Photosynthesis and Photorespiration Summary

Objectives

  • Understand light & dark reactions

  • Evaluate photorespiration's impact on plant evolution

  • Explain the function of photosynthesis genes

Energy Transformation

  • Life on Earth relies on energy from the sun, utilizing carbon dioxide and water to produce oxygen and glucose.

Photosynthesis Overview

  • Photosynthesis converts light energy into chemical energy.

  • Key Equation: 6CO<em>2+12H</em>2O→C<em>6H</em>12O<em>6+6O</em>2+6H2O6CO<em>2 + 12H</em>2O \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2 + 6H_2O

  • Process involves two stages: light-dependent reactions and light-independent reactions (Calvin Cycle).

Light-Dependent Reactions

  • Occur in thylakoid membranes.

  • Convert light energy to ATP and NADPH; split water producing O2.

  • Involves photosystems I (P700) and II (P680).

Light-Independent Reactions (Calvin Cycle)

  • Takes place in the stroma of chloroplasts.

  • Carboxylation of ribulose-1,5-bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA).

  • G3P ultimately forms sugars using 6 ATP and 6 NADPH.

Photorespiration

  • Occurs when Rubisco fixes O2 instead of CO2, lowering photosynthetic efficiency.

  • Results from high O2 and low CO2 conditions.

Plant Adaptations to Photorespiration

  • C4 Pathway: Fixes CO2 into a 4-carbon molecule; minimizes photorespiration.

  • CAM Pathway: Fixes CO2 at night to reduce water loss during the day.

Summary of C4 and CAM Pathways

  • C4 plants (e.g., corn) use spatial separation; CAM plants (e.g., cacti) use temporal separation for CO2 fixation.

Final Notes

  • Photosynthesis is essential for producing glucose for energy storage, enabling plant growth and sustaining ecosystems.

  • Efficient carbon fixation pathways in plants optimize photosynthetic rates under various environmental conditions.