Question

CO2 and O2 release are the major events during night and day respectively.Justify.

Answer 1

During the day the plants consume CO2 and release O2 from the photosynthesis process.  This is the major process.  The plants also breathe (respiration) O2 though their surface pores.  But it is a small quantity.

During the night also plants do respire releasing CO2.  This is major process as photosynthesis is very little or nil due to lack of light.

Answer 2

at night O2 is released by plants whereas at day time co2 is released by animals.