Types of Micro-organismsTypes 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-organismsUseful 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

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-organismsUseful Micro-organisms

decomposers & nitrifying bacteria– decomposers decompose organic

waste & dead body into ammonia

– nitrifying bacteria change ammonia into nitrate for plants to make protein

Useful Micro-organismsUseful Micro-organisms

Harmful Micro-Harmful Micro-organismsorganisms

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

athlete's foot

Dust Mite - multicellular

• 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)

decay food & other useful materials– microorganisms are

saprophytic

– take in decaying food: cause food poisoning

Harmful Micro-organismsHarmful Micro-organisms

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

AntibioticsAntibiotics

Broad-spectrum antibiotics: can attack many different strains of bacteria

Narrow-spectrum antibiotics can attack only one or a few strains of bacteria

AntibioticsAntibiotics

Clear zone - indicates the absence of bacteria which had been killed by the antibiotic

AntibioticsAntibiotics

Clear zone with larger diameter indicates a more powerful antibiotic against the bacteria

Food PreservationFood Preservation Heating

– kill most microorganisms & their spores by high temperature

Canning & Bottling

– sealing in cans to avoid bacterial entry

– should work together with sterilization

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 the

n sealed

Food PreservationFood 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 PreservationFood Preservation

Drying (Dehydration)

– micro-organism dies due to water deficiency

Smoking

– dry, coat with smoke which has chemical to stop bacterial growth

Food PreservationFood 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 PreservationFood Preservation

Irradiation

– expose food to -radiation

– kill bacteria and moulds & prevent food spoilage

Preservatives

– add to food to stop bacterial growth or kill them

Food PreservationFood Preservation

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