Untitled Quiz

Grade 12 Biology Unit 2: Microorganisms

• Microorganisms (also called microbes) are life forms too small to be seen with the naked eye.
• Most are unicellular (single-celled), some form complex structures (multicellular).
• They live in complex communities and their activities are regulated by interactions with each other, their environment, and other organisms.
• Microbiology is the study of microbes (what they are, how they work, and what they do).

Learning Objectives

• Categorize microorganisms based on morphology, mode of nutrition, and biochemical analysis.
• Explain transmission and prevention of pathogenic microorganisms.
• Explain the significance of Koch's postulates for microbiological techniques.
• Apply the principles of microbiological technique.
• Discuss the economic importance of microorganisms.

Types of Microorganisms

• Organisms grouped into three domains: Bacteria, Archaea, and Eukarya.
• Visual representation of evolutionary relationships(Phylogenetic tree) showing various bacterial and archaeal groups. Eukaryotes include microorganisms like fungi, some algae, protozoa and animals.

Eubacteria (Bacteria)

• Literally means "true bacteria".
• Relatively simple structure with no nuclear membrane, mitochondria, or endoplasmic reticulum.
• Reproduce by asexual division.
• Omnipresent (found in soil, air, and water).
• Unicellular.
• Cell wall made of peptidoglycan.
• Heterotrophic (autotrophic, parasitic or saprophytic) mode of nutrition.
• Lack true nucleus and other organelles (mitochondria, Golgi apparatus, plastid, EPR).
• DNA & RNA are present.
• Key bacterial cell structures: Cell Wall (peptidoglycan), Nucleoid (contains genophore), cytoplasmic matrix, ribosomes, slime capsule, pili, and flagella.
• Classified based on shapes: Cocci (spherical), Bacilli (rod-shaped ), Spirilla (spiral or corkscrew-shaped), and Comma (Vibrio cholera)
• Distinguishing between Gram-positive and Gram-negative bacteria based on cell wall composition (thick vs. thin peptidoglycan layer, presence/absence of outer membrane, and specific molecules like teichoic acids, lipopolysaccharides,etc).

Archaea

• Prokaryotic, unicellular organisms.
• Live in extreme environments.
• Lack true peptidoglycan in their cell walls.
• Cell membrane lipids have branched hydrocarbon chains.
• Three major groups: methanogens (produce methane), extreme halophiles (live in high salt environments), and extreme thermophiles (live in high temperature environments).

Fungi

• Eukaryotic, often multicellular, microorganisms (some yeasts are unicellular).
• Filamentous, with a network of hyphae called a mycelium.
• Cell walls typically contain chitin or glucans (although some contain cellulose)
• Heterotrophic that cannot perform photosynthesis.
• Three types of reproduction: asexual (sporulation- sporangia, conidia, and fragmentation), and Sexual (fusion).
• Economic importance: decomposers, food sources, production of antibiotics and some acids (citric, oxalic).
• Examples of fungi: yeasts, molds, and mushrooms.
• Common types of fungi infections: dermatophytosis, candidiasis, aspergillosis, thrush, ringworms.

Protozoa

• Eukaryotic single-celled microorganisms.
• Lack cell walls.
• Obtain nutrients through absorption, ingestion, or engulfment (phagocytosis)
• Reproduce asexually by binary fission, budding, multiple fission (schizogony).
• Reproduce sexually through conjugation or syngamy.
• Common protozoan diseases: amoebiasis, giardiasis, trichomoniasis, malaria, toxoplasmosis, African trypanosomiasis, leishmaniasis, and cryptosporidiosis.

Bacteria

• Microorganisms found in soil, water, plants, animals and humans.
• Essential roles in nutrient cycling and decomposition.
• Involved in a range of diseases in humans and other organisms.
• Can reproduce by binary fission, budding, or multiple fission
• Classified based on different features like shape, gram reaction, cell wall structure, oxygen requirements, etc.

Viruses

• Non-cellular, parasitic entities.
• Consist of nucleic acid (DNA or RNA) enclosed in a capsid (protein coat).
• Cannot reproduce independently; they require host cell machinery.
• Classified based on their genome, symmetry, and presence of an envelope.
• Replication: Attachment, penetration, uncoating, biosynthesis, assembly, and release.
• Types of viruses: RNA (HIV, influenza, common colds, COVID); DNA (Herpes, adenoviruses).
• Methods of transmission: contact, vehicles, airborne, and vectors.
• Can produce diseases such as HIV/AIDS, influenza, hepatitis, and smallpox.
• Classification based on different factors such as structure, genome, and replication strategy.

Microbial Growth

• Different physical factors influence microbial growth such as temperature, pH, water activity, oxygen levels, osmotic conditions, pressure, and radiation.
• Different types of microorganisms responding to these factors like Psychrophiles, Psychrotrophs, Mesophiles, Thermophiles, and Hyperthermophiles based on optimal growth temperature.
• Microbes requiring O₂ are called aerobes, while those tolerate oxygen are facultative anaerobes; microbes not requiring O₂ are called anaerobes.
• Also include microbes responding to salt and acidic conditions as well as examples of such microbes, and how they respond to these conditions

Controlling Microorganisms

• Techniques for sterilization: heat (dry, moist, and tyndallization) and chemical agents (germicides like disinfectants and antiseptics).
• Different methods of microbial control and their applications in various settings.

Microorganisms in various ecological systems and their significant role

• Role in agriculture (nitrogen cycle, decomposition),
• Waste treatment.
• Bioremediation
• Food production and processing.

The Nitrogen, Phosphorus, and Sulfur cycles

• Key processes and prokaryotic microorganisms which play crucial roles in these cycles.
• Roles in nutrient cycling.

Normal Microbiota

• Definition of normal microbiota in humans.
• Resident vs. transient microbiota.
• Protective roles of normal microbiota (preventing overgrowth of other microbes, producing useful substances).
• How microbiota composition can change over time.
• Koch’s postulates and their significance in microbiology.