Question

Plants take in oxygen and give out carbon dioxide during respiration all the time. Why do we then say that plants supply oxygen to the air?

Answer 1

Plants take in carbon dioxide and release oxygen during day time....
And during night they take in oxygen and release carbon dioxide ....

Answer 2

ANSWER:

             The respiration process in plant takes place at the night. And in the daytime they produce food with the help of photosynthesis and its by-products oxygen. Photosynthesis is the necessary process for all the green plant to be performed for producing food that is a starch.

             For this process Nitrogen, Sunlight and Chlorophyll required. This chemical reaction result in in the production of glucose and oxygen.  

EXPLANATION:

             The respiration process in plants occurs in the absence of sun. At this period the plant behave as a human and takes Oxygen and release carbon dioxide in the air. But at the daytime it supplies pure oxygen to the atmosphere.