PATHOGENS
Pathogens – How They Cause Harm
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How Bacteria Cause Disease
Bacteria cause illness in two main ways:
1️⃣ Damage host cells and tissues by dividing rapidly inside the body.
2️⃣ Produce toxins (poisons) that:
Damage cells and tissues
Interfere with cell processes
Cause symptoms such as fever, vomiting, or diarrhoea
Example: In food poisoning, bacterial toxins irritate the gut lining → vomiting and diarrhoea.
🔹 4️⃣ How Bacteria Reproduce — Binary Fission
Bacteria reproduce asexually by binary fission.
The cell copies its DNA, grows, and then splits into two identical cells.
In ideal conditions (warmth, nutrients, moisture), some can divide every 20 minutes.
Formula (Higher Tier):
Number of bacteria=2n\text{Number of bacteria} = 2^nNumber of bacteria=2n
where n = number of divisions
Example:
If a bacterium divides every 30 minutes, how many after 3 hours?
3 hours = 180 min → 180 ÷ 30 = 6 divisions → 2⁶ = 64 bacteria
🔹 5️⃣ Bacterial Growth Conditions
Bacteria grow best when:
Warm (around 37°C for pathogens)
Moist
Nutrient-rich
Oxygen available (for aerobic species)
Limiting any of these slows or stops growth.
🔹 6️⃣ Examples of Bacterial Diseases (AQA SPEC)
Disease Pathogen How It Spreads Symptoms Prevention/Treatment
Eating
Fever, vomiting,
Salmonella contaminated Poultry vaccinated; cook
Salmonella diarrhoea
food food, especially food thoroughly;
bacteria caused by
poisoning undercooked maintain hygiene
toxins
poultry
, Disease Pathogen How It Spreads Symptoms Prevention/Treatment
Thick
Neisseria Antibiotics (though
yellow/green
Gonorrhoea gonorrhoeae Sexual contact resistance developing),
discharge, pain
(bacterium) use condoms
when urinating
Cholera Severe
Contaminated Clean water, sanitation,
(extension Vibrio cholerae diarrhoea,
water rehydration
example) dehydration
Tuberculosis Mycobacterium Lung damage, Antibiotics, vaccination
Airborne droplets
(TB) tuberculosis cough, fatigue (BCG), isolation
Crown gall
Agrobacterium Enters plant Tumour-like
disease Remove infected plants
tumefaciens wounds growths
(plants)
🔹 7️⃣ Bacterial Defence & Treatment
🧪 Antibiotics
Kill bacteria or stop them reproducing.
Do not work on viruses.
Must be taken for full course to avoid antibiotic resistance.
🧫 Preventing bacterial disease:
Vaccination
Hygiene (handwashing, sterilising equipment)
Proper food handling/cooking
Safe sex (condoms)
Quarantine/isolation
🔹 8️⃣ Key Terms (must be precise for Grade 9)
Term Definition
Pathogen A microorganism that causes disease
Prokaryote Cell without a nucleus
Poison released by bacteria that damages
Toxin
cells
Binary fission Simple asexual reproduction of bacteria
Antibiotic Medicine that kills or stops bacterial growth
Antibiotic When bacteria evolve so antibiotics no longer
resistance kill them
Infection When pathogens invade the body
Pathogens – How They Cause Harm
.
How Bacteria Cause Disease
Bacteria cause illness in two main ways:
1️⃣ Damage host cells and tissues by dividing rapidly inside the body.
2️⃣ Produce toxins (poisons) that:
Damage cells and tissues
Interfere with cell processes
Cause symptoms such as fever, vomiting, or diarrhoea
Example: In food poisoning, bacterial toxins irritate the gut lining → vomiting and diarrhoea.
🔹 4️⃣ How Bacteria Reproduce — Binary Fission
Bacteria reproduce asexually by binary fission.
The cell copies its DNA, grows, and then splits into two identical cells.
In ideal conditions (warmth, nutrients, moisture), some can divide every 20 minutes.
Formula (Higher Tier):
Number of bacteria=2n\text{Number of bacteria} = 2^nNumber of bacteria=2n
where n = number of divisions
Example:
If a bacterium divides every 30 minutes, how many after 3 hours?
3 hours = 180 min → 180 ÷ 30 = 6 divisions → 2⁶ = 64 bacteria
🔹 5️⃣ Bacterial Growth Conditions
Bacteria grow best when:
Warm (around 37°C for pathogens)
Moist
Nutrient-rich
Oxygen available (for aerobic species)
Limiting any of these slows or stops growth.
🔹 6️⃣ Examples of Bacterial Diseases (AQA SPEC)
Disease Pathogen How It Spreads Symptoms Prevention/Treatment
Eating
Fever, vomiting,
Salmonella contaminated Poultry vaccinated; cook
Salmonella diarrhoea
food food, especially food thoroughly;
bacteria caused by
poisoning undercooked maintain hygiene
toxins
poultry
, Disease Pathogen How It Spreads Symptoms Prevention/Treatment
Thick
Neisseria Antibiotics (though
yellow/green
Gonorrhoea gonorrhoeae Sexual contact resistance developing),
discharge, pain
(bacterium) use condoms
when urinating
Cholera Severe
Contaminated Clean water, sanitation,
(extension Vibrio cholerae diarrhoea,
water rehydration
example) dehydration
Tuberculosis Mycobacterium Lung damage, Antibiotics, vaccination
Airborne droplets
(TB) tuberculosis cough, fatigue (BCG), isolation
Crown gall
Agrobacterium Enters plant Tumour-like
disease Remove infected plants
tumefaciens wounds growths
(plants)
🔹 7️⃣ Bacterial Defence & Treatment
🧪 Antibiotics
Kill bacteria or stop them reproducing.
Do not work on viruses.
Must be taken for full course to avoid antibiotic resistance.
🧫 Preventing bacterial disease:
Vaccination
Hygiene (handwashing, sterilising equipment)
Proper food handling/cooking
Safe sex (condoms)
Quarantine/isolation
🔹 8️⃣ Key Terms (must be precise for Grade 9)
Term Definition
Pathogen A microorganism that causes disease
Prokaryote Cell without a nucleus
Poison released by bacteria that damages
Toxin
cells
Binary fission Simple asexual reproduction of bacteria
Antibiotic Medicine that kills or stops bacterial growth
Antibiotic When bacteria evolve so antibiotics no longer
resistance kill them
Infection When pathogens invade the body
