What is the Difference Between Photooxidation and Photorespiration

The key difference between photooxidation and photorespiration is that photooxidation is the oxidation process induced by the sunlight, while photorespiration is a wasteful reaction of photosynthesis in which the enzyme Rubisco oxygenates RuBP, causing some of the energy to be wasted.

Photooxidation and photorespiration are two processes that are induced by sunlight. In plants, both these processes affect the normal functioning of the tissues. Photooxidation is responsible for the accumulation of harmful reactive oxygen species in tissues. On the other hand, photorespiration is responsible for energy-wasting in plants.

CONTENTS

1. Overview and Key Difference
2. What is Photooxidation
3. What is Photorespiration
4. Similarities – Photooxidation and Photorespiration
5. Photooxidation vs Photorespiration in Tabular Form
6. Summary – Photooxidation vs Photorespiration

What is Photooxidation?

Photooxidation is a light-induced process of losing electrons from chemical species or a process of reacting a substance with oxygen. In plants, photooxidation occurs when there is environmental stress. Hence, it is known as photooxidative stress. Absorption of excess excitation energy leads to the generation of reactive oxygen species in plant tissues. Accumulation of these reactive oxygen species is a harmful process in plants that damages chloroplasts. This photooxidative stress happens mainly in the presence of high-intensity light and a low concentration of CO₂. It is a light-dependent process. In C3 plants, photorespiration protects plants from photooxidation.

In addition, photooxidation is able to change the composition of oil. Sunlight and oxygen cause the oxidation of oil. This is an important process since it removes large volumes of oil spills at sea. Therefore, when oil spills are exposed to sunlight due to the photooxidation process, they are cleared from the sea.

What is Photorespiration?

Photorespiration is a side reaction of the Calvin cycle that causes the wasting of some energy produced by photosynthesis. During the Calvin cycle, one major enzyme called RuBP oxygenase-carboxylase (rubisco) converts RuBP into phosphoglyceraldehyde by incorporating carbon dioxide. This is the normal process of producing glucose molecules. However, this enzyme has the ability to incorporate oxygen instead of carbon dioxide. That means rubisco has the ability to use oxygen as its substrate instead of carbon dioxide. When this occurs, it initiates the above-called process: photorespiration. Photorespiration actually wastes energy and some of the fixed carbon. Furthermore, it reduces the number of sugar molecules that can be produced by the normal Calvin cycle.

Photorespiration is favored by several conditions such as low carbon dioxide: oxygen ratio, high temperature, etc. When temperature increases, the rubisco enzyme has a higher affinity towards oxygen than carbon dioxide. Hence, plants that grow under hot and dry conditions undergo photorespiration more than plants grown in other areas. However, plants show different adaptations and mechanisms to minimize photorespiration and loss of energy. One example is C4 plants.

What are the Similarities Between Photooxidation and Photorespiration?

• Photooxidation and photorespiration are light-dependent processes.
• Both processes can be seen in plants.
• These are natural processes.
• Both reactions may occur in chloroplasts.
• They are chemical reactions.
• Oxygen is involved in both processes.

What is the Difference Between Photooxidation and Photorespiration?

Photooxidation is the oxidation process induced by the sunlight, while photorespiration is a wasteful reaction of photosynthesis in which the enzyme Rubisco oxygenates RuBP causing some of the energy to be wasted. Thus, this is the key difference between photooxidation and photorespiration. Moreover, photooxidation is detrimental for plants, while photorespiration is not detrimental for plants.

The below infographic presents the differences between photooxidation and photorespiration in tabular form for side by side comparison.

Summary – Photooxidation vs Photorespiration

Photooxidation and photorespiration are light-dependent processes. Photooxidation is the oxidation process induced by the sunlight while photorespiration is a wasteful reaction of photosynthesis in which the enzyme Rubisco oxygenates RuBP, causing some of the energy to be wasted. So, this summarizes the difference between photooxidation and photorespiration.

Reference:

1. “Photorespiration (Article) | Photosynthesis.” Khan Academy, Khan Academy.
2. Foyer, Christine H., et al. “Photooxidative Stress in Plants.” Wiley Online Library, John Wiley & Sons, Ltd, 28 Apr. 2006.

Image Courtesy:

1. “Biodegradation of Pollutants” By Timmer26 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Simplified photorespiration diagram” By !Original: Rachel PurdonVector: GKFX – Own work based on: Simplified photorespiration diagram.jpg (CC BY-SA 3.0) via Commons Wikimedia