Excretory Products and Their Elimination — Class 11 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 11 Biology chapter "Excretory Products and Their Elimination" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 11 Biology chapter "Excretory Products and Their Elimination" — 8 important questions with detailed answer…
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NCERT Solutions for Class 11 Biology — Excretory Products and Their Elimination. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Excretory Products and Their Elimination — All 8 Questions Solved
Q1. Define excretion. Why is it necessary for living organisms?
Excretion is the process of removing metabolic waste products from the body. It is necessary because:
- Prevents accumulation of toxic waste like urea, uric acid, and CO2
- Maintains internal osmotic balance and pH
- Prevents damage to cells and tissues
- Helps maintain homeostasis
Q2. Name the main nitrogenous wastes in humans and their sources.
Main nitrogenous wastes:
- Urea: formed from breakdown of amino acids and proteins in liver; most common in humans
- Uric acid: end product of nucleic acid metabolism; requires water for excretion
- Ammonia: toxic, produced during amino acid catabolism; converted to urea in liver
Q3. Draw and label a nephron. What are its main parts?
Main parts of nephron:
- Renal corpuscle: Bowman's capsule + glomerulus (filtration)
- Proximal convoluted tubule: selective reabsorption of glucose, amino acids, ions
- Loop of Henle: creates concentration gradient for water reabsorption
- Distal convoluted tubule: fine-tuning of reabsorption
- Collecting duct: final concentration of urine, water reabsorption via ADH
Q4. Explain the three processes involved in urine formation.
Three-stage process:
- Ultrafiltration: in Bowman's capsule; high blood pressure forces small molecules (glucose, urea, ions, water) through glomerular filtration barrier; large proteins and RBCs remain in blood
- Selective reabsorption: useful substances reabsorbed in PCT (glucose, amino acids, 80% ions, 85% water)
- Tubular secretion: additional wastes secreted from blood into tubule lumen for concentration; occurs in DCT and collecting duct
Q5. What is the role of ADH and aldosterone in osmoregulation?
ADH (antidiuretic hormone):
- Released by pituitary when blood osmotic pressure increases
- Increases permeability of collecting duct to water
- More water reabsorbed, concentrated urine formed
Aldosterone:
- Secreted by adrenal cortex
- Increases reabsorption of Na+ and water
- Maintains blood pressure and Na+ balance
Q6. What is the difference between a pyramid of energy and a pyramid of biomass?
Energy pyramid:
- Always upright; each trophic level has less energy than the one below
- Energy loss at each transfer (~10% rule)
- Cannot be inverted
Biomass pyramid:
- Usually upright but can be inverted
- In aquatic ecosystems, small algae support large zooplankton
- Biomass does not directly relate to energy content
Q7. What is glomerular filtration? State conditions necessary for it.
Glomerular filtration is ultrafiltration of blood in Bowman's capsule forming filtrate.
Necessary conditions:
- High hydrostatic pressure in glomerulus (from afferent arteriole)
- Large surface area of capillaries and podocytes
- High permeability of filtration membrane
- Pressure difference favoring filtration
Q8. How is urea concentration higher in the urine than in the blood?
Mechanism of urea concentration:
- Urea undergoes both filtration and some reabsorption
- Water is reabsorbed significantly more than urea in collecting duct
- As water is removed, urea concentration increases
- Final urine has 300-500 times more urea than blood
- This concentration effect is due to selective water reabsorption
Excretory Products and Their Elimination — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the primary nitrogenous waste product in humans?
- A. Ammonia
- B. Urea
- C. Uric acid
- D. Creatinine
Answer: B. Urea — Humans are ureotelic organisms, meaning they primarily excrete urea as their nitrogenous waste product, which is less toxic than ammonia.
MCQ 2. Flame cells are the excretory structures in which of the following organisms?
- A. Earthworm
- B. Cockroach
- C. Flatworm
- D. Prawn
Answer: C. Flatworm — Flame cells (protonephridia) are specialized excretory cells found in platyhelminthes like flatworms, helping in osmoregulation and excretion.
MCQ 3. Which part of the nephron is impermeable to water but permeable to electrolytes in its ascending limb?
- A. Proximal Convoluted Tubule
- B. Descending limb of Henle's loop
- C. Ascending limb of Henle's loop
- D. Distal Convoluted Tubule
Answer: C. Ascending limb of Henle's loop — The ascending limb of the loop of Henle is characterized by its impermeability to water and active transport of electrolytes, which is crucial for establishing the medullary osmotic gradient.
MCQ 4. A decrease in blood pressure or blood volume triggers the release of which hormone from the Juxta Glomerular Apparatus?
- A. Aldosterone
- B. ADH
- C. Renin
- D. Angiotensin II
Answer: C. Renin — Renin is secreted by the JG cells in response to a fall in GFR, blood pressure, or blood volume, initiating the Renin-Angiotensin-Aldosterone System (RAAS) to restore blood pressure.
MCQ 5. Which of the following substances is completely reabsorbed in a healthy kidney and is typically absent in urine?
- A. Urea
- B. Creatinine
- C. Glucose
- D. Uric acid
Answer: C. Glucose — In a healthy individual, glucose is completely reabsorbed in the PCT and is normally absent in urine. Its presence indicates conditions like diabetes mellitus.
MCQ 6. The counter-current mechanism operates between which two structures in the kidney?
