🔬 Interactive Microbiology Study Guide

BTEC Unit 13 – Health & Disease | Comprehensive Revision Tool

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📘 Section A1 – Micro-organisms

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Types of Micro-organisms

Bacteria

Prokaryotic (no nucleus), single-celled organisms with cell walls made of peptidoglycan. Reproduce by binary fission.

Examples: E. coli, Staphylococcus aureus, Mycobacterium tuberculosis (causes TB)

Viruses

Acellular particles that require a host cell to replicate. Consist of genetic material (DNA/RNA) surrounded by a protein coat (capsid).

Examples: Influenza virus, HIV, SARS-CoV-2 (COVID-19)

Fungi

Eukaryotic organisms with cell walls made of chitin. Can be unicellular (yeast) or multicellular (molds).

Examples: Candida albicans (thrush), Tinea (athlete's foot)

Protozoa

Eukaryotic, single-celled organisms that are often motile. Can cause parasitic diseases.

Examples: Plasmodium (malaria), Giardia (diarrheal disease)

Key Definitions

Term	Definition	Example
Pathogen	Disease-causing micro-organism	Mycobacterium tuberculosis (causes TB)
Normal Flora	Beneficial microbes living on/in the body	Gut bacteria that produce Vitamin K
Vector	Organism that transmits a pathogen	Mosquito (malaria), tick (Lyme disease)
Host	Organism harbouring a pathogen	Human infected with influenza virus

Quick Quiz: Micro-organisms

1. Which micro-organism is acellular and requires a host to replicate?

a) Bacteria

b) Fungi

c) Virus

d) Protozoa

2. Which pathogen is most commonly associated with athlete's foot?

a) Bacteria

b) Fungi

c) Viruses

d) Protozoa

Relative Sizes of Micro-organisms

Viruses (20-300 nm) < Bacteria (0.5-5 μm) < Eukaryotic Cells (10-100 μm)

Viruses are 10-100× smaller than bacteria!

📘 Section A2 – Microbial Growth Requirements

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Essential Growth Factors

Factor	Optimal Conditions	Examples
Temperature	- Psychrophiles: 0–15°C - Mesophiles: 20–45°C (human pathogens) - Thermophiles: 40–70°C	E. coli (37°C)
pH	Most prefer neutral (pH 6.5–7.5) - Acidophiles: Low pH - Alkaliphiles: High pH	Helicobacter pylori (acidic stomach)
Oxygen	- Aerobes: Require O₂ - Anaerobes: No O₂ - Facultative: With/without O₂	Clostridium tetani (anaerobic)
Moisture	High water activity (aw > 0.85)	Bacteria need moisture for nutrient transport

Bacterial Growth Curve

Four Phases of Bacterial Growth

LAG PHASE

Cells adjust to environment

LOG PHASE

Rapid cell division

STATIONARY PHASE

Growth = Death

DEATH PHASE

Cell death exceeds growth

Lag Phase

Adaptation to environment. Metabolic activity but no division. Duration: Minutes to hours.

Exponential (Log) Phase

Rapid, constant division. Generation time: 20 min–1 hour. Cells most susceptible to antibiotics.

Stationary Phase

Growth = Death. Nutrient depletion, waste accumulation. Spore formation in some bacteria.

Death Phase

Cell death exceeds growth. Exponential death rate. Some survivors (persister cells).

Quick Quiz: Microbial Growth

1. Thermophiles grow best at which temperature range?

a) 0–10°C

b) 20–30°C

c) 40–70°C

d) 80–100°C

2. What happens in the "lag phase" of bacterial growth?

a) Rapid cell division

b) Cells adjust to the environment

c) Cell death

d) Competition for space

📘 Section A3 – Structure & Reproduction

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Bacterial Structure & Function

Component	Function	Medical Relevance
Cell Wall	Shape, protection, prevents osmotic lysis	- Gram-positive: Thick peptidoglycan - Gram-negative: Thin peptidoglycan + outer membrane
Capsule	Protection from phagocytosis, adhesion	Virulence factor (e.g., Streptococcus pneumoniae)
Flagella	Motility	Chemotaxis (movement toward nutrients)
Pili/Fimbriae	Attachment to surfaces	Colonisation, biofilm formation
Plasmids	Extra DNA, carry resistance genes	Antibiotic resistance transfer

Reproduction Methods

Organism	Primary Method	Details
Bacteria	Binary fission	Asexual; one cell → two identical daughter cells
Yeast (Fungi)	Budding	Small bud forms, enlarges, separates
Protozoa	Binary fission/Mitosis	Asexual; also sexual reproduction in some
Viruses	Host-dependent replication	Not true reproduction; assembly of new particles

Why Viruses Need Host Cells

Viruses Lack:

Ribosomes (cannot make proteins)
ATP production machinery
Enzymes for replication

Viruses Depend on Host for:

