Communicable Diseases and Types of Pathogen
Joe Wolfensohn
Teacher
Contents
Recall Questions
This topic requires prior knowledge of the basic structure and differences between animal cells, plant cells and prokaryotic cells.
What is a prokaryotic cell?
A cell that does not contain a nucleus or membrane-bound organelles – e.g., a bacterial cell.
What are the key differences between plant and animal cells?
Plant cells have a cell wall, chloroplasts, and a permanent vacuole. Animal cells do not.
Bacterial cells do not have a cell wall. True or False
False, they have a cell wall, but it is not made of cellulose like a plant cell wall.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains communicable diseases and types of pathogen, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What Are Communicable Diseases?
- Diseases that can be spread from one organism to another.
- Caused by pathogens, which are microorganisms that cause disease.
- There are 4 main types of pathogens.
Types of Pathogens
|
Pathogen Type |
Key Features |
How They Cause Disease |
|
Bacteria |
Prokaryotic, reproduce quickly by binary fission. |
Reproduce rapidly and release toxins that damage tissues. |
|
Viruses |
Non-cellular (not made of cells), much smaller than bacteria. |
Reproduce inside host cells, causing cell damage. |
|
Fungi |
Can be single-celled or multicellular. |
Produce spores, grow on host surfaces (e.g., skin). |
|
Protists |
Eukaryotic, often parasites. |
Live in or on a host, may cause damage via toxins or cell damage. |
Transmission of Pathogens
|
Mode of Spread |
Examples |
|
Direct Contact |
Touching infected skin, STIs |
|
Water |
Cholera (via contaminated water) |
|
Air (droplets) |
Coughing / sneezing – e.g., influenza |
|
Food |
Contaminated food (e.g. Salmonella) |
|
Vectors |
Vectors are animals that carry the pathogen and transfer it between organisms, but are unaffected by it. e.g., Mosquitoes. |
Reducing the Spread
- Good Hygiene – e.g., handwashing with soap after using the toilet or before preparing food.
- Vaccinations.
- Isolating infected individuals.
- Destroying vectors – e.g., mosquitoes.
- Safe food and water practices - Decontaminating water sources and hygienic food preparation.
Transmission of Plant Pathogens
Pathogens can also infect plants.
Plant pathogens (bacteria, viruses, fungi, and protists) can spread between plants in several ways:
|
Mode of Spread |
Description / Examples |
|
Direct contact |
Touch between healthy and infected plants – e.g. through roots or stems. |
|
Water (rain / splashes) |
Rain can carry pathogens in water droplets from one plant to another. |
|
Air (wind) |
Fungal spores can be blown over long distances – e.g. black spot in roses. |
|
Insects (vectors) |
Aphids feed on sap and can carry viruses from one plant to another. |
|
Soil |
Pathogens can remain in the soil and infect roots – e.g. fungal infections like clubroot. |
|
Human activity |
Contaminated tools, clothing, or hands can transfer pathogens between plants. |
Preventing the Spread of Plant Diseases
- Burn infected plants to kill pathogens completely.
- Sterilise tools between uses to avoid transferring pathogens.
- Control vectors, such as using insecticides to stop aphids spreading viruses.
- Crop rotation to prevent build-up of soil-borne pathogens.
- Use disease-resistant varieties developed through selective breeding or genetic modification.
- Regulate imports of plants to avoid introducing new pathogens.
Key Terms
- Pathogen: A microorganism that causes disease.
- Communicable disease: A disease that can spread between individuals. Also known as an infectious disease.
- Toxin: Poisonous substance produced by bacteria.
- Vector: An organism that transmits a pathogen (e.g., mosquito).
- Insecticides: Chemicals that kill pests.
No answer provided.
Exam Tips
- Don't confuse bacteria and viruses: bacteria release toxins, viruses live inside cells and replicate within them, destroying them.
- Be specific about how pathogens are spread – use terms like “droplet transmission” or “contaminated water.” not just “in the air”
No answer provided.
Practice Question
Salmonella causes food poisoning. Describe how the spread of Salmonella can be reduced. (2 marks)
Model Answer:
Any two from:
- Isolating infected individuals prevents them from passing pathogens to others.
- Washing hands with soap after using the toilet or before preparing food.
- Ensuring food (particularly meat) is cooked fully.
More Practice
Try to answer the practice question from the TikTok video on your own, then watch the video to see how well you did!