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Difference Between C3 and C4 Cycle

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Difference Between C3 and C4 Cycle

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How C3 Cycle Different From C4 Cycle?

The C3 and C4 cycles are two distinct pathways used by plants during photosynthesis to fix carbon dioxide. The C3 cycle is the primary pathway employed by most plants, where carbon dioxide is directly fixed into a three-carbon compound. In contrast, the C4 cycle is an adaptation found in certain plant species, particularly those inhabiting hot and arid environments. It involves an additional step where carbon dioxide is initially captured and converted into a four-carbon compound before being converted back into three-carbon molecules. This spatial separation of initial carbon fixation and the subsequent steps in the C4 cycle helps plants optimize photosynthetic efficiency by reducing energy loss through photorespiration. The C4 cycle is thus a specialised mechanism that enables certain plants to thrive in challenging environmental conditions.

Last updated date: 25th Sep 2023

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What is C3 and C4 Cycle?

C3 Cycle: C3 cycle means carbon dioxide is directly incorporated into a three-carbon compound called 3-phosphoglycerate.

C4 Cycle: C4 cycle is an alternative pathway found in certain plant species, where carbon dioxide is initially captured and converted into a four-carbon compound before being converted back to three-carbon molecules.

Interesting Facts

C3 Cycle : The C3 cycle is considered more ancient and is present in a wider range of plant species. It is estimated to have evolved around 3.5 billion years ago.

C4 Cycle : The C4 cycle is thought to have evolved independently multiple times in different plant lineages, demonstrating its importance as an adaptation to certain environmental conditions.

Characteristics of C3 and C4 Cycle

C3 Cycle:

Efficiency: C3 plants have relatively lower photosynthetic efficiency under high light, high temperature, and water-limited conditions due to the occurrence of photorespiration.

Carbon Fixation: In the C3 cycle, carbon dioxide is directly fixed into a three-carbon compound called 3-phosphoglycerate (3-PGA) using the enzyme Rubisco.

C4 Cycle:

Adaptation: C4 plants have specialised leaf anatomy with distinct mesophyll and bundle sheath cells, enabling the efficient compartmentalisation of the C4 pathway.

Distribution: C4 plants are found in regions with high light intensity, high temperatures, and limited water availability, such as tropical and subtropical areas.

Difference between C3 and C4 Cycle

S.No	Category	C3 Cycle	C4 Cycle
1.	Cells	C3 cycle is carried out by mesophyll cells.	C4 cycle is carried out by both mesophyll cells and bundle sheath cells.
2.	Sunlight	C3 cycle can be saturated with sunlight.	C4 cycle does not saturate with sunlight.
3.	Effect of Oxygen	C3 cycle is inhibited by oxygen.	No inhibition of C4 cycle is observed with C4 cycle
4.	Kranz Anatomy in Leaves	Kranz anatomy is absent in leaves of the C3 plants.	Kranz anatomy is present in leaves of the C4 plants.
5.	Optimum Temperature	The optimum temperature of the C3 cycle is 20-25 degrees of Celsius.	The optimum temperature of the C4 cycle is 30-45 degrees of Celsius.

Summary

The C3 and C4 cycles are two different pathways used by plants for carbon fixation during photosynthesis. In the C3 cycle, carbon dioxide is directly fixed into a three-carbon compound, while in the C4 cycle, carbon dioxide is initially captured and converted into a four-carbon compound before being processed into three-carbon molecules. The C4 cycle is an adaptation found in certain plant species, particularly in hot and dry environments, as it minimizes photorespiration and enhances photosynthetic efficiency. C3 plants are widespread and include many common crops, while C4 plants are specialised for regions with high light intensity, high temperatures, and limited water availability. Overall, the C4 cycle is an evolutionary strategy that optimizes carbon fixation and enables plants to thrive in challenging environmental conditions.

FAQs on Difference Between C3 and C4 Cycle

1. Why do certain plants use the C4 cycle?

Plants that use the C4 cycle, known as C4 plants, have evolved this pathway as an adaptation to overcome limitations of the C3 cycle, especially in hot and dry environments. The C4 cycle minimizes photorespiration and enhances photosynthetic efficiency, allowing these plants to thrive in regions with high light intensity, high temperatures, and limited water availability.

2. Which plants use the C3 cycle and which plants use the C4 cycle?

The C3 cycle is utilised by a wide range of plant species, including most trees, shrubs, and common crops like wheat, rice, and soybeans. On the other hand, the C4 cycle is found in specific plant species such as corn, sugarcane, and various grasses that are adapted to tropical and subtropical regions. Plants that predominantly utilize the C3 cycle include most trees, shrubs, and common crops like wheat, rice, oats, barley, and soybeans. These plants are typically found in temperate regions with abundant water availability.

3. Are C4 plants more efficient than C3 plants in photosynthesis?

Yes, C4 plants generally exhibit higher photosynthetic efficiency compared to C3 plants, especially under high light intensity, high temperatures, and water-limited conditions. The spatial separation of carbon fixation and the Calvin cycle in the C4 pathway reduces energy loss through photorespiration, resulting in increased efficiency and productivity.