Kranz anatomy

Definition

Kranz anatomy refers to a specialized leaf structure found in C4 plants, characterized by the arrangement of mesophyll and bundle sheath cells that optimize photosynthesis. This anatomical feature allows for an efficient capture of carbon dioxide and reduces photorespiration by spatially separating the initial carbon fixation from the Calvin cycle, enhancing the plant's ability to thrive in hot and dry environments.

5 Must Know Facts For Your Next Test

1. Kranz anatomy is named after the German word 'Kranz,' meaning 'wreath,' reflecting the wreath-like arrangement of chloroplasts in bundle sheath cells.
2. In C4 plants with Kranz anatomy, mesophyll cells capture CO2 and convert it into a four-carbon compound, which is then transported to bundle sheath cells for the Calvin cycle.
3. This adaptation significantly reduces photorespiration, allowing C4 plants to maintain high rates of photosynthesis even under high temperatures and low water availability.
4. Kranz anatomy is commonly found in many grasses and some other plant families, including maize and sugarcane, which are crucial for agriculture.
5. The evolution of Kranz anatomy is thought to be a response to environmental pressures such as increased temperatures and fluctuating CO2 levels during periods of global change.

Review Questions

• How does Kranz anatomy improve the efficiency of photosynthesis in C4 plants compared to C3 plants?
  • Kranz anatomy enhances photosynthesis in C4 plants by spatially separating the initial fixation of carbon dioxide from the Calvin cycle. In C4 plants, CO2 is first fixed in mesophyll cells into a four-carbon compound before it enters bundle sheath cells where the Calvin cycle occurs. This arrangement allows for higher concentrations of CO2 around the Rubisco enzyme, reducing photorespiration and improving overall efficiency compared to C3 plants, which do not have this specialized structure.
• Discuss the role of bundle sheath cells in Kranz anatomy and how they contribute to reduced photorespiration.
  • Bundle sheath cells play a critical role in Kranz anatomy by housing the enzymes and processes necessary for the Calvin cycle. They surround vascular bundles and are tightly packed with chloroplasts, facilitating high concentrations of CO2 derived from the four-carbon compounds produced in mesophyll cells. This spatial separation helps minimize photorespiration, as the conditions within bundle sheath cells favor carbon fixation over oxygen fixation, thereby increasing sugar production and plant efficiency.
• Evaluate the ecological significance of Kranz anatomy in relation to environmental stressors such as drought and high temperatures.
  • Kranz anatomy provides ecological advantages for C4 plants by enabling them to thrive under environmental stressors like drought and high temperatures. The efficient carbon fixation pathway reduces water loss through transpiration while maintaining high photosynthetic rates. As climate change progresses and these stressors become more prevalent, C4 plants with Kranz anatomy may become increasingly important for food security and ecosystem resilience, showcasing their evolutionary adaptations to changing environments.

Related terms

C4 Photosynthesis: A type of photosynthesis that occurs in certain plants, where carbon dioxide is initially fixed into a four-carbon compound before entering the Calvin cycle, leading to increased efficiency in carbon fixation.

Bundle Sheath Cells: Specialized cells that surround the vascular tissue in C4 plants, where the Calvin cycle takes place, allowing for a higher concentration of CO2 for efficient sugar production.

Photorespiration: A process that occurs when oxygen is fixed instead of carbon dioxide during photosynthesis, leading to a loss of energy and carbon; minimized in C4 plants due to their unique anatomy.