IGCSE Biology Paper-1: Specimen Questions with Answers 133 - 133 of 208

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Question 133



The table shows the percentage composition of three gases in the atmospheric air.

The Table Shows the Percentage Composition of Three Gases in the Atmospheric Air
nitrogenoxygencarbon dioxide

What is the composition of the air breathed out by a person?


Choice (4)


nitrogen-20, oxygen-2, carbon dioxide-78


nitrogen-78, oxygen-18, carbon dioxide-4.0


nitrogen-78, oxygen-0.04, carbon dioxide-21


nitrogen-22, oxygen-72, carbon dioxide-6




Partial pressure of a gas is the pressure it exerts in a mixture of gases and is equal to the total pressure of the mixture divided by percentage of that gas in the mixture. For instance, if the pressure of atmospheric air at sea level is 760 mm. Of mercury (Hg) and oxygen forms 21% of the air, the partial pressure of oxygen will be 21% of 760, or 159 mm. Hg. In other words, the partial pressure of a gas is proportional to its concentration in the mixture. Only about 0. 3 ml. of can dissolve in 100 ml. of plasma, about 20 ml. of is carried by hemoglobin in 100 ml. of blood. In atmospheric air except these gases some traces of helium, argon and neon are also found.

Composition of three samples of air

Composition of Three Samples of Air
GasesInspired airExpired airAlveolar airGain/loss %
Oxygen20.84 %15.70 %13.6 %Gain 5.14 %
Carbon dioxide0.04 %4.00 %5.3 %Loss 3.96 %
Nitrogen78.62 %74.50 %74.9 %Gain 4.12 %
Water0.5 %6.2 %6.2 %Loss 5.7 %

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