These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 2 Notes – Microorganisms: Friends or Foes act as excellent revision resources, particularly in preparation for board exams.
Microorganisms: Friends or Foes Class 8 DAV Notes
→ Microorganisms: Organisms which are invisible to the naked eye but visible under the microscope are called microorganisms. Examples: bacteria, yeast, protozoans and algae.
→ Types of Microorganisms: Microorganisms can be divided into four groups, i.e. bacteria, fungi, protozoa and some algae.
→ Virus: Viruses are unique because they show characteristics of both living and non-living. When they are outside their host’s body, they are non-living. But when a virus enters a host, it becomes living.
→ Habitat of Microorganisms: Microorganisms are found in almost all kinds of environment like ice-cold water, hot springs and in dry, marshy or saline areas. They are also found in the human body and in the bodies of other animals and plants.
→ Microbial Population in Human Body: A large number of microorganisms are present in the human body. They help in many biological activities.
→ Microorganisms are our friends
- ○Lactobacillus is a bacterium which helps in the formation of curd.
- Yeast: which is a fungus helps in fermentation. Fermentation is a process which is used in bakery for making bread and cakes. It is used in wine industry for making alcohol. Batter of dosa and idli are also fermented with the help of yeast.
- Some bacteria are used in biological treatment of sewage. This process is known as bioaugmentation.
→ Importance of Microorganisms in Human Health
- Many microorganisms are present in the alimentary canal of some animals like cows. They help in digestion and absorption of food. Bacteria are present in our large intestine as well. They help in bowel movement.
Microorganisms are used in production of antibiotics. Penicillin is an antibiotic which is prepared from a fungus Penicillium notatum. - When a disease causing microorganism enters our body, the body produces antibodies to fight the disease causing microbe.
- Weak strains of many microorganisms are used for producing vaccines. Vaccines help our bod to fight many infections.
→ Microorganisms in Agriculture:
Some bacteria and blue-green algae (cyanobacteria) help in nitrogen fixation. This is important as this is the only way through which a plant can get nitrogenous nutrients. Rhizobium bacteria live in the root nodules of leguminous plants. They help in nitrogen fixation in soil.
→ Use in Energy/Fuel Production: Many microorganisms produce ethanol by fermentation of sugars and produce methane in the biogas plants. Ethanol and methane are used as fuel.
→ Cleaning the environment: Microorganisms decompose dead remains of plants and animals. While doing so, they return the fundamental raw materials to the environment. Bacteria and fungi are the common decomposers.
→ Microorganisms: The Foe
→ Bacteria and tooth decay: Many bacteria live in our mouth. They eat the food particles which remain stuck between the teeth. During eating the food particles, bacteria produce acids which corrode the tooth enamel and it results in tooth cavities in the long run.
→ Pathogens: Disease causing microorganisms are known as pathogens. The pathogens release harmful chemicals called toxins in the body.
→ Food Poisoning: It happens because of consumption of contaminated food. Vomiting, nausea, severe pain in abdomen, diarrhoea and dehydration are the symptoms of food poisoning. Clostridium and Staphylococci are the bacteria which cause food poisoning and Aspergillus is a fungus which causes food poisoning.
→ Food Preservation: The process of treating and handling food to stop or greatly slow down spoilage of food (which is caused by microorganisms) is called food preservation.
→ Goals of Food Preservation: Prevention of growth of microorganism and retarding the oxidaton of fats are the main goals of food preservation.
→ Some common methods of food preservation:
- Drying: Food is usually dried in the sun. This reduces water content and thus prevents the growth of microorganisms in food.
- Preservation using sugar and salt: Sugar and salt reduce water content of the food. Thus, sugar and salt help in food preservation. Jams and pickles are preserved because of sugar or salt.
- Preservation using acetic acid: Acetic acid is used in the form of vinegar. Sometimes, citric acid and phosphoric acid are also used. These acids prevent the growth of microorganisms in food.
- Preservation using chemical preservatives: Sodium benzoate and potassium meta bisulphate (KMS) are some of the chemicals which are used as food preservatives. These chemicals prevent the growth of microorganisms.
- Heat and cold treatment: Milk is boiled before being stored. Boiling kills many microorganisms. Some food items are stored in refrigerator. Low temperature inhibits the growth of bacteria.
- Pasteurization: Milk is quickly heated and then quickly cooled down in this process. Pasteurization kills many microorganisms and increases the shelf life of milk.
- Vacuum packing: Some food items are stored in airtight packets. Lack of air inhibits the growth of microorganisms.
- Canning: Canning involves cooking the food and sealing it in sterile cans or jars. The container is then boiled to kill or weaken the remaining microorganisms.
→ Microbiology: The branch of science in which we study about microorganisms.
→ Commensals: The friendly microorganisms living in our body.
→ Pathogens: Disease causing microorganisms.
→ AIDS: Acquired Immuno Deficiency Syndrome; is a disease which affects the immune system.
→ HIV: Human Immuno Deficiency Virus which is the causative organism of AIDS.
→ Plasmodium: Malaria parasite.
→ Aedis egypti: Carrier mosquito of dengue virus.
→ Female Anopheles: Carrier mosquito of malaria parasite.
→ Communicable Disease: A disease which can spread from one person to another is called communicable disease.
| Infectious Diseases | |
| Microorganisms | Diseases |
| Bacteria | Tuberculosis, diphtheria, cholera, tetanus, typhoid |
| Viruses | Common cold, influenza, mumps, polio, AIDS, chickenpox |
| Fungi | Ringworm, athlete’s foot |
| Protozoa | Malaria, amoebic dysentery, sleeping sickness |
|
Modes of Transmission |
|
| Modes of transmission | Diseases |
| Air | Tuberculosis, common cold, influenza, swine flu |
| Water | Typhoid, amoebic dysentery, cholera |
| Soil | Tetanus |
| Animals | Rabies, malaria |
|
Prevention of Diseases |
|
| Methods of prevention | Diseases which can be prevented |
| Vaccination | Tuberculosis, polio, mumps, tetanus |
| Using mosquito nets, mosquito repellants, controlling mosquito population | Malaria, dengue |
| Proper disposal of waste and using disinfected water | Cholera |
| Maintaining good personal hygiene | Ringworm and athlete’s foot |
|
Microorganisms and Animal Diseases |
||
| Disease | Causative Microorganism | Animats infected |
| Anthrax | Bacteria | Cattle |
| Foot and mouth disease | Virus | Cattle |
| Rabies | Virus | Dogs, monkeys |
| Tuberculosis | Bacteria | Cattle, poultry |
| Ringworm | Fungi | Cattle, poultry |
| Aspergillosis | Fungi | Poultry |
| Canine distemper | Virus | Dogs |
|
Microorganisms and Plant Diseases |
|
| Microorganisms | Plant diseases |
| Virus | Tobacco mosaic virus (appearance of uneven spots and discolouration on leaves) |
| Bacteria | Citrus canker (lesions on leaves, stems and fruit with raised, brown, water soaked margins) |
| Fungus | Rust of wheat (rust coloured orange patches on infected parts) |
| Fungus | Smut of rice (smut balls in grains which become greenish black, burst and infect other grains) |
| Fungus | Red rot of sugar cane (dull red colour; interrupted by occasional whitish patches across the stalk; on stem, elongated red lesions on midribs of leaves) |