Protein synthesis
Energy (ATP)
Nucleotide building blocks

Quick Quiz: Structure & Reproduction

1. Bacteria reproduce mainly through:

a) Binary fission

b) Budding

c) Fragmentation

d) Spore release

2. A bacterial cell wall is made mainly of:

a) Cellulose

b) Peptidoglycan

c) Chitin

d) Protein

📘 Section A4 – Control Methods

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Sterilisation vs Disinfection vs Antisepsis

Method	Definition	Examples	Use
Sterilisation	Destroys ALL microbes including spores	Autoclave (121°C, 15 psi, 15 min), radiation	Surgical instruments, culture media
Disinfection	Reduces pathogens on non-living surfaces	Bleach, alcohol wipes, UV light	Benches, floors, equipment
Antisepsis	Reduces microbes on living tissue	Iodine, chlorhexidine, alcohol swabs	Skin before injection, wound cleaning

Antibiotics & Resistance

Antibiotics:

Effective against bacteria only (not viruses or fungi)

Mechanisms:

Inhibit cell wall synthesis (penicillins)
Disrupt cell membrane (polymyxins)
Inhibit protein synthesis (tetracyclines)
Inhibit nucleic acid synthesis (quinolones)

Antibiotic Resistance Mechanisms:

Enzyme production (β-lactamases break down penicillin)
Altered target site (MRSA: altered penicillin-binding protein)
Reduced permeability (change porins in Gram-negative bacteria)
Efflux pumps (actively pump antibiotic out of cell)

Hand Hygiene Science

Soap Action:

Amphipathic molecules (hydrophilic + hydrophobic ends)
Hydrophobic tails embed in lipid membranes/envelopes
Disrupts membranes, inactivates microbes
Forms micelles that trap microbes, rinsed away

Alcohol-based Sanitisers:

60–80% ethanol/isopropanol most effective
Denatures proteins, dissolves lipids
Less effective against spores, non-enveloped viruses

Quick Quiz: Control Methods

1. Which method sterilizes equipment?

a) Boiling

b) Autoclaving

c) Wiping with alcohol

d) UV light

2. Antibiotics are effective against:

a) Viruses

b) Bacteria

c) Fungi only

d) All pathogens

📘 Section B1-B5 – Epidemiology & Transmission

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Epidemiological Terms

Term	Definition	Example
Endemic	Constant presence in a population/area	Malaria in sub-Saharan Africa
Epidemic	Sudden increase above expected levels	Cholera outbreak after flood
Pandemic	Worldwide spread across continents	COVID-19, 1918 influenza
Sporadic	Occasional cases, irregular pattern	Tetanus in unvaccinated individuals

Transmission Routes

Route	Mechanism	Examples	Prevention
Direct Contact	Skin-to-skin, kissing, sexual contact	Herpes, MRSA, STIs	PPE, hand hygiene, barriers
Airborne	Small droplets/nuclei remain suspended	Tuberculosis, measles	N95 respirators, ventilation
Vector-borne	Arthropod transmission	Malaria (mosquito), Lyme (tick)	Insect repellent, bed nets
Faecal-Oral	Contaminated food/water	Salmonella, Hepatitis A	Food safety, water treatment

Chain of Infection (6 Links)

Infectious agent (pathogen)
Reservoir (where pathogen lives)
Portal of exit (how leaves reservoir)
Mode of transmission
Portal of entry (how enters host)
Susceptible host

Breaking any link in this chain prevents infection!

Quick Quiz: Epidemiology

1. Epidemiology is the study of:

a) Individual cells

b) Spread and patterns of disease in populations

c) DNA only

d) Viruses only

2. Which is an example of direct contact transmission?

a) Sharing a spoon

b) Sneezing across a room

c) Shaking hands with an infected person

d) Mosquito bite

🎯 Exam Strategy & Time Management

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Time Management

Section	Questions	Suggested Time
Bio Data	-	2 minutes
MCQs (A)	50	45 minutes (≈1 min/question)
Short Answer (B)	10	20 minutes (2 min/question)
Essay (C)	1	10 minutes
Case Study (D)	4	13 minutes
Total	65 items	90 minutes

MCQ Tips

Eliminate obviously wrong answers first
Watch for absolutes: "always", "never", "all" → often incorrect
Look for clues in other questions
Flag uncertain questions, return later
Never leave blank – guess if unsure

Written Response Tips

Short answers: Be concise but complete
Use bullet points if allowed
Define terms before explaining
Include examples where possible
Check spelling of scientific names (capitalise genus: E. coli)

📋 Final Review Checklist

Before the exam, make sure you can:

Define all key terms (pathogen, vector, fomite, etc.)
Name disease-agent pairs for common infections
Draw and label the bacterial growth curve
Compare bacteria vs. viruses (at least 2 differences)
Explain transmission routes with examples
Describe sterilisation vs disinfection vs antisepsis
Explain antibiotic resistance mechanisms
Analyse a case study for transmission routes and control measures