Overview
This lecture explains the First and Second Laws of Thermodynamics, their definitions, and how they apply to biological systems, with a focus on entropy and energy flow in living organisms.
Systems and Surroundings
- A system is the part of the universe under study; everything else is the surroundings.
- An open system exchanges both energy and matter with its surroundings.
- A closed system exchanges only energy, not matter, with its surroundings.
- An isolated system exchanges neither energy nor matter with its surroundings.
- Living organisms are open systems, constantly exchanging matter and energy with their environment.
The First Law of Thermodynamics
- The First Law states that energy cannot be created or destroyed—only transferred or changed in form.
- Examples: plants convert sunlight to chemical energy, humans convert food into kinetic energy.
- Energy transfers are never 100% efficient; some energy is always lost as heat.
The Second Law of Thermodynamics
- The Second Law states that every energy transfer increases the entropy (disorder) of the universe.
- Some energy becomes less useful after each transfer, usually as heat.
- Heat increases randomness by spreading energy more evenly across molecules.
- No process can occur with 100% energy efficiency; some usable energy is always lost.
Entropy in Biological Systems
- Entropy is a measure of disorder or randomness in a system.
- Even organized biological systems increase the overall entropy of the universe by releasing heat and breaking down complex molecules.
- Organisms maintain order locally by constant energy input, but this increases the entropy of their surroundings.
- When an organism dies, it no longer resists equilibrium, leading to increased entropy as its components disperse.
Key Terms & Definitions
- System — The part of the universe being studied.
- Surroundings — Everything outside the system.
- Open System — Can exchange matter and energy with surroundings.
- Closed System — Can exchange energy but not matter with surroundings.
- Isolated System — Cannot exchange energy or matter with surroundings.
- First Law of Thermodynamics — Energy cannot be created or destroyed.
- Second Law of Thermodynamics — Entropy of the universe increases with every energy transfer.
- Entropy — A measure of randomness or disorder.
Action Items / Next Steps
- Review the examples of open, closed, and isolated systems.
- Watch the linked videos for more on entropy and thermodynamics.
- Prepare to discuss how biological order is maintained by energy input in class.