CBSE Class 8 Science Chapter 2 Microorganisms: Freind and Foe Revision Notes
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A microorganism or microbe is a microscopic organism that may exist in its single-celled or colony of cells.
Nature and occurrence:-
▪ Life on earth depends on microorganisms. They play a very critical role in the ecosystem of our planet. Microbes perform the important role of breaking down dead organisms into the basic nutrients that are essential for life on our planet.
▪ Bacteria, fungi, algae, and protozoa are the 4 major groups of microbes.
▪ Viruses are another class of microbes which totally depend on the host for food, growth, and reproduction. They are incapable of independent existence.
▪ Nature: Microbes may be unicellular e.g. bacteria, protozoa, or multicellular (2 or more cells) e.g. some algae and fungi.
▪ Habitat: Microbes can be found in all types of habitats. They can withstand all extremes of climate, e.g. ice-cold regions, hot springs, deserts, or marshy regions.
▪ Occurrence: They may be free-living (capable of independent existence) e.g., amoeba or they may be seen in colonies e.g. fungi. They may also be parasitic and found on or inside the host organism
Microbes in the food industry
▪ Lactobacillus – converts milk to curd.
▪ Acetobacter (acetic acid bacteria) – produce acetic acid. A dilute solution of acetic acid (vinegar) is used as a preservative.
▪ Yeast – baking of bread and cakes.
▪ The action of yeast: It acts on sugar to release carbon dioxide. This CO2 rises through the dough making it soft, spongy and also increases the volume.
Microbes are used in large-scale production of acetic acid, wine, alcohol, and cheese. Sugarcane juice, sugar beet, grains like barley, wheat, and rice contain sugar. When yeast cells act on these sugars, alcohol and carbon dioxide are produced. This is called fermentation
Yeast + sugar → alcohol + carbon dioxide
Microbes in medicine
▪ Antibiotics are made from bacteria and fungi.
▪ The first antibiotic was Penicillin discovered by Sir Alexander Fleming.
▪ Streptomycin, Tetracycline, Ampicillin, and erythromycin are other commonly used antibiotics.
▪ Different bacteria and fungi produce different classes of antibiotics.
▪ Antibiotics are also beneficial to animals and plants. They may be sprayed on fields to prevent infections in plants or mixed with the food to protect livestock or poultry.
Production of vaccine
▪ WBCs present in our blood produce antibodies to fight against disease-causing microbes or antigens.
▪ Each antibody can fight only a specific antigen. The specialty is that once an antibody is produced against an antigen, it can be produced instantly at the time of another invasion by the same antigen.
▪ The substance which is used to stimulate the production of antibodies and provide immunity to fight against several disease-causing agents is called VACCINE.
CBSE Class 8 Science Chapter 2 Microorganisms: Freind and Foe Revision Notes PDF