Aerobic Respiration Basics

Key Equations

• Word Equation
  • Glucose + Oxygen → Carbon Dioxide + Water + Energy
• Balanced Chemical Equation
  • C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Overview

• Aerobic respiration occurs in two stages:
  1. Glycolysis
  2. Krebs Cycle and Electron Transport Chain

Stage 1: Glycolysis

• Location: Cytosol of the cell (liquid part of the cytoplasm)
• Oxygen Role: Not involved
• Process:
  • Starts with glucose (a 6-carbon molecule)
  • Ends with two 3-carbon molecules of pyruvic acid
  • Key Reaction:
    • Removal of hydrogen atoms from glucose
    • Formation of NADH from NAD⁺, electrons, and protons
  • Energy Yield: Net gain of 2 ATP

Stage 2: Krebs Cycle

• Location: Mitochondria
• Requirements: Oxygen is essential
• Pyruvic Acid Conversion:
  • Converted to acetyl CoA (2-carbon molecule)
  • Involves removal of a carbon dioxide and hydrogen atoms (forming NADH)
• Krebs Cycle Process:
  • Acetyl CoA (2-carbon) joins with a 4-carbon molecule to form a 6-carbon molecule
  • Cycle breaks down this 6-carbon molecule back to a 4-carbon molecule
  • Removal of two carbon dioxides and hydrogen atoms
• Key Products of Krebs Cycle:
  • 3 NADH molecules
  • 1 ATP
  • 2 Carbon dioxide molecules

Electron Transport Chain

• Location: Mitochondria
• Process:
  • NADH transfers electrons and protons to the electron transport chain
  • Electrons pass through a series of molecules, releasing energy
  • Energy is used to create ATP (some energy lost as heat)
  • Low energy electrons combine with protons and oxygen to form water
• NADH Role: Reverts to NAD⁺ after transferring electrons and protons

Study Tips

• Familiarize yourself with both stages, glycolysis and Krebs cycle.
• Practice answering exam questions on these topics.
• Use textbooks and past exam papers for additional practice.