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Types of Micro-organisms Bacteria Viruses Fungi Protozoa • • • • fungi ( eg. Mucor , Rhizopus ) protozoa ( eg. Amoeba , Paramecium ) algae (unicellular / colonial form) ( eg. Spirogyra ) Algae - Diatoms Zooplankton (some multicellular) 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 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 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 Harmful Micro-organisms disease causing (pathogens) – bacterial disease : e.g. cholera, sore throat, tuberculosis Dust Mite - multicellular – 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 athlete's foot • bacteria – prokaryotic cells (without nuclear membrane) – reproduce by binary fission – some are pathogenic, some are useful • viruses – with only DNA/RNA + protein coat – all are parasitic (they are considered living only when they are inside living cells) Harmful Micro-organisms decay food & other useful materials – microorganisms are saprophytic – take in decaying food: cause food poisoning 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 Antibiotics Broad-spectrum antibiotics: can attack many different strains of bacteria Narrow-spectrum antibiotics can attack only one or a few strains of bacteria 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 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 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 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 Food Preservation Drying (Dehydration) – micro-organism dies due to water deficiency Smoking – dry, coat with smoke which has chemical to stop bacterial growth Food Preservation Pickling – add vinegar (usually together with salt) – kill bacteria by acid Osmotic preservation – by adding salt or sugar – to remove water from micro-organisms by osmosis 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 ~END~
