Classification of Organisms

Biology Notes

13.1 Classification of Organisms

Life on Earth originated approximately 3.6 billion years ago, starting with unicellular organisms, eventually evolving into complex multicellular organisms. Today, there are about 8.7 million species of living organisms.

These species are classified into hierarchical categories based on shared characteristics and genetic relationships, which generally include domains, kingdoms, phyla, classes, orders, families, genera, and species. This system not only helps in organizing the vast diversity of life but also aids in understanding the evolutionary relationships among different organisms.

Overview of Classification

The grouping of organisms based on shared characteristics is known as classification. This process is significant for various reasons:

• Facilitates the study of organisms

• Helps identify and understand distinct characteristics

• Provides an overview of biosphere diversity

• Reveals relationships between different groups

• Aids in the identification of economically important species

Methods of Classification

The first scientific classification was proposed by Aristotle in the 4th century B.C. Carolus Linnaeus later introduced a successful classification system.

Types of Classification:

1. Artificial Classification

   • Based on observable traits, e.g., ability to fly or habitat.

   • Does not reflect evolutionary relationships (e.g., grouping birds and insects by wings).

2. Natural Classification

   • Reflects evolutionary relationships.

   • Involves morphological, physiological, and molecular characteristics.

   • Example: Fins in fish, feathers in birds, and legs in humans indicate relationships.

Organisms are grouped into different taxonomic levels, illustrated by examples of Modern Humans (Homo sapiens) and Coconut Trees (Cocos nucifera).

• Domain: Eukarya

• Kingdom: Animalia / Plantae

• Phylum/Division: Chordata / Magnoliophyta

• Class: Mammalia / Liliopsida

• Order: Primates / Arecales

• Family: Hominidae / Arecaceae

• Genus: Homo / Cocos

• Species: Homo sapiens / Cocos nucifera

Three Domain System

Carl Woese introduced one of the most relevant classification systems, differentiating organisms into three domains:

1. Domain Archaea

   • Prokaryotic organisms.

   • Capable of surviving extreme environments (e.g., Methanogens, Halophiles).

   • not sensitive to antibiotics

2. Domain Bacteria

   • Also prokaryotic but sensitive to antibiotics.

   • Includes Bacteria and Cyanobacteria; significant for ecological roles such as decomposing organic matter and nitrogen fixation.

   • found everywhere in env

   • most abundant group or organisms

   • harmful- diseases, food spoilage

   • useful- produce curd, decompose dead bodies

3. Domain Eukarya

   • Includes all eukaryotic organisms divided into four kingdoms:

     • **Kingdom Protista (Algae, Protozoans)

     • Kingdom Fungi (Mushrooms, Yeast)

     • Kingdom Plantae (Plants)

     • Kingdom Animalia (Animals)

     • found everywhere, not sensitive to antibiotics, eukaryotic cells

/

Kingdoms Breakdown

Kingdom Protista:

• Eukaryotic, mostly unicellular organisms found in aquatic environments, photosynthetic, some are heterotrophic.

• Example: Algae (Ulva) and Protozoans (Paramecium).

• harmful- diseases like malaria, sleep sickness

• useful- base of food chain in aq envs, extract alginic acid for ice cream.

Kingdom Fungi:

• Unicellular or multicellular organisms with chitinous cell walls.

• Play vital roles in decomposition and nutrient cycling, forms symbiotic asso w organisms, 1.5 - 5 million species.

• harmful- food spoilage, diseases like pityriasis

• useful- produce antibiotics (penicillium), decompose dead bodies, bread and alcohol fermentation(yeast)

Kingdom Plantae:

• Multicellular organisms (e.g., plants) capable of photosynthesis.

• Divided into non-flowering (gymnosperms) and flowering plants (angiosperms).

Non-flowering Plants:

• Examples: Ferns (e.g., Selaginella), Cycas, Pinus.

Flowering Plants:

• Divided into Monocots (e.g., Paddy, Coconut) and Dicots (e.g., Mango, Orange).

Kingdom Animalia:

• Multicellular and heterotrophic.

• Grouped into Invertebrates and Vertebrates

  • Key phyla of Invertebrates:

    • Cnidaria (Hydra, Jellyfish)

    • Annelida (Earthworm, Leech)

    • Mollusca (Snail, Octopus)

    • Arthropoda (Insects, Spiders)

    • Echinodermata (Starfish)

  • Vertebrates divided into:

    • Pisces (Fish)

    • Amphibia (Frogs)

    • Reptilia (Tortoise, Snakes)

    • Aves (Birds)

    • Mammalia (Humans, Dolphins)

Nomenclature of Organisms:

Binomial Nomenclature

• Developed by Carolus Linnaeus (1753).
  Each organism is given a name consisting of two parts: genus and specific epithet.

Examples:

• Homo sapiens - Modern Humans

• Cocos nucifera - Coconut

• Identify scientific names of plants and animals from various resources.

• Observe classroom discussions on classification systems and the significance of coral reefs from Cnidaria.

Kingdom Plantae

Overview:

• Comprises multicellular organisms that perform photosynthesis and derive energy from sunlight, green bcz of chlorophyll and cell walls with cellulose.

• Plants are categorized into non-flowering (gymnosperms) and flowering plants (angiosperms).

Table 13.2: Non-Flowering Plants

Table 13.3: Flowering Plants

Table 13.4: Examples of Various Plant Types

Binomial Nomenclature Standards:

• Developed by Carolus Linnaeus in 1753.

• Each organism is identified by a two-part name: the genus name (capitalized) and the species name (lowercase).

• Both names are italicized (or underlined) when handwritten (e.g., Homo sapiens).

• The genus name can be abbreviated after its first use (e.g., H. sapiens).

Overview: KINGDOM ANIMALIA

Kingdom Animalia comprises multicellular and heterotrophic organisms, with diverse characteristics and adaptations. They are grouped into Invertebrates and Vertebrates, each with unique features.

Invertebrates:

• Exhibit a wide range of body structures and lifestyles, from simple to complex organisms.

• Lack a backbone or vertebral column.

Key Phyla of Invertebrates:

• Cnidaria (e.g., Hydra, Jellyfish):

  • Have stinging cells (nematocysts) for capturing prey.

  • Exhibit radial symmetry.

  • diploblastic, aquatic

  • coelenteron is digestive tract

  • 2 forms- medusa and polyp

• Annelida (e.g., Earthworm, Leech):

  • Possess segmented bodies, which help in movement and adaptability, first organism w a body cavity called coelom.

  • Have a closed circulatory system.

  • triploblastic

  • water, damp, marine env

  • segmented body

  • bilateral symmetry

• Mollusca (e.g., Snail, Octopus):

  • Have soft bodies, usually protected by a hard shell.

  • triploblastic, multicellular

  • Exhibit varied forms of locomotion (e.g., crawling, swimming).

  • terrestrial and fresh water env

  • head, muscular foot and visceral mass

  • moist body with mucus

  • bilaterel symmetry

• Arthropoda (e.g., Insects, Spiders):

  • Possess exoskeletons made of chitin.

  • highest number of species

  • Segmented bodies and jointed appendages for mobility.

  • marine, fresh water, terrestrial env

  • triploblastic, coelomic and jointed limbs

  • some have wings

  • bilateral symmetry

• Echinodermata (e.g., Starfish, sea urchin):

  • Have a unique water vascular system for movement and feeding.

  • Exhibit radial symmetry as adults, with spiny skin, star, cylindrical, flower shaped bodies

  • phylogenetic relationship with phylum chordata

  • all marine

  • triploblastic, coelomic, penta radial symmetry(5 arms)

  • tube feet for locomotion

  • no heart, brain or eyes

Vertebrates:

• Possess a backbone or vertebral column.

• Exhibit a more complex structure and advanced organ systems compared to invertebrates.

Key Classes of Vertebrates:

• Pisces (Fish, seahorse, skate):

  • Have gills for breathing underwater and scales covering their bodies.

  • fresh water and marine env

  • Can be divided into bony (Osteichthyes) and cartilaginous (Chondrichthyes) fish.

  • streamlined body

  • fins to swim

  • lateral line system

  • two chambered heart

  • cold blooded

  • eyes without eye lids

• Amphibia (Frogs, toads, salamander):

  • Typically undergo metamorphosis from aquatic larvae to terrestrial adults.

  • first organisms to invade land

  • Have moist skin that allows for gas exchange.

  • no scales

  • pentadactyle limbs

  • three chambered heart

  • cold blooded

• Reptilia (Tortoise, Snakes, crocodile):

  • Have dry, scaly skin, and lay eggs with protective shells

  • terrestrial, fresh water, marine env

  • Many are ectothermic, relying on external sources for body heat.

  • pentadactyle limbs

  • lungs to breathe

  • cold blooded

• Aves (Birds):

  • Characterized by feathers, wings, and beaks adapted for various lifestyles, light bony endoskeleton

  • Endothermic, maintaining a constant body temperature.

  • streamlined body

  • feathers, scales only on legs

  • no teeth

  • eyes with eyelids

  • pentadactyle limbs

  • four chambered heart

  • warm blooded

• Mammalia (Humans, Dolphins):

  • Have fur or hair and mammary glands to nurse young, ear lobes

  • Exhibit a high level of intelligence and complex social behaviors.

  • four chambered heart

  • warm blooded

  • double circulation