Summary of Key Concepts in Biology

Biology: The Study of Life

• Definition of Life: No concise definition; defined by key characteristics.

Characteristics of Life

1. Organization: Hierarchical structure from atoms to the biosphere:
   • Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere
2. Sensitivity/Response to Stimuli: Organisms react to stimuli (e.g., movement towards light = positive response).
3. Energy Use: Metabolism allows acquisition and use of energy; categorized into:
   • Autotrophs (producers), Heterotrophs (consumers), Decomposers.
4. Homeostasis: Maintenance of constant internal conditions despite environmental changes.
5. Reproduction, Growth, and Development:
   • Asexual: identical offspring from one parent (e.g., bacterial division).
   • Sexual: genetic mixing from two parents results in diversity.
6. Evolution: Gradual change resulting in new species; adaptation leads to greater reproductive success.

Taxonomy and Classification

• Taxonomy: Science of classifying organisms into hierarchical categories.
• Binomial Nomenclature: Two-term naming system (Genus species) for organisms.
• Three Domains of Life: Archaea, Bacteria, Eukarya.
  • Eukarya Kingdoms: Protista, Fungi, Plantae, Animalia.
• Evolutionary Relationships: Taxonomists classify organisms based on shared ancestry.