What are Diseases and Pathogens? | Orchids The International School
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Diseases and Pathogens

Concept: Meaning of Diseases and Pathogens

What is a disease?

  • Any disorder or malfunctioning of the body or mind that leads to impaired mental and physical health is considered a disease.
  • Every disease has a particular set of characteristic symptoms to identify the type of disease.

Classification of Diseases:

  1. Based on origin/onset:
    • Inherited diseases: The diseases which are passed from parents to their offspring.
    • Examples : Haemophilia, sickle-cell anaemia.

    • Acquired diseases: The diseases which develop after birth due to different environmental factors.
    • Examples : Influenza, malaria.

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  3. Based on transmission:
    • Communicable diseases: Such diseases spread from infected persons to healthy persons. They are also called infectious diseases.
    • Examples : Measles, chicken pox.

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  5. Non-communicable diseases: Such diseases do not spread from the infected person to a healthy person. They are also called non-infectious diseases.

    Examples : Diabetes, cancer.

  6. Based on duration:
    • Chronic diseases: The diseases that continue for a long time and may worsen over time. Such diseases cannot be cured but can be controlled.
    • Examples : Arthritis, heart diseases.

    • Acute diseases: An acute disease appears suddenly and lasts for a short time. This is different from chronic diseases that develop gradually and last for months.
    • Examples : Pneumonia, appendicitis.

  7. Based on causal organism:
    • Viral diseases: Diseases that are caused by viruses.
    • Examples : Flu, herpes.

    • Bacterial diseases: Diseases that are caused by bacteria.
    • Examples : Cholera, tuberculosis.

    • Fungal diseases: Diseases that are caused by fungus.
    • Examples : Athlete’s foot, ringworm.

What are pathogens?

  • Only the disease-causing microbes or microorganisms are called pathogens.
  • They are not visible to the naked eyes and are viewed using a microscope.
  • They exist in all places, including soil, air, water, and living organisms and on their surface.
  • The study of microorganisms is called microbiology.

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    Classification of microbes:

    1. Bacteria:
      • Bacteria (singular: bacterium) are single-celled organisms that are found in the natural environment.
      • They reproduce very quickly.
      • Bacteria are found on decaying things, inside human body and in air, water and soil.
      • Examples : Escherichia coli, Streptococcus pyrogenes.

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    3. Viruses:
      • The size of a virus is smaller than a bacterium.
      • They are an intermediate between living and non-living organisms.
      • They need a host body to multiply. Without a host, they act as non-living organisms.
      • They cause diseases, such as chickenpox and rubella, and many of these diseases spread from infected persons to healthy people.
      • Examples : Influenza virus, Herpes virus.

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    5. Fungi
      • Fungi have some plant-like features like the presence of small roots called rhizoids, but they do not perform photosynthesis due to the absence of chlorophyll.
      • All fungi are not microscopic, and some are visible through naked eyes (macroscopic).
      • Fungi act on dead things leading to their decay.
      • The presence of bacteria and fungi in food can cause food poisoning.
      • Examples : Mushrooms, yeasts, moulds.

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    7. Protozoa
      • This group includes microscopic animal-like organisms.
      • They depend on other organisms for food.
      • They are generally single-celled.
      • Examples : Amoeba, Paramecium.

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      New Words

      Symptoms: The physical or mental problems that a person experiences that indicate the presence of a disease.

      Food poisoning: A diseases caused by bacteria or fungi and is accompanied with vomiting and diarrhoea.


      • All microorganisms are harmful.
      • Salt, sugar, vinegar, and castor oil are natural preservatives used to preserve food for long durations.
      • Not all microorganisms are harmful. Some of them play a vital role in our lives. Some examples of useful microbes are as follows—

        1. Escherichia coli, a bacterium found in our intestines, helps in digestion.
        2. Lactobacillus helps in turning milk into curd.
        3. Yeast is used for making bread.
        4. Penicillium notatum is a fungus from which an antibiotic was derived for the first time.
        5. Acetobacter aceti, a fungus that is used for making acetic acid.
        6. Fungi help in fermentation, a process that converts sugar into alcohol.
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