Biological Classification Overview

Study Notes

Classification systems for living organisms have evolved, maintaining the plant and animal kingdoms while altering understanding of included groups.
Initially, five kingdoms are recognized: Monera, Protista, Fungi, Plantae, and Animalia, which differ in cell type, structure, organization, and nutrition.

Monera: Prokaryotic, non-cellulosic cell wall, lacks nuclear membrane, unicellular body, autotrophic and heterotrophic nutrition.
Protista: Eukaryotic, cell wall present, with a defined nucleus, unicellular, primarily aquatic, autotrophic and heterotrophic modes of nutrition.
Fungi: Eukaryotic, cell wall present (chitin), multicellular/loose tissue organization, heterotrophic (saprophytic or parasitic).
Plantae: Eukaryotic, cellulose-based cell wall, tissue/organ system organization, primarily autotrophic (photosynthesis).
Animalia: Eukaryotic, no cell wall, tissue/organ system organization, heterotrophic (holozoic nutrition).

Encompasses all single-celled eukaryotes but is often poorly defined, with examples including Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds, and Protozoans.
Protists are primarily aquatic and serve as a link to plants, animals, and fungi.
Reproduction can be both sexual and asexual.

Includes diatoms and golden algae, found in freshwater and marine environments, and are mostly photosynthetic.
Diatom cell walls are silica-embedded, forming indestructible overlapping shells.

All protozoans are heterotrophic, existing as predators or parasites.
Major groups include:
- Amoeboid Protozoans: Move and capture prey with pseudopodia (e.g., Amoeba).
- Flagellated Protozoans: Possess flagella, some being parasitic (e.g., Trypanosoma).
- Ciliated Protozoans: Move via cilia, directing food into their gullet (e.g., Paramoecium).
- Sporozoans: Include organisms with a spore stage, such as Plasmodium (causes malaria).

Comprises heterotrophic organisms with diverse morphology and habitat.
Fungi reproduce mainly through asexual spores (conidia) and can be saprophytes, parasites, or decomposers.
Common examples include mushrooms and parasitic fungi on plants.

Encompasses chlorophyll-containing eukaryotic organisms, including algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
Life cycles feature alternation of generations between diploid (sporophyte) and haploid (gametophyte) phases, which can vary in length and independence.

Comprises unicellular and multicellular eukaryotic organisms that lack cell walls.
Nutrition is holozoic, relying on ingestion.
Early studies identified viruses as pathogens causing specific diseases, noting their classification and structure:
- Viruses are obligate parasites, composed of proteins and either RNA or DNA.
- Regular symptoms of viral infections in plants and animals include various growth and structural abnormalities.

Viruses were first discovered as smaller pathogens affecting tobacco plants, leading to understanding virus structure, including capsid and nucleic acids.
Viroids, identified in 1971, represent a simpler form of infectious agents.