Introduction to Biology

THE SCIENCE OF LIFE

  • Biology Unification

    • Biology unifies much of natural science.

    • Living systems are the most complex chemical systems on Earth.

    • Life is constrained by the properties of chemistry and physics.

    • Science is becoming more interdisciplinary, combining multiple fields.

CHARACTERISTICS OF LIVING ORGANISMS

  • Seven Characteristics

    1. Composed of cells.

    2. Complex and ordered.

    3. Respond to their environment.

    4. Can grow, develop, and reproduce.

    5. Obtain and use energy.

    6. Maintain internal balance (Homeostasis).

    7. Allow for evolutionary adaptation.

HIERARCHICAL ORGANIZATION OF LIVING SYSTEMS

  • Levels of Organization

    • Cellular level: Includes atoms, molecules, organelles, and cells.

    • Cells are the basic units of life.

    • Organismal level: Involves tissues, organs, and organ systems.

    • Populational level: Includes populations and communities.

    • Ecosystem level: Involves ecosystems and the biosphere.

    • Earth is referred to as an ecosystem known as the biosphere.

BIOLOGICAL LEVELS OF ORGANIZATION

  • Organelles:

    • Example: The nucleus, identified by blue dye in onion cells, serves as an example of an organelle.

  • Cells:

    • Example: Human blood cells typify cell structure.

  • Tissues:

    • Example: Human skin tissue represents a tissue type.

  • Organs and Organ Systems:

    • Example: The stomach and intestine constitute the human digestive system.

  • Organisms, Populations, and Communities:

    • Example: In a forest, each pine tree is an organism; collectively, all the pine trees comprise a population, while all plant and animal species in the forest constitute a community.

  • Ecosystems:

    • Example: A coastal ecosystem in the southeastern United States includes both living organisms and their environment.

  • The Biosphere:

    • Encompasses all the ecosystems present on Earth.

THE NATURE OF SCIENCE

  • Purpose of Science

    • Aims to understand the natural world through observation and reasoning.

    • Begins with observations; thus, much of science is purely descriptive, including:

    • Classification of all life on Earth.

    • Human genome sequencing.

REASONING IN SCIENTIFIC DISCOURSE

  • Types of Reasoning:

    • Inductive reasoning:

    • Builds general principles from specific observations (e.g., homeobox genes discovered in fruit flies).

    • Deductive reasoning:

    • Applies general principles to reach specific conclusions (e.g., lizards have 4 legs).

SCIENTIFIC METHOD

  • Steps of the Scientific Method:

    1. Formulation of a hypothesis.

    2. Testing the hypothesis through experimentation.

    3. If a hypothesis is not supported by experimental data, propose a new hypothesis.

PHILOSOPHICAL APPROACHES TO SCIENCE

  • Reductionism:

    • The practice of breaking complex processes down into simpler parts.

  • Systems Biology:

    • Focuses on emergent properties that cannot be understood by examining simpler parts (e.g., Google and flu outbreaks).

    • Metagenomic investigation offers insight into system interactions.

MODELS IN SCIENCE

  • Purpose of Models:

    • Serve as a way to organize thought.

    • Parts are provided by reductionist approaches.

    • Models illustrate how these parts fit together.

    • Suggest experiments to test and validate the model.

SCIENTIFIC THEORY

  • Definition of Scientific Theory:

    • A body of interconnected concepts supported by extensive experimental evidence and scientific reasoning.

    • Represents ideas we are most certain about.

    • Open to change as new information becomes available.

UNIFYING THEMES IN BIOLOGY

  • Cell Theory:

    • All organisms are composed of cells.

    • Cells are the basic units of life.

    • All cells arise from preexisting cells.

MOLECULAR BASIS OF INHERITANCE

  • DNA (Deoxyribonucleic acid):

    • Sequence of 4 nucleotides encodes the cell's information.

    • Gene: A discrete unit of information.

    • Genome: The entire set of DNA instructions.

    • Continuity of life depends on the faithful copying of DNA into daughter cells.

STRUCTURE AND FUNCTION

  • Concept:

    • Study the structure to understand function.

    • Knowing a specific function can guide the search for that structure in other organisms.

    • Example:

    • A receptor for insulin in human cells can lead to discovering similar molecules in other organisms, such as a worm, which might function similarly.

DIVERSITY OF LIFE AND EVOLUTION

  • Evolutionary Basis of Diversity:

    • The underlying unity of biochemistry and genetics supports the idea of life stemming from a common origin event.

    • Diversity results from evolutionary changes over time.

    • Life is categorized into three domains:

    1. Bacteria: Single-celled prokaryotes.

    2. Archaea: Single-celled prokaryotes.

    3. Eukarya: Can be single-celled or multicellular eukaryotes.

INFORMATION PROCESSING IN CELLS

  • Cells as Information-Processing Systems:

    • Information in DNA directs the synthesis of cellular components.

    • Control of gene expression results in different cell and tissue types.

    • Cells process environmental information, such as glucose levels and the presence of hormones.

    • Cells in multicellular organisms must coordinate their activities with one another to maintain homeostasis and overall function.