Chapter 8 Pt. 1 (March 10, 2024)

Overview of Photosynthesis

• Last chapter of the semester focuses on photosynthesis as the foundation of food chains on Earth.

• Photosynthesis traces the flow of organic fuel and energy from producers to consumers and back to inorganic waste products.

Light Reactions vs. Calvin Cycle

• Photosynthesis Equation:

  • Summarized as water and carbon dioxide transforming into glucose and oxygen.

  • Inverse of cellular respiration with similar energetic events taking place in both processes.

  • Importance of electron transport chains in generating ATP.

Light-Dependent Reactions

• Key products: ATP and NADPH used for sugar synthesis.

• Involved in generating a proton motive force that drives ATP synthesis through ATP synthase.

• Byproduct of the light reactions is oxygen, derived from water splitting.

Light-Independent Reactions (Calvin Cycle)

• Also referred to as dark reactions, do not require light but rely on products from the light-dependent reactions.

• The cycle regenerates the CO2 accepting molecule (RuBP).

• Works to synthesize glucose utilizing the high-energy electrons from NADPH.

Importance of Chloroplasts

• Chloroplasts contain thylakoid membranes crucial for photosynthesis

• Thylakoids stack into granum, facilitating the light reactions and associated electron transport.

• Photosystems (PSI and PSII) work together to capture light energy and generate energy carriers.

Role of Stomata in Photosynthesis

• Stomata are pores on the leaf allowing CO2 to enter and oxygen to exit during gas exchange.

• Guard cells manage the opening and closing of stomata, playing a crucial role in regulating transpiration and gas exchange.

Chlorophyll and Light Absorption

• Chlorophyll pigments absorb specific wavelengths of light, crucial for initiating photosynthesis.

• Three fates of absorbed energy:

  • Converted to heat,

  • Transferred to other chlorophylls (resonance transfer),

  • Excited electrons may be transferred to an electron acceptor, initiating the electron transport chain.

Electron Transport Chain and ATP Synthesis

• Photosystem II starts the electron transport chain, exciting electrons that eventually lead to NADPH production through Photosystem I.

• Protons are pumped into the thylakoid lumen creating a concentration gradient that drives ATP synthesis.

Cyclic Electron Flow

• Sometimes, the system shifts from linear to cyclic flow under intense light conditions to produce extra ATP without generating NADPH or oxygen.

• This is a response to the different consumption rates of ATP and NADPH during the Calvin cycle.

Summary and Exam Review

• Key concepts include the navigation of energy transformation in photosynthesis, importance of chloroplast structure, and the participating mechanisms in light-dependent and light-independent reactions.

• Redox potentials and electron flow dynamics will be highlighted in the exam.

• A comprehensive review will be conducted prior to the exam.