Overview
This lecture covers the distinction between equilibrium and homeostasis in biological systems, focusing on chemical and biological equilibrium and the concept of dynamic steady state.
Biological Organization & System Integration
- Molecules form subcellular structures; cells interact to create tissues, organs, and organ systems.
- Multicellular organisms rely on cooperation between systems (circulatory, respiratory, digestive) for survival.
- Organ system integration enables the body to maintain homeostasis, or internal balance.
Chemical vs. Biological Equilibrium
- Chemical equilibrium: when the rates of the forward and reverse chemical reactions are equal.
- In chemistry, equilibrium is not about equal concentrations but about equal reaction rates.
- Example: If reactants are high, the forward reaction is favored until forward and reverse rates match.
Biological Equilibrium Across Membranes
- Biological equilibrium considers both rate and concentration.
- Example: A solute moves from high to low concentration across a permeable membrane until concentrations and rates equalize.
- Passive processes reach equilibrium without external energy (e.g., solute movement, osmosis).
Homeostasis & Dynamic Steady State
- Biological systems often maintain unequal concentrations across membranes with equal rates in and out.
- Maintaining this imbalance requires external energy input (active process).
- This state is called dynamic steady state or homeostasis, distinct from equilibrium.
- Chemical disequilibrium and energy investment are hallmarks of homeostasis (e.g., body temperature regulation).
Key Terms & Definitions
- Equilibrium — In chemistry, when forward and reverse reaction rates are equal; not necessarily equal concentrations.
- Chemical Equilibrium — Equal concentrations of a solute inside and outside the cell.
- Osmotic Equilibrium — Balance of water concentration across a membrane.
- Dynamic Steady State (Homeostasis) — A stable internal environment maintained with unequal concentrations and continuous energy input.
Action Items / Next Steps
- Review four physiological themes to be discussed in the next module.