key term - Photorespiration

Definition

Photorespiration is a metabolic pathway that occurs in plants, where oxygen is taken up and carbon dioxide is released, often occurring when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide. This process generally results in the loss of fixed carbon and reduces the efficiency of photosynthesis, especially under high light and low carbon dioxide conditions. It serves as a way for plants to protect themselves from excessive light energy and helps to balance the process of photosynthesis.

5 Must Know Facts For Your Next Test

1. Photorespiration can occur when the concentration of oxygen is higher than that of carbon dioxide, particularly in hot and dry conditions.
2. This process can lead to a significant decrease in plant productivity by reducing the amount of usable carbohydrates produced during photosynthesis.
3. Some plants have evolved adaptations, like C4 and CAM pathways, to minimize photorespiration and improve their photosynthetic efficiency.
4. Photorespiration typically occurs in the chloroplasts, peroxisomes, and mitochondria of plant cells, indicating its complex nature.
5. Despite its negative effects on photosynthesis, photorespiration may play a role in protecting plants from photoinhibition under certain environmental conditions.

Review Questions

• How does photorespiration affect the efficiency of photosynthesis in plants?
  • Photorespiration negatively affects the efficiency of photosynthesis because it leads to the loss of fixed carbon. When RuBisCO reacts with oxygen instead of carbon dioxide, it diverts resources away from producing carbohydrates. This means that less energy is available for plant growth and development, especially in conditions where photorespiration rates are high due to environmental stressors like heat or drought.
• Discuss the conditions under which photorespiration is most likely to occur and its implications for plant health.
  • Photorespiration is most likely to occur under high light intensity and low carbon dioxide conditions, such as during hot and dry weather when stomata close to conserve water. This leads to an increased concentration of oxygen relative to carbon dioxide inside the leaf. As a result, plants may suffer from reduced growth and productivity due to inefficient carbon fixation, making them more vulnerable to environmental stresses.
• Evaluate the significance of adaptations such as C4 and CAM pathways in mitigating photorespiration in certain plant species.
  • C4 and CAM pathways represent significant adaptations that help plants reduce the occurrence of photorespiration and enhance their photosynthetic efficiency. By effectively concentrating carbon dioxide in specific cells or during specific times (like night for CAM plants), these pathways minimize the likelihood that RuBisCO will react with oxygen. This leads to better growth outcomes in environments where photorespiration would otherwise limit productivity, showcasing how evolution shapes plant responses to varying environmental conditions.

Related terms

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first step of carbon fixation in photosynthesis but can also facilitate photorespiration when it reacts with oxygen.

C3 Plants:

Plants that utilize the C3 pathway for photosynthesis, characterized by the fixation of carbon dioxide into a three-carbon compound, which is prone to photorespiration.

Calvin Cycle:

A series of biochemical reactions in photosynthesis where carbon dioxide is converted into glucose using energy from ATP and NADPH, significantly impacted by the occurrence of photorespiration.