9 Cellular Respiration

Cellular Respiration

Learning Objectives

• Define cellular respiration.

• Describe the role of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) during cellular respiration.

• Recall the percentage of energy released during cellular respiration that forms ATP and is released as heat energy.

• Describe anaerobic respiration: its role, location, timing, and chemical steps.

• Provide the word equation for anaerobic respiration.

• Describe aerobic respiration: its role, location, timing, and chemical steps.

• Provide the word and chemical equations for aerobic respiration.

• List examples of cell activities that require ATP.

Overview of Cellular Respiration

• Metabolism: The total of all chemical reactions in a cell.

• Mitochondria: Organelles functioning as the site of cellular respiration to produce ATP.

Definition of Cellular Respiration

• Cellular respiration is a chemical process where food molecules (usually glucose) are broken down to release energy (stored as ATP).

• This occurs in the mitochondria and involves over 20 different reactions. Each reaction releases a small amount of energy.

Major Steps of Cellular Respiration

1. Glycolysis

   • Converts glucose into pyruvic acid, generating 2 ATP.

   • Occurs in the cytoplasm.

   • If O2 is available, further processes continue; if not, anaerobic pathways take place.

2. Krebs Cycle (Citric Acid Cycle)

   • Occurs in the mitochondria and produces CO2 + 2 ATP by processing acetyl CoA.

   • Involves a cyclical series of oxidation reactions.

3. Electron Transport Chain

   • Also occurs in the mitochondria and produces up to 34 ATP, along with water as a waste product.

   • Utilizes NADH and FADH from previous steps to transfer electrons.

Energy Efficiency

• Energy Yield: About 60% of the energy released during respiration is lost as heat, while 40% is used for ATP formation.

• ATP is formed by adding an inorganic phosphate group to ADP, storing energy in the bond between the ADP and the third phosphate group.

Anaerobic Respiration

• Definition: An anaerobic process that does not require oxygen and occurs in the cytoplasm.

• Converts glucose through 10 steps into 2 pyruvic acid molecules.

• If oxygen is limited, pyruvic acid converts to lactic acid, yielding 2 ATP.

• Word Equation: Glucose → Lactic Acid + 2 ATP

Importance of Anaerobic Respiration

• Accumulation of lactic acid in muscles causes fatigue/pain.

• Lactic acid is transported to the liver to regain oxygen and reform glucose or glycogen.

• This leads to an oxygen debt that needs to be repaid.

Energy Yield in Anaerobic Respiration

Aerobic Respiration

• Definition: Requires oxygen for complete glucose breakdown in the mitochondria.

• Begins with glycolysis, further progressing to Krebs cycle and Electron Transport Chain.

Pathways After Glycolysis

• Anaerobic Respiration: Without oxygen, pyruvic acid → lactic acid, yielding 2 ATP.

• Aerobic Respiration: With oxygen, pyruvic acid enters mitochondria to produce acetyl CoA, continue with Krebs cycle and Electron Transport Chain.

Energy Yield in Aerobic Respiration

Differences between Aerobic and Anaerobic Respiration

Cellular Activities Using Energy

• ATP Usage: 60% of energy lost as heat; 40% used for activities such as:

  • Muscle contraction

  • Active transport across membranes

  • Synthesis of large molecules for growth/repair

  • Transmission of nerve impulses

  • Cell division and growth

  • Maintenance of body temperature

  • Movement of substances/cells

Activities and Review Tasks

• Complete "Cellular Respiration Notetake" worksheet.

• Review textbook chapters and Moodle resources for further studies.