Choose the correct statement from the following options
(a)The lungs allow only CO2 to enter the respiratory system
(b)The nostrils filter the air and allow only O2 to pass through them.
(c)The percentage of O2 in expired air is 16%
(d)The percentage of CO2 in expired air is 4%
a and c
b and c
b, c and d
c and d
c and d
When we breathe, we intake a mixture of gases. It contains 78% nitrogen, 21% oxygen and 0.04% of carbon dioxide. The air passes through the respiratory system and enters the alveolus. The diffusion of oxygen from the alveolus into blood happens with the help of haemoglobin. The haemoglobin absorbs the oxygen into the blood and the carbon dioxide from the blood diffuses into the alveolus which is exhaled out. So all gases enter the respiratory system but only oxygen is absorbed by the blood.
The percentage of O2 in expired air is 16% and the percentage of CO2 in expired air is 4%.