O Levels Biology (5090)•5090/11/M/J/23
Explanation
Pressure Decreases in Pulmonary Circulation
Steps:
- Blood flows from pulmonary artery to capillaries to pulmonary vein, with pressure dropping due to vascular resistance.
- Pulmonary artery pressure is highest, then capillaries, then lowest in pulmonary vein.
- Convert kPa to mmHg if needed (1 kPa ≈ 7.5 mmHg), but pattern matters: artery > capillary > vein.
- Evaluate options for decreasing sequence.
Why A is correct:
- Shows progressive pressure drop (14 > 8 > 5 kPa), matching flow direction and resistance in pulmonary circuit.
Why the others are wrong:
- B: Pressure rises (5 to 8 to 14 kPa), violating flow physics.
- C: Capillary pressure (5 kPa) below vein (8 kPa), impossible as veins receive lower pressure.
- D: Capillary pressure highest (14 kPa), contradicting resistance drop.
Final answer: A
Topic: Circulatory system
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