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Biology > 3.4 Microbiology > Flashcards

3.4 Microbiology Flashcards

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1
Q

Cocci

A

Spherical

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2
Q

Bacillus

A

Rod shaped

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3
Q

Spirillum

A

Corkscrew

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4
Q

Gram positive stain

A

Purple

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5
Q

Gram negative stain

A

Red

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6
Q

Gram positive contain

A

-Thick outer wall of peptidoglycan
-No lipopolysaccharide layer
-Crystal violet can remain

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7
Q

Gram negative contain

A

-Thin peptidoglycan wall
-Outer lipopolysaccharide membrane
-Alcohol removes lipopolysaccharide layer
-Thin peptidoglycan layer allows stain to be washed away

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8
Q

Gram staining steps

A

Fixation
Stain with Crystal violet
Iodine
Decolorisation
Safranin

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9
Q

Needed for growth of bacteria

A

-Carbon source (glucose or lactose)
-Nitrogen source (ammonia or amino acids)
-Sulphur and phosphorus
-Vitamins and minerals
-Suitable pH
-Suitable temperature

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10
Q

Obligate aerobe

A

Needs oxygen

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11
Q

Obligate anaerobe

A

No oxygen

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12
Q

Facultative anaerobe

A

Grows best with oxygen but can respire anaerobically if needed

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13
Q

Aseptic technique prevents

A

-Contamination of the environment by the microorganism being handled
-Contamination of the bacterial culture by environment

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14
Q

How to sterilise tools

A

Pass through blue Bunsen burner flame until it glows red

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15
Q

How to serialise glassware

A

High pressure and temperature in autoclave for 15 min

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16
Q

Pouring a sterile agar plate

A

-Open bottle using little finger and do not pace on bench
-Flame neck of bottle
-Work close to flame as updraft prevents contamination
-Open sterile Petri dish at an angle
-Pour and close immediately
-Swirl to move air bubbles
-Secure lid with tape

17
Q

Inoculating nutrient agar plate

A

-Sterilise inoculating loop in blue flame until glows red
-Dip into milk
-Hold Petri dish lid at an angle to reduce contamination
-Spread milk across surface of agar in zig zag while rotating
-Tap lid shut
-Do not completely seal as anaerobic conditions encourage pathogenic bacteria
-Incubate at 25c and not 37c as human pathogen

18
Q

Staining

A

-Crystal violet is absorbed by the peptidoglycan as binds to it in the cell wall
-Add iodine which crystallises the purple stain
-Add alcohol which dissolves the lipopolysaccharide layer of the gram negative and dehydrates the peptidoglycan
-Gram positive is purple
-Gram negative is colourless as purple is washed away
-Safranin stains the gram negative pink/red and is not seen in the positive

19
Q

What does safranin do

A

Stain gram negative red
Does not stain gram positive

20
Q

What alcohol does

A

Dissolves the lipopolysaccharide layer of the gram negative and dehydrates the peptidoglycan

21
Q

What iodine does

A

Crystallises the violet

22
Q

2 categories for counting bacteria

A

-Viable count
-Total count

23
Q

Viable count

A

Counts only living bacteria
E.g serial dilutions

24
Q

Total count

A

-Counts living and dead bacteria

25
Q

Bacteria in a liquid can be counted

A

Directly
Indirectly (cloudiness)

26
Q

Viable count method

A

-Sterile water
-1cm3 of sample into tube (10^-1)
-Mix and then take 1ml and place into second tube
-This is 10^-2
-Repeat until 10^-4

27
Q

To estimate the number of bacteria present in original sample

A

Multiply the number of colonies counted by the dilution factor

28
Q

Why is count an estimate

A

-It does not include dead or noon viable bacteria
-We cannot be sure that each colony has grown from a single bacterium

29
Q

Why is log scale used

A

Allows a rapidly growing population to be accurately plotted on a graph

30
Q

Lag phase

A

-Initial exposure to the environment
-Little growth but the cells are taking up water and carrying out protein synthesis and producing enzymes

31
Q

Stationary phase

A

-Carrying capacity of the environment
-Dying at same rate as they are reproduced

32
Q

Death phase

A

Build up of toxic waste products in cells or due to lack of oxygen or nutrients

33
Q

Log phase

A

-Population increases rapidly

Biology (5 decks)

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