Ultimately, the oxygen necessary for cellular respiration come from
a. waste products of photosynthesis.
b. water vapor
c. carbon dioxide
d. glucose

Option A

Explanation:

Plants intake the carbon dioxide that is present in the atmosphere. They absorb it and along with water and other materials in the presence of sunlight is converted into chemical energy.

This chemical energy is glucose and the by-product that is released by splitting of water into oxygen and hydrogen ions is released into the environment.

This oxygen is required for the process of cellular respiration.

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i don't know why i put this, i know its not the i was just bored : p

delete this answer while you can