What Is Biology?

The Science of Life

Biology is the scientific study of life and living organisms. It seeks to understand how life works, from the molecular to the ecosystem level.

• Definition of Life: Life is a self-sustained chemical system capable of undergoing Darwinian evolution (Joyce 1995, NASA definition).

• Alternative Definitions: Life is a self-replicating, evolving system based on organic chemistry (Page 2001).

• Medical Perspective: Life is the quality that distinguishes a vital and functional being from a dead body.

Fundamental Properties of Life

Essential Characteristics

Living organisms share several fundamental properties that distinguish them from non-living matter.

• Membrane Delimited: Life is separated from its environment by a membrane.

• Cellular Organization: Life is, or is made up of, cells.

• Information Storage and Transmission: Life stores and follows instructions (genetic information).

• Energy Utilization: Life stores energy and uses it for cellular processes.

• Self-Replication: Life is capable of reproducing itself.

• Response to Environment: Life controls its functions and responds to environmental changes.

• Evolution: Life evolves over generations.

Properties of Life: Examples and Exceptions

• Cellular Example: Mature red blood cells lack DNA, mitochondria, and do not divide, yet are part of a living organism.

• Hybrid Example: Mules are hybrids that cannot reproduce, challenging the definition of life.

Main Biomolecules Supporting Life

Types and Functions

Four major classes of biomolecules are essential for life, each supporting key properties.

• Lipids: Form membranes, store energy, provide insulation.

• Carbohydrates: Store and provide energy, structural support.

• Nucleic Acids: Store and transmit genetic information (DNA, RNA).

• Proteins: Catalyze reactions, provide structure, regulate functions, respond to environment.

Nucleic Acids: Information Storage and Transmission

DNA and RNA

Nucleic acids are polymers that store and transmit genetic information.

• DNA (Deoxyribonucleic Acid): Stores hereditary information.

• RNA (Ribonucleic Acid): Transmits information and facilitates protein synthesis (mRNA, tRNA, rRNA).

Self-Replication

Biomolecular Facilitation

All biomolecules contribute to the self-replication of life, enabling reproduction and growth.

Membrane Delimitation

Lipids and Cell Membranes

Lipids form the selectively permeable barrier of cell membranes, compartmentalizing cellular functions.

• Phospholipids: Main component of membranes, with hydrophilic heads and hydrophobic tails.

• Functions: Compartmentation, energy storage, insulation.

Energy Storage and Utilization

ATP and Energy Sources

Cells convert energy from sunlight or organic compounds into ATP, the universal energy currency.

• ATP (Adenosine Triphosphate): Used by cells to perform work.

• Energy Sources: Sunlight (photosynthesis) or organic molecules (cellular respiration).

Biomolecule Structure: Monomers to Polymers

Carbohydrates and Amino Acids

• Carbohydrates: Monomers (monosaccharides) form polymers (polysaccharides).

• Amino Acids: Monomers form proteins (polypeptides).

Control and Response to Environment

Role of Proteins

Proteins facilitate cellular control and response to environmental signals, acting as enzymes, receptors, and structural components.

Evolution

Heritable Change

Evolution is the change in heritable characteristics of biological populations over successive generations.

• Mechanisms: Mutation, natural selection, genetic drift.

• Importance: Drives diversity and adaptation.

Cells: The Smallest Unit of Life

Cellular Organization

The cell is the smallest unit that meets all properties of life. All organisms are made of one or more cells.

• Single-celled organisms: Bacteria, archaea, some protists.

• Multicellular organisms: Plants, animals, fungi.

Types of Cells

Prokaryotic vs. Eukaryotic Cells

Cells are classified into two main types based on their structure.

Are Viruses Alive?

Viruses and Life Criteria

Viruses exhibit some but not all properties of life.

• Membrane Delimited: Sometimes, must enter a cell.

• Information Storage: Yes, viruses store and follow instructions.

• Energy Storage: No, viruses do not store energy.

• Energy Use: Yes, viruses use energy from host cells.

• Self-Replication: Questionable, depends on host.

• Response to Environment: Yes.

• Evolution: Yes, viruses evolve.

Class Recap/Objectives

Summary of Key Concepts

• Practice designing controls in experiments.

• Understand that the definition of "living" can vary.

• Set up a course definition of life.

• Introduce biomolecules and their roles in supporting life: lipids, nucleic acids, proteins, carbohydrates.

• Recognize that cells are the units of life.

• Know types of cells and compare their features.

Additional info:

• Students are encouraged to explore cell parts using online resources for deeper understanding.