Question

how do plants takes in air and utilize carbondioxide for photosynthesis and oxygen for respiration

Answer 1

the whole process is known as photosynthesis  where stomata or small pores in leaves takes in carbon dioxide which is necessary in the process and oxygen is respierd out

Answer 2

Plants have small , minute pores on the lower surface of their leaves known as stomata , which help in the exchange of gases and they have certain semi-permeable membranes which allows only the desired gases to enter ($CO_{2} andO _{2}$) and blocks the entry of other substances. The reactions are Given below....
Respiration:
$C_{6} H _{12} O _{6} +6O _{2} =6CO _{2} +6H _{2} O+38 ATP + 420 Kcal.$
Energy is released in the form of Adenosine Triphosphate (ATP) and Heat is released in Kilocalories.
Photosynthesis:
$6CO _{2} +6H _{2} O=C_{6} H _{12} O _{6} +6O _{2}$ 
Glucose is the food whereas oxygen is a by-product.