarity, salt concentration, blood pressure, and blood volume.

Question 3.
State the normal and abnormal constituents of human urine.

Answer:
Urine is a pale yellow colored slightly acidic watery fluid.

• Abnormal Urine: Various metabolic errors of kidney malfunctioning changes the composition of urine.
• Proteinuria: Excess of protein level.
• Albuminuria: The presence of albumin, usually occurs in nephritis.
• Glycosuria: Presence of glucose in urea as in case of diabetes mellitus.
• Ketonuria: Presence of abnormally high ketone bodies.
• Hematuria: Presence of blood or blood cells in urine.
• hemoglobinuria: Presence of hemoglobin in urine.
• Uremia: Presence of excess urea.
• Normal Urine: Normal urine is slightly heavier than water. It gives an aromatic odor due to the presence of volatile, bad-smelling organic substances, the ruined water, organic and inorganic materials are the main constituents of normal urine.

The other nitrogenous constituents of normal urine are ammonia, uric acid, hippuric acid, and creatinine.

Non-nitrogenous substances are vitamin C, oxalic acid, phenolic substances. In inorganic substances, sodium chloride is the principal mineral salt in the urine.

Question 4.
State the role of skin and lungs in excretion.

Answer:
Role of Skin: Human skin possesses glands for secreting sweat and sebum (from the sebaceous gland). Sweat contains NaCl, lactic acid, urea, amino acids, and glucose. The volume of sweat various negligible to 14 L a day. The principal function of sweat is the evaporative cooling of the body surface.

Sebum is a waxy protective secretion to keep the skin oily and this secretion eliminates some lipids, such as waxes, sterols, other hydrocarbons, and fatty acids. Integument in many animals is excreting ammonia into the surrounding by diffusion.

Role of lungs in excretion: Human lungs eliminate around 18L of CO₂ per day and about 400 ml of water in normal resting conditions. Water loss via lungs is small in hot humid climates and large in cold dry climates. The rate of ventilation and ventilation pattern also affects the water loss through the lungs. Different volatile materials are also readily eliminated through the lungs.

Question 5.
Briefly state the mechanism of urine formation in the human kidney.

Answer:
Three main processes are involved in urine formation
1. Glomerular filtration: Kidneys filter the equivalent of blood volume every 4 – 5 minutes. Filtration slits are formed by the assemblages of fine cellular processes of podocytes (foot cells). The process of ultra-filtration depends upon two main factors, first the net hydrostatic pressure difference between the lumen of the capillary and the lumen of the Bowman’s capsule favor filtration.

The glomerular ultrafiltrate contains essentially all the constituents of the blood except for blood corpuscles and plasma proteins. Nearly 15% – 25% of the water and salutes are removed from the plasma that flows through the glomerulus. The glomerular filtration rate is about 125 ml min1 or about 180 L day^-1 in human kidneys.

2. Two important intrinsic mechanisms provide autoregulation of glomerular filtration rate.
(a) Myogenic mechanism: Increase in blood pressure will tend to stretch the efferent arteriole, which would increase the blood flow to the glomerulus. The diameter of the arteriole is reduced, increasing the resistance to flow. This myogenic mechanism thus reduced variations inflow to the glomerulus in case of fluctuations in blood pressure.

(b) Juxtaglomerular apparatus (JGA): This specialized cellular apparatus is located where the distal convoluted tubule passes close to the Bowman’s capsule between the afferent and efferent arterioles. JGA cells secrete substances like renin that modulate blood pressure and renal blood flow and GFR are regulated.

Myogenic and juxtaglomerular mechanisms work together to autoregulate the GFR over a wide range of blood pressure. In addition to these extrinsic neural control also regulates the filtration rate.

3. Tubular re-absorption: The selective transport of substances across the epithelium of the excretory tubule from the ultrafiltrate to the interstitial fluid is called re-absorption. Nearly all the sugar, vitamins, organic substances (nutrients), and most of the water are reabsorbed.

4. Tubular secretion: It is a very selective process involving both passive and active transport. The filtrate travel through the nephron, substances that are transported across the epithelium from the surrounding interstitial fluid and join it. The net effect of renal secretion is the addition of plasma solutes to the filtrate within the tubule.

