Overview
This lecture explains the first and second laws of thermodynamics and their importance in biological systems, especially regarding energy transfer, transformation, and entropy.
Thermodynamics and Biological Systems
- Thermodynamics studies energy and how it is transferred involving matter.
- A system includes the matter under study; everything else is the surroundings.
- Open systems exchange energy and matter with surroundings; closed systems exchange only energy.
- Biological organisms are open systems, constantly exchanging energy with their environment.
- The laws of thermodynamics govern energy transfers in all systems, including living organisms.
The First Law of Thermodynamics
- The first law states the total energy in the universe is constant.
- Energy cannot be created or destroyed, only transferred or transformed.
- Energy transformations commonly seen: electrical to light (bulbs), chemical to heat (gas stove), light to chemical (photosynthesis).
- Cells transform chemical energy from food into ATP, which powers cellular work like movement and molecule synthesis.
The Second Law of Thermodynamics
- The second law states that no energy transfer is completely efficient; some energy is always lost as unusable heat.
- Heat energy is energy transferred that does not do work, often due to friction or inefficiencies.
- Living organisms rely on constant energy input, since energy losses increase system disorder.
- The measure of disorder or randomness in a system is called entropy.
- As energy is lost to the surroundings, entropy increases in those surroundings.
Entropy in Physical and Biological Systems
- High entropy means high disorder and low available energy; low entropy is high order.
- Living things require energy to maintain low entropy (order) against the natural trend toward disorder.
- Physical examples: ice (low entropy, molecules fixed), water (higher entropy, molecules move), gas (highest entropy).
- All energy transfers and chemical reactions in cells increase the universe’s overall entropy.
Key Terms & Definitions
- Thermodynamics — the study of energy and its transfer in physical matter.
- System — the matter under study in energy transfer.
- Surroundings — everything outside the system.
- Open system — exchanges both energy and matter with surroundings.
- Closed system — exchanges only energy, not matter, with surroundings.
- First Law of Thermodynamics — energy cannot be created or destroyed, only transferred or transformed.
- Second Law of Thermodynamics — every energy transfer increases the universe’s entropy.
- Entropy — a measure of disorder or randomness in a system.
- ATP (Adenosine Triphosphate) — molecule that stores and transfers energy in cells.
Action Items / Next Steps
- Review the concepts of entropy and both laws of thermodynamics.
- Conduct the suggested experiment: observe ice melting and boiling to see changes in entropy.
- Read next section on ATP for deeper understanding of energy use in cells.