This document is a student paper on the topic of photorespiration in plants. It defines photorespiration as a process in plant metabolism that attempts to reduce the wasteful oxygenation reaction of the enzyme RuBisCO. The paper then discusses what happens during photorespiration, noting that oxygen replaces carbon dioxide in a non-productive reaction, decreasing the net carbon dioxide converted to sugars. Finally, it mentions that photorespiration limits plant growth and is favored by high oxygen, low carbon dioxide, and warm temperatures.

1. University of Salahaddin
College of Education
Biology department
1
Halala Rahman Qadir
M.Sc. Plant physiology
11/14/2015

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3. The objectives are:
Definition of photorespiration
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What happens during the process
called "photorespiration"?
Photorespiration in plants
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4. Definition of photorespiration
Photorespiration: (also known as the oxidative
photosynthetic carbon cycle, or C2
photosynthesis) is a process in plant
metabolism which attempts to reduce the
consequences of a wasteful oxygenation reaction
by the enzyme RuBisCO.
• Or the process that leads to only one 3PGA being
produced in the dark reaction in chloroplasts
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6. Photorespiration in plants
The end result is that photorespiration
decreases the net amount of carbon dioxide
which is converted into sugars by a
photosynthesizing plant. By interfering with
photosynthesis in this way, photorespiration
may significantly limit the growth rate of some
plants.
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Photorespiration
• depends on light
• “wastes” CO2
• protects against light
damage
• favored by high O2, low
CO2 and warm
temperatures

8. What happens during the process called "photorespiration"?
• It has long intrigued biologists that O2 has an
inhibitory effect upon photosynthesis. As shown
in the following hypothetical experiment, in the
presence of elevated O2 levels, photosynthesis
rates are lower.
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9. It is now known that this response to oxygen is due
to competition between O2 and CO2 on the
Rubisco enzyme of the Calvin-Benson cycle. You
will recall that in the "normal" reaction, CO2 is
joined with RUBP to form 2 molecules of 3PGA.
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In the process called photorespiration, O2 replaces
CO2 in a non-productive, wasteful reaction.

11. It is believed that photorespiration in plants has
increased over geologic time and is the result
of increasing levels of O2 in the atmosphere--
the byproduct of photosynthetic organisms
themselves. The appearance of C4-type plants
appears to be an evolutionary mechanism by
which photorespiration is suppressed.
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12. It has long been the dream of biologists to
increase the production of certain crop plants,
such as wheat, that carry on C3-type
photosynthesis by genetically re-engineer
them to perform C4-type photosynthesis. It
seems unlikely that this goal will be
accomplished in the near future due to the
complex anatomical and metabolic differences
that exist between C3- and C4-type plants.
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