Introduction to MicrobiologyClass 10 Science Part 2 Chapter 7 Notes – Maharashtra Board

Summary: Introduction to Microbiology

Microbiology studies microorganisms (microbes) too small to see without a microscope. Major groups include bacteria (prokaryotes), viruses (non-living), fungi, and protists (eukaryotes). Bacteria are single-celled prokaryotes; lack a nucleus but have nucleoid region containing DNA. They reproduce by binary fission (asexual) and are found everywhere—soil, water, air, living organisms. Some bacteria are pathogenic (cause disease), but most are beneficial: decomposers, nitrogen fixers in soil, producers of antibiotics, living in human gut aiding digestion.

Viruses are non-living particles of protein and genetic material (RNA or DNA). They require a host cell to reproduce. Important human viruses include influenza, COVID-19, measles, HIV, hepatitis. Fungi include yeasts and molds; they are eukaryotic, heterotrophic, and reproduce via spores. Many fungi are decomposers breaking down dead matter. Some cause disease (athlete's foot, candida), but others are beneficial (baker's yeast, mushrooms, antibiotics like penicillin from Penicillium mold). Protists are diverse eukaryotic microorganisms; some are plant-like (algae, photosynthetic), others animal-like (amoeba, paramecium), others fungus-like (slime molds).

Microorganisms are essential to ecosystems and human survival. Bacteria break down waste, cycle nutrients, fix nitrogen, produce oxygen. Algae are primary producers in aquatic ecosystems. Yeast ferments foods and beverages. However, some microbes cause disease—bacteria (tuberculosis, cholera), viruses (polio, COVID-19), fungi (ringworm), protists (malaria). Understanding microbiology helps us fight disease, improve food safety, biotechnology, and appreciate the microbial world's importance.

Key points to remember

• Microorganisms (microbes): organisms too small to see with naked eye (<0.1 mm). Studied with electron and light microscopes.
• Bacteria: prokaryotes (no nucleus), single-celled, reproduce by binary fission (asexual reproduction), ~0.5-5 μm diameter.
• Bacterial shapes: cocci (spherical), bacilli (rod-shaped), spirilla (helical/spiral).
• Bacterial cell structure: cell wall (peptidoglycan), cell membrane, nucleoid (DNA), ribosomes, plasmids (small DNA loops), flagella (movement).
• Gram staining: Gram-positive (thick peptidoglycan, purple) vs. Gram-negative (thin peptidoglycan, pink). Predicts antibiotic effectiveness.
• Bacterial reproduction: binary fission (parent cell divides into two identical daughter cells); conjugation (transfer DNA between cells).
• Beneficial bacteria: decompose dead matter, fix atmospheric nitrogen (Rhizobium in legumes), produce antibiotics, ferment foods, aid digestion.
• Pathogenic bacteria: cause tuberculosis (TB), cholera, typhoid, strep throat, food poisoning, urinary tract infections.
• Viruses: non-living, protein coat (capsid) + genetic material (DNA or RNA). Obligate parasites—require host cell to replicate.
• Viral replication: attachment to host cell, injection of genetic material, replication, assembly, lysis (release from cell).
• Important human viruses: influenza (respiratory), COVID-19 (respiratory), measles, mumps, polio, HIV/AIDS, hepatitis.
• Antiviral treatments: vaccines (prevent infection), antiretrovirals (slow HIV replication), monoclonal antibodies. Antibiotics don't work against viruses.
• Fungi: eukaryotes, heterotrophic (consume organic matter), reproduce via spores, cell walls contain chitin (like insects).
• Yeasts: single-celled fungi, reproduce by budding, used in bread/beer/wine fermentation. Candida overgrowth causes yeast infections.
• Molds: filamentous fungi with hyphae; decompose dead matter; produce antibiotics (penicillin), cause food spoilage and respiratory allergies.
• Protists: eukaryotic microorganisms, diverse: plant-like (algae - photosynthetic), animal-like (amoeba, paramecium, malaria parasite), fungus-like (slime molds).
• Algae: photosynthetic protists, form base of aquatic food chains, produce oxygen, some multicellular (seaweeds).
• Protozoa: animal-like protists, mostly heterotrophic. Amoeba (pseudopods), paramecium (cilia), malaria parasite (Plasmodium).
• Microbial diseases: bacteria (TB, cholera), viruses (polio, COVID-19), fungi (ringworm, candida), protists (malaria, sleeping sickness, dysentery).

Introduction to Microbiology – Notes

1. Bacterial structure and classification

• Prokaryotic cell (bacteria): no membrane-bound nucleus; DNA in nucleoid region; no mitochondria (respiration on cell membrane).
• Cell wall: rigid structure outside cell membrane; provides shape and protection. Composition: peptidoglycan (sugar + amino acids).
• Gram staining: crystal violet + iodine stains Gram-positive purple (thick peptidoglycan); alcohol wash removes stain from Gram-negative (pink with safranin).
• Cell membrane: selectively permeable, regulates transport. Pili: short protein projections (attachment, conjugation). Flagella: long whip-like structures (movement).
• Plasmids: small, circular DNA loops outside chromosome. Contain antibiotic resistance genes, virulence factors. Transferred between cells.
• Bacterial diversity: metabolically diverse (aerobic, anaerobic, chemosynthetic), diverse habitats (hot springs, deep ocean, human gut).

