• Understand the overall reactants and products of photosynthesis and cellular respiration, and how these processes are linked.
• Explain the role of enzymes (biological catalysts) and coenzymes (e.g. NAD⁺/NADH, NADP⁺/NADPH, ADP/ATP, FAD/FADH₂) in facilitating and regulating each step of these pathways.
• Identify factors affecting enzyme function – including temperature, pH, substrate concentration, and inhibitors (competitive, non-competitive, feedback) – and how these factors regulate the rate of biochemical pathways.

Photosynthesis and Cellular Respiration

Photosynthesis captures light energy to produce glucose, while cellular respiration breaks down glucose to release ATP. These processes are interdependent: photosynthesis provides the oxygen and glucose needed for respiration, while respiration returns carbon dioxide and water for photosynthesis.

Overall Equations

• Photosynthesis: 12 H₂O + 6 CO₂ → C₆H₁₂O₆ + 6 O₂ + 6 H₂O (in the presence of light & chlorophyll).
• Occurs in plants, algae, and some bacteria. Converts solar energy into chemical energy (glucose).
• Cellular Respiration: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ~30–32 ATP.
• Occurs in all living cells, including plants at night. Releases stored energy from glucose for cellular functions.

Regulation of Biochemical Pathways

Enzymes and Coenzymes in Photosynthesis and Respiration

• Enzymes control each step of biochemical pathways, ensuring reactions proceed efficiently.
• Coenzymes assist in energy transfer:
• NAD⁺/NADH & FAD/FADH₂ (respiration) and NADP⁺/NADPH (photosynthesis) carry electrons for energy transfer.
• ATP/ADP acts as the cell’s rechargeable battery.
• Coenzyme A (CoA) transports acetyl groups in respiration.

Factors Affecting Enzyme Function

• Temperature: Moderate heat increases enzyme activity, but extreme heat denatures enzymes, stopping reactions.
• pH: Each enzyme has an optimal pH. Deviations can alter enzyme shape, reducing function.
• Substrate & Enzyme Concentration: Increased substrate or enzyme boosts reaction rate until saturation is reached.
• Inhibitors:
• Competitive inhibitors block the enzyme's active site.
• Non-competitive inhibitors bind elsewhere, altering enzyme shape.
• Feedback inhibition occurs when excess product slows its own production, preventing unnecessary energy use.

Big Picture: Energy Flow in Ecosystems

Photosynthesis fuels ecosystems by providing oxygen and glucose. Cellular respiration uses these to generate ATP while returning CO₂ and H₂O for photosynthesis. Understanding these pathways helps improve crop yields (e.g., optimizing photosynthesis in agriculture) and manage food storage (e.g., controlling respiration rates to extend shelf life).