i think they might need it for producing amino acids. ya know ill actually look it up.
okay. the roots use it, and the plant uses it when it burns glucose.
Cellular respiration (process that uses oxygen to break sugar into energy
for life functions) and photosynthesis (green plants converting sunlight
energy into sugars using water and carbon dioxide) are distinct and
separate processes. Animals only use cellular respiration. Plants do not
have muscles and the other functions necessary in animals functioning that
require a high levels of oxygen. Plants also CAN NOT take the energy
directly for their energy needs from photosynthesis. Photosynthesis
produces a far greater amount of oxygen and sugars, etc. then the small
amount the plant requires to produce its energy needs. OK - but only
during the day when the sun light is available! During the night, the
plant actually uses oxygen it has left over from the daylight
photosynthesis or takes the oxygen from the air surrounding the plant to
meet its energy needs. This is not nearly the amount of oxygen an animal
needs over the same period of time.
To answer your question, during the day the plant produces far more oxygen
from photosynthesis than it produces carbon dioxide from cellular
respiration. It is a waste gas and if not expelled from the plant, can
cause serious harm. Since plants do not utilize large amounts of oxygen
over a twenty-four hour period (ideal conditions, winter is another issue),
oxygen wins.