General Biology: Study Guide on Life, Classification, and Scientific Method

Characteristics of Life

Defining Features of Living Organisms

Living organisms share a set of fundamental characteristics that distinguish them from non-living matter. Understanding these features is essential for studying biology.

• Order: Organisms exhibit complex organization, from molecules to cells to tissues and organs.

• Reproduction: Living things can produce offspring, passing genetic information to the next generation.

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

• Response to the Environment: Organisms detect and respond to stimuli in their environment.

• Energy Processing: Living things acquire and use energy to power their activities (e.g., photosynthesis, cellular respiration).

• Regulation: Organisms maintain stable internal conditions (homeostasis) despite external changes.

• Evolutionary Adaptation: Populations of organisms evolve over generations through natural selection.

Classification of Organisms

Taxonomic Hierarchy and Domains

Biologists classify organisms using a hierarchical system that reflects evolutionary relationships. The broadest category is the domain, followed by increasingly specific levels.

• Taxonomic Levels: Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

• Domains: The most inclusive category, grouping all life into three domains: Bacteria, Archaea, and Eukarya.

• Species Example: Homo sapiens (humans) is classified as follows: Domain Eukarya, Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Primates, Family Hominidae, Genus Homo, Species sapiens.

• Genus and Species: The scientific name of an organism consists of its genus and species (binomial nomenclature).

Scientific Method and Experimental Design

Hypotheses, Theories, and Variables

Scientific inquiry involves forming hypotheses, testing them through experiments, and developing theories based on evidence.

• Hypothesis: A testable statement or prediction about a natural phenomenon.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

• Variables:

  • Independent Variable: The factor that is changed or manipulated in an experiment.

  • Dependent Variable: The factor that is measured or observed in response to changes in the independent variable.

• Observational Data: Information collected by observing natural phenomena, often used when experiments are not possible.

Levels of Biological Organization

Hierarchy from Molecules to Biosphere

Biological systems are organized into a hierarchy, with each level building on the previous one. Understanding these levels helps explain the complexity of life.

• Levels:

  1. Atom

  2. Molecule

  3. Organelle

  4. Cell

  5. Tissue

  6. Organ

  7. Organ System

  8. Organism

  9. Population

  10. Community

  11. Ecosystem

  12. Biosphere

• Emergent Properties: New properties arise at each level of organization due to the interactions of components (e.g., life emerges at the cellular level).

• Example: A heart is an organ made of tissues, which are made of cells, which contain organelles and molecules.

Level	Description	Example
Cell	Basic unit of life	Neuron
Tissue	Group of similar cells performing a function	Nervous tissue
Organ	Structure composed of tissues	Brain
Organ System	Group of organs working together	Nervous system
Organism	Individual living thing	Human
Ecosystem	Community plus environment	Forest ecosystem
Biosphere	All ecosystems on Earth	Earth

Additional info: Expanded explanations and examples were added for clarity and completeness.