Photosynthesis and Cellular Respiration Explained

Light and Pigments

• Absorbed: Blue and Red light
• Reflected: Green (chloroplasts appear green)
• Other pigments: Carotenoids, Xanthophylls
• Fall colors: Chlorophyll breaks down, revealing other pigments

Photosynthesis

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

• CO₂: Carbon source for glucose
• H₂O: Source of hydrogen and electrons
• Light: Energy source
• Performed by: Plants, algae, and cyanobacteria

Chloroplast Structure

• Outer and inner membrane
• Stroma: Fluid-filled space
• Thylakoid: Flat sacs forming grana
• Chlorophyll located in the thylakoid membrane

Light Reactions (Thylakoid Membrane)

• PSII absorbs light, exciting electrons
• Water splits, releasing O₂
• ETC pumps H⁺ to create ATP (chemiosmosis)
• PSI re-excites electrons to produce NADPH
• Products: ATP, NADPH, O₂

Calvin Cycle (Light-Independent)

• Location: Stroma
• Needs: CO₂, ATP, NADPH
• Produces: Glucose (G3P)
• Steps: Carbon fixation, Reduction, Regeneration

Cellular Respiration

ATP Production

• Most ATP is generated by the ETC
• Powers cell activities: transport, movement, and synthesis

Respiration Equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

• Occurs in: Cytoplasm and mitochondria
• Organisms: All eukaryotes and many prokaryotes

Glycolysis (Cytoplasm)

• Inputs: Glucose
• Outputs: 2 Pyruvate, 2 ATP, 2 NADH

Krebs Cycle (Mitochondrial Matrix)

• Inputs: Acetyl-CoA
• Outputs (per glucose): 4 CO₂, 6 NADH, 2 FADH₂, 2 ATP

ETC (Inner Membrane)

• NADH/FADH₂ donate electrons to proteins
• H⁺ gradient powers ATP synthase, producing ~32–34 ATP
• Oxygen acts as the final electron acceptor, forming H₂O

Aerobic Respiration Order

1. Glycolysis (Cytoplasm)
2. Pyruvate Oxidation (Matrix)
3. Krebs Cycle (Matrix)
4. ETC (Inner Membrane)

Fermentation (Anaerobic)

• Alcohol (Yeast): Produces Ethanol and CO₂
• Lactic Acid (Muscles): Produces Lactic acid

Lactic Acid Indicators

• Muscle burning and fatigue indicate lactic acid fermentation

Yeast in Bread

• Alcohol fermentation produces CO₂ to rise dough; alcohol evaporates

ATP Yield

• Aerobic: 36–38 ATP per glucose
• Anaerobic: 2 ATP per glucose

Lactic Acid Threshold

• Point where lactic acid builds faster than it is removed, causing fatigue

VO₂ Max

• Maximum oxygen consumption during exercise; a measure of fitness