Podcast
Questions and Answers
What is the primary product of the Calvin cycle in C3 plants?
What is the primary product of the Calvin cycle in C3 plants?
- Oxygen (Oâ‚‚)
- Glycerate-3-phosphate (3-PGA) (correct)
- Ribulose-1,5-bisphosphate
- Glucose
What unstable molecule is formed as a result of Rubisco binding to oxygen in C3 plants?
What unstable molecule is formed as a result of Rubisco binding to oxygen in C3 plants?
- Glucose
- 2-phosphoglycolate (2-PG) (correct)
- Ribulose-1,5-bisphosphate
- Glycerate-3-phosphate
Which phase of the photorespiratory pathway involves the conversion of glycolate back to 2-phosphoglycolate?
Which phase of the photorespiratory pathway involves the conversion of glycolate back to 2-phosphoglycolate?
- Mitochondrial phase
- Calvin cycle phase
- Chloroplastic phase
- Peroxisomal phase (correct)
What happens to glycolate after it is converted back to 2-phosphoglycolate in peroxisomes?
What happens to glycolate after it is converted back to 2-phosphoglycolate in peroxisomes?
What is the main drawback of photorespiration on the Calvin cycle?
What is the main drawback of photorespiration on the Calvin cycle?
Which adaptive strategy helps plants offset losses due to photorespiration?
Which adaptive strategy helps plants offset losses due to photorespiration?
Why is photorespiration considered a 'necessary evil' in C3 photosynthesis?
Why is photorespiration considered a 'necessary evil' in C3 photosynthesis?
Which plant process separates carbon fixation and oxygenation reactions to minimize the effects of photorespiration?
Which plant process separates carbon fixation and oxygenation reactions to minimize the effects of photorespiration?
How does lower carbon dioxide concentration impact photorespiration?
How does lower carbon dioxide concentration impact photorespiration?
What effect does closed stomata have on the likelihood of oxygen binding to Rubisco?
What effect does closed stomata have on the likelihood of oxygen binding to Rubisco?
Under high light conditions, what generally happens to the speed of photorespiration?
Under high light conditions, what generally happens to the speed of photorespiration?
What is a benefit of photorespiration for plants?
What is a benefit of photorespiration for plants?
How does photorespiration impact plant productivity?
How does photorespiration impact plant productivity?
What is the toxic compound produced when Rubisco binds to oxygen instead of carbon dioxide in the photorespiratory pathway?
What is the toxic compound produced when Rubisco binds to oxygen instead of carbon dioxide in the photorespiratory pathway?
What is the full form of the enzyme Rubisco discussed in the text?
What is the full form of the enzyme Rubisco discussed in the text?
Which factor increases the rate of photorespiration by promoting oxygen binding to Rubisco?
Which factor increases the rate of photorespiration by promoting oxygen binding to Rubisco?
What critical process does Rubisco catalyze in photosynthesis?
What critical process does Rubisco catalyze in photosynthesis?
How do higher temperatures influence the occurrence of photorespiration?
How do higher temperatures influence the occurrence of photorespiration?
Study Notes
Photorespiration: A Closer Look at the Photorespiratory Pathway
Photosynthesis, the process by which plants harness sunlight to convert carbon dioxide and water into glucose, is a vital source of energy for life on Earth. However, not all is perfect in the world of photosynthesis. In the case of plants and algae that use C3 photosynthesis, there exists a less efficient byproduct: photorespiration.
The Photorespiratory Pathway
Photorespiration is a process that occurs in C3 plants, which regulate their photosynthesis through the Calvin cycle. The Calvin cycle is intrinsically linked to the pathway of carbon fixation in C3 plants, where the primary product is 3-carbon molecules (3-C) such as glycerate-3-phosphate (3-PGA).
Photorespiration occurs when ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the enzyme responsible for carbon fixation, inadvertently binds to oxygen (Oâ‚‚) instead of carbon dioxide (COâ‚‚). This leads to the formation of an unstable molecule called 2-phosphoglycolate (2-PG), which eventually results in a loss of fixed carbon and the expenditure of energy.
The photorespiratory pathway can be divided into two phases: the mitochondrial phase and the peroxisomal phase. The mitochondrial phase begins when 2-PG is converted into glycolate, which is then transported to peroxisomes. In peroxisomes, glycolate is converted back to 2-PG and released, which is then recycled through the chloroplasts into glycerate-3-phosphate by the Calvin cycle.
The Cost of Photorespiration
The photorespiratory pathway may account for up to 25% of a plant's daily photosynthetic capacity. This seemingly inefficient process ultimately results in a loss of carbon, water, and energy. The key drawback of photorespiration is that it reduces the overall efficiency of the Calvin cycle and thus the net photosynthetic rate, which can limit plant growth and productivity.
Adaptations to Photorespiration
To offset the losses due to photorespiration, plants have developed various adaptive strategies, including the C4 photosynthetic pathway, which separates the carbon fixation and oxygenation reactions, and CAM (Crassulacean Acid Metabolism) photosynthesis, where stomatal opening and COâ‚‚ fixation occur during the night.
Conclusions
Photorespiration is a necessary evil in C3 photosynthesis, but it can limit plant growth and productivity. Despite its limitations, photorespiration plays an essential role in maintaining the balance of the Calvin cycle and preventing the accumulation of toxic intermediates in the chloroplasts. Understanding the photorespiratory pathway is crucial for developing strategies to optimize photosynthesis in crops, ultimately leading to increased food production and a healthier planet.
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Description
Test your knowledge on the photorespiratory pathway in plants and how it impacts photosynthesis. Explore the process of photorespiration, its consequences, and the adaptations developed by plants to minimize its effects.