Physiological buffers in vivo: Which acid/base pairs serve as natural buffers in living systems?

Introduction / Context:
Maintaining pH is vital for enzyme activity and metabolic control. Several buffering systems operate in blood, intracellular fluid, and within proteins themselves.

Given Data / Assumptions:

• Bicarbonate buffer predominates in blood plasma.
• Phosphate buffer is important intracellularly.
• Histidine side chains buffer locally in proteins (pKa near physiological pH).

Concept / Approach:
The bicarbonate system (CO2/H2CO3/HCO3−) couples to respiration and renal function to maintain blood pH. The phosphate pair (H2PO4−/HPO4^2−) buffers cytosolic and urinary pH. Histidine’s imidazole toggles between protonated and deprotonated states around neutral pH, stabilizing local microenvironments and participating in enzyme catalysis.

Step-by-Step Solution:
Identify each pair’s physiological niche.Relate pKa values to effectiveness near physiological pH.Select the inclusive option acknowledging all contribute.

Verification / Alternative check:
Clinical acid–base physiology emphasizes bicarbonate; cell biology texts highlight phosphate and amino acid side chain buffering.

Why Other Options Are Wrong:

• Any single pair alone: Incomplete; multiple buffers operate in parallel.
• None: Contradicts established physiology.

Common Pitfalls:
Ignoring protein side-chain buffering, which fine-tunes local pH near active sites.

Final Answer:
All of these.