Energy in Biological Systems

Definition and Types of Energy

Energy is the ability to perform work. In biological systems, work involves the transfer of energy that causes an overall change in a system. There are two main types of energy relevant to biology: potential energy and kinetic energy.

• Potential Energy: Stored energy due to position or structure. Example: A ball at the top of a hill, chemical bonds in molecules.

• Kinetic Energy: Energy of motion. Example: A rolling ball, muscle contractions.

Example: A cyclist at the top of a hill has high potential energy. As the cyclist moves down the hill, potential energy is converted to kinetic energy.

Thermodynamics: System vs. Surroundings

Basic Concepts

Thermodynamics is the study of energy transfers between bodies of matter. In this context:

• System: The specific portion of matter being studied (e.g., a cell, an organism).

• Surroundings: Everything else outside of the system.

• Biological Systems: Transfer both energy and matter with their surroundings.

Example: A plant (system) exchanges energy (sunlight) and matter (CO2, O2, H2O) with its environment (surroundings).

First Law of Thermodynamics

Law of Conservation of Energy

The first law states that energy can be transferred and transformed, but it cannot be created or destroyed. This is also known as the Principle of Conservation of Energy. The total amount of energy in the universe remains constant.

• Equation: (Change in internal energy equals heat added minus work done by the system)

Example: In photosynthesis, plants convert light energy into chemical energy, but the total energy remains constant.

Entropy and the Second Law of Thermodynamics

Entropy

Entropy is a measure of disorder or randomness in a system. The second law of thermodynamics states that every energy transfer increases the entropy of the universe. This means that energy conversions are never 100% efficient; some energy is always lost as heat, increasing disorder.

• Low Entropy: Ordered systems (e.g., neatly arranged molecules)

• High Entropy: Disordered systems (e.g., randomly distributed molecules)

Example: When a living organism uses energy, some is lost as heat, increasing the entropy of the surroundings.

Second Law of Thermodynamics

• 100% efficient energy conversion is impossible; some energy is always lost as heat.

• Heat is a form of energy transfer between objects with different temperatures.

Example: In a food chain, energy is transferred from the sun to plants to animals, but some energy is lost as heat at each step.

Chemical Reactions in Biology

Reactants and Products

Chemical reactions involve the making and/or breaking of chemical bonds, leading to changes in matter.

• Reactants: The starting materials in a chemical reaction.

• Products: The resulting materials after the reaction.

Example: In cellular respiration, glucose and oxygen (reactants) are converted to carbon dioxide, water, and energy (products).

Types of Chemical Reactions

• Endergonic Reactions: Require an input of energy (energy enters the reaction). These reactions build complex molecules from simpler ones (anabolism).

• Exergonic Reactions: Release energy (energy exits the reaction). These reactions break down complex molecules into simpler ones (catabolism).

Equation for Free Energy Change:

• = change in free energy

• = change in enthalpy (total energy)

• = temperature in Kelvin

• = change in entropy

Example: Building proteins from amino acids (endergonic); breaking down glucose during respiration (exergonic).

Summary Table: Key Concepts

Additional info:

• Practice questions in the file reinforce understanding of key concepts such as energy types, thermodynamics, entropy, and chemical reactions.

• Diagrams and tables are used to illustrate the flow of energy and matter in biological systems.