C3 vs C4 Photosynthesis

Definition

C3 and C4 photosynthesis are two different pathways that plants use to fix carbon dioxide during the process of photosynthesis. While C3 photosynthesis is the most common pathway, occurring in many plants like wheat and rice, C4 photosynthesis is an adaptation found in certain plants like maize and sugarcane that allows them to minimize photorespiration and optimize carbon fixation under high light intensity and temperature conditions.

5 Must Know Facts For Your Next Test

1. C3 photosynthesis occurs in three main stages: carbon fixation, reduction, and regeneration, using RuBisCO as the primary enzyme to fix carbon.
2. C4 photosynthesis has two distinct stages: an initial fixation of CO2 into a four-carbon compound in mesophyll cells, followed by a second stage in bundle sheath cells where CO2 is released for the Calvin Cycle.
3. C4 plants have a higher photosynthetic efficiency than C3 plants under high temperature and light conditions due to their ability to concentrate CO2 around RuBisCO and reduce photorespiration.
4. Examples of C4 plants include maize, sugarcane, and sorghum, which thrive in warm climates and have adapted to conserve water more effectively than C3 plants.
5. C3 plants are more common in cooler, wetter climates where photorespiration is less of a concern, such as wheat, rice, and most trees.

Review Questions

• How do the mechanisms of carbon fixation differ between C3 and C4 photosynthesis?
  • C3 photosynthesis relies on the enzyme RuBisCO to fix carbon dioxide directly from the atmosphere into a three-carbon compound. In contrast, C4 photosynthesis first converts CO2 into a four-carbon compound in mesophyll cells before transporting it to bundle sheath cells for further processing. This difference allows C4 plants to concentrate CO2 around RuBisCO, reducing photorespiration and increasing efficiency under conditions of high light and temperature.
• Discuss the advantages of C4 photosynthesis over C3 photosynthesis in specific environmental conditions.
  • C4 photosynthesis offers several advantages over C3 photosynthesis in environments characterized by high temperatures and intense sunlight. C4 plants can effectively concentrate CO2 around RuBisCO, minimizing photorespiration which tends to waste energy and carbon. This adaptation allows C4 plants to maintain higher rates of photosynthesis and better conserve water through reduced stomatal opening. As a result, they thrive in arid or semi-arid regions where other plants may struggle.
• Evaluate the impact of climate change on the distribution of C3 and C4 plant species across different ecosystems.
  • Climate change is expected to alter temperature and precipitation patterns globally, impacting the distribution of both C3 and C4 plant species. As temperatures rise, regions previously dominated by C3 plants may become more suitable for C4 species due to their superior efficiency under high light and heat. This shift could lead to changes in plant community structures and ecosystem functions. Additionally, shifts in moisture availability may affect water-use efficiency among these plant types, further influencing their competitive dynamics in various environments.

Related terms

Photorespiration: A process that occurs when the enzyme RuBisCO oxygenates RuBP, leading to a wasteful pathway that decreases the overall efficiency of photosynthesis.

Calvin Cycle: A series of biochemical reactions in the chloroplasts that form the basis of carbon fixation in C3 plants, converting CO2 into glucose.

Kranz Anatomy: A specialized leaf structure found in C4 plants where bundle sheath cells surround vascular tissue, allowing for more efficient CO2 fixation.