NCERT Class 8 Science Chapter 2: Microorganisms – Friends and Foes YouTube Lecture Handouts

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  • Microorganisms/Microbes are small and cannot be seen by unaided eye – we use microscope or magnifying glass

  • E.g., fungus growing on the bread

Classification (4 Types)

Algae

Image of Chlamydomonas And Sptrogyra

Image of Chlamydomonas and Sptrogyra

Image of Chlamydomonas And Sptrogyra

Bacteria – Typhoid and Tuberculosis

Image of Bacteria – typhoid and tuberculosis

Image of Bacteria – Typhoid and Tuberculosis

Image of Bacteria – typhoid and tuberculosis

Fungi

Image of Fungi - (Bread Mould and Penicillium)

Image of Fungi - (Bread Mould and Penicillium)

Image of Fungi - (Bread Mould and Penicillium)

Protozoa – Dysentery and Malaria

Image of Protozoa – dysentery and malaria

Image of Protozoa – Dysentery and Malaria

Image of Protozoa – dysentery and malaria

Virus – these are different and reproduce only inside host organisms which can be bacterium, plant and animal – cold, influenza and can even lead to polio and chicken pox

Image of Virus

Image of Virus

Image of Virus

  • Unicellular – bacteria, algae, protozoa

  • Multicellular – algae and fungi

  • These live from hot to cold climate, can grow on other organism or freely

Friendly Microorganisms

  • Curd, bread and cake

  • Soil fertility by nitrogen fixation - rhizobium

  • Organic wastes are broken down into harmless and usable substances by bacteria

  • Curd – Lactobacillus (multiples)

  • Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter. Rising dough explains fermentation – bubbles fill the dough and increase volume.

  • Yeast reproduce rapidly and release during respiration

  • Production of wine, alcohol and acetic acid – commercial production requires yeast

  • Yeast is grown on sugars present in barley, wheat, rice and crushed fruit juices

  • Smell of alcohol as sugar has been converted into alcohol by yeast. This process of conversion of sugar into alcohol is known as fermentation.

  • Antibiotics – stop the growth of microorganisms – streptomycin, tetracycline & erythromycin

  • In 1929, Alexander Fleming worked on a culture of disease causing bacteria – discovered penicillin

  • Antibiotics are even mixed with feed of livestock and poultry to check microbial infection in animals (control plant diseases)

Antibiotics taken unnecessarily may kill the beneficial bacteria in the body. Antibiotics are not effective against viruses.

Vaccine

  • When disease enters the body, body produces antibodies to fight invaders (antibodies protect us from diseases like cholera, TB, small pox, hepatitis)

  • Edward Jenner – vaccine for smallpox in 1798 (now eradicated worldwide)

  • Polio drops for Pulse Polio Program (actually a vaccine)

Cleaning Environment

  • Plant waste has been converted into manure by action of microbes.

  • Microorganisms decompose dead organic waste of plants and animals converting them into simple substances – degrade harmful substances and clean the environment

Harmful Microorganisms

  • Pathogens: Disease causing microorganisms spoil food, clothing and leather

  • Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases - cholera, common cold, chicken pox and tuberculosis.

  • Virus enters a healthy person and causes infection

  • Insects and animals act as carriers of disease causing microbes (housefly – sit on garbage and excreta and spread germs on uncovered food)

  • Female Anopheles mosquito which carries the parasite of malaria (Plasmodium)

  • Female Aedes mosquito acts as carrier of dengue virus

  • Mosquitos breed in stagnant waters

Image of Human Disease

Image of Human Disease

Image of Human Disease

Diseases in Animals

  • Anthrax is a human and cattle disease by bacterium

  • Foot and Mouth Disease of Cattle by Virus

Diseases in Plants

Microorganisms causing disease in plants reduce crop yield 7 can be controlled by chemicals

Image of pland diseases

Image of Pland Diseases

Image of pland diseases

Food Poisoning - due to consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances

Food Preservation

  • How pickles remain for so long but mangoes are damaged?

  • Chemical Method – preservatives like sodium benzoate and sodium metabisulphite – in jams and squashes

  • Salt – preserve meat, fish, amla, raw mango, tamarind

  • Sugar – jam, jelly, squash – reduces moisture and inhibits bacterial growth

  • Oil & Vinegar – bacteria cannot live in this environment – vegetable, fruit, fish and meat

  • Hot & Cold treatment – boiling kills microorganisms and lower temperature inhibits growth of microbes

  • Pasteurization – pasteurized milk can be consumed without boiling as it is free from harmful bacteria

    • Low Temperature Long Time (LTLT) - 62.5 /144.5 for 30 minutes

    • High Temperature Short Time (HTST) - 72 /161.5 for 15 seconds

  • Storage and Packing – In airtight packets

Nitrogen Fixation

  • Rhizobium – involved in fixation of nitrogen in leguminous plants in root nodules of leguminous plants like beans, peas

  • Nitrogen fixation can also occur by action of lightning

Image of Nitrogen Fixation

Image of Nitrogen Fixation

Image of Nitrogen Fixation

  • 78% is nitrogen gas

  • Nitrogen found in proteins, chlorophyll, nucleic acids and vitamins

  • Bacteria & blue green algae fix nitrogen and convert to nitrates (used by plants from soil through the root system)

  • When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.

  • Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere

  • Nitrosomonas bacteria convert nitrogen gas to nitrite (NO2-) and subsequently nitrobacter convert nitrite to nitrate (NO3-), a plant nutrient.

  • Plants absorb ammonium and nitrate during the assimilation process, after which they are converted to nitrogen-containing organic molecules, such as amino acids and DNA.