2. Bacterial reproduction and ecology

• Binary fission: DNA replicates, cell grows, septum forms, two identical daughter cells. Asexual—offspring genetically identical to parent.
• Conjugation: transfer DNA via pilus from donor to recipient; increases genetic diversity, spreads antibiotic resistance.
• Transformation: uptake of DNA from environment (dead bacteria).
• Ecological roles: decomposers (break down dead matter, recycle nutrients), nitrogen fixers (convert atmospheric N₂ to NH₃ in legume nodules), producers in chemosynthetic ecosystems (no sunlight).
• Human microbiome: ~40 trillion bacteria in human gut aid digestion, produce vitamins, compete with pathogens.
• Antibiotic resistance: overuse of antibiotics selects for resistant bacteria; resistant genes spread via conjugation, creating 'superbugs'.

3. Viruses and viral diseases

• Viral structure: capsid (protein shell) + genetic material (DNA or RNA, single or double-stranded). Some enveloped (lipid layer from host).
• Viral replication: 1) Attachment (receptor recognition), 2) Penetration (injection of genetic material), 3) Replication (hijack host machinery), 4) Assembly (new viruses formed), 5) Release (lysis kills host or budding keeps host alive).
• Retroviruses (like HIV): RNA genome; carry reverse transcriptase enzyme to convert RNA to DNA; integrate into host chromosome.
• HIV replication: infects CD4+ T cells (immune cells); mutates rapidly, evades immune system.
• Viral diseases: influenza (respiratory, seasonal, mutates annually), COVID-19 (respiratory, pandemic 2020), measles (highly contagious, vaccine-preventable), polio (paralysis, vaccine-preventable).
• Vaccines: live-attenuated (weakened virus), inactivated (dead virus), mRNA (genetic instructions to make viral protein), recombinant (viral protein produced in lab).

4. Fungi and fungal diseases

• Fungal structure: eukaryotic, cell wall with chitin, cannot photosynthesize, release enzymes to break down food externally before absorbing.
• Hyphae: filamentous structures; mycelium: network of hyphae forms main body.
• Reproduction: asexual (spores from sporangia), sexual (meiospores from sexual stages). Spores disperse via air, water, animals.
• Yeasts: single-celled, reproduce by budding, exist as both haploid and diploid forms.
• Uses: S. cerevisiae (baking, brewing), nutritional yeast (food additive), probiotics (restore beneficial bacteria).
• Fungal diseases: athlete's foot (Trichophyton), candida (yeast infection), aspergillosis (inhalation of Aspergillus spores), cryptococcal meningitis.
• Beneficial: decomposers (break down dead wood), mycorrhizal associations (symbiosis with plant roots), antibiotic production (penicillin from Penicillium).

5. Protists and protozoal diseases

• Protists: eukaryotic, mostly aquatic/moist, diverse nutrition (photosynthesis, phagocytosis, osmotrophy).
• Algae: photosynthetic protists, unicellular (diatoms, Chlamydomonas) to multicellular (green/red/brown algae). Base of aquatic food chains.
• Diatoms: unicellular algae with silica shells; produce ~20% of Earth's oxygen despite being <1% of photosynthesizers.
• Protozoa: animal-like protists, heterotrophic predators. Amoeba (pseudopods for movement/feeding), paramecium (cilia, oral groove for food).
• Protozoan diseases: malaria (Plasmodium, transmitted by mosquitoes, ~400,000 deaths/year), sleeping sickness (Trypanosoma), dysentery (Entamoeba), giardiasis (Giardia).
• Slime molds: fungus-like protists; plasmodial stage (multinucleated) moves/engulfs bacteria; fruiting bodies produce spores.

Formulas at a glance

Key terms

Introduction to Microbiology – Flashcards

Read the question, answer it in your head, then tap the card to check. 20 cards.

Introduction to Microbiology – MCQ Quiz

15 questions. Tap an option — you will see at once if it is right and why.

How to study Introduction to Microbiology

⏱ About 4 hours over 3 days

1. Day 1 — Prokaryotes and viruses
   Learn bacteria, archaea, viruses structure and replication.
2. Day 2 — Eukaryotic microbes
   Study protists and fungi characteristics and roles.
3. Day 3 — Applications and interactions
   Learn beneficial and pathogenic roles, control methods, human interactions.

✍️ Diagrams to practise

• Prokaryotic (bacteria) vs eukaryotic cell structure
• Bacterial shapes: cocci, bacilli, spirilla
• Virus structure: nucleic acid and capsid
• Gram-positive vs gram-negative bacteria cell walls
• Fermentation pathways: lactate and ethanol production