Question 6.
Explain the following:
(a) Skin functions as an accessory excretory organ.

Answer:
The skin retains some excretory role in many animals. Human skin possesses two glands for secreting fluid on its surface. These are; sweat from sweat glands and sebum from sebaceous glands.

(b) Mammals can eliminate hypotonic and hypertonic urine according to body needs.
Answer:
When the animal takes a large quantity of water the kidneys excrete a very high amount of hypotonic urine. At the same time when the animal takes a small number of water kidneys to excrete a very high amount of hypertonic urine.

At the same time when the animal takes a small number of water kidneys to excrete a small amount of hypertonic urine, as kidneys need to conserve water. In this way, the osmotic concentration of blood is maintained by the kidneys. This flexibility of kidney nephrons is highly observed in mammals.

Hypotonic urine removes excess water from the body in order to raise the osmotic concentration of the blood to normal. Excess of water in body fluids generally lowers the osmotic pressure of blood and increases the volume of blood. This increase in the volume of blood raises the blood pressure and hydrostatic pressure which increases the rate of ultrafiltration. In this way, a large amount of hypotonic urine is produced in order to bring the volume of fluids to normal.

(c) Micturition is a reflex process but is under some voluntary control.
Answer:
It is the process of passing out urine. Nephrons produce urine and drain. When enough urine collects in the bladder the distension of its walls raises enough pressure which generates a spontaneous nervous activity under the stimulation of the sympathetic and parasympathetic nervous system. This nervous stimulation causes the smooth muscles on the urinary bladder to rise too high to control.

Similarly, micturition can voluntarily be initiated even before enough urine has accumulated in the bladder. Backflow of the urine into the ureters from the urinary bladder is prevented because the terminal part of each ureter passes through the bladder and gets closed as soon as the contraction of the bladder occurs.

(d) Mammals are ureotelic, but birds are uricotelic.
Answer:
Mammals are ureotelic animals as they eliminate nitrogen mainly urea. It is very soluble in water and needs a considerable amount of water for its elimination. Mammals can thus form hypertonic urine which they excrete. While the birds cannot excrete urine as hypertonic since nitrogen occurs mainly in the form of uric acid. The uric acid is insoluble in water and does not require much water for its elimination.

Question 7.
Describe the functional anatomy of a human nephron.

Answer:
Nephrons are structural and functional units of each kidney to form the urine. Each nephron is fine; microscopic highly coiled tubular structure differentiated into malpighian body and the renal tubule. The malpighian body comprises a large double-walled cup-shaped structure the Bowman’s capsule present in the renal cortex. It is lined by thin, semipermeable epithelial cells, the podocytes. Bowman’s capsule receives the blood supply through a branch of the renal artery.

The afferent arteriole forms a fine capillary network in the form of glomerules with high hydrostatic pressure. The lumen between two layers of Bowman’s capsule is continuous with the lumen of the tubule. The Bowman’s capsule and the glomerulus together form a globular body, the Malpighian body or the renal capsules.

The capillaries forming the glomerulus at the exit of Bowman’s capsule unite to form a narrow efferent arteriole which breaks up into a peritubular network of capillaries with low hydrostatic pressure.

The renal tubule is a long highly coiled tubular structure differentiated into proximal convoluted tubule (PCT) Henle’s loop, distal convoluted tubule (DCT). The U-shaped loop-like structure, descending and ascending from the renal tubule is called Henle’s loop.

Collecting tubules of several nephrons open into a wider duct called the collecting duct. A number of collecting ducts unite with each other in the medulla to form the ducts of Bellini, which drains down the urine into the ureter from each kidney to be stored in the urinary bladder.

The efferent arteriole emerges out from the glomerules breaks up into a peritubular capillary network around the renal tubule in the cortex. These capillaries also form a thin-walled, straight capillary the vasa recta. The vasa recta help in retaining the reabsorbed ions and urea in medullary interstitial fluid to maintain high osmotic pressure in kidneys.

Glomerular filtrate undergoes tubular reabsorption and tubular secretion for the formation of urine. (See diagram opposite page)

Uriniferous tubules Or nephron of the kidney

Question 8.
Describe the gross anatomical features of the human kidney with a suitable diagram.

Answer:
Kidney: Kidney is chocolate brown, bean-shaped, large-sized about 10 cm long and 5 – 7 cm broad, 3 – 4cm thick flattened, metamorphic. The weight of each kidney is 150 to 170 gm. They are situated against the back wall of the abdominal cavity, just below the diaphragm, between the 12th thoracic and 3rd lumbar vertebrae.

The outer margin is convex. The inner concave presents a longitudinal opening called the hilum. The renal artery and renal vein respectively enter and leave the kidney through its hilum.

The two kidneys are slightly asymmetrical in position because the right kidney is slightly at a lower level than the left. Kidneys are held in position by a mass of adipose tissue called Renal fat. These rest against the abdominal muscles. Each kidney is covered on the ventral side by the peritoneum and is thus retroperitoneal in nature.

Surrounding the kidneys and the renal fat is a sheath of fibro elastic tissue known as renal fascia or capsule. They protect the kidney. The renal fat forms a shock-absorbing cushion. The renal fascia fixes the kidney to the abdominal wall.

Longitudinal section (Diagrammatic of Kidney)

Question 9.
(a)What is the role of the liver in excretion in mammals?

Answer:
Role of liver in excretion: The liver changes ammonia into urea which is less toxic than ammonia. Urea is eliminated from the body by the kidneys through urine.

The liver is the principal organ of excretion of cholesterol, bile pigments (bilirubin and biliverdin) some vitamins, drugs, and inactivated products of steroid hormones. The liver excretes these substances in the bile which carries them to the small intestine. Ultimately, these substances get eliminated along with feces.

(b) What are the diseases associated with the urinary system?
Answer:
Diseases associated with the urinary system:
1. Polynephritis: It is a bacterial infection, which causes inflammation of renal pelvic nephrons and medullary tissues of the kidney. It affects the counter-current mechanism. Its main symptoms are frequent and painful urination, fever, and pain in the lumbar region.

2. Uremia: It causes the presence of a high concentration of urea, uric acid, creatinine, etc, in the blood due to some bacterial infection or some obstruction in the passage of the urinary system. Urea poisons the cells. It is not passed in the urine and accumulates in the blood.

3. Renal stones: When uric acid precipitates and accumulates in the nephrons of kidneys in the form of renal stones or when calcium phosphates and oxalates accumulate in the nephrons of the kidneys in the form of renal stones. It causes blockage or frequent painful urination along with blood in the urine. Renal stone causes severe colic pain starting in the back and radiating down to the front of the thigh or vulva or testicle on that side.

4. Glomerulonephritis: It is characterized by the inflammation of Glomeruliduct, some injury to the kidney, abnormal allergic reaction, or by some streptococci bacteria infection. Proteins and red blood corpuscles become filtered into the glomerular filtrate. It may lead to kidney failure in severe infection.

5. Oedema: It is characterized by the increased volume of interstitial fluid mainly caused by retention of excess Na+ ions which in turn causes water retention. Blood pressure increases dining edema.

Question 10.
Write a short account on hemodialysis.

Answer:
In case of renal failure, an artificial kidney is used for removing excess urea from the blood of the patient by a process called hemodialysis. Blood is taken out from the artery of the patient, cooled to 0°C, mixed with an anticoagulant such as heparin, and then pumped into the apparatus called artificial kidney. In this apparatus, blood flows through channels

Working of artificial kidneys for hemodialysis

bounded by cellophane membrane. The membrane is impermeable to macromolecules but permeable to small solutes. The membrane separates the blood flowing inside the channels from a dialyzing fluid flowing outside the membrane. The wastes like urea, uric acid, and creatinine diffuse from the blood to the dialyzing fluid across the cellophane membrane.

Thus the blood is considerably cleared of nitrogenous waste products without losing plasma proteins. Such a processor separation of macromolecules from small solute particles with the help of a permeable membrane is called dialysis. The blood coming out of the artificial kidney is warmed to body temperature, mixed with an Antiheparin to restore its normal coagulability, and returned to a vein of the patient.

Hemodialysis saves and prolongs the life of many uremic patients.