Biology: Cellular Respiration (Chapter 9)

Section 9-1: Chemical Pathways

Chemical Energy in Food

• Calories: Energy needed to raise temperature of 1 gram of water by 1°C (calorie) or 1 kg of water by 1°C (Calorie/Kcal).
• Glucose: 1 gram releases 3811 calories of heat energy when burned.
• Cells release energy gradually from glucose through glycolysis.

Glycolysis

• Glycolysis: Initial breakdown of glucose into pyruvic acid (3-carbon compound).
  • Yields 2 ATP (net gain) per glucose molecule.
  • Produces NADH, a high-energy electron carrier.
• Results:
  • With Oxygen: Leads to Krebs cycle, Electron Transport Chain.
  • Without Oxygen: Leads to Fermentation.

Fermentation

• Anaerobic process: Occurs in absence of oxygen.
• Regenerates NAD+ to keep glycolysis running.
• Types:
  • Alcoholic fermentation: Used by yeast; produces ethyl alcohol, CO2.
  • Lactic acid fermentation: Occurs in muscle cells; produces lactic acid.

Section 9-2: Krebs Cycle and Electron Transport

Overview

• Aerobic Pathway: Requires oxygen.
• Follows glycolysis to further break down pyruvic acid for more energy extraction.

Krebs Cycle

• Process: Pyruvic acid breaks down into CO2, extracting energy.
• Key Steps:
  • Citric Acid Production: Combines acetyl-CoA with a 4-carbon compound; forms citric acid.
  • Energy Extraction: Citric acid is reduced, releasing electrons that form NADH and FADH2; also produces ATP.

Electron Transport Chain (ETC)

• Purpose: Converts ADP to ATP using high-energy electrons from Krebs cycle.
• Key Steps:
  • Electron Transport: Electrons passed along an inner membrane, combine with oxygen to form water.
  • Hydrogen Ion Movement: Creates a charge difference across mitochondrial membrane.
  • ATP Production: Hydrogen ions pass through ATP synthase, generating ATP.

Energy Totals

• From 1 Glucose:
  • Glycolysis: 2 ATP.
  • Krebs/ETC: Additional 36 ATP.
• Efficiency: Only 38% of glucose's energy converted to ATP; rest lost as heat.

Energy and Exercise

• Quick Energy: Uses stored ATP and lactic acid fermentation (lasts ~90 seconds).
• Long-Term Energy: Uses stored glycogen then switches to fats and other molecules.

Comparing Photosynthesis and Cellular Respiration

• Photosynthesis: Captures energy (deposits) using light, water, CO2; produces glucose, O2.
• Cellular Respiration: Releases energy (withdraws) using glucose, O2; produces CO2, water, ATP.

Key Concepts Review

• Describe cellular respiration.
• Products of glycolysis.
• Two main types of fermentation.
• Fate of pyruvic acid in Krebs cycle.
• How electron transport chain uses electrons.