Characteristics and Classification of Living Organisms

Classification of Living Organisms

  • Principles of Classification:

    • Living organisms can be classified into distinct groups based on their similarities and differences.
    • Simple Classification Systems:
    • Simple classifications are made based on directly observable characteristics.
    • Examples of observable characteristics used for simple classification include:
      • Number of legs
      • Presence of antennae
      • Presence of wings
      • Hairiness

  • Standard Taxonomic Hierarchy:

    • Standard schemes of classification divide living organisms into several large groups or hierarchical ranks:
    • Kingdoms: The largest groups into which living organisms are initially divided.
    • Phyla: Divisions of kingdoms.
    • Classes: Divisions of phyla.
    • Orders: Divisions of classes.
    • Families: Divisions of orders.
    • Genera: Divisions of families.
    • Species: Divisions of genera.
    • Characteristics and Definition of Species:
    • Members of a species all share the exact same basic characteristics.
    • Members of a species can only reproduce successfully with members of the same species.

Overview of Major Organism Groups

  • Viruses:

    • Structure: Minute 'particles' composed of nuclear material (DNA) enclosed in a protein coat (referenced in Fig. 14.1, p. 89).
    • Example: Herpes virus.

  • Bacteria:

    • Cellular Organization: Unicellular organisms.
    • Nuclear Structure: Cells lack a true nucleus; DNA is spread throughout the cell (referenced in Fig. 14.1, p. 89).
    • Example: Typhoid bacterium.

  • Fungi:

    • Structural Composition: Body consists of a network of thread-like hyphae which make up a mycelium.
    • Reproductive Method: Reproduce by spores.
    • Examples: Pin mould, mushrooms.

  • Plant Groups — Dicotyledons:

    • Fruit and Flower Structure: Part of the main groups of plants (Fig. 1.3) where seeds are enclosed inside fruits that develop from the ovaries of flowers.
    • Leaf Morphology: Broad leaves with a network of veins.
    • Seed and Embryo Structure: Seed contains an embryo which has two cotyledons.
    • Examples: Hibiscus, pride of Barbados.

Characteristics of Living Organisms

There are seven fundamental characteristics common to all living organisms:

  • 1. Feeding:

    • Definition: The obtaining or making of food.

  • 2. Respiration:

    • Definition: The release of energy from food.

  • 3. Excretion:

    • Definition: The removal of waste products of metabolism.

  • 4. Movement:

    • Definition: The change in position of a whole organism or parts of an organism.

  • 5. Sensitivity:

    • Definition: The ability to detect and respond to changes in the environment.

  • 6. Growth:

    • Definition: A permanent increase in size and complexity.

  • 7. Reproduction:

    • Definition: Giving rise to new organisms which have similar characteristics to their parent(s).