Characteristics and Classification of Living Organisms Study Notes

The Eight Characteristics of Living Organisms

  • Made up of Cells     * Every living organism is composed of cells.     * A cell is defined as the basic unit of life.     * Cells are responsible for carrying out the vital activities necessary for an organism to remain alive.     * Example: Cells in the leaves of plants are specialized to carry out photosynthesis.

  • Nutrition     * Definition: Nutrition is the taking in of materials for the purposes of energy, growth, and development.     * Plant Nutrition: Plants take in raw materials to manufacture their own food through the process of photosynthesis.     * Animal Nutrition: Animals must feed on plants or other animals to survive, grow, and provide the energy needed for daily activities.

  • Respiration     * Definition: Respiration is the chemical breakdown of nutrient molecules within cells to release energy for metabolism.     * Metabolism refers to chemical processes in cells, such as growth, which require energy to function.

  • Excretion     * Definition: Excretion is the removal of metabolic waste products and substances that are in excess of the body’s requirements.     * Plant Example: Plants excrete oxygen gas, which is a byproduct produced during photosynthesis, through their leaves.     * Human Example: Humans excrete carbon dioxide from the body through the lungs.

  • Growth and Development     * Growth Definition: Growth is the permanent increase in dry mass and size of an organism.     * The process involves converting food into living matter within cells.     * New matter is utilized to repair worn-out parts of the cell or is added to the original living matter to increase size.     * Development Definition: Development involves an organism becoming more complex and potentially changing its form.     * Case Study: The body of a caterpillar undergoes development to become more complex as it transforms into a butterfly.

  • Movement     * Movement Definition: Movement is an action performed by an organism, or a part of an organism, that causes a change in position or place.     * Locomotion: This is the specific movement of an organism from one place to another.     * Exceptions: Some animals, such as corals, do not exhibit locomotion and remain stationary.

  • Reproduction     * Definition: Reproduction is the biological process that produces more individuals of the same kind of organism.     * Significance: Organisms eventually die due to diseases, old age, or predation. Therefore, reproduction is essential for the continuity of a species.

  • Sensitivity     * Definition: Sensitivity is the ability of an organism to detect and respond to changes in the external or internal environment.     * Example 1: Cockroaches exhibit sensitivity by immediately hiding when light is present.     * Example 2: Humans react to unpleasant smells or the sensation of touching something very hot by immediately moving away.     * Example 3: The leaves of Mimosa pudica (commonly known as the touch-me-not plant) automatically fold up when they are touched.

Classifying Living Organisms

  • The Purpose of Classification     * Organisms are classified based on the features they share.     * Classification systems provide valuable information regarding the evolutionary relationships among organisms.     * Evidence of Evolution: Anatomical similarities, such as the skeletons of bird wings, mammal limbs, and fish fins, show that bones are arranged in similar patterns, suggesting a common ancestry.

  • The Biological System of Classification     * Living organisms are grouped based on their similarities and differences using a hierarchical structure.     * Hierarchy Principle: As one moves down the hierarchy from kingdom toward species, the resemblance between organisms becomes significantly closer.     * Differentiating Species: While it is relatively easy to distinguish different families or genera, it can be more difficult to differentiate between two closely related species, such as different species of penguins (e.g., Gentoo and Adelie penguins).

  • The Binomial System of Naming Species     * This is the standard international system for naming organisms.     * Structure of the Name:         1. First Name: Refers to the Genus to which the organism belongs. It must always start with a capital letter.         2. Second Name: Refers to the specific species. It must start with a small (lowercase) letter.     * Formatting Rules: Both the genus and species names must be either italicized or underlined.     * Example: The domestic cat is named Felis domestica (or Felis domestica).

Characteristics of Major Groups and Kingdoms

  • Viruses     * Structure: A virus consists of genetic material enclosed within a protein coat.     * Life Characteristics: Viruses do not feed, respire, excrete, or grow.     * Reproduction: They cannot reproduce on their own. They can only multiply rapidly once they have entered the cells of a living host organism.     * Examples: Viruses that cause measles, rabies, and coronavirus.

  • The Plant Kingdom

    * Flowering Plants         * Main Features: They possess roots, stems, and leaves. They produce flowers and seeds.         * Reproduction: They reproduce via seeds.         * Classes: They are divided into Monocotyledons (monocots) and Dicotyledons (dicots).

    * Ferns         * Main Features: They possess roots, stems, and leaves.         * Reproduction: They do not produce flowers or seeds; instead, they reproduce by spores.         * Specific Detail: Spores in ferns like the bird's nest fern are found in parallel rows on the underside of the leaves, which are called fronds.

  • The Animal Kingdom

    * Arthropods (Invertebrates)         * Definition: Animals that lack a vertebral column or backbone.         * Main Features:             1. Segmented bodies.             2. Jointed limbs (legs).             3. Exoskeleton: An outer skeleton made of a substance called chitin.         * Major Groups: Includes crabs, millipedes, scorpions, and grasshoppers.

    * Vertebrates         * Definition: Animals that possess a vertebral column or backbone.         * Major Groups:             1. Fish (e.g., Scad, Tilapia).             2. Amphibians (e.g., Toad, Frog).             3. Reptiles (e.g., Crocodile, Water Monitor).             4. Birds (e.g., Penguin, Pigeon).             5. Mammals (e.g., Dolphin, Goat, Leopard Cat, Domestic Cat, Lion, Tiger).

Dichotomous Keys

  • Definition and Purpose     * A dichotomous key is a tool used to identify and classify organisms based on observable features.     * It can be presented as a written list of choices or in the form of a branching chart.

  • Steps to Construct a Dichotomous Key     1. List the observable features of the organisms to be identified.     2. Select a main feature that is not shared by all the organisms to divide the entire group into two distinct sets.     3. Select another specific feature to further divide those two groups into smaller sub-groups.     4. Continue this binary branching process until every organism has been individually identified.

Classification Example: The Felidae Family

  • The domestic cat, tiger, and lion all belong to the same family.
  • Example Scientific Names:     * Tiger: Panthera tigris     * Lion: Panthera leo     * Domestic Cat: Felis domestica