Microorganism Classification: Bacteria, Archaea, Fungi

• Microorganisms are classified into various groups based on characteristics
• Major groups: bacteria, archaea, fungi, protozoa, algae, and viruses

Bacteria

• Single-celled prokaryotic organisms
• Lack a nucleus and membrane-bound organelles
• Have diverse shapes: spherical (cocci), rod-shaped (bacilli), and spiral (spirilla)
• Reproduce via binary fission
• Obtain nutrients from organic and inorganic compounds
• Some are pathogenic, causing diseases in humans, animals, and plants
• Some are beneficial, playing essential roles in nutrient cycling, decomposition, and food production

Archaea

• Single-celled prokaryotic organisms
• Initially classified as bacteria but now a distinct domain
• Similarities with bacteria in cell structure and reproduction exist
• Differ from bacteria in genetic makeup and metabolic pathways
• Many are extremophiles, thriving in harsh conditions like hot springs, salt lakes, and acidic environments
• Do not cause disease in humans

Fungi

• Eukaryotic organisms
• Possess a nucleus and membrane-bound organelles
• Can be unicellular (yeasts) or multicellular (molds and mushrooms)
• Have chitin cell walls
• Obtain nutrients by absorption, breaking down organic matter with secreted enzymes
• Reproduce through spores (sexual or asexual)
• Some are decomposers, breaking down dead organic material
• Some are pathogens, causing diseases in plants and animals
• Some are used in food production, like yeast in bread and molds in cheese

Protozoa

• Unicellular eukaryotic organisms
• Diverse in shape, size, and locomotion
• Lack cell walls
• Obtain nutrients by ingestion or absorption
• Reproduce primarily asexually, such as by binary fission
• Some are free-living; others are parasites
• Pathogenic protozoa cause diseases like malaria, giardiasis, and amoebic dysentery

Algae

• Eukaryotic organisms that perform photosynthesis
• Can be unicellular or multicellular
• Contain chloroplasts with chlorophyll for photosynthesis
• Have cellulose cell walls
• Reproduce sexually or asexually
• Important primary producers in aquatic ecosystems
• Some are used as food or as a source of biofuels

Viruses

• Acellular entities
• Composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid)
• Obligate intracellular parasites
• Replicate inside a host cell
• Infect various organisms, including bacteria, plants, and animals
• Viral infections can cause diseases like the common cold, influenza, and HIV/AIDS

Immunity

• Ability of an organism to resist infection by pathogens
• The immune system is a complex network of cells, tissues, and organs that defend the body
• Two main types: innate and adaptive immunity

Innate Immunity

• The body's first line of defense against pathogens
• Non-specific, responds to a broad range of pathogens
• Includes physical barriers (skin, mucous membranes) and internal defenses (phagocytes, natural killer cells, inflammation)
• Physical barriers prevent pathogen entry
• Phagocytes engulf and destroy pathogens
• Natural killer cells kill infected cells
• Inflammation is a localized response to infection or injury, characterized by redness, swelling, heat, and pain

Adaptive Immunity

• A specific response to pathogens that develops over time
• Recognition of specific antigens, molecules found on the surface of pathogens, is involved
• Includes lymphocytes (white blood cells) that recognize and respond to antigens
• Two main types of lymphocytes: B cells and T cells
• B cells produce antibodies, proteins that bind to antigens, neutralizing or marking them for destruction
• T cells directly kill infected cells or help activate other immune cells
• Can provide long-lasting protection against specific pathogens through memory cell formation
• Memory cells are lymphocytes that remain in the body after an infection and can quickly respond to future encounters with the same pathogen

Learn the key characteristics and differences between bacteria, archaea, and fungi. Explore their cellular structures, reproduction methods, and ecological roles. Discover how these microorganisms impact health, environment, and industry.