Ask A Scientist© Botany Archive

name         Valerie V.
status       student
age          20s

Question -   I vaguely remember having learned in biology that plants
emit carbon dioxide at night.  Is this true?  How is it done?
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My botany is a bit rusty but as I recall, during the day while
photosynthesis is the dominant process in leaves, carbon dioxide is taken up
from the air and used in the process of making sugars. At night, when
photosynthesis does not occur - no sunlight for energy - respiration does
occur, which gives off carbon dioxide just as it does in animals. On
balance, though, plants take up much more carbon dioxide in photosynthesis
than they give off in respiration.
J. Elliott
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I was told by a nurse that before modern ventilation systems in hospitals, 
plants were removed from rooms because they would absorb the oxygen from the air
of the patients.  The fact of the matter is that plants use cellular respiration
at night and therefore, act like animals in terms of gas exchange.

Steve Sample
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Plant respiration.
http://www.nytimes.com/learning/students/scienceqa/archive/950912a.html
http://www.orst.edu/extension/mg/botany/respire.html
http://www.cbs.umn.edu/class/spring2000/eeb/4609/lectures/10_Feb.html

Anthony R. Brach, Ph.D.
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Plants generate carbon dioxide by much the same mechanism as animals.  They
combine glucose with oxygen in many steps to make carbon dioxide and water,
giving them the energy they need to carry out their life processes.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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