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1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

9. Photosynthesis

Photorespiration

9. Photosynthesis

Photorespiration: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Photorespiration is a process in plants that occurs under hot conditions when stomata close, preventing carbon dioxide (CO₂) from entering and causing oxygen (O₂) to accumulate. This leads to the enzyme Rubisco binding O₂ instead of CO₂, resulting in the production of CO₂ and wasting ATP and NADPH, making photosynthesis inefficient. Understanding stomata's role in gas exchange is crucial, as their closure during high temperatures protects plants from dehydration but hinders photosynthesis, highlighting the balance between water conservation and efficient energy production.

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Photorespiration

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Photorespiration Video Summary

Photorespiration is a process that occurs in plants, contrasting sharply with photosynthesis. While photosynthesis utilizes carbon dioxide (CO₂) from the atmosphere to produce sugars like glucose, photorespiration generates CO₂, effectively making it the opposite of photosynthesis. This process can significantly reduce the efficiency of photosynthesis, as it leads to an increase in carbon dioxide levels rather than a decrease.

The term "photorespiration" combines "photo," indicating that it occurs in the presence of light, and "respiration," which refers to the release of carbon dioxide. Both photorespiration and photosynthesis occur in light, leading to competition between the two processes. Understanding the role of stomata is crucial in this context. Stomata are small openings on plant leaves that regulate gas exchange, allowing CO₂ to enter and oxygen (O₂) to exit during photosynthesis.

In cooler temperatures, stomata remain open, facilitating gas exchange and allowing CO₂ to diffuse into the leaf. However, in hot environments, plants often close their stomata to prevent dehydration due to excessive water loss through evaporation. This closure, while protecting the plant from dehydration, also restricts gas exchange. Consequently, CO₂ levels inside the leaf decrease, while O₂ levels increase as it cannot escape.

When O₂ concentrations rise, it competes with CO₂ for binding to the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO), which is essential for the Calvin cycle. Under these conditions, RuBisCO may bind O₂ to ribulose bisphosphate (RuBP) instead of CO₂, leading to photorespiration. This process wastes the ATP and NADPH produced during the light reactions of photosynthesis, ultimately resulting in the production of CO₂ rather than glucose.

In summary, photorespiration occurs primarily in hot environments when stomata are closed, leading to decreased CO₂ and increased O₂ levels. This situation causes RuBisCO to favor O₂ over CO₂, wasting energy and reducing the efficiency of photosynthesis. Understanding these dynamics is essential for grasping how plants adapt to varying environmental conditions and the implications for their growth and productivity.

Problem

Plants are more likely to use Photorespiration instead of the Calvin Cycle when:

Stomata remain open and CO₂ concentrations within the plant are high

Stomata remain closed and O₂ concentrations within the plant are high

Glucose concentrations within the plant are low

CO₂ binds to Rubisco

Dig Deeper into Photorespiration

Photorespiration is a light-dependent process in plants where oxygen is consumed and carbon dioxide is released, reducing photosynthetic efficiency.

Key Terminology

Stomata: Openings or pores on the leaf surface that regulate gas exchange and water loss by opening or closing.
Rubisco: An enzyme that catalyzes the fixation of carbon dioxide to RuBP in the Calvin cycle but can also bind oxygen during photorespiration.
Calvin cycle: The set of light-independent reactions in photosynthesis where carbon fixation occurs to produce glucose.
ATP: Adenosine triphosphate, the energy currency of the cell used during the Calvin cycle and wasted during photorespiration.
NADPH: A reducing agent produced in the light reactions of photosynthesis, used in the Calvin cycle and consumed inefficiently in photorespiration.
Carbon fixation: The process of converting inorganic carbon dioxide into organic molecules during photosynthesis.
Mesophyll: The inner tissue of a leaf where chloroplasts are abundant and photosynthesis primarily occurs.
Gas exchange: The movement of gases like carbon dioxide and oxygen between the plant and the environment through stomata.
Evaporation: The loss of water vapor from plant leaves, which increases in hot environments and is controlled by stomatal opening.
Photorespiration: A process occurring in light where oxygen competes with carbon dioxide for Rubisco, leading to the release of carbon dioxide and reduced photosynthetic efficiency.
Photosynthesis: The process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.
RuBP (Ribulose bisphosphate): A 5-carbon molecule that reacts with carbon dioxide or oxygen in the Calvin cycle or photorespiration, respectively.
Light reactions: The initial phase of photosynthesis that produces ATP and NADPH using light energy.
Dehydration: The loss of water from plant tissues, which plants prevent by closing stomata in hot environments.
Concentration gradient: The difference in concentration of a substance, such as gases, across a membrane that drives diffusion.

