Cellular Energetics: Metabolism & Energetics Notes

Unit 3: Cellular Energetics - Metabolism & Energetics

Enduring Understandings

  • Living systems require a continuous input of energy and the exchange of macromolecules to maintain their complex structure and function.

Forms of Energy

  • Energy:
    • Definition: Capacity to cause change; ability to do work.
    • Organisms are energy transformers.
  • Kinetic Energy:
    • Energy of motion (e.g., thermal energy).
    • Associated with the random movement of atoms or molecules.
    • Considered the most random form of energy.
  • Potential Energy:
    • Stored energy, related to an object's position or structure.
    • Chemical Energy:
    • A form of potential energy available to release during a chemical reaction.
    • Found in the bonds of molecules (e.g., carbohydrates, fats).
    • In chemical reactions, such as photosynthesis:
      • Inputs: Carbon dioxide (CO₂), Water (H₂O)
      • Outputs: Glucose, Oxygen

Laws of Thermodynamics

  • First Law of Thermodynamics (Conservation of Energy):
    • Energy can be transferred and transformed.
    • Energy cannot be created or destroyed.
  • Second Law of Thermodynamics:
    • Every energy transformation increases the randomness (entropy) of the universe.
    • Example: Cellular respiration releases heat as it transforms glucose and oxygen into ATP, CO₂, and H₂O.
    • Living systems increase the entropy of their surroundings.

Entropy and Living Systems

  • While organisms can become more organized over time, they are islands of low entropy in an increasingly random universe.
  • The loss of order or energy flow in organisms ultimately leads to death.

Reactions and Energy Flow

  • Reactants → Products:
    • In photosynthesis (endergonic reaction):
    • Energy is required, and the process is non-spontaneous.
    • In cellular respiration (exergonic reaction):
    • Molecules undergo hydrolysis.
  • Gibbs Free Energy (ΔG):
    • Represents the change in free energy of a system.
    • If ΔG > 0, the reaction is non-spontaneous (requires energy input).
    • Example:
    • Anabolic reactions produce larger molecules from smaller ones (e.g., dehydration synthesis) and store energy in molecules.
    • Products have more energy than reactants.
    • These reactions are termed endergonic, reflecting the energy required to “climb uphill.”