Aerobic Respiration: The Basics

Overview

• Aerobic respiration is a two-stage process.
• Frequently tested in higher and ordinary levels.

Stage One: Glycolysis

• Definition: Splitting of glucose.
• Location: Cytosol of the cell (liquid part of the cytoplasm).
• Oxygen Involvement: Oxygen plays no role in glycolysis.
• Process:
  • Begins with glucose, a six-carbon molecule.
  • End product: two three-carbon molecules of pyruvic acid.
  • Hydrogen Atoms:
    • Removal of pairs of hydrogen atoms to form NADH (electron and proton carrier).
    • Important to revise how NAD+ combines with electrons and protons to form NADH.
  • Energy Yield:
    • Net gain of two ATP.
• Condition for Stage Two: Presence of oxygen.

Stage Two: Krebs Cycle and Electron Transport Chain

• Location: Mitochondria of the cells.

Krebs Cycle (Citric Acid Cycle)

• Entry Molecule: Pyruvic acid is converted to acetyl CoA (two-carbon molecule).
  • Involves removal of carbon dioxide and hydrogen atoms.
• Cycle Reaction:
  • Acetyl CoA (2C) combines with a four-carbon molecule to form a six-carbon molecule.
  • Breakdown of the six-carbon molecule back to the four-carbon molecule involves:
    • Removal of two carbon dioxide molecules.
    • Formation of NADH from hydrogen atoms.
• Products:
  • 3 NADH
  • 1 ATP
  • 2 carbon dioxide molecules
  • Energy Yield: Minimal, only one ATP.

Electron Transport Chain

• Process:
  • NADH transfers electrons and protons to the electron transport chain.
  • Electrons release energy as they pass through the chain, some of which is used to make ATP; some energy is lost as heat.
  • Low energy electrons combine with protons and oxygen to form water at the end of the chain.
  • NADH reverts to NAD+ after transfer.

Study Recommendations

• Practice exam questions after mastering each stage.
• Use textbooks and exam papers for practice.
• Understand processes thoroughly to answer questions effectively.