Bacteria
Bacteria
Things that are unique to bacteria
Slime capsule
This stops the cells from drying out. This also protects the cells from attack’s from other cells and lets them bind onto host cells.
Bacterial Chromosomes
Free floating DNA
Plasmid
Extra loops of DNA in bacteria
Remember that bacteria have no nucleus and no membrane bound organelles.
The growth of bacteria
Pathogenic bacteria (bad) best grows at 37 C so when trying to grow bacteria (like in yoghurt making) grow good bacteria at 28 C because the un-harmful bacteria will still be able to multiply but the pathogenic bacteria wont.
Bacteria reproduce asexually by a
process called binary fission
In this process the DNA molecule makes an identical copy
of itself and then divides the cell in two. This forms two cells. (One is new). These two cells are called daughter cells. The process of forming the two identical cells is called mitosis.
The best way to culture bacteria in a lab are to have
Warmth of around 28-30 C. Look at above point for reasons
Water for chemical reactions in the cell
Nutrients like glucose and amino acids
Mineral ions
A lot of bacteria also require oxygen for respiration to produce energy and survive, although some don’t and are called anaerobic bacteria.
Yoghurt making progress
Remember first to sterilise
equipment using aseptic techniques.
Pasteurise milk at at least 65 C. This heat kills any pathogenic bacteria that may be in the milk.
Cool milk and add bacterial culture (for yogurt it is Lactobacillus).
Cool milk so lacto isn’t killed.
Leave milk to 28 C and leave
for a few hours. The bacteria will multiply as they can feed of
the lactose in the milk. Lactose is a food source. When multiplying the bacteria converts the lactose to lactic acid which curdles the milk making it yogurt.
Samples are taken to test
if ready
Cool to 5 C
Add flavours and colours after.
Reason for this is if added with lacto the bacteria may
feed and multiply on the fruit contaminating the produce. Also the heat could ruin the taste of the fruit
Ways that lacto prevents other
bacteria growing in yoghurt that may be pathogenic
Bacteria lowers the pH by
excreting acid which other bacteria can’t survive in
They are able to grow and out compete
other bacteria in acidic conditions
They eat up sugars in the milk before other
bacteria gets there meaning the other bacteria isn’t able to grow as much and take out larger colony of lacto
Asceptic techniques include
Wipe down workbench before starting
This is so no bacteria on workbench can get into petri dish that could kill bacteria you are trying to grow.
Work near a yellow Bunsen flame
This creates a convection current that pushes any bacteria in the
air away from the Petri dish. Yellow so you can see it and don’t accidentally burn yourself.
Sterilise metal implements
Do this by heating with a hot Bunsen flame
Autoclaving
This is a saturated steam under a high pressure
Chemical sterilants
Ethylene gas kills bacteria
Bacteria structure.
As well as all the features unique to bacteria, bacteria cells also contain these features.
Cytoplasm
Cell membrane
Cell wall
In bacteria cell walls are made of peptidoglycan
Cell wall is a permeable membrane that lets everything through and supports the structure of the cell.
Flagellum which moves the cell