Chapter 5: Photosynthesis and Cellular Respiration

5.1 Matter and Energy Pathways in Living Systems

• Photosynthesis:

  • Occurs in chloroplasts where solar energy is trapped.
  • Involves light-dependent reactions using pigments to trap solar energy, converting it to chemical energy (ATP) and reducing power (NADPH).
  • Light-independent reactions convert ATP and NADPH into glucose through carbon dioxide reduction.

• Cellular Respiration:

  • Occurs in mitochondria, breaking down energy-rich compounds to generate ATP.
  • Involves glycolysis, the Krebs cycle, and an electron transport system.
  • Aerobic respiration fully oxidizes glucose, while fermentation incompletely oxidizes it.

• ATP: Source of energy for chemical reactions in cells.

5.2 Photosynthesis Stores Energy in Organic Compounds

• Light-dependent Reactions:

  • Solar energy is used to generate ATP and NADPH.
  • Chlorophyll absorbs light, exciting electrons which are transferred via an electron transport system.

• Chemiosmosis:

  • Mechanism where energy stored in a gradient is used to generate ATP.

• Light-independent Reactions (Calvin-Benson Cycle):

  • Uses ATP and NADPH to reduce CO2 and synthesize glucose.

• Photosystems:

  • Photosystem I and II are involved, with electrons transferred to NADP+ forming NADPH.

• Key Pigments:

  • Chlorophyll a, chlorophyll b, and carotenoids.
  • Pigments absorb specific wavelengths aiding photosynthesis.

5.3 Cellular Respiration Releases Energy from Organic Compounds

• Glycolysis:

  • Occurs in the cytoplasm, splitting glucose into pyruvate and generating ATP and NADH. Does not require oxygen.

• Krebs Cycle:

  • Occurs in mitochondria, breaking down acetyl CoA to CO2 and transferring energy to NADH and FADH2.

• Electron Transport Chain:

  • High-energy electrons are transferred through carriers, generating ATP through chemiosmosis.
  • Oxygen is the final electron acceptor, forming water.

• Types of Respiration:

  • Aerobic: Requires oxygen, yields more ATP.
  • Anaerobic (Fermentation): Does not use oxygen; lactate or ethanol is produced, and less ATP is generated.

• Fermentation:

  • Lactate Fermentation: Converts pyruvate to lactate in muscles under low oxygen.
  • Ethanol Fermentation: Yeasts convert pyruvate to ethanol.

Experiments and Investigations

• Photosynthesis:

  • Floating leaf disk assay to measure photosynthesis rate using oxygen production.

• Cellular Respiration:

  • Measuring oxygen consumption and heat production in germinating seeds.

Applications and Technological Implications

• Hydrogen as a Clean Fuel:

  • Research into artificial systems to harness solar energy to split water, producing hydrogen.

• Bioenergy from Fermentation:

  • Potential use of ethanol as a renewable fuel source.

Summary

• Photosynthesis captures solar energy, converting it to chemical energy stored as glucose.
• Cellular respiration releases stored energy from glucose to ATP for cellular functions.
• ATP and NADPH are essential energy carriers in both photosynthesis and respiration.
• Enzymes and metabolic pathways are crucial for these processes.

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These notes provide a comprehensive summary of photosynthesis and cellular respiration, their mechanisms, and their roles in energy transformation within living organisms. They're useful for understanding the biochemical energy transfer in cells and the broader implications for energy use and sustainability.