Biology Chapter on Protista

Kingdom Protista

• Protista includes Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds, and Protozoans.
• Members are primarily aquatic and serve as a link between plants, animals, and fungi.
• Eukaryotic cells have a defined nucleus and membrane-bound organelles; some possess flagella or cilia.
• Reproduction can be asexual or sexual, involving cell fusion and zygote formation.

Chrysophytes

• Comprises diatoms and golden algae (desmids), found in both freshwater and marine environments.
• Microscopic organisms that float in water currents (plankton) and are primarily photosynthetic.
• Diatom cell walls have silica, forming indestructible two-shell structures, resulting in deposits known as 'diatomaceous earth,' used in polishing and filtration.
• Diatoms are the chief producers in ocean ecosystems.

Dinoflagellates

• Mostly marine, photosynthetic organisms with pigments that create various colors (yellow, green, brown, blue, red).
• Possess stiff cellulose plates in their cell walls and two flagella (one longitudinal and the other transverse).
• Rapid multiplication of red dinoflagellates, like Gonyaulax, can cause 'red tides,' releasing toxins harmful to marine life.

Euglenoids

• Primarily freshwater organisms found in stagnant waters.
• Have a flexible protein-rich layer (pellicle) instead of a cell wall and possess two flagella.

Viruses

• Considered non-living acellular entities; composed primarily of proteins and genetic material (either RNA or DNA).
• Viruses infect host cells to replicate, often causing cell death.
• Dmitri Ivanowsky recognized viruses in 1892, calling them "venom" or "poisonous fluid."
• Bacterial viruses, known as bacteriophages, primarily consist of double-stranded DNA.
• Pathogenic viruses cause diseases such as mumps, smallpox, herpes, and influenza.

Kingdom Fungi

• Diverse kingdom of heterotrophic organisms; includes edible mushrooms and parasitic fungi (e.g., Puccinia, causing wheat rust).
• Bodies consist of hyphae (thread-like structures), forming a mycelium network; cell walls are made of chitin.
• Fungi can be saprophytic, parasitic, or symbiotic.
• Reproduction occurs vegetatively (fragmentation, fission, budding) and by spores (conidia, sporangiospores).
• The sexual cycle involves plasmogamy (fusion of protoplasm), karyogamy (fusion of nuclei), and meiosis.

Basidiomycetes

• Includes mushrooms, bracket fungi, and puffballs; the mycelium is branched and septate.
• Asexual reproduction is rare; vegetative reproduction occurs through fragmentation.
• Karyogamy and meiosis occur in specialized structures called basidia, producing basidiospores.

Deuteromycetes

• Known as imperfect fungi; sexual forms were only discovered later and classified accordingly.
• Reproduce solely by asexual spores (conidia) and play roles as saprophytes, parasites, or decomposers.

Kingdom Plantae

• Comprises eukaryotic, chlorophyll-containing organisms; includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
• Life cycle includes alternating sporophytic (diploid) and gametophytic (haploid) phases.
• Some plants are partially heterotrophic (e.g., insectivorous plants like Venus flytrap).

Kingdom Animalia

• Characterized by multicellular, heterotrophic organisms lacking cell walls; depend directly or indirectly on plants for nutrition.
• Nutritional process is holozoic (ingestion of food); store food reserves as glycogen or fat.
• Sexual reproduction involves male and female copulation, followed by embryological development.

Acellular Organisms

• Viruses, viroids, and prions are not categorized within the traditional kingdoms due to their acellular nature.
• Viruses lack cellular structure and are inert outside a living cell.