Kidney's Role in Gas Exchange, Waste Removal, and Fluid Balance

Steps:

• Blood enters the kidney via the renal artery with high oxygen for tissue metabolism and high urea from bodily waste.
• In the nephrons, oxygen is consumed by kidney cells for energy, reducing its level in the blood.
• Urea is filtered out at the glomerulus and mostly excreted in urine, lowering its concentration in the remaining blood.
• Water is filtered and partially reabsorbed, but net loss occurs via urine formation, decreasing water content in the blood.

Why C is correct:

• The kidney removes waste (urea) and water while consuming oxygen, directly matching the composition changes: less oxygen (metabolic use), less urea (excretion), less water (urine output).

Why the others are wrong:

• A: Carbon dioxide increases (from metabolism), not decreases.
• B: Water decreases due to urine, not increases; carbon dioxide does increase but water is incorrect.
• D: Oxygen decreases from kidney use, not increases.

Final answer: C