Introduction to Metabolism and Thermodynamics in Biology

Introduction to Metabolism

Overview

Metabolism encompasses all the chemical reactions that occur within living organisms to maintain life. These reactions are organized into metabolic pathways, which are governed by the principles of thermodynamics.

Thermodynamics and Biological Systems

First Law of Thermodynamics

The First Law of Thermodynamics states that energy can neither be created nor destroyed, only converted from one form to another. In biological systems, this means that the energy organisms use must come from their environment and is transformed during metabolic processes.

• Definition: The total amount of energy in a closed system remains constant.

• Example: Plants convert light energy into chemical energy during photosynthesis.

Second Law of Thermodynamics

The Second Law of Thermodynamics states that every energy transfer or transformation increases the entropy (disorder) of the universe. No energy transfer is completely efficient; some energy is always lost as heat.

• Definition: In any closed system, entropy will increase over time.

• Example: When cells convert chemical energy from food into usable energy, some is lost as heat, increasing entropy.

Application to Biological Processes

• Energy flow in living things demonstrates the first law: energy is transferred and transformed, not created or destroyed.

• Every energy transformation in cells releases some energy as heat, demonstrating the second law.

• As a result, the entropy of the universe increases with every energy transfer or transformation in biological systems.

Key Equations

• The change in free energy ($\Delta G$) during a process is related to the change in enthalpy ($\Delta H$), change in entropy ($\Delta S$), and temperature (T):

$\Delta G = \Delta H - T\Delta S$

• Processes with a negative $\Delta G$ are spontaneous.

Summary Table: Laws of Thermodynamics in Biology

Law	Description	Biological Example
First Law	Energy cannot be created or destroyed	Photosynthesis converts light to chemical energy
Second Law	Entropy increases in a closed system	Heat loss during cellular respiration

Additional info:

• These notes are based on the first few slides of a General Biology lecture on metabolism and thermodynamics. Later sections would likely cover metabolic pathways, enzymes, and energy coupling in more detail.