Real-World Applications

Understanding photorespiration helps improve crop efficiency by guiding genetic engineering efforts to reduce photorespiration and increase photosynthetic output, especially in hot climates.
Photorespiration knowledge is crucial in developing drought-resistant plants that manage stomatal closure to prevent dehydration without severely compromising carbon fixation.
Research on photorespiration informs ecological studies on plant adaptation and survival strategies in environments with varying temperature and water availability.

Common Misconceptions

Photorespiration is not just "respiration" like in animals; it specifically involves oxygen binding to Rubisco in plants and occurs in the light.
People often think stomata are always open during photosynthesis, but in hot environments, plants close stomata to prevent water loss, which triggers photorespiration.
Photorespiration does not produce glucose; instead, it wastes energy and releases carbon dioxide, making photosynthesis less efficient.
Rubisco is not perfectly selective; it can bind oxygen instead of carbon dioxide, which is why photorespiration happens, especially under certain environmental conditions.
Photorespiration is not beneficial for plants; it is generally a wasteful process that plants try to minimize through adaptations.

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Here’s what students ask on this topic:

What is photorespiration and how does it differ from photosynthesis?

Photorespiration is a process in plants that occurs under hot conditions when stomata close, preventing carbon dioxide (CO₂) from entering and causing oxygen (O₂) to accumulate. This leads to the enzyme Rubisco binding O₂ to RuBP instead of CO₂, resulting in the production of CO₂ and wasting ATP and NADPH. In contrast, photosynthesis uses CO₂ to produce glucose, reducing CO₂ levels. Therefore, photorespiration makes photosynthesis inefficient by counteracting the carbon fixation process essential for glucose production.

Why does photorespiration occur more frequently in hot environments?

Photorespiration occurs more frequently in hot environments because plants close their stomata to prevent water loss through evaporation. When stomata are closed, CO₂ cannot enter the leaf, and O₂ accumulates inside. High O₂ levels lead to Rubisco binding O₂ to RuBP instead of CO₂, initiating photorespiration. This process wastes ATP and NADPH and produces CO₂ instead of glucose, making photosynthesis inefficient. Thus, hot conditions favor photorespiration due to the need for plants to conserve water.

How do stomata function in regulating photorespiration?

Stomata are openings on the leaf surface that regulate gas exchange. In cooler temperatures, stomata remain open, allowing CO₂ to enter and O₂ to exit, facilitating photosynthesis. In hot environments, stomata close to prevent water loss, which also prevents CO₂ from entering and causes O₂ to accumulate. This leads to photorespiration, where Rubisco binds O₂ to RuBP instead of CO₂, wasting ATP and NADPH and producing CO₂. Therefore, stomatal behavior directly influences the occurrence of photorespiration.

What role does the enzyme Rubisco play in photorespiration?

Rubisco is the enzyme responsible for carbon fixation in the Calvin cycle during photosynthesis. However, in photorespiration, Rubisco binds to O₂ instead of CO₂ when O₂ levels are high and CO₂ levels are low, such as when stomata are closed in hot environments. This binding leads to the production of CO₂ and the waste of ATP and NADPH, making photosynthesis inefficient. Thus, Rubisco's dual affinity for O₂ and CO₂ is central to the process of photorespiration.

How does photorespiration affect the efficiency of photosynthesis?

Photorespiration significantly reduces the efficiency of photosynthesis. During photorespiration, Rubisco binds O₂ to RuBP instead of CO₂, leading to the production of CO₂ and the waste of ATP and NADPH. This process counteracts the carbon fixation in the Calvin cycle, which is essential for glucose production. As a result, the energy and resources that would normally be used to produce glucose are instead used in a process that produces CO₂, making photosynthesis less efficient.

Previous Topic: Calvin Cycle Next Topic: C3, C4 & CAM Plants

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