Hemoglobin affinity determines oxygen dissociation curve position

Steps:

• Oxygen dissociation curves show hemoglobin saturation versus pO2; a right shift indicates lower oxygen affinity.
• Statement 1 concerns hemoglobin concentration, which affects oxygen-carrying capacity but not curve shape or affinity.
• Statement 2 directly describes lower affinity in species S, shifting its curve right relative to species T.
• Statement 3 implies adaptation to altitude, but without curve details, it does not specify which species has the shifted curve.

Why C is correct:

• The curve's position is defined by hemoglobin's oxygen affinity; lower affinity in S (statement 2) alone explains a rightward shift per the Bohr effect principles.

Why the others are wrong:

• A includes 1 and 3, but concentration (1) does not alter curve shape, and 3 lacks specificity on curve direction.
• B includes 1, which is irrelevant to affinity-based shifts.
• D is only 3, which suggests environmental cause but not direct biochemical difference.

Final answer: C