The diagram shows the percentage of gases in inspired and expired air.

(a) Identify I, II, X, Y, and Z.

I: Inspired air

II: Expired air

X: Oxygen (O₂)

Y: Carbon dioxide (CO₂)

Z: Nitrogen (N₂)

(b) Why is gas X almost negligible in Figure I?
Answer: Gas X (carbon dioxide) is negligible in inspired air because atmospheric CO₂ is present in very low amounts (0.04%).

(c) How is the percentage of X increased in Figure II?
Answer: The percentage of carbon dioxide increases in expired air due to cellular respiration, where oxygen is used, and CO₂ is produced as a waste product.

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