Bioenergetics Lecture Notes

Overview

• Focus: Photosynthesis, respiration, inverse square law, and metabolism.
• Applicable to: AQA GCSE Combined Science Biology and Triple Science Biology.

Photosynthesis

• Definition: Process by which plants and algae convert CO2 and water into glucose and oxygen using sunlight.
• Key Components:
  • Carbon dioxide enters leaves by diffusion.
  • Water enters roots through osmosis.
  • Sunlight is absorbed by chlorophyll in chloroplasts.
  • Glucose is produced in leaves; oxygen is a waste product.
• Equation:
  • Word: Carbon dioxide + water -> glucose + oxygen.
  • Balanced Formula: 6CO2 + 6H2O -> C6H12O6 + 6O2.
  • Type of Reaction: Endothermic (energy absorbed from surroundings).

Uses of Glucose

• Respiration to release energy.
• Converted to starch for storage.
• Produces fats/oils for energy storage.
• Produces cellulose for cell walls.
• Combined with nitrates to make amino acids (proteins).

Limiting Factors

• Factors Affecting Photosynthesis Rate:
  • Light intensity, CO2 concentration, temperature, chlorophyll amount.
• Graphs:
  • Light intensity: Initial increase in photosynthesis rate, then plateaus.
  • CO2 concentration: Similar pattern as light intensity.
  • Temperature: Increase to optimal, then rapid decrease due to enzyme denaturation.

Practical Applications

• Greenhouses use knowledge of limiting factors to optimize conditions.
• Graphs showing effects of varying CO2 and temperature.

Measuring Photosynthesis

• Methods:
  • Counting bubbles from pondweed (bubbles/minute).
  • Collect oxygen gas in measuring cylinder (volume/minute).
• Experiment: Adjust lamp distance and count bubbles to determine rate.
• Control Variables: Pondweed, temperature, CO2 concentration, repeat for accuracy.

Inverse Square Law

• Formula: Light intensity ∝ 1/distance².
• Application: Doubling distance reduces light intensity and photosynthesis rate to a quarter.

Respiration

• Types: Aerobic (with oxygen) and Anaerobic (without oxygen).
• Aerobic Respiration:
  • Occurs in cells using glucose and oxygen.
  • Produces CO2, water, and energy.
  • Equation: Glucose + oxygen -> carbon dioxide + water.
• Anaerobic Respiration:
  • Animal cells: Glucose -> lactic acid + energy.
  • Plants/Yeast: Glucose -> ethanol + CO2.
  • Used in fermentation (bread rising, alcohol production).

Exercise and Respiration

• During exercise, increased energy demand:
  • Breathing and heart rate increase to supply oxygen for aerobic respiration.
  • If insufficient oxygen, anaerobic respiration occurs, producing lactic acid.
• Lactic Acid: Causes muscle fatigue, converted back to glucose in liver.

Metabolism

• Definition: Sum of all chemical reactions in an organism.
• Examples:
  • Conversion of glucose to starch, cellulose, amino acids.
  • Formation of lipids from fatty acids and glycerol.
  • Breakdown of amino acids to urea for excretion.
  • Conversion of glucose to glycogen for storage.

Conclusion

• Covered photosynthesis, respiration, and metabolism processes relevant for GCSE Biology courses.
• Emphasized practical applications and experimental setups for understanding key concepts.