Blood flow properties vary along circulatory system

Steps:

• Blood pressure declines steadily from arteries to veins due to resistance.
• Total cross-sectional area peaks in capillaries, where many small vessels sum to largest area.
• Blood flow speed is inversely proportional to cross-sectional area, per continuity equation (Q = A × v, constant flow rate Q).
• Match graph curves: decreasing line (X) for pressure; mid-peak hump (Y) for area; mid-dip valley (Z) for speed.

Why C is correct:

• Assigns Z (valley) to speed, X (decline) to pressure, Y (peak) to area, aligning with continuity principle and pressure drop law.

Why the others are wrong:

• A: Assigns X (decline) to speed, but speed dips then rises, not steadily declines.
• B: Assigns Y (peak) to speed, but speed minimizes in capillaries, not peaks.
• D: Uses inconsistent lowercase labels (z, y), mismatching standard curve notation.

Final answer: C