Excretory System & Homeostasis
Level 1: Recognition
Time: 20 minutes Total Marks: 30
Section A — Multiple Choice (choose ONE answer)
(1 mark each — 10 marks)
Q1. The functional unit of the kidney is the: a) Glomerulus b) Nephron c) Ureter d) Medulla
Q2. Ultrafiltration in the nephron occurs at the: a) Loop of Henle b) Collecting duct c) Bowman's capsule / glomerulus d) Distal tubule
Q3. Which substance is normally NOT found in glomerular filtrate of a healthy person? a) Glucose b) Urea c) Water d) Large plasma proteins
Q4. Most reabsorption of glucose and amino acids occurs in the: a) Proximal convoluted tubule b) Loop of Henle c) Bowman's capsule d) Collecting duct
Q5. ADH (antidiuretic hormone) increases water reabsorption by acting on the: a) Glomerulus b) Proximal tubule only c) Collecting duct and distal tubule d) Ureter
Q6. Aldosterone primarily regulates the reabsorption of: a) Glucose b) Sodium ions (Na⁺) c) Urea d) Proteins
Q7. The MOST toxic nitrogenous waste, requiring large amounts of water to excrete, is: a) Urea b) Uric acid c) Ammonia d) Creatinine
Q8. Nitrogenous waste is converted into urea mainly in the: a) Kidney b) Liver c) Spleen d) Pancreas
Q9. During overheating, the body cools itself by: a) Vasoconstriction of skin arterioles b) Shivering c) Sweating and vasodilation d) Erecting hairs
Q10. Osmoregulation is best defined as the control of the body's: a) Temperature b) Water and solute (osmotic) balance c) Blood pH only d) Blood glucose only
Section B — Matching
(1 mark each — 6 marks)
Q11. Match the structure/hormone in Column X to its function in Column Y.
| Column X | Column Y |
|---|---|
| (a) Loop of Henle | (i) Site of ultrafiltration |
| (b) Glomerulus | (ii) Creates salt gradient for water reabsorption |
| (c) ADH | (iii) Increases Na⁺ reabsorption |
| (d) Aldosterone | (iv) Deaminates amino acids / makes urea |
| (e) Liver | (v) Increases water permeability of collecting duct |
| (f) Uric acid | (vi) Nitrogenous waste of birds & insects |
Section C — True/False WITH Justification
(2 marks each: 1 for T/F, 1 for correct justification — 14 marks)
Q12. Filtration in the nephron is a selective process that excludes glucose but allows proteins through.
Q13. ADH is released when the blood is too dilute (low solute concentration).
Q14. Uric acid is excreted using very little water compared to ammonia.
Q15. The liver plays a role in homeostasis by regulating blood glucose levels.
Q16. Vasoconstriction of skin blood vessels helps conserve body heat in cold conditions.
Q17. Secretion in the nephron moves substances from the blood into the tubule.
Q18. Aldosterone directly increases urine volume by promoting water loss.
Answer keyMark scheme & solutions
Section A (1 mark each)
| Q | Ans | Why |
|---|---|---|
| 1 | b | The nephron is the microscopic filtering/functional unit; kidney contains ~1 million. |
| 2 | c | High glomerular pressure forces plasma into Bowman's capsule (ultrafiltration). |
| 3 | d | Large plasma proteins are too big to pass the filtration membrane. |
| 4 | a | The PCT reabsorbs ~100% of glucose/amino acids via active transport. |
| 5 | c | ADH increases aquaporin insertion in collecting duct/DCT walls. |
| 6 | b | Aldosterone promotes Na⁺ reabsorption (and K⁺ excretion) in the DCT. |
| 7 | c | Ammonia is highly toxic and needs much water to dilute for excretion. |
| 8 | b | The liver deaminates amino acids and forms urea (ornithine/urea cycle). |
| 9 | c | Sweating (evaporative cooling) + vasodilation lose heat. |
| 10 | b | Osmoregulation = control of water and dissolved solute balance. |
Section B (1 mark each)
Q11.
- (a) Loop of Henle → (ii) creates salt gradient for water reabsorption
- (b) Glomerulus → (i) site of ultrafiltration
- (c) ADH → (v) increases water permeability of collecting duct
- (d) Aldosterone → (iii) increases Na⁺ reabsorption
- (e) Liver → (iv) deaminates amino acids / makes urea
- (f) Uric acid → (vi) nitrogenous waste of birds & insects
Section C (2 marks each: 1 T/F + 1 justification)
Q12. FALSE. Justification: It is the reverse — filtration is passive/non-selective by size; glucose passes freely into filtrate while proteins are excluded.
Q13. FALSE. Justification: ADH is released when blood is too concentrated (high solute/low water), to conserve water and dilute the blood.
Q14. TRUE. Justification: Uric acid is nearly insoluble and excreted as a paste/crystals, saving water — an adaptation in birds/insects.
Q15. TRUE. Justification: The liver stores glucose as glycogen (glycogenesis) and releases it (glycogenolysis) to maintain constant blood glucose.
Q16. TRUE. Justification: Vasoconstriction reduces blood flow near skin surface, reducing heat loss to the environment.
Q17. TRUE. Justification: Tubular secretion actively moves substances (e.g. H⁺, K⁺, drugs) from blood/capillaries into the tubule filtrate.
Q18. FALSE. Justification: Aldosterone increases Na⁺ reabsorption, so water follows osmotically → decreases urine volume / conserves water.
[
{"claim":"Q1 answer is option b (index 2 of 4)","code":"options=['Glomerulus','Nephron','Ureter','Medulla']; result = (options[1]=='Nephron')"},
{"claim":"Q7 most toxic waste is ammonia","code":"toxicity={'ammonia':3,'urea':2,'uric_acid':1}; result = (max(toxicity,key=toxicity.get)=='ammonia')"},
{"claim":"Section C awards 2 marks each over 7 questions = 14 marks","code":"result = (7*2==14)"},
{"claim":"Total marks = 10 (A) + 6 (B) + 14 (C) = 30","code":"result = (10+6+14==30)"}
]