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I. Introduction to Biology

  • Definition: Biology is the study of life that gathers knowledge about the natural world through observation and reasoning.
  • Scope: The scope of biology is vast, encompassing everything from the smallest unit (the atom) to the entire planet (the biosphere).
  • The Big Questions: Biology has historically wrestled with four key questions:
    1. What are the shared properties that make something "alive"?
    2. How do living things function?
    3. How do we organize the diversity of life?
    4. How did this diversity arise (evolution)?

II. The Properties of Life

  • Defining Life: Although viruses can attack organisms and reproduce, they are not considered "alive" because they do not fulfill all criteria (e.g., they lack cellular structure).
  • The 8 Key Characteristics: All living organisms share the following specific functions:
    1. Order: Organisms exhibit highly organized structures. For example, single-celled organisms have complex internal structures, while multicellular organisms have specialized cells that form tissues and organs.
    2. Sensitivity (Response to Stimuli): Organisms respond to their environment.
    • Example: Plants bending toward light (phototaxis) or bacteria moving away from chemicals (chemotaxis).
    • Illustration: The sensitive plant (Mimosa pudica) droops and folds its leaves instantly when touched and returns to normal after a few minutes.
    1. Reproduction: The ability to pass genetic information (DNA) to offspring.
    2. Adaptation: Evolution allows organisms to adapt to their environment over generations through natural selection.
    3. Growth and Development: Genes provide instructions for cellular growth, ensuring that offspring exhibit characteristics of their parents.
    • Illustration: Although no two kittens look alike, they inherit genes from both parents, leading to shared characteristics.
    1. Regulation: Coordination of internal functions such as nutrient transport.
    2. Homeostasis: Maintenance of constant internal conditions (e.g., temperature, pH) despite external changes.
    • Illustration: Polar bears and other mammals in icy regions maintain body temperature by generating heat and minimizing heat loss through thick fur and fat layers.
    1. Energy Processing: All organisms utilize a source of energy for metabolic activities, such as sunlight for plants and food for animals.
    • Illustration: Significant energy is needed for a California condor to fly, and chemical energy from food powers this flight.

III. Levels of Biological Organization

  • The Hierarchy: Life is organized on a scale from smallest to largest:
    1. Atom: The smallest unit of matter, consisting of a nucleus surrounded by electrons.
    2. Molecule: A chemical structure formed from at least two atoms bonded together (e.g., DNA).
    • Illustration: A large DNA molecule is composed of atoms.
    1. Organelle: Membrane-bound sacs within cells (e.g., mitochondria).
    2. Cell: The smallest fundamental unit of structure and function in living organisms (Viruses are excluded as they lack cellular structure).
    3. Tissue: Groups of similar cells performing a similar function.
    4. Organ: Composed of collections of tissues (e.g., heart, stomach).
    5. Organ System: Functionally related organs (e.g., circulatory system).
    6. Organism: Individual living entities (e.g., a tree, a person, a bacterium).
    7. Population: All individuals of a species within a specific area.
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