Overview
This lecture explains the two laws of thermodynamics and their impact on biological systems, focusing on energy transfer, transformation, and the concept of entropy.
Thermodynamics and Systems
- Thermodynamics studies energy and energy transfer involving physical matter.
- A system is the matter and environment relevant to a specific energy transfer case; everything else is the surroundings.
- Open systems exchange both energy and matter with surroundings, as in heating a pot of water.
- Closed systems can transfer energy but not matter with surroundings.
- Living organisms are open systems that regularly exchange energy with the environment.
The First Law of Thermodynamics
- The first law states the total amount of energy in the universe is constant: energy cannot be created or destroyed.
- Energy can transfer or transform, such as electrical energy becoming light, or chemical energy in food becoming kinetic energy.
- Plants convert solar energy to chemical energy during photosynthesis.
- Cells transform stored chemical energy into ATP to do cellular work like building molecules and movement.
The Second Law of Thermodynamics and Entropy
- No energy transfer or transformation is completely efficient; some energy is always lost as unusable heat.
- Heat energy is energy transferred that does not perform work, such as friction heating air during flight.
- Entropy is the measure of randomness or disorder in a system; higher entropy equals more disorder and less usable energy.
- All physical systems naturally increase in entropy unless energy is applied to maintain order.
- Living things maintain low entropy (order) but increase the entropy of their environment through energy transfers.
- The second law states that every energy transfer increases the universe's total entropy.
Scientific Method Example: Entropy Changes
- Ice (solid water) has low entropy due to high structural order.
- Melting ice increases entropy as molecules move freely.
- Boiling water further increases entropy as molecules spread out in the gas phase.
Key Terms & Definitions
- Thermodynamics — study of energy and its transfer within physical systems.
- System — matter under study and its environment.
- Open system — exchanges energy and matter with surroundings.
- Closed system — exchanges energy but not matter.
- Entropy — measure of a system’s disorder or randomness.
- First Law of Thermodynamics — total energy in the universe is constant.
- Second Law of Thermodynamics — every energy transfer increases the universe’s entropy.
Action Items / Next Steps
- Review Figures 6.11 and 6.12 for visual examples of energy transformation and entropy.
- Reflect on daily biological processes and how they demonstrate these laws.