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Classifying Life: An Introduction

Classifying Life: Introduction to Living Things

The Naming System of Linnaeus

  • Carolus Linnaeus devised a system of naming organisms that is still used today.
  • This system uses a two-part scientific name, known as binomial nomenclature.
  • Examples:
    • Puma concolor (puma)
      • concolor means "the same color"
    • Felis domesticus (house cat)
      • domesticus means "of the house" in Latin
    • Felis margarata (marbled cat)
      • margarata means "marble," referring to the animal's coat

Genus and Species

  • The first word in an organism's scientific name is its genus.
    • A genus contains similar, closely related organisms.
    • Example: Pumas, house cats, and marbled cats are all classified in the genus Felis.
    • Organisms within the same genus share characteristics, such as sharp, retractable claws, and behaviors like hunting other animals.
  • The second word in a scientific name often describes a distinctive feature of the organism.
    • This feature could relate to where it lives or its appearance.
  • Together, these two words (genus and species) form the scientific name of a unique kind of organism.
  • A species is defined as a group of similar organisms that can mate with each other and produce offspring that can also mate and reproduce.

Using Binomial Nomenclature

  • Binomial nomenclature is crucial for clear communication in science.
  • It resolves confusion caused by multiple common names for the same animal.
  • Example: An animal might be called a groundhog, a woodchuck, a marmot, or a whistlepig depending on location.
  • However, this animal has only one scientific name: Marmota monax.
  • Scientific names ensure that scientists worldwide are referring to the exact same organism.

Levels of Classification

  • Today's classification system uses a hierarchy of many levels to classify organisms.
  • Organisms are grouped at each level based on shared characteristics.
  • The Major Levels of Classification (from broadest to most specific):
    • Domain: The broadest level of organization.
    • Kingdom: Within a domain.
    • Phylum: Within kingdoms.
    • Class: Within phyla.
    • Order: Within classes.
    • Family: Within orders. Each family contains one or more genera.
    • Genus: Each genus contains one or more species.
    • Species: The most specific level.

Example Classification Journey (Illustrated with Lion and Canine examples)

  • DOMAIN: Eukarya (Includes lion, mouse, whale, fish, earthworm, paramecium, dog, wolf, coyote, fox, seal, human, bat, snake, moth, tree)
  • KINGDOM: Animalia (Includes lion, mouse, whale, fish, earthworm, dog, wolf, coyote, fox, seal, human, bat, snake, moth)
  • PHYLUM: Chordata (Includes lion, mouse, whale, fish, dog, wolf, coyote, fox, seal, human, bat, snake)
  • CLASS: Mammalia (Includes lion, mouse, whale, dog, wolf, coyote, fox, seal, human, bat)
  • ORDER: Carnivora (Includes lion, dog, wolf, coyote, fox, seal)
  • FAMILY: Canidae (Specific family for dog, wolf, coyote, fox. Lion is not in Canidae.)
  • GENUS: Canis (Specific genus for dog, wolf, coyote)
  • SPECIES: Canis lupus (Specific species for wolf. Dog is Canis familiaris or a subspecies of Canis lupus depending on classification.)

How Are Taxonomic Keys (Dichotomous Key) Useful?

  • Taxonomic keys are valuable tools that help scientists and enthusiasts determine the identity of organisms.
  • They consist of a series of paired statements that describe physical characteristics.
  • How to Use a Taxonomic Key:
    • Step 1: Start by reading the first set of paired statements (e.g., 1a and 1b).
    • Step 2: Choose the statement that best describes the organism you are trying to identify.
    • Step 3: Follow the direction provided with your chosen statement, which will lead you to the next step.
    • Step 4: Continue this process, choosing the best descriptive statement and following directions, until the organism is identified.
  • Example Dichotomous Key for Arthropods (FIGURE 5):
    • 1a. Has 8 legs $\rightarrow$ Go to Step 2
    • 1b. Has more than 8 legs $\rightarrow$ Go to Step 3
    • 2a. Has one oval-shaped body region $\rightarrow$ Go to Step 4
    • 2b. Has two body regions $\rightarrow$ Go to Step 5
    • 3a. Has one pair of legs on each body segment $\rightarrow$ Centipede
    • 3b. Has two pairs of legs on each body segment $\rightarrow$ Millipede
    • 4a. Is less than 1 millimeter long $\rightarrow$ Mite
    • 4b. Is more than 1 millimeter long $\rightarrow$ Tick
    • 5a. Has clawlike pincers $\rightarrow$ Go to Step 6
    • 5b. Has no clawlike pincers $\rightarrow$ Spider
    • 6a. Has a long tail with a stinger $\rightarrow$ Scorpion
    • 6b. Has no tail or stinger $\rightarrow$ Pseudoscorpion
  • This key allows for systematic identification based on observable traits.