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BACTERIA
• The oldest form of life on earth, evolving 5 billion years ago.
• The most numerous form of life on earth (there are more bacteria in a tub of natural yoghurt
than there are humans on the entire planet!!)
• The most ubiquitous form of life on earth. They are EVERYWHERE!!
• They are possibly the most successful form of life on earth.
• If mammals disappeared bacteria wouldn’t even blink. If bacteria disappeared all other life
would be dead inside a month
STRUCTURE
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Unicellular
Prokaryotic (no nucleus or other organelles)
3 basic shapes:
– Round (cocci)
– Rod Shaped (bacilli)
• (Lacto-bacillus caseii immunitas)
– Spiral (spirillum)
NUTRITION
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Autotrophic (make their own food!)
– Photosynthetic (use light as a source of energy).
– Chemosynthetic (use chemicals as a source of energy
Heterotrophic (get their food elsewhere!)
– Parasites- feed on live hosts – pathogenic?
– Saprophytes- feed on dead organisms - decomposers
– Symbionts- live inside a host with mutual benefit.
(They may be Aerobic or Anaerobic)
REPRODUCTION
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Sexual Reproduction – very complex! – involves the exchange of plasmids
Asexual Reproduction:
– By Binary Fission
– In optimum conditions (H2O, Warmth, Nutrients, pH, Oxygen?) can reproduce every
20 minutes.
Growth Curve for Population of
Bacteria (or other micro-organisms)
5 Stages on the graph
1. Lag
2. Log
3. Plateau (stationary)
4. Decline (death)
5. Survival and Endospore
formation
ENDOSPORES:
If conditions become intolerable the DNA
replicates and the contents of the bacterial
cell shrink. A thick wall then forms around it.
This is called an ENDOSPORE. The endospore
can survive dormant for many years until
favourable conditions return.
ECONOMIC IMPORTANCE
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Beneficial:
– Production of yoghurt and cheese
– Some produce antibiotics
– Can be genetically engineered to produce commercial products
Harmful:
– Disease: TB, Cholera, Pneumonia, Syphilis, Salmonella (‘Pathogens’)
– Food Spoilage
Food Preservation:
Need to know how each method works!
• Drying
• Salting
• Chilling/Freezing
• Canning
• Pickling
• Vacuum packing