Both external respiration and internal respiration takes place in capillaries.

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Capillaries are the smallest blood vessels where gas exchange takes place between the blood and the surrounding tissues. During external respiration, oxygen from the air inhaled into the lungs diffuses across the capillary walls into the bloodstream, and carbon dioxide diffuses from the blood into the lungs to be exhaled. During internal respiration, oxygen diffuses from the capillaries into the tissues, and carbon dioxide from the tissues diffuses into the capillaries to be transported back to the lungs for exhalation. Therefore, both external and internal respiration occur in the capillaries.

Both External Respiration and Internal Respiration Takes Place in Capillaries