Page 1 - 4-Lesson notes-Harmful microorganism
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SAI International School

                                             Subject- Biology, Class-VIII
                                      Topic- Microorganisms: Friend and Foe
                                        Subtopic- Harmful Microorganisms
                                                     Lesson Notes


               Disease causing microorganisms in Humans (Pathogens)

                   •  Microorganisms that cause diseases are called pathogens.
                   •  Spread through air, water, food, contact, and insects.
                   •  Examples:
                          ❖  Bacteria → Tuberculosis, Typhoid
                          ❖  Virus → Cold, Polio, COVID-19
                          ❖  Protozoa → Malaria (by Plasmodium, spread by mosquitoes)
                          ❖  Fungi → Skin infections
               Communicable Diseases & Examples


                   •  Diseases that spread from one person to another are called communicable diseases.
                   •  Caused by viruses, bacteria, protozoa, or fungi.
                   •  Spread through air, water, food, physical contact, or vectors.
                   •  Examples:
                          ❖  Tuberculosis – Bacterial, spreads through air
                          ❖  Cholera – Bacterial, spreads through contaminated water
                          ❖  Malaria – Protozoan, spread by mosquito
                          ❖  Common Cold – Viral, spreads through air/contact



               How Communicable Diseases Spread
                   •  Air:
                          ❖  Coughing/sneezing releases droplets (e.g., common cold, TB)
                   •  Water:
                          ❖  Drinking contaminated water (e.g., cholera, typhoid)
                   •  Food:
                          ❖  Eating infected/uncooked food (e.g., food poisoning)
                   •  Direct Contact:
                          ❖  Touching, sharing items (e.g., fungal infections)
                   •  Insects (Vectors):
                          ❖  Biting insects like mosquitoes (e.g., malaria, dengue)

               Carriers – What Are They?
                   •  Carriers are organisms that carry disease-causing microbes but do not get the
                       disease themselves.
                   •  They help spread pathogens to healthy individuals.
                   •  Examples of Carriers:
                          ❖  Female Anopheles mosquito – Spreads Plasmodium (malaria)
                          ❖  Housefly – Carries germs from garbage to uncovered food, causing diseases
                              like cholera and typhoid
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