by: joe schwarcz, special to the montreal gazette
t
he garbage heap of science is filled with ideas and practices that were at one time thought to be on the mark. lobotomies for mental illness, lying immobilized after cataract surgery and bed rest for heart attacks were once common practices. and if you were hospitalized, plants that visitors brought to introduce some cheeriness were routinely removed from the room at night. this was based on the erroneous belief that the plants use up oxygen at night and deplete the oxygen in the air that is available for patients to breathe.
while it is true that plants use up oxygen at night through the process of respiration, the amount is insignificant in comparison to the amount of oxygen contained in air. a visitor breathing in a patient’s room uses up much more oxygen. over a 24-hour period, plants produce more oxygen through photosynthesis than they use up through respiration.
during the day, plants carry out two processes. they photosynthesize and they respire. photosynthesis is perhaps the most critical chemical reaction in the world because without it there would be no life. it is what allows plants to grow, and all life either directly or indirectly depends on plants. through photosynthesis, plants absorb carbon dioxide from the air and combine it with water to produce glucose, which then serves as the starting material for the biosynthesis of carbohydrates, proteins, fats, vitamins and the diverse other molecules that make up a plant. as the term implies, “photosynthesis” is dependent on light. (“photo” derives from the greek for light.) it is also dependent on chlorophyll, the green pigment responsible for the absorption of the light that provides the energy needed for photosynthesis. it is often said that chlorophyll, from the greek for “green” and “leaf,” is the most important chemical in the world because without it plants cannot grow. and without plants neither can we.