Nutrition, respiration, transport, excretion MCQs

Q1. If the renal artery of a person is partially blocked, which of the following is most likely?

• A.Decrease in glomerular filtration rate and reduced urine output
• B.Increase in glomerular filtration rate due to back pressure
• C.No change because tubular reabsorption compensates
• D.Increase in glucose in urine due to PCT damage

Answer: A. Decrease in glomerular filtration rate and reduced urine output

The core fact here is - Glomerular filtration depends on the hydrostatic pressure of blood entering the glomerulus. Partial blockage of the renal artery reduces this pressure, lowering GFR and consequently reducing urine output. Back pressure does not increase GFR. Reabsorption cannot compensate for a fall in filtration. PCT damage is unrelated to renal artery stenosis. Hence the answer is A) Decrease in glomerular filtration rate and reduced urine output.

Q2. In dialysis (artificial kidney), which of the following principles is exploited?

• A.Selective diffusion of wastes across a semipermeable membrane along their concentration gradient
• B.Active transport of urea using ATP supplied by the machine
• C.Endocytosis of waste molecules by membrane-bound vesicles
• D.Mechanical sieving of urea molecules by size-based filtration only

Answer: A. Selective diffusion of wastes across a semipermeable membrane along their concentration gradient

Going back to the NCERT chapter, Haemodialysis works by passing the patient's blood across one side of a semipermeable membrane while a dialysis fluid (lacking urea/creatinine) flows on the other side. Wastes diffuse passively into the dialysis fluid along their concentration gradient. There is no ATP-dependent transport, no endocytosis, and no purely mechanical sieving - pressure and gradient together do the job. Hence the answer is A) Selective diffusion of wastes across a semipermeable membrane along their concentration gradient.

Q3. Which of the following ordered combinations is CORRECT in moving from inhaled air to blood capillary in the alveolus?

• A.Alveolar air → alveolar epithelium → fused basement membrane → capillary endothelium → plasma → RBC
• B.Alveolar air → plasma → alveolar epithelium → capillary endothelium → RBC
• C.Alveolar air → capillary endothelium → alveolar epithelium → RBC → plasma
• D.Alveolar air → bronchiole → alveolar epithelium → RBC → plasma

Answer: A. Alveolar air → alveolar epithelium → fused basement membrane → capillary endothelium → plasma → RBC

Which principle settles this? Oxygen in the alveolar lumen diffuses across the very thin respiratory membrane: it crosses the alveolar squamous epithelium, then the fused basement membrane (alveolar plus capillary), then the capillary endothelium, enters the plasma, and finally binds haemoglobin inside the RBC. The order is anatomical and cannot be reversed. The bronchiole is upstream of the alveolus, not between alveolus and capillary. Pick: A) Alveolar air → alveolar epithelium → fused basement membrane → capillary endothelium → plasma → RBC.