The Classification of Living Things for the GED Science Test

By Murray Shukyn, Achim K. Krull

The system of classifying livings things is a definite knowledge necessity for doing well on the GED Science test. In an attempt to organize nature, humans have developed a system of classifying all living things called a taxonomy. The most widely accepted taxonomy divides all living things into broad categories, or kingdoms, based on their structure. Following is a list of the five kingdoms with a brief description of each:

  • Monera: Simple, single cells that don’t have membrane-bound nuclei, such as parasitic bacteria and photosynthesizing blue-green algae.

  • Protista: Complex, single-cell organisms that have distinct nuclei, including slime molds, protozoa, and single or multiple cell algae. Members of this group are distinguished from one another by whether they feed off of other organisms or feed themselves through photosynthesis — a process by which an organism uses sunlight to synthesize foods from carbon dioxide and water.

  • Fungi: Immobile, multicellular organisms that can’t perform photosynthesis and must decompose other dead organisms for food. Fungi include mushrooms, yeasts, and molds.

  • Planta: Multicellular organisms, such as mosses and plants, that can perform photosynthesis to create food.

  • Animalia: Mobile, multicellular organisms that feed on other organisms (plant or animal) for food. The main division within this kingdom is between vertebrates and invertebrates (with or without a backbone).

Kingdoms are the broadest category for classifying plants and animals. Six more categories further subdivide the kingdoms. Each subcategory contains a progressively smaller number of different organisms. Here’s a complete list of categories in increasing specificity:

  • Kingdom contains several related phyla.

  • Phylum contains several related classes.

  • Class contains several related orders.

  • Order contains several related families.

  • Family contains several related genera.

  • Genus contains several related species.

  • Species contains organisms so similar that they can reproduce together.

For human beings, it goes like this: kingdom: Animalia; phylum: Chordata (vertebrate); class: Mammalia; order: Primate; family: Hominidae; genus: Homo; species: Sapiens.