Class 8, Science, Chapter-2, Lecture-3, Harmful Microorganism (Notes)
Harmful Microorganisms:
- May cause diseases in humans, plants and animals.
- Microbes enter our body, multiply in a host cell and damage the body cells, thus hampering the functioning of vital organs and causing diseases.
- Disease causing microorganisms are called pathogens. They may enter the body through
- Food, Water or air
- Cuts in the skin or through direct contact
- Through carriers such as mosquitoes and flies
- Spoil food, clothing and leather.
Communicable Diseases
Diseases caused by microorganisms are infectious in nature. They are transmitted from one person to another by direct or indirect contact. Such diseases are called communicable diseases.
Tuberculosis, Cholera, Typhoid, Malaria, Dysentery are some common communicable diseases.
Communicable diseases are transmitted through contaminated food, water, air, insects, infected clothes, utensils
Modes of transmission of Communicable Diseases
Direct Transmission
- By direct contact – infection may be caused by skin to skin, mucosa to mucosa or mucosa to skin contact. Ex: Leprosy, Eczema, Conjunctivitis are transmitted through direct contact
- By droplet infection: droplets of moisture from sneezing, spitting or coughing may carry disease causing microorganism which may sicken someone. Ex: Whooping cough, Tuberculosis are transmitted this way.
- By using an infected needle/syringe. Ex: Rabies virus enter human body through dog bite, AIDS virus enters through infected blood.
Indirect transmission of Communicable Diseases
Various modes of indirect transmission are:
- Through infected food and water.
- Through any carriers such as mosquito, housefly, rat, flea etc.
- Through clothes, towel, handkerchief, and personal utensils of the patient.
- Through dirty hands or dirty utensils, unwashed fruits or vegetables.
Food Poisoning:
Disease caused by consumption of food spoiled by the action of enzymes present in it or due to growth of bacteria or fungi is termed as food poisoning.
Symptoms of food poisoning:
(i) Headache (ii) Fever (iii) Vomiting (iv) Diarrhoea
Caused by:
- Microorganisms like bacteria and fungi. Common bacteria which causes food poisoning are Salmonella, Staphylococci, Clostridium botulinum and Aspergillus.
- Toxins produced in the food by bacteria and fungi.
- Traces of pesticides in the fruits and vegetables.
- Metal salts produced by the action of food with material of container or utensils.
Food Preservation:
Process by which spoilage of perishable food is prevented using chemical or physical methods is called food preservation.
Common methods of preservation:
- By cooling: Low temperatures prevent food spoilage as it retards growth of bacteria and inactivates enzymes present in food.
- By Pasteurization: Milk is heated to 60-65 °C for about 30 minutes and quickly cooled to prevent remaining bacteria from growing. This method is called pasteurization.
- By dehydration
- By using salt, sugar
- By using oil and vinegar
- By heating and canning
- By using chemical preservatives
- By vacuum packaging
Advantages of Food Preservation:
- decreases food wastage .
- increases shelf-life of perishable food products.
- ensures availability of out-of-season food items.
- ensures availability of perishable food items at distant places.