Back to: Botany 200 Level
Hello, dear learner! I hope you’re doing well today! Have you ever seen a farmer plant crops, but instead of getting a good harvest, the plants grow weak and produce very little food? Sometimes, despite all efforts, plants face challenges that reduce their productivity. One such challenge is photorespiration—a process that reduces the efficiency of photosynthesis and wastes energy. Today, we’ll learn about what photorespiration is, why it happens, and its consequences for plants.
Photorespiration and its consequences
What Is Photorespiration?
Photorespiration is a process in plants where the enzyme RuBisCO mistakenly binds to oxygen (O₂) instead of carbon dioxide (CO₂). This leads to the production of a toxic byproduct (phosphoglycolate), which plants must process in a way that wastes energy and does not produce glucose.
This happens because RuBisCO, which is responsible for fixing CO₂ during the Calvin cycle, can also react with O₂—especially when the CO₂ concentration is low or when temperatures are high.
Why Does Photorespiration Occur?
Low CO₂ Levels – When there is little CO₂ in the leaf (e.g., when stomata are closed due to hot weather), RuBisCO starts using O₂ instead.
High Temperature – At high temperatures, RuBisCO’s affinity (preference) for O₂ increases, leading to more photorespiration.
Oxygen Build-up – When stomata close to prevent water loss, less CO₂ enters, but O₂ (produced during photosynthesis) accumulates, forcing RuBisCO to react with O₂ instead of CO₂.
Steps of Photorespiration
RuBisCO binds to O₂ instead of CO₂, forming a toxic compound (2-phosphoglycolate).
The plant spends extra energy trying to recycle this compound back into something useful.
Instead of producing glucose, the plant wastes ATP and NADPH.
Consequences of Photorespiration
Photorespiration has several negative effects on plant growth and productivity:
Wastes Energy – Instead of making glucose, the plant burns energy trying to fix the mistake.
Reduces Photosynthesis Efficiency – Less CO₂ is converted into food, meaning the plant grows more slowly.
Lowers Crop Yields – Crops like rice, wheat, and beans suffer from reduced productivity, leading to food shortages.
Increases Water Loss – In hot conditions, stomata close to prevent dehydration, increasing the likelihood of photorespiration.
How Do Plants Minimise Photorespiration?
Some plants have evolved special pathways to reduce the effects of photorespiration:
C4 Photosynthesis (Used by maize, sugarcane, and sorghum)
These plants use a different enzyme called PEP carboxylase, which only binds to CO₂, preventing mistakes.
They store CO₂ in a special cell layer before passing it to RuBisCO, ensuring that oxygen does not interfere.
CAM Photosynthesis (Used by cacti, pineapples, and aloe vera)
These plants open their stomata at night to absorb CO₂, storing it for daytime use when RuBisCO is active.
This adaptation reduces water loss and decreases the chance of photorespiration.
Summary
Photorespiration is a wasteful process that happens when RuBisCO binds to oxygen instead of carbon dioxide, leading to energy loss and reduced photosynthesis efficiency. It occurs in hot and dry conditions when CO₂ levels are low. To reduce photorespiration, some plants have developed C4 and CAM pathways that help them survive in tough environments.
Let’s Test Your Understanding:
- Why does RuBisCO bind to oxygen instead of carbon dioxide?
- What are the main consequences of photorespiration?
- How do C4 and CAM plants avoid photorespiration?
Fantastic work, superstar! Keep learning, and always remember—plants are constantly adapting to their environment, just like we do! See you in the next lesson!
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