Chapter_4_Biology12

Chapter 4: Photosynthesis

Specific Expectations

• Terminology Related to Metabolism

  • C2.1: Use appropriate terminology related to metabolism (Photosynthesis steps).

• Laboratory Investigation

  • C2.3: Conduct a laboratory investigation into photosynthesis to identify products and display them appropriately.

• Chemical Changes and Energy Conversions

  • C3.2: Explain chemical changes and energy conversions during photosynthesis.

• Matter and Energy Transformations

  • C3.4: Describe and illustrate matter and energy transformations, including roles of oxygen and chloroplasts.

Overview of Photosynthesis

• Photosynthesis is crucial for the sustainable management of Canada's boreal forest, impacting both ecology and economy.

• This process allows trees and plants to convert about 12.5 million tonnes of carbon dioxide into organic compounds annually.

• Metabolic pathways within cells convert high-energy compounds (like glucose) into usable energy (ATP).

Launch Activity: Seeing Green

• Chlorophyll absorbs light energy and synthesizes carbohydrates from CO2 and water.

• Materials Needed:

  • Beaker of chlorophyll solution, light source.

• Procedure:

  1. Shine a strong light on chlorophyll solution in a dark room.

  2. Observe chlorophyll color at different angles and analyze fluorescence.

Section 4.1: Light-Dependent Reactions

• Key Terms:

  • Light-dependent reaction, light-independent reaction, thylakoid, pigment, photosystem, photophosphorylation.

• Photosynthesis transforms sunlight into chemical energy.

• Only 1-2% of sunlight reaching Earth is used by photosynthesizing organisms (e.g., cyanobacteria, plants).

Energy Conversion

• Photosynthesis produces 1.4 x 10^15 kg of energy-storing compounds like glucose each year.

• Structural components (cellulose) and metabolic substances (sugars, amino acids) are made from glucose.

• General Equation for Photosynthesis:

  • 6CO2 + 6H2O + energy → C6H12O6 + 6O2

Photosystem and Pigments

• Photosystems: Two types present: PS I (P700) and PS II (P680).

• Photosystem II absorbs light, creating an energized electron and splitting water, releasing oxygen.

• Pigments: Chlorophyll a and b absorb red and blue light but reflect green, giving leaves their color.

Structure of Chloroplasts

• Chloroplasts contain thylakoids, granum, and stroma, essential for photosynthesis.

• CO2 enters through stomata, while water is absorbed through the roots, entering the thylakoids.

Light Harvesting Complex

• Pigments, embedded in thylakoid membranes, absorb light energy crucial for energy synthesis.

• The antenna complex gathers light and transfers energy to the reaction center.

Noncyclic vs. Cyclic Photophosphorylation

• Noncyclic photophosphorylation: Photon energies from PS II and I create NADPH and ATP for Calvin cycle.

• Cyclic photophosphorylation: Provides additional ATP without producing NADPH or oxygen.

The Calvin Cycle (4.2)

• Carbon fixation occurs in the stroma, turning CO2 into G3P, the foundational block for glucose.

• Enzyme: ribulose bisphosphate carboxylase (RuBisCO) catalyzes initial reactions.

• Phases of Calvin Cycle:

  1. Carbon dioxide fixation.

  2. Reduction phase - G3P formation.

  3. Regeneration of RuBP.

Adaptations to Photosynthesis

• C3 Plants: Struggle with photorespiration; can utilize CO2 efficiently under optimal conditions.

• C4 Plants: Separate initial CO2 fixation and the Calvin cycle reactions to enhance efficiency in hot climates.

• CAM Plants: Fix CO2 at night, store it for daytime use, minimizing water loss.

Conclusion and Impacts

• Understanding photosynthesis has implications for agriculture, bioengineering, and combating climate change.

• Current research focuses on improving efficiency and mimicking photosynthetic processes for sustainable energy solutions.