C3 Cycle vs. C4 Cycle — What's the Difference?
Edited by Tayyaba Rehman — By Fiza Rafique — Published on December 24, 2023
The C3 Cycle, also known as the Calvin cycle, involves carbon fixation by ribulose bisphosphate carboxylase/oxygenase (RuBisCO) in mesophyll cells. The C4 Cycle utilizes a CO₂-concentrating mechanism, initially fixing carbon in mesophyll cells.
Difference Between C3 Cycle and C4 Cycle
Table of Contents
ADVERTISEMENT
Key Differences
The C3 Cycle and the C4 Cycle are both essential pathways that plants use for carbon fixation during photosynthesis. The C3 Cycle, more commonly known as the Calvin cycle, directly converts CO₂ and ribulose bisphosphate into a three-carbon compound using the enzyme RuBisCO. On the other hand, the C4 Cycle initially captures CO₂ in mesophyll cells, converting it into a four-carbon compound, which is then shuttled to bundle sheath cells for decarboxylation and use in the Calvin cycle.
Plants that primarily use the C3 Cycle, such as wheat and rice, are termed C3 plants. They thrive in cooler environments with moderate sunlight. However, plants that employ the C4 Cycle, including maize and sugarcane, are called C4 plants. These plants are more efficient in hot, sunny environments, as the C4 Cycle helps reduce photorespiration, a process that wastes energy and reduces CO₂ fixation efficiency.
One key distinction between the C3 Cycle and the C4 Cycle lies in their spatial arrangements. In the C3 Cycle, carbon fixation occurs solely in the mesophyll cells. In contrast, the C4 Cycle operates across two types of cells: CO₂ is initially fixed in the mesophyll cells, and then the carbon is transferred to the bundle sheath cells, where it enters the Calvin cycle.
The C3 Cycle's direct approach to carbon fixation can lead to challenges in hot and dry conditions. Under these circumstances, the oxygenase activity of RuBisCO can result in photorespiration. The C4 Cycle, with its unique spatial separation and CO₂-concentrating mechanism, is an evolutionary solution that minimizes photorespiration, making it particularly advantageous in harsher climates.
Both the C3 Cycle and the C4 Cycle play vital roles in the global carbon cycle. While the C3 Cycle is more prevalent in many of the world's staple crops, the C4 Cycle, with its increased efficiency in certain conditions, represents an evolutionary adaptation that allows some plants to excel in environments where C3 plants might struggle.
ADVERTISEMENT
Comparison Chart
Primary Process
Calvin cycle
CO₂-concentrating mechanism
Carbon Compound Produced
Three-carbon compound
Four-carbon compound
Key Enzyme Involved
RuBisCO
PEP carboxylase
Spatial Arrangement
Carbon fixation in mesophyll cells
Initial fixation in mesophyll, then Calvin cycle in bundle sheath cells
Efficiency in Hot/Dry Conditions
Lower due to photorespiration
Higher, reduced photorespiration
Compare with Definitions
C3 Cycle
The C3 Cycle refers to the Calvin cycle, where CO₂ is fixed directly into a three-carbon compound.
In many temperate plants, the C3 Cycle is the primary pathway for carbon fixation during photosynthesis.
C4 Cycle
It's an adaptation to reduce photorespiration in hot and dry conditions.
The C4 Cycle offers a competitive advantage to plants in tropical regions by minimizing energy-wasting photorespiration.
C3 Cycle
It's a photosynthetic carbon reduction pathway utilizing RuBisCO.
In the C3 Cycle, RuBisCO plays a pivotal role in converting CO₂ into organic molecules.
C4 Cycle
The C4 Cycle involves an initial carbon fixation into a four-carbon compound.
In maize, the C4 Cycle efficiently captures carbon dioxide in hot environments.
C3 Cycle
This cycle can lead to photorespiration in hot and dry conditions.
When temperatures rise, the C3 Cycle in certain plants becomes less efficient due to increased photorespiration.
C4 Cycle
Named after the four-carbon compound produced during its initial CO₂ fixation.
Oxaloacetate, a four-carbon molecule, is the first product of the C4 Cycle.
C3 Cycle
It's named after the three-carbon compound produced during CO₂ fixation.
The initial product of the C3 Cycle is a three-carbon molecule, giving the cycle its name.
C4 Cycle
The C4 Cycle operates across both mesophyll and bundle sheath cells.
In the C4 Cycle, carbon fixation starts in the mesophyll cells and culminates in the bundle sheath cells.
C3 Cycle
The C3 Cycle operates predominantly in mesophyll cells.
In C3 plants, the mesophyll cells are the primary site of the C3 Cycle's carbon fixation.
C4 Cycle
It uses a CO₂-concentrating mechanism to enhance carbon fixation.
The C4 Cycle enhances photosynthetic efficiency by concentrating CO₂ in bundle sheath cells.
Common Curiosities
What are the primary plants using the C3 Cycle?
Plants like wheat, rice, and barley primarily use the C3 Cycle.
Which plants predominantly exhibit the C4 Cycle?
Maize, sugarcane, and sorghum are examples of plants that use the C4 Cycle.
How does the C4 Cycle achieve a CO₂-concentrating mechanism?
By initially fixing carbon in mesophyll cells and then utilizing it in bundle sheath cells for the Calvin cycle.
Is photorespiration beneficial for plants?
Generally, photorespiration is considered wasteful as it reduces the efficiency of photosynthesis.
Are there intermediate plants between C3 and C4?
Yes, CAM plants (Crassulacean Acid Metabolism) are considered intermediate, using a time-based CO₂-concentrating mechanism.
Why is the C4 Cycle more efficient in hot conditions?
The C4 Cycle reduces photorespiration, which increases under hot conditions in C3 plants.
In which cellular compartments do the C3 and C4 Cycles operate?
The C3 Cycle operates in the chloroplasts of mesophyll cells, while the C4 Cycle spans mesophyll and bundle sheath cells.
Are C4 plants more water-use efficient than C3 plants?
Yes, C4 plants generally have a higher water-use efficiency compared to C3 plants.
How do the C3 and C4 Cycles impact crop yield?
C4 plants can have higher yields in hot and sunny environments, while C3 plants may yield better in cooler conditions.
Why is the C4 Cycle considered an evolutionary adaptation?
It evolved in response to hot and dry conditions to increase photosynthetic efficiency by reducing photorespiration.
What is the primary enzyme involved in the C3 Cycle?
RuBisCO is the primary enzyme in the C3 Cycle.
Are there any environmental implications of the increasing cultivation of C4 plants?
C4 plants can be more drought-resistant and may play a role in sustainable agriculture in changing climate conditions.
Can C3 plants be genetically modified to use the C4 Cycle?
Scientists are exploring the possibility, but it's a complex process with multiple genes involved.
Which cycle is older evolutionarily, C3 or C4?
The C3 Cycle is older evolutionarily, with the C4 Cycle evolving as an adaptation to specific environmental conditions.
Do all plants exhibit either the C3 or C4 Cycle?
While many plants use one of these pathways predominantly, some plants can exhibit characteristics of both.
Share Your Discovery
Previous Comparison
Primer vs. Dehydrator
Next Comparison
JAR vs. WARAuthor Spotlight
Written by
Fiza RafiqueFiza Rafique is a skilled content writer at AskDifference.com, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
Edited by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
