4.2 Respiration in Plants

Overview of Cellular Respiration

1. Glycolysis: Cytoplasm
2. Krebs Cycle (TCA Cycle): Mitochondrial Matrix
3. Electron Transport System (ETS): Inner Mitochondrial Membrane

Glycolysis (EMP Pathway)

• Location: Cytoplasm
• Process: 1 Glucose (6C) → 2 Pyruvate (3C)
• Net Products per Glucose:
  • 2 Pyruvate
  • 2 ATP
  • 2 NADH

Fermentation (Anaerobic Respiration)

• Occurs in the absence of oxygen.
• Types:
  • Alcoholic Fermentation (Yeast): Pyruvate → Ethanol + CO₂
  • Lactic Acid Fermentation (Muscles): Pyruvate → Lactic Acid
• Purpose: Regenerates NAD+ for glycolysis to continue.

Krebs Cycle (TCA Cycle)

• Location: Mitochondrial Matrix
• Process: Acetyl-CoA is completely oxidized.
• Net Products per Glucose (2 turns):
  • 6 NADH
  • 2 FADH₂
  • 2 ATP (or GTP)
  • 4 CO₂

Electron Transport System (ETS)

• Location: Inner Mitochondrial Membrane
• Process:
  • Electrons from NADH and FADH₂ are passed down a series of protein complexes.
  • Oxygen is the final electron acceptor, forming water.
  • A proton gradient is created, driving ATP synthesis via oxidative phosphorylation.

ATP Yield

• The complete aerobic respiration of one glucose molecule yields approximately 30-32 ATP.

Amphibolic Pathway

• Respiration is a central metabolic pathway that is both catabolic (breaking down molecules) and anabolic (building up molecules).
• Intermediates of the Krebs cycle can be used as precursors for the synthesis of other biomolecules (e.g., amino acids, chlorophyll).

Respiratory Quotient (RQ)

• Definition: RQ = Volume of CO₂ evolved / Volume of O₂ consumed
• RQ Values:
  • Carbohydrates: 1.0
  • Fats: ~0.7
  • Proteins: ~0.9
  • Organic Acids: > 1.0
  • Anaerobic Respiration: ∞