C4 Photosynthesis

Definition

C4 photosynthesis is a specialized pathway that some plants use to capture carbon dioxide (CO2) more efficiently, particularly in high light and temperature conditions. This process enhances the efficiency of photosynthesis by initially fixing CO2 into a four-carbon compound, oxaloacetate, before entering the Calvin cycle. This adaptation allows C4 plants to minimize water loss and optimize their energy use in challenging environments.

5 Must Know Facts For Your Next Test

1. C4 photosynthesis is primarily found in plants like maize, sugarcane, and sorghum, which thrive in hot, dry climates.
2. In C4 plants, the initial carbon fixation occurs in mesophyll cells, where CO2 is converted to oxaloacetate and then to malate before being transported to bundle sheath cells for the Calvin cycle.
3. The process of C4 photosynthesis allows for a greater concentration of CO2 around RuBisCO in bundle sheath cells, reducing photorespiration rates.
4. C4 photosynthesis is more water-efficient than C3 photosynthesis because it allows plants to close their stomata during the hottest parts of the day without compromising CO2 fixation.
5. The evolution of C4 photosynthesis is thought to have occurred independently in over 60 plant species as an adaptation to high temperatures and light intensities.

Review Questions

• How does C4 photosynthesis improve carbon fixation in plants compared to C3 photosynthesis?
  • C4 photosynthesis improves carbon fixation by using a two-step process that first captures CO2 into a four-carbon compound in mesophyll cells before it enters the Calvin cycle in bundle sheath cells. This separation allows for higher concentrations of CO2 around RuBisCO, minimizing the occurrence of photorespiration. As a result, C4 plants can perform photosynthesis more efficiently under conditions of high temperature and light intensity.
• Discuss the role of Kranz anatomy in C4 photosynthesis and how it contributes to the efficiency of this pathway.
  • Kranz anatomy plays a crucial role in C4 photosynthesis by providing a structural adaptation that facilitates efficient CO2 capture and minimizes photorespiration. In this anatomy, mesophyll cells surround bundle sheath cells, allowing for the quick transfer of the four-carbon compound from mesophyll to bundle sheath cells. This spatial arrangement ensures that CO2 is concentrated around RuBisCO in the bundle sheath cells, enhancing the overall efficiency of photosynthesis under stress conditions.
• Evaluate how the evolutionary adaptation of C4 photosynthesis has influenced plant distribution and survival in varying environments.
  • The evolutionary adaptation of C4 photosynthesis has significantly influenced plant distribution by enabling certain species to thrive in hot and dry environments where C3 plants struggle. By minimizing water loss and increasing carbon fixation efficiency under high temperatures and light conditions, C4 plants have expanded their range into regions with challenging climates. This adaptation has allowed these species to occupy ecological niches where they can dominate, thus impacting biodiversity and ecosystem dynamics across various habitats.

Related terms

Calvin Cycle: The Calvin Cycle is a series of biochemical reactions that occur in the stroma of chloroplasts, where carbon fixation takes place, converting CO2 into glucose using ATP and NADPH generated during the light-dependent reactions.

Photorespiration: Photorespiration is a process that occurs when the enzyme RuBisCO reacts with oxygen instead of carbon dioxide, leading to reduced efficiency in photosynthesis, particularly in C3 plants under stress conditions.

Kranz Anatomy: Kranz anatomy refers to the specialized leaf structure found in C4 plants, characterized by a unique arrangement of mesophyll and bundle sheath cells that facilitate efficient CO2 capture and minimize photorespiration.