Energy and Respiration in the Human Body

Sources of Energy

• Energy is required for various body activities.
• The energy comes from the food we consume daily.

Respiration

• Process by which chemical energy stored in food is released.
• Types of Respiration:
  • Aerobic Respiration: Requires oxygen.

Stages of Aerobic Respiration

1. Glycolysis

   • Occurs in the cytoplasm of the cell.
   • Process:
     • Glucose is activated by phosphorylation using two ATP molecules.
     • Activated glucose is split into two trios phosphate molecules (3-carbon).
     • Each trios phosphate is oxidized to pyruvate (3-carbon).
     • ATP is formed.
     • NAD is reduced to NADH.

2. Krebs Cycle

   • Occurs in the mitochondrial matrix.
   • Process:
     • Pyruvate from glycolysis enters mitochondria.
     • Pyruvate loses a carbon atom, released as CO2.
     • Remaining 2-carbon compound donates hydrogen, accepted by NAD to form NADH.
     • Combines with co-enzyme A to form acetyl CoA.
     • Acetyl CoA enters the Krebs Cycle.
     • Combines with a 4-carbon compound to form a 6-carbon compound, regenerating co-enzyme A.
     • Undergoes oxidation, losing 2 carbon atoms as CO2.
     • Hydrogen atoms are accepted by NAD and FAD to form NADH and FADH2.
     • ATP is generated.
     • 4-carbon compound is ready to accept another acetyl CoA.

3. Oxidative Phosphorylation

   • Occurs on the inner mitochondrial membrane.
   • Process:
     • NADH and FADH2 from glycolysis and Krebs cycle are oxidized to NAD and FAD.
     • Hydrogen atoms split into ions and electrons.
     • Electrons move through the electron transport chain.
     • Series of redox reactions occur, forming ATP.
     • Electrons and hydrogen ions combine with oxygen to form water.
     • Oxygen acts as the final electron acceptor.

Summary

• Energy is vital for body activities and obtained through the breakdown of food via aerobic respiration.
• Aerobic respiration involves glycolysis, the Krebs cycle, and oxidative phosphorylation, ultimately producing ATP and water while utilizing oxygen.