Taxonomy of Living Organisms

Taxonomy of Living Organisms

• Taxonomy is a formal system for organizing, classifying, and naming living organisms.
• Bacteria: Prokaryotic, single-celled organisms.
• Archaea: Prokaryotic, single-celled organisms, thriving in extreme environments (high salt, high temperature).
• Algae: Eukaryotic organisms that perform photosynthesis.
• Fungi: Eukaryotic organisms, either single-celled or multicellular.
• Protozoa: Eukaryotic, single-celled or multicellular organisms.
• Viruses: Non-cellular agents, only visible with electron microscopes, consisting of nucleic acid surrounded by a protein coat.
• Viroids: Non-cellular plant pathogens, RNA-based, unable to produce proteins or have a protein coat.
• Virusoids: Non-cellular plant pathogens primarily, RNA-based. One type (HDV) infects humans.
• Prions: Non-cellular, misfolded normal animal proteins, infectious (lack nucleic acid).

Bacterial Life Cycle

• Bacteria exist in a vegetative form, actively metabolizing, growing, and multiplying.
• Under unfavorable conditions, some vegetative cells convert to spores (endospores) through sporulation.
• Spores are dormant, resistant structures that can survive for years.
• Spores revert to their vegetative form (germinates) when environmental conditions improve.

Cytoplasmic Organelles

• Mitochondria: Fluid-filled sacs, responsible for ATP production (energy).
• Ribosomes: Small RNA granules, either free in the cytoplasm or attached to the endoplasmic reticulum, essential for protein synthesis.
• Endoplasmic Reticulum (ER): Network of membranes.
  • Smooth ER: Involved in lipid synthesis.
  • Rough ER: Involved in protein synthesis and transportation.
• Golgi Apparatus: Flat sacs connected to ER, processing and packaging proteins.
• Lysosomes: Sacs containing enzymes that break down particles (e.g., bacteria).
• Centrioles: Two rods at right angles, crucial for cell division.
• Cilia: Short, numerous hair-like projections that move substances across cell surfaces (e.g., respiratory tract).
• Flagella: Long, few structures that enable cell movement.
• Chloroplasts: Found in algae and plant cells, converting sunlight into chemical energy (photosynthesis).

Defense Mechanisms Against Infection

• Nonspecific mechanisms: Provide general resistance against all harmful agents.
• Specific mechanisms: Provide immunity, aimed at specific harmful agents.
• Susceptibility: Lack of resistance.
• Virulence: The degree of pathogenicity or disease-causing potential of a microbe.