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Classification of Diseases and pathogens

Classification of Diseases and Pathogens for Class 5 Science

Diseases harm our mental and physical health. Different diseases are caused by many types of pathogens that can enter the body through air, water, food, etc. In this concept, the students will know about pathogenic diseases.

After reading the concept, students will be able to:

  • Answer- what is disease?
  • Differentiate between inherited diseases and acquired diseases.
  • Explain how inherited diseases are different from acquired diseases.
  • Categorise diseases into communicable diseases and non-communicable diseases.
  • Remembers the examples of viral, fungal and bacterial diseases.
  • Define what the study of microorganisms is called.
  • Understand the classification of microorganisms.
  • Associate food poisoning with its causal organisms.


Each concept is explained to class 5 students using descriptions, illustrations, and concept maps. After you go through a concept, assess your learning by solving the two printable worksheets given at the end of the page.

Download the worksheets and check your answers with the worksheet solutions for the concept Classification of Diseases and Pathogens provided in PDF format.


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:

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.

Based on Disease Transmission:
  • Communicable Diseases: Such diseases spread from infected persons to healthy persons. They are also called infectious diseases.

Examples : Measles, chicken pox.

  1. 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.

  2. 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.

  3. 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.
Types of pathogens and examples


Classification of Microbes:

  • 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.

Harmful bacteria examples

  • 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.

  • 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.

  • This group includes microscopic animal-like organisms.
  • They depend on other organisms for food.
  • They are generally single-celled.

Examples : Amoeba, Paramecium.


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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