- A. Bowman's capsule and Glomerulus
- B. PCT and DCT
- C. Henle's loop and Vasa recta
- D. Renal artery and Renal vein
Answer: C. Henle's loop and Vasa recta — The counter-current mechanism involves the interaction between the Henle's loop and the vasa recta, which helps in maintaining the medullary interstitial osmotic gradient, crucial for concentrating urine.
MCQ 7. Which enzyme converts angiotensinogen into angiotensin I?
- A. Renin
- B. Aldosterone
- C. ACE (Angiotensin-Converting Enzyme)
- D. ADH
Answer: A. Renin — Renin, secreted by the JG apparatus, acts on angiotensinogen (a plasma protein) to convert it into angiotensin I, which is then further processed into angiotensin II.
MCQ 8. The accumulation of urea in the blood, a condition known as uremia, is best treated by:
- A. Blood transfusion
- B. Dialysis
- C. Antihistamines
- D. Diuretics
Answer: B. Dialysis — Uremia is a serious condition where urea accumulates in the blood due to kidney failure. Hemodialysis is an artificial kidney procedure used to remove urea and other wastes from the blood.
MCQ 9. Which of the following organisms primarily excretes ammonia?
- A. Birds
- B. Mammals
- C. Marine fish
- D. Bony fish
Answer: D. Bony fish — Bony fish are ammonotelic, directly excreting highly toxic ammonia because it is readily soluble in water and can be easily flushed out of their body.
MCQ 10. The cortical region of the kidney extends into the medulla as renal columns called:
- A. Renal pyramids
- B. Renal papillae
- C. Columns of Bertini
- D. Calyces
Answer: C. Columns of Bertini — The renal cortex extends between the medullary pyramids as renal columns, also known as Columns of Bertini.
MCQ 11. Which of the following is actively secreted into the renal tubule to maintain ionic and acid-base balance of the body fluids?
- A. Glucose
- B. Amino acids
- C. K+ ions
- D. Water
Answer: C. K+ ions — Tubular secretion involves the active transport of substances like K+, H+, and ammonia into the filtrate, playing a critical role in acid-base balance and maintaining ion concentrations.
MCQ 12. The Glomerular Filtration Rate (GFR) in a healthy individual is approximately:
- A. 125 ml/minute
- B. 180 ml/day
- C. 1.5 litres/day
- D. 125 ml/hour
Answer: A. 125 ml/minute — GFR is the amount of filtrate formed by the kidneys per minute, which is approximately 125 ml/minute or 180 litres per day in a healthy person.
MCQ 13. Besides kidneys, which organ plays a significant role in the excretion of carbon dioxide and water?
- A. Liver
- B. Skin
- C. Lungs
- D. Spleen
Answer: C. Lungs — Lungs are primary organs for gaseous exchange and play a crucial role in eliminating a large amount of carbon dioxide (about 18 litres/day) and also significant amounts of water.
MCQ 14. Which part of the nephron is responsible for the maximum reabsorption of essential nutrients and water?
- A. Bowman's capsule
- B. Loop of Henle
- C. Proximal Convoluted Tubule
- D. Distal Convoluted Tubule
Answer: C. Proximal Convoluted Tubule — The PCT is the site of maximum reabsorption, reabsorbing nearly all essential nutrients, 70-80% of electrolytes, and a large proportion of water.
MCQ 15. Atrial Natriuretic Factor (ANF) is released in response to:
- A. Low blood pressure
- B. High blood pressure
- C. Low blood volume
- D. High blood glucose
Answer: B. High blood pressure — ANF is released by the atrial wall of the heart in response to an increase in blood pressure. It acts as a check on the RAAS, causing vasodilation and decreasing Na+ reabsorption to lower blood pressure.
MCQ 16. Presence of blood in urine is medically termed as:
- A. Glycosuria
- B. Hematuria
- C. Ketonuria
- D. Pyuria
Answer: B. Hematuria — Hematuria refers to the presence of red blood cells (blood) in the urine, which can indicate various underlying medical conditions affecting the urinary tract.
MCQ 17. Which of the following substances is present in highest concentration in the urine of a healthy adult?
- A. Urea
- B. Creatinine
- C. Uric acid
- D. Sodium chloride
Answer: A. Urea — Urea is the primary nitrogenous waste product in humans and is present in the highest concentration among the listed excretory products in normal urine.
MCQ 18. The maximum reabsorption of water from the collecting duct is regulated by which hormone?
- A. Aldosterone
- B. Renin
- C. ADH
- D. Thyroxine
Answer: C. ADH — Antidiuretic Hormone (ADH) or Vasopressin increases the permeability of the collecting duct and DCT to water, thereby promoting water reabsorption and the formation of concentrated urine.
MCQ 19. Malpighian tubules are the excretory organs of:
- A. Molluscs
- B. Annelids
- C. Insects
- D. Crustaceans
Answer: C. Insects — Malpighian tubules are characteristic excretory and osmoregulatory organs found in insects and some other arthropods.
MCQ 20. The filtration membrane in the glomerulus consists of:
- A. Endothelium of glomerular blood vessels
- B. Basement membrane
- C. Epithelium of Bowman's capsule
- D. All of the above
Answer: D. All of the above — The filtration membrane (or glomerular filter) is formed by the fenestrated endothelium of glomerular capillaries, the basement membrane, and the podocytes (epithelium of Bowman's capsule).
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.