2,3-BPG Shifts Oxygen Dissociation Curve Rightward

Steps:

• 2,3-BPG binds deoxyhemoglobin, stabilizing low-affinity T-state and increasing P50 (PO2 for 50% saturation).
• Statement 1 correct: right shift requires higher PO2 for 50% saturation, matching question description.
• Statement 2 incorrect: 2,3-BPG binds only deoxyhemoglobin, not reducing affinity of oxyhemoglobin directly.
• Statement 3 correct: absent 2,3-BPG causes left shift, raising oxygen affinity so oxyhemoglobin holds O2 tighter in tissues.

Why B is correct:

• Combines accurate descriptions of curve shift (1) and unloading effect without BPG (3), per oxygen-hemoglobin dissociation principles.

Why the others are wrong:

• A includes incorrect statement 2 on binding-affinity link.
• C pairs incorrect 2 with correct 3.
• D references nonexistent statement 4.

Final answer: B