Final answer:
The human respiratory system uses bidirectional flow, not unidirectional flow. Gas exchange occurs in alveolar sacs. The term for blood flow through the lungs is pulmonary circulation.
Step-by-step explanation:
The statement that the flow geometry in human lungs can be best described as unidirectional flow is false. In humans, the respiratory system operates on a bidirectional or tidal flow, where air enters and leaves through the same pathways. The alveolar sacs are the site of gas exchange, and they are structured like clusters of grapes at the end of the bronchioles where oxygen is absorbed and carbon dioxide is released into the exhaled air. This is in contrast to birds, which have a unidirectional flow-through respiratory system, allowing air to move in one direction through the lungs for efficient respiration.
Regarding the blood flow in the human body, the correct term is pulmonary circulation, which refers to the pathway of deoxygenated blood from the heart to the lungs where it becomes oxygenated and then returns to the heart.