Excretory Products and their EliminationClass 11 Biology NCERT Solutions
12 Solutions
Generated by KedovoAI
Solution 1 of 12
Q1Exercises
Define Glomerular Filtration Rate (GFR)
Solution
Glomerular Filtration Rate (GFR) is defined as the amount of filtrate formed by the kidneys per minute. In a healthy individual, the GFR is approximately 125 ml/minute, which amounts to 180 litres per day.
Q2Exercises
Explain the autoregulatory mechanism of GFR.
Solution
The kidneys have an efficient built-in mechanism for the regulation of the glomerular filtration rate (GFR). This is carried out by the Juxta Glomerular Apparatus (JGA), which is a special sensitive region formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at their point of contact.
A fall in GFR can activate the juxtaglomerular (JG) cells to release an enzyme called renin. Renin converts a plasma protein, angiotensinogen, into angiotensin I, which is further converted to angiotensin II. Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure. It also stimulates the adrenal cortex to release aldosterone, which causes reabsorption of and water from the distal parts of the tubule. This combined effect increases blood volume and blood pressure, which in turn increases the glomerular blood flow and brings the GFR back to normal. This entire mechanism is known as the Renin-Angiotensin mechanism.
Q3Exercises
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. The process of release of urine is called micturition, and the neural mechanism causing it is called the micturition reflex.
(b) False. ADH (Antidiuretic Hormone) facilitates water reabsorption from the distal parts of the tubule, thereby preventing water loss (diuresis) and making the urine more concentrated (hypertonic).
(c) True. The filtration membrane allows almost all constituents of the plasma to pass into the Bowman's capsule, except for proteins. This process is known as ultrafiltration.
(d) True. The counter-current mechanism involving Henle's loop and vasa recta is responsible for creating a concentration gradient in the medullary interstitium, which helps in concentrating the urine.
(e) True. Nearly all essential nutrients, including glucose and amino acids, are actively reabsorbed in the Proximal Convoluted Tubule (PCT).
Q4Exercises
Give a brief account of the counter current mechanism.
Solution
The counter current mechanism is a process that helps mammals produce concentrated urine. It primarily involves the Henle's loop and the vasa recta.
-
Counter Current Flow: The flow of filtrate in the two limbs of Henle's loop is in opposite directions. Similarly, the flow of blood in the two limbs of the vasa recta is also in opposite directions (counter-current pattern).
-
Creation of Gradient: The ascending limb of Henle's loop actively transports NaCl into the medullary interstitium, making the interstitium hypertonic. This NaCl then enters the descending limb of the vasa recta.
-
Maintenance of Gradient: The ascending portion of the vasa recta returns the NaCl to the interstitium. Similarly, small amounts of urea move from the collecting duct into the medullary interstitium to maintain the high osmolarity. This special arrangement prevents the gradient from being washed away.
-
Concentration of Urine: This high osmolarity gradient in the interstitium (from 300 mOsmolL⁻¹ in the cortex to 1200 mOsmolL⁻¹ in the inner medulla) allows for the easy passage of water from the collecting tubule into the interstitium via osmosis, thereby concentrating the filtrate into urine.
Q5Exercises
Describe the role of liver, lungs and skin in excretion.
Solution
Besides the kidneys, other organs like the liver, lungs, and skin also play a role in eliminating excretory wastes.
-
Lungs: The lungs are the primary organs for the removal of carbon dioxide (), a major metabolic waste product. They excrete approximately 200 mL of per minute and also remove significant quantities of water in the form of water vapour during exhalation.
-
Liver: The liver, the largest gland in the body, secretes bile. Bile contains substances like bilirubin and biliverdin (breakdown products of haemoglobin), cholesterol, degraded steroid hormones, vitamins, and drugs. These substances are passed into the digestive tract and are ultimately eliminated along with the faeces.
-
Skin: The skin has two types of glands that contribute to excretion:
- Sweat Glands: These glands produce sweat, a watery fluid containing NaCl, small amounts of urea, and lactic acid. While the primary function of sweat is cooling, it also helps in the removal of these wastes.
- Sebaceous Glands: These glands secrete sebum, an oily substance that eliminates sterols, hydrocarbons, and waxes. Sebum also provides a protective oily covering for the skin.
Q6Exercises
Explain micturition.
Solution
Micturition is the process of releasing urine from the urinary bladder. It is controlled by a neural mechanism known as the micturition reflex.
The process involves the following steps:
- Urine formed by the nephrons is transported by the ureters to the urinary bladder, where it is stored.
- As the bladder fills with urine, it stretches. This stretching stimulates stretch receptors located on the walls of the bladder.
- These receptors send signals to the Central Nervous System (CNS).
- The CNS processes these signals and sends motor messages back to the bladder and urethral sphincter.
- These motor signals initiate the contraction of the smooth muscles of the bladder and, simultaneously, the relaxation of the urethral sphincter.
- This coordinated action causes the release of urine through the urethra. The process is ultimately under voluntary control, allowing an individual to consciously control the timing of urination.
Q7Exercises
Match the items of column I with those of column II : Column I (a) Ammonotelism (b) Bowman's capsule (c) Micturition (d) Uricotelism (e) ADH Column II
(i)
Birds
(ii)
Water reabsorption
(iii)
Bony fish
(iv)
Urinary bladder
(v)
Renal tubule
Solution
The correct matches are as follows:
- (a) Ammonotelism - (iii) Bony fish (Bony fishes excrete ammonia as their primary nitrogenous waste.)
- (b) Bowman's capsule - (v) Renal tubule (The renal tubule begins with the double-walled Bowman's capsule.)
- (c) Micturition - (iv) Urinary bladder (Micturition is the process of emptying the urinary bladder.)
- (d) Uricotelism - (i) Birds (Birds excrete uric acid as their primary nitrogenous waste.)
- (e) ADH - (ii) Water reabsorption (Antidiuretic Hormone facilitates the reabsorption of water from the tubules.)
Q8Exercises
What is meant by the term osmoregulation?
Solution
Osmoregulation is the biological process by which an organism maintains the constant osmotic pressure of its body fluids by regulating the water and salt concentrations. It is concerned with the maintenance of ionic and fluid volume balance within the body. In vertebrates, the kidneys are the primary organs responsible for osmoregulation.
Q9Exercises
Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why?
Solution
Terrestrial animals are generally not ammonotelic due to the high toxicity of ammonia and the large amount of water required for its elimination.
Ammonia, the primary nitrogenous waste in many aquatic animals, is highly toxic and must be diluted with a large volume of water to be excreted safely. This is feasible for aquatic organisms that live in a water-rich environment.
However, terrestrial animals live in environments where water conservation is crucial for survival. To conserve water, they convert the highly toxic ammonia into less toxic forms like urea (ureotelism) or uric acid (uricotelism). Urea is less toxic than ammonia and requires less water for its removal. Uric acid is the least toxic and can be excreted as a semi-solid paste or pellet with a minimum loss of water. This adaptation allows terrestrial animals to thrive in habitats with limited water availability.
Q10Exercises
What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Solution
The Juxta Glomerular Apparatus (JGA) has a significant role in regulating kidney function, particularly the Glomerular Filtration Rate (GFR). The JGA is a specialized structure located where the distal convoluted tubule comes into contact with the afferent arteriole.
Its primary significance is its role in the renin-angiotensin-aldosterone system. When there is a fall in glomerular blood flow, glomerular blood pressure, or GFR, the JG cells of the apparatus are activated to release an enzyme called renin. Renin initiates a cascade of reactions that leads to the formation of angiotensin II, which raises blood pressure and GFR by causing vasoconstriction and stimulating aldosterone secretion. Aldosterone promotes the reabsorption of sodium ions and water. This complex feedback mechanism helps to maintain the GFR at a relatively constant rate, ensuring normal kidney function.
Q11Exercises
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 (a cephalochordate)
(b) Columns of Bertini (or Renal columns)
(c) Vasa recta
Q12Exercises
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 ADH (Antidiuretic hormone).
(c) Dialysis fluid contain all the constituents as in plasma except nitrogenous wastes.
(d) A healthy adult human excretes (on an average) 25-30 gm of urea/day.