Microbiology Quiz - Types and Characteristics

Introduction to Microbiology

• Microbiology is the study of microorganisms, tiny living organisms that are too small to be seen with the naked eye.
• Microorganisms can be single-celled (unicellular) or multicellular, even relatively complex, organisms.
• Microorganisms include bacteria, viruses, archaea, fungi, protozoa, algae, and multicellular animal parasites (helminths).
• Microorganisms play diverse roles, some are beneficial, such as producing oxygen and decomposing organic matter. Others can cause diseases in plants and humans.

Types of Microorganisms

• Bacteria: Unicellular prokaryotic organisms lacking a nucleus.
• Fungi: Eukaryotic organisms (with a true nucleus). Most fungi are multicellular. Their cell walls are composed of chitin.
• Viruses: Non-cellular entities consisting of a nucleic acid core (DNA or RNA) surrounded by a protein coat. They are not considered living organisms.
• Parasites: Eukaryotic organisms, like flatworms and roundworms (helminths). Although not microorganisms by strict definition (they are large enough to be seen with the naked eye), their life cycle often involves microscopic stages.
• Protozoa: Unicellular, aerobic eukaryotes with nuclei and complex organelles. They obtain nutrition by absorption or ingestion.
• Algae (cyanobacteria/blue-green algae): Unicellular or multicellular eukaryotes obtaining nutrients through photosynthesis. They produce oxygen and carbohydrates vital for many ecosystems.

3 Domains of Life

• Organisms are classified into three domains: Bacteria (prokaryotes), Archaea (prokaryotes), and Eukarya (eukaryotes).

Prokaryotic and Eukaryotic Cells

• Prokaryotes: Always single-celled, lack a membrane-bound nucleus.
• Eukaryotes: Can be single-celled or multicellular, have a membrane-bound nucleus and other organelles.

Characteristics Shared by Prokaryotic and Eukaryotic Cells

• Surrounded by a plasma membrane that regulates what enters and exits the cell.
• "Filled" with cytoplasm.
• Contain ribosomes needed for protein synthesis.
• Contain DNA to control cellular activities.

Differences Between Prokaryotic and Eukaryotic Cells

• Nucleus: Prokaryotes lack a nucleus – their DNA is in a region called the nucleoid. Eukaryotes have a nucleus, containing their DNA.
• DNA: Prokaryotes typically have a single, circular chromosome. Eukaryotes have multiple, linear chromosomes.
• Organelles: Prokaryotes lack membrane-bound organelles. Eukaryotes have many membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum, Golgi apparatus).
• Cytoskeleton: Eukaryotes have a cytoskeleton for structural support and movement. Prokaryotes generally lack this.
• Cell Wall: In some prokaryotes (bacteria), the cell wall contains peptidoglycan. Plant and fungi cells have cell walls, but their structure is different than bacterial cell walls.
• Cell Division: Prokaryotes divide by binary fission. Eukaryotes use mitosis or meiosis.
• Reproduction: Prokaryotic reproduction is asexual. Eukaryotic reproduction can be asexual or sexual.

Bacteria: Classification of Bacteria

• Shape: Bacilli (rod-shaped), cocci (spherical), spirilla (spiral), vibrios (curved).
• Cell Wall: Gram-positive or Gram-negative (distinguishable by Gram staining).
• Energy Acquisition: Autotrophs (produce their own food), or heterotrophs (obtain food from other organisms). Autotrophs using sunlight are photoautotrophs, those using other chemical reactions are chemoautotrophs. Heterotrophs using decaying matter are saprophytes.
• Oxygen Response: Aerobes (require oxygen), anaerobes (cannot tolerate oxygen), facultative anaerobes (can use oxygen or grow without it), aerotolerant anaerobes (can tolerate oxygen but don't use it for growth).
• Microaerophilic bacteria need reduced levels of atmospheric oxygen for optimal growth.

Common Bacteria Shapes and Arrangements

• Cocci (spherical): Diplococci (pairs), Streptococci (chains), Tetrads (groups of four), Sarcinae (groups of eight), Staphylococci (clusters).
• Bacilli (rod-shaped): Coccobacilli (short rod shape), Diplobacilli (pairs), Streptobacilli (chains), Palisades (side by side in a row).
• Spiral (spiral shaped): Vibrios (comma shaped), Spirilla (rigid spirals), Spirochetes (flexible spirals).

Additional Concepts

• Size of Bacteria: Prokaryotes are typically much smaller than eukaryotes. Their small size allows rapid nutrient uptake.
• Gram-positive bacteria: Bacteria that retain the crystal violet stain during the Gram staining process
• Gram-negative bacteria: Bacteria that lose the crystal violet stain during the Gram staining process.