Summary
Rubisco binds oxygen instead of carbon dioxide, wasting energy and releasing CO2.
In depth
Rubisco's oxygenase activity makes phosphoglycolate, recovered through a costly pathway through peroxisomes and mitochondria, releasing CO2 and losing up to 25 percent of fixed carbon. It increases at high temperature.
It wastes energy but may protect against photodamage by consuming excess ATP and NADPH. Rates rise with temperature as rubisco's oxygenation increases relative to carboxylation and the solubility of CO2 falls.
Remember: it is not related to cellular respiration, despite the name.
It is called photorespiration because it uses oxygen and releases CO2 in the light, but makes no ATP. About 20 to 30 percent of fixed carbon can be lost in warm conditions, and it is a major drag on crop yield. Recovery of phosphoglycolate involves chloroplasts, peroxisomes and mitochondria, with glycine to serine conversion releasing CO2 and ammonia, which must be refixed. It may protect plants by dissipating excess energy and has roles in nitrogen metabolism.
Engineered bypasses, such as those developed in tobacco, which shortcut the pathway within the chloroplast, raised biomass by up to 40 percent in field trials. Heat and drought favour photorespiration because stomata close, which lowers internal CO2 and raises the O2 ratio.
Key idea: photorespiration is a consequence of rubisco's dual activity and is reduced in C4 and CAM plants.
Frequently asked questions
What is Photorespiration?
Rubisco binds oxygen instead of carbon dioxide, wasting energy and releasing CO2.
Which area of biology covers Photorespiration, and how advanced is it?
Photorespiration is one of the 56 topics in Plant Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Photosynthesis Efficiency Engineering, Rubisco, C4 Photosynthesis.
Can you give an example of Photorespiration?
C4 and CAM plants reduce it.
What should I learn before Photorespiration?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Photorespiration. Advanced topics assume the Intermediate vocabulary.
What topics are related to Photorespiration?
The closest topics to Photorespiration are Photosynthesis Efficiency Engineering, Rubisco, C4 Photosynthesis, Light-Dependent Reactions. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Photorespiration?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Photorespiration. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Photorespiration different from Photosynthesis Efficiency Engineering?
Photorespiration: Rubisco binds oxygen instead of carbon dioxide, wasting energy and releasing CO2. Photosynthesis Efficiency Engineering: Strategies include improving rubisco, adding carbon concentrating mechanisms and optimising canopy light use. Read both side by side and note what each one explains.
How should I study Photorespiration step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Photosynthesis Efficiency Engineering and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.