Biology Chapter on Energy Molecules and Photosynthesis

Energy Molecules

• ATP (adenosine triphosphate) is a high-energy molecule providing energy for cellular functions.
• ADP (adenosine diphosphate) is a lower-energy molecule that converts to ATP through the addition of a phosphate group.

Photosynthesis

• Photosynthesis converts light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.
• Chlorophyll is the pigment responsible for absorbing light in photosynthetic organisms, located in chloroplasts.
• Photosynthesis occurs in two stages: light-dependent reactions (capture sunlight) and light-independent reactions (Calvin Cycle uses captured energy).

Chloroplast Structure

• Thylakoids are membrane-bound structures within chloroplasts containing chlorophyll for light-dependent reactions.
• Grana (stacks of thylakoids) and stroma (fluid surrounding grana) are critical for photosynthesis.

Light Reactions

• Light-dependent reactions absorb sunlight, split water molecules, and produce ATP and NADPH for the Calvin Cycle.
• Energy captured during these reactions drives carbohydrate synthesis in light-independent reactions.

Cellular Respiration

• Cellular respiration produces ATP by breaking down carbon-based molecules (glucose) with oxygen (aerobic process).
• Takes place mainly in mitochondria, involving glycolysis, Krebs Cycle, and Electron Transport Chain.

Glycolysis and Fermentation

• Glycolysis is the initial step in cellular respiration, converting glucose into two pyruvate molecules and producing two ATP molecules.
• Fermentation, an anaerobic process, occurs when oxygen is absent, allowing ATP production to continue in glycolysis and recycling NAD+.

Krebs Cycle

• The Krebs Cycle further breaks down carbon molecules after glycolysis, generating electron carriers for the Electron Transport Chain.

Importance of Oxygen

• Oxygen acts as the final electron acceptor in cellular respiration, forming water and enabling energy production.

Chemical Equations

• Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
• Cellular Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O

Comparison of Processes

• Photosynthesis and cellular respiration are interconnected; photosynthesis captures energy, while cellular respiration releases it, with equations being reverses of each other.
• Both glycolysis and Krebs cycle play roles in energy production, with each contributing to ATP synthesis through different pathways.

Role of Fermentation

• Fermentation allows glycolysis to continue when oxygen is not available, producing energy in the form of ATP and generating byproducts like lactic acid.

Key Concepts

• Light-dependent reactions capture energy from sunlight, while light-independent reactions synthesize sugars.
• Cellular respiration has two main stages: aerobic (requires oxygen) and anaerobic (does not require oxygen, e.g., fermentation).
• Carbon compounds like carbohydrates, lipids, and proteins are primary energy sources broken down to generate ATP.