Classification of Organisms

Five-Kingdom Classification System

The five-kingdom classification system categorizes all organisms into one of five kingdoms.

Kingdom Monera

• Includes microscopic, single-celled organisms.
• Cell wall is present but there is no proper nucleus (prokaryotic).
• Examples: All bacteria.

Kingdom Protista

• Includes single-celled organisms.
• Well-formed nucleus is present (eukaryotic).
• Examples: Amoeba, malarial parasite, Chlamydomonas.

Kingdom Fungi

• Includes multicellular (many-celled) organisms.
• The body is made of a network (mycelium) of fine threads called hyphae.
• Fungi feed on dead and decaying matter (saprophytes).
• Examples: Mushroom, yeast, bread mold, etc.

Kingdom Plantae

• Includes multicellular eukaryotes.
• Cellulose cell wall is present.
• Chlorophyll is present in their cells, making them autotrophs capable of carrying out photosynthesis.

Kingdom Animalia

• Includes multicellular eukaryotes.
• Special organs are present for locomotion or movement from one place to another.
• Heterotrophic in nature.
• Possess a nervous system with sense organs.

Characteristics of the Five Kingdoms

Kingdom Plantae (Plants)

• Includes eukaryotic, multicellular photosynthetic green plants.
• May be vascular or non-vascular.
• May be flowering or non-flowering plants.

Non-Flowering Plants

• Plants which do not bear flowers.
• Examples: Spirogyra, Merchantia, moss, fern, etc.

Flowering Plants

• Plants which bear flowers.
• Examples: Mustard plant, orange, apple, wheat, barley, etc.

Divisions of Kingdom Plantae

1. Algae
2. Bryophyta
3. Tracheophyta

Division: Algae

• Simple green plants, unicellular or multicellular.
• Found in both marine and fresh water.
• Can prepare their own food due to the presence of chlorophyll (autotrophic).
• The body cannot be differentiated into roots, stems, and leaves.

Characteristics of Algae

1. Aquatic: Found in both marine and fresh water, and moist places (soil, rocks).
2. May be unicellular or multicellular.
3. Green, autotrophic, and non-vascular (lacking conducting tissues).
4. Store food materials in the form of starch.
5. Cell wall made of cellulose.
6. Reproduce by vegetative, asexual, and sexual methods.

Examples of Algae

• Chlamydomonas
• Volvox
• Spirogyra
• Ulothrix
• Ulva

Division: Bryophyta (Bryophytes)

• Grow in moist places, such as damp soil and shady areas.
• Have stems and leaves but no roots.
• Rhizoids are present, allowing them to absorb water.
• Utilize water for fertilization, known as the amphibians of the plant kingdom.

Characteristics of Bryophytes

1. Mostly grow in moist and shady places.
2. Multicellular plants.
3. Green, autotrophic, and non-vascular.
4. Require water for fertilization, so they are amphibians of the plant kingdom.
5. Remain attached to the substratum.
6. Show the alternation of generation in their life cycle, with the gametophytic stage lasting longer than the sporophytic stage.

Examples of Bryophytes

• Moss
• Liverworts
• Merchantia
• Riccia
• Pellia

Division: Tracheophyta (Tracheophytes)

• Developed plants with well-developed conducting tissues (xylem and phloem).

Sub-Divisions of Tracheophyta

1. Pteridophyta
2. Gymnosperm
3. Angiosperm

Sub-division: Pteridophyta (Pteridophytes)

• Bear roots, a stem, and leaves, but do not contain seeds and flowers.
• Vascular bundles (xylem and phloem) are present.
• Most developed among non-flowering plants.

Characteristics of Pteridophytes

1. Mostly grown in moist, shady, and cool places.
2. Developed non-flowering plants whose body is differentiated into roots, stems, and leaves.
3. Contain conducting tissues (xylem and phloem).
4. Reproduce asexually by sporulation (i.e., by the formation of spores).
5. Show a distinct alternation of generations.

Examples of Pteridophytes

• Fern
• Lycopodium
• Horsetail
• Selaginella
• Paniamala
• Oteris
• Selaginaella

Division: Gymnosperm

• Cone-bearing plants.
• Do not have seeds enclosed in fruits; instead, they bear cones.
• Contain needle-shaped leaves to prevent harm from frost or snow.

Characteristics of Gymnosperms

1. Cone-bearing plants.
2. Have naked seeds that are not enclosed in fruits.
3. Leaves are long and needle-shaped.
4. Have unisexual flowers.
5. Pollination occurs by wind.

Examples of Gymnosperms

• Cycas
• Pinus
• Fir
• Juniper
• Himalayan yew
• Cedar

Division: Angiosperm

• Bear flowers, fruits, and seeds enclosed inside fruits.
• Can be hydrophytes, mesophytes, xerophytes, or epiphytes.
• Most developed among the plantae.

Characteristics of Angiosperms

1. Found in water and on land.
2. Vascular plants (i.e., contain conducting tissues: xylem and phloem).
3. Have well-developed flowers, fruits, etc.

Introduction to Organism Classification

• Living organisms are found all around us, varying from microscopic single-celled organisms to large animals.
• Estimated $10$ to $15$ million different kinds of organisms on Earth, including those that lived in the past.

Classification of Organisms

• Arranging organisms into groups and subgroups based on similarities and differences.
• Establishes a hierarchical structure: Kingdom, Phylum, Class, Order, Family, Genus, and Species.
• Indicates the organism's evolutionary relationship with other living beings.

Taxonomy

• Developed by Linnaeus Carolous (father of taxonomy).
• Branch of biology dealing with the identification, classification, and nomenclature of organisms based on resemblances and differences in their morphology.

Nomenclature

• Assigning a proper or scientific name to all living organisms to easily distinguish them from one another.
• The first name is the generic name, and the second name is the specific name, indicating the genus and species.

Species

• Population of closely related organisms that are morphologically similar and can interbreed freely among each other in a natural way.
• Basic unit of classification.

Genus

• Group of closely related species that have evolved from common ancestors.

Binomial System of Nomenclature

• Assigning two names to an organism, where the first is the generic name and the second is the specific name.

Historical Context

• Earlier, there were only two kingdoms of plants and animals.
• In $1969$, Whittaker suggested that bacteria cannot be in the plant kingdom and protozoa cannot be in the animal kingdom.