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A level Biology > Unit 3.4 - Microbiology > Flashcards

Unit 3.4 - Microbiology Flashcards

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1
Q

What is microbiology?

A

The study of microorganisms including prokaryotes (bacteria and archaea), protoctists, fungi and viruses

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2
Q

Which element of microbiology does the A level course mostly focus on?

A

Bactria

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3
Q

Examples of protoctists

A

Amoeba
Macroalga (seaweed)
Paramecium
Slime mole

(There’s a large variety)

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4
Q

What are amoeba and paramecium examples of?

A

Protoctists

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5
Q

How come fungi are involved in microbioloy?

A

Although they appear to behave like multicellular organisms in mushrooms and toadstools, the individual cells can live as single celled organisms

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6
Q

How do viruses reproduce?

A

By taking over host cells

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7
Q

What are viruses the borderline between?

A

Living organisms and complex chemicals like proteins

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8
Q

What can be though of as the borderline between living organisms and complex chemicals like proteins?

A

Viruses

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9
Q

Are viruses fully functioning living organisms?

A

No - more of a borderline between living organisms and complex chemicals (e.g - proteins)

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10
Q

Examples of prokaryotes

A

Bacteria
Archaea

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11
Q

Size of a prokaryotic cell

A

0.5 - 10 micrometres

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12
Q

Ribosomes in prokaryotic cells

A

70s

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13
Q

2 types of circular DNA in prokaryotic cells

A

Plasmids
Nucleoid

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14
Q

What does the cell wall of prokaryotic cells contain?

A

Peptidoglycan

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15
Q

Why do all prokaryotic cells have cell walls? Explain

A

They live in water-filled environments
The water potential of the cell is lower than the external water potential
Water diffuses in via osmosis
The cell wall avoids the lysis of the cell (stops it from bursting)

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16
Q

What would happen to prokaryotic cells if they didn’t have their peptidoglycan cell walls? Why?

A

They would burst (lyse) due to water diffusing in via osmosis from their environment

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17
Q

How do some antibiotics work because of the structure of prokaryotic cells?

A

They prevent the cell wall from working properly so that the cell cannot stand the pressure of the water diffusing in from its environment and bursts

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18
Q

What does the capsule of a prokaryotic cell do?

A

Protects the cell from chemicals and enzymes

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19
Q

What are the pilus of prokaryoties?

A

Tubular protein molecules

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20
Q

What do pili (more than 1 pilus) allow prokaryotic cells to do?

A

Allow cells next to each other to connect so that plasmids can move from 1 cell to the next

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21
Q

Plasmids

A

Circular DNA in prokaryotic cells that’s separate to the main chromosomal DNA

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22
Q

What can be transferred from one prokaryotic cell to another using pili?

A

Plasmids

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23
Q

Multiple pilus

A

Pili

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24
Q

What do plasmids allow prokaryotic cells to do?

A

Pass genes on plasmids from one cell to another without reproducing

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25
Q

How do prokaryotic cells pass on genes from one cell to another without reproducing?

A

Using plasmids

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26
Q

How are antibiotic resistance genes spread throughout a population of prokaryotic cells?

A

Using plasmids, which can be passed from one cell to another without reproducing

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27
Q

Mesosome

A

Infolding of the cell membrane

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28
Q

What are mesosomes in prokaryotic cells similar to in eukaryotic cells?

A

Similar to cristae in mitochondria

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29
Q

Where is the site of aerobic respiration in bacterial cells?

A

Mesosome

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30
Q

What is the mesosome of a prokaryotic cell useful for?

A

Is the site of aerobic respiration in bacterial cells

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31
Q

What does the flagellum of a prokaryotic cell do?

A

Rotates from a protein in the membrane to provide movement

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32
Q

Motile bacteria

A

Bacteria that can move on its own

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33
Q

Bacteria that can move on its own

A

Motile bacteria

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34
Q

Compare the differences between eukaryotic and prokaryotic cells

A

(Eukaryotic first each time)
Larger cells
80s larger ribosomes bound to the rough endoplasmic reticulum, 70s smaller ribosomes, free in the cytoplasm
Membrane bound organelles, no membrane bound organelles
DNA contained to the nucleus and is linear, DNA free in the cytoplasm and is circular
Nucleus has a double membrane, no nuclear envelope (double membrane(
No plasmids, plasmids
Cell wall (when present) is composed of cellulose or chitin, cell wall is composed of peptidoglycan (mucopolysaccharide)
Mitochondria are used for aerobic respiration (no mesosome), no mitochondria, uses a mesosome for aerobic respiration
DNA associated with histones, DNA not associated with histones

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35
Q

Ribosomes in eukaryotic cells

A

80s

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36
Q

Ribosomes in prokaryotic cells

A

70s

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37
Q

DNA in eukaryotic cells

A

Contained to the nucleus + linear

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38
Q

DNA in prokaryotic cells

A

Free in the cytoplasm + circular

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39
Q

Cell wall in eukaryotic cells

A

(When present) is composed of cellulose or chitin

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40
Q

Cell wall in prokaryotic cells

A

Composed of peptidoglycan (mucopolysaccharide)

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41
Q

What’s used for aerobic respiration in prokaryotic cells?

A

A mesosome

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42
Q

Similarities between prokaryotic cells and eukaryotic cells

A

Both contain ribosomes, cell membranes, DNA and genetic material

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43
Q

How can we identify different types of bacteria?

A

From their shapes

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44
Q

Rod shaped bacteria

A

Bacillus

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45
Q

Bacillus bacteria shape

A

Rod shapes

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46
Q

Examples of bacillus bacteria

A

Escherichia coli (E.Coli)
Salmonella

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47
Q

What can both of the bacillus bacteria E.Coli and Salmonella cause?

A

Food poisoning

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48
Q

Pathogen

A

An organism that can produce disease

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49
Q

Describe the bacillus bacteria salmonella

A

Pathogenic

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50
Q

Is all bacteria pathogenic? Give an example

A

No
Although E.Coli can be pathogenic, there’s already some in our intestine which isn’t pathogenic

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51
Q

Sphere shaped bacteria

A

Cocci

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52
Q

Cocci bacteria shape

A

Sphere shaped

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53
Q

Example of cocci bacteria

A

Staphylococcus aureus

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54
Q

Example of a staphylococcus aureus bacteria and explain why it’s problematic

A

MRSA
Is resistant to most of antibiotics, making it very difficult to treat (only 2 antibiotics are effective, and they have bad side effects)

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55
Q

What do the different arrangements of cocci depend on?

A

The species of the coccus bacteria

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56
Q

What are the 2 less common types of bacteria?

A

Vibrio
Spirillum

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57
Q

Comma shapes bacteria

A

Vibrio

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58
Q

Vibrio bacteria shape

A

Comma shaped

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59
Q

Example of vibrio bacteria

A

Vibrio cholerae

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60
Q

What is vibrio cholerae and how is it caused?

A

Cholera, caused by drinking contaminated drinking water

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61
Q

Spiral shapes bacteria

A

Spirillum

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62
Q

What shape is spirillum bacteria?

A

Spiral shaped

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63
Q

Example of a spirillum bacteria and what it causes

A

Leptospira, which causes Weil’s disease

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64
Q

How is Weil’s disease obtained?

A

By drinking water contaminated with rat urine

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