Learning Objectives

• Identify the first two laws of thermodynamics and explain their relevance to biological systems.

• Explain the concept of free energy change and its relationship to spontaneous reactions, work capacity, stability, and exergonic/endergonic reactions.

• Illustrate the coupling of ATP hydrolysis to endergonic reactions with examples.

• Describe how enzymes accelerate metabolic reactions.

• Discuss how regulation of enzyme activity controls metabolism.

How Do the Laws of Thermodynamics Relate to Biological Processes?

The First Law of Thermodynamics

The first law of thermodynamics states that energy can be transferred or transformed, but it cannot be created or destroyed. In biological systems, this means that organisms cannot create energy; they can only convert it from one form to another.

• Example: Plants convert light energy from the sun into chemical energy stored in organic molecules.

The Second Law of Thermodynamics

The second law of thermodynamics states that every energy transfer or transformation increases the entropy (disorder) of the universe. In living systems, some energy is always lost as heat, making it unavailable to do work.

• Entropy: A measure of molecular disorder or randomness.

• As entropy increases, systems become less ordered and less energy is available for useful work.

Application to Biological Systems

• Energy transformations in organisms (e.g., photosynthesis, cellular respiration) follow these laws.

• Organisms are open systems: they exchange energy and matter with their environment.

Concept 8.1: An Organism’s Metabolism Transforms Matter and Energy

Definition of Metabolism

Metabolism is the totality of an organism’s chemical reactions. It is an emergent property of life that arises from orderly interactions between molecules.

Metabolic Pathways

A metabolic pathway is a series of chemical reactions in which a specific molecule is altered in a series of steps to produce a product. Each step is catalyzed by a specific enzyme, which accelerates the reaction.

• Enzyme: A macromolecule (usually a protein) that acts as a catalyst to speed up a specific chemical reaction.

Types of Metabolic Pathways

• Catabolic Pathways: Release energy by breaking down complex molecules into simpler compounds.

  • Example: Cellular respiration (breakdown of glucose in the presence of oxygen).

  • Analogy: "Downhill" reactions because they release energy.

• Anabolic Pathways: Consume energy to build complex molecules from simpler ones.

  • Example: Protein synthesis (forming proteins from amino acids).

  • Analogy: "Uphill" reactions because they require an input of energy.

Forms of Energy

Energy is the capacity to cause change or do work, such as moving matter against opposing forces like gravity or friction.

• Kinetic Energy: Energy associated with motion.

  • Moving objects can perform work by imparting motion to other matter (e.g., water turning turbines).

• Thermal Energy: Kinetic energy associated with the random movement of atoms or molecules.

  • Heat: The transfer of thermal energy from one body of matter to another.

• Light: A form of energy that can be harnessed to do work, such as in photosynthesis.

• Potential Energy: Energy that matter possesses because of its location or structure.

  • Example: Water behind a dam has potential energy due to its altitude.

  • Molecules have potential energy due to the arrangement of electrons in bonds.

  • Chemical Energy: Potential energy available for release in a chemical reaction (e.g., glucose).

The Laws of Energy Transformation

Thermodynamics

Thermodynamics is the study of energy transformations within a collection of matter.

Isolated System

• Definition: A system that cannot exchange energy or matter with its surroundings.

• Example: Liquid in a thermos bottle.

Open System

• Definition: A system that can exchange energy and matter with its surroundings.

• Organisms as Open Systems:

  • Absorb energy from light or food.

  • Release heat and metabolic wastes (e.g., CO2) into the surroundings.

Summary Table: Types of Metabolic Pathways

Key Terms

• Metabolism: All chemical reactions in an organism.

• Catabolic Pathway: Pathway that releases energy by breaking down molecules.

• Anabolic Pathway: Pathway that consumes energy to build molecules.

• Enzyme: Protein catalyst that speeds up reactions.

• Entropy: Measure of disorder or randomness.

• Thermodynamics: Study of energy transformations.

• Isolated System: No exchange of energy/matter with surroundings.

• Open System: Exchanges energy/matter with surroundings.