Photorespiration

Definition

Photorespiration is a metabolic process that occurs in plants, where the enzyme RuBisCO reacts with oxygen instead of carbon dioxide, leading to a wasteful pathway that counteracts photosynthesis. This process typically happens when carbon dioxide levels are low and oxygen levels are high, particularly under hot and dry conditions. Photorespiration can reduce the efficiency of the Calvin cycle and overall plant productivity.

5 Must Know Facts For Your Next Test

1. Photorespiration can reduce the net gain of carbohydrates by consuming energy and releasing fixed carbon as carbon dioxide.
2. The rate of photorespiration increases when temperatures rise, making it a significant issue for plants during heat stress.
3. Unlike the Calvin cycle, photorespiration does not produce any sugar; instead, it leads to the release of carbon dioxide and consumption of ATP and NADPH.
4. C3 plants are more prone to photorespiration than C4 plants, which have adapted mechanisms to minimize its occurrence.
5. The balance between photorespiration and photosynthesis is influenced by environmental factors like light intensity, temperature, and water availability.

Review Questions

• How does photorespiration affect the efficiency of the Calvin cycle in plants?
  • Photorespiration negatively impacts the efficiency of the Calvin cycle by causing RuBisCO to bind with oxygen instead of carbon dioxide. This wasteful reaction leads to a decrease in the production of sugars since it generates carbon dioxide rather than incorporating it into organic compounds. As a result, the overall yield of carbohydrates is reduced, which can limit plant growth and productivity.
• What role does RuBisCO play in both photorespiration and the Calvin cycle, and how does this dual function affect plant metabolism?
  • RuBisCO is critical for both photorespiration and the Calvin cycle, as it is the enzyme responsible for fixing carbon dioxide in photosynthesis. However, its ability to react with oxygen during photorespiration diverts resources away from sugar production. This dual function can create metabolic inefficiencies in C3 plants, especially under conditions that favor oxygen binding over carbon dioxide binding, ultimately affecting their growth and survival.
• Evaluate the adaptive strategies that C4 plants employ to minimize photorespiration compared to C3 plants, considering their ecological implications.
  • C4 plants employ a specialized mechanism that spatially separates carbon fixation from the Calvin cycle, allowing them to effectively concentrate carbon dioxide around RuBisCO while minimizing exposure to oxygen. This adaptation significantly reduces the incidence of photorespiration compared to C3 plants. As a result, C4 plants can thrive in hotter and drier environments where C3 plants might struggle due to increased photorespiration rates. This difference illustrates how variations in photosynthetic pathways can influence plant distribution and ecosystem dynamics.

Related terms

RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first major step of carbon fixation in the Calvin cycle.

Calvin Cycle:

The series of biochemical reactions in photosynthesis that convert carbon dioxide and other compounds into glucose.

C4 Photosynthesis:

A type of photosynthesis that allows plants to efficiently fix carbon dioxide and minimize photorespiration by spatially separating carbon fixation from the Calvin cycle.