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Class 8 Science — Microorganisms around us

Name the main groups of microorganisms and say what they do for soil, food and crops.

Name: ________________________

  1. 1.Why do pickles and murabbas keep for months without going mouldy?

    • a) Microorganisms cannot live on fruit once it has been cut
    • b) They are sealed so tightly that no microorganism can reach them
    • c) The high concentration of salt or sugar stops microorganisms growing on them
    • d) The spices in them kill any microorganism that lands

  2. 2.Sort these by whether the whole living thing is one cell or many.

    Groups: Unicellular · Multicellular

    • Mould
    • Amoeba
    • Bacteria
    • Yeast

  3. 3.Match each microorganism to the job it does for us.

    • Yeast
    • Lactobacillus
    • Rhizobium
    • makes bread and cake dough rise
    • turns milk into curd
    • traps nitrogen from the air for legume plants

  4. 4.Bacteria and fungi living without oxygen can break down plant and animal waste and release a mixture of gases. What is that mixture called, and what is it mainly?

    • a) Biogas, mainly oxygen with a little nitrogen
    • b) Biogas, mainly carbon dioxide with a high proportion of methane
    • c) Manure gas, mainly hydrogen
    • d) Marsh gas, mainly carbon monoxide

  5. 5.Where does the chapter say microorganisms can be found?

    • a) In water, in soil, in air, and inside the bodies of plants and animals
    • b) In water and soil, but not in air
    • c) Chiefly in food that has been left out to rot
    • d) In soil and air, but not inside living bodies

  6. 6.Some microorganisms live in hot water springs and snow-cold zones. What does that tell you about them as a group?

    • a) They cannot survive anywhere that a plant cannot grow
    • b) They live in extreme conditions and cannot survive moderate ones
    • c) They can live in extreme conditions as well as moderate ones
    • d) They can live at high temperatures but not at low ones

  7. 7.Fruit and vegetable peels are buried in a pot of garden soil. Three weeks later they have become a dark crumbly material. What is it, and what made it?

    • a) Compost, made by the peels drying out in the heat
    • b) Charcoal, made by the peels being pressed under the soil
    • c) Manure, made by fungi and bacteria breaking the peels down
    • d) Manure, made by the soil dissolving the peels

  8. 8.Which bacterium ferments milk into curd, feeding on the milk sugar lactose? Give its name.

Answer key — Class 8 Science — Microorganisms around us

  1. 1. c) The high concentration of salt or sugar stops microorganisms growing on them
  2. 2. Bacteria → Unicellular; Amoeba → Unicellular; Yeast → Unicellular; Mould → Multicellular
  3. 3. Yeast → makes bread and cake dough rise; Lactobacillus → turns milk into curd; Rhizobium → traps nitrogen from the air for legume plants
  4. 4. b) Biogas, mainly carbon dioxide with a high proportion of methane
  5. 5. a) In water, in soil, in air, and inside the bodies of plants and animals
  6. 6. c) They can live in extreme conditions as well as moderate ones
  7. 7. c) Manure, made by fungi and bacteria breaking the peels down
  8. 8. lactobacillus