Biology Classification Overview

Classification Overview

• Classification is the scientific method for identifying, naming, and grouping living organisms based on their similarities and differences.
• Initial classification was based on physical traits such as size, body parts, and life span, but was superficial.
• Carolus Linnaeus developed a systematic classification method based on structural similarities, establishing taxonomic ranks that are still used today.

Taxonomic Ranks

• Living organisms are primarily divided into two kingdoms: plants and animals.
• Below kingdoms, organisms are classified into:
  • Phyla: Groups of closely related classes.
  • Classes: Groups of closely related orders.
  • Orders: Groups of closely related families.
  • Families: Groups of closely related genera.
  • Genera: Groups of closely related species.
  • Species: The most specific category, comprising organisms that closely resemble each other and are capable of reproduction.

Classification Characteristics

• Organisms are classified based on characteristics such as physical structure and cellular composition.
• For plants, the cell wall is made of cellulose, and they possess chlorophyll for photosynthesis.
• Animals are multicellular, heterotrophic, and lack a cell wall.

Diversity of Organisms

• Earth is home to over 1.5 million different species, with the majority being animals (1.2 million) and the rest plants.

Plant Kingdom

• Composed entirely of green plants that are multicellular and autotrophic due to photosynthesis.
• Possess chlorophyll contained in chloroplasts, enabling them to produce their food.
• Exhibit a wide range of forms, from microscopic entities to tall trees, and have cell walls made of cellulose.
• Generally immobile and lack a definitive shape.

Animal Kingdom

• Encompasses all animals which are multicellular and heterotrophic, obtaining food from other organisms.
• Cells are characterized by a cell membrane without a rigid cell wall, containing membrane-bound organelles.
• Typically mobile, moving to find food, shelter, and suitable breeding conditions.

Importance of Classification

• Organisms are classified to help in understanding and organizing biological diversity and relationships among various species.
• Classification aids in the identification, study, and conservation of organisms.