Types of Micro-organisms

1. Types of Micro-organisms • Bacteria • Viruses • Fungi • Protozoa

2. fungi ( eg. Mucor , Rhizopus ) • protozoa ( eg. Amoeba , Paramecium ) • algae(unicellular / colonial form) • ( eg. Spirogyra ) Algae - Diatoms Zooplankton (some multicellular)

3. Useful Micro-organisms • yeast • carry out alcoholic fermentation in the presence of carbohydrates & the absence of O2 • baking bread • produces carbon dioxide to raise the dough • brewing beer / making wine • fermentation to produce alcohol

4. Useful Micro-organisms • nitrogen-fixing bacteria in leguminous plant[root nodules] • carry out nitrogen fixation which changes N2 gas from the air to nitrogenous compounds for plants to produce protein

5. Useful Micro-organisms • decomposers & nitrifying bacteria • decomposers decompose organic waste & dead body into ammonia • nitrifying bacteria change ammonia into nitrate for plants to make protein

6. Harmful Micro-organisms • disease causing (pathogens) • bacterial disease : e.g. cholera, sore throat, tuberculosis • viral disease : e.g. AIDS, bird flu, common cold, influenza • fungal disease : e.g. athlete’s foot, ringworm • protozoa disease : e.g. malaria, sleeping sickness Dust Mite - multicellular athlete's foot

7. bacteria • prokaryotic cells(without nuclear membrane) • reproduce by binary fission • some are pathogenic, some are useful

8. viruses • with only DNA/RNA + protein coat • all are parasitic(they are considered living only when they are inside living cells)

9. Harmful Micro-organisms • decay food & other useful materials • microorganisms are saprophytic • take in decaying food: cause food poisoning

10. Antibiotics • chemicals produced by microorganisms which can kill or stop the growth of bacteria & fungi • e.g. penicillin • importance:effective in treating many diseases such as meningitis, syphilis, etc

11. Antibiotics • Broad-spectrum antibiotics:can attack many different strains of bacteria • Narrow-spectrum antibioticscan attack only one or a few strains of bacteria

12. Antibiotics Clear zone - indicates the absence of bacteria which had been killed by the antibiotic Clear zone with larger diameter indicates a more powerful antibiotic against the bacteria

13. Food Preservation • Heating • kill most microorganisms & their spores by high temperature • Canning&Bottling • sealing in cans to avoid bacterial entry • should work together with sterilization

14. Food Preservation • Pasteurization • kill most microorganisms without changing the flavour of milk • 75 ℃ for 15s and then quickly cooled & bottled • UHT (Ultra High Temperature) treatment • common in killing bacteria in milk • superheat to ~150℃ for a few seconds and then sealed

15. Food Preservation • Refrigeration • to decrease or stop the activities & growth of microorganisms (NOT killing them) • Freezing • stop the activities of micro-organisms • NOT killing them • they can resume activity when ice melts

16. Food Preservation • Drying (Dehydration) • micro-organism dies due to water deficiency • Smoking • dry, coat with smoke which has chemical to stop bacterial growth

17. Food Preservation • Pickling • add vinegar (usually together with salt) • kill bacteria by acid • Osmoticpreservation • by adding salt or sugar • to remove water from micro-organisms by osmosis

18. Food Preservation • Irradiation • expose food to-radiation • kill bacteria and moulds & prevent food spoilage • Preservatives • add to food to stop bacterial growth or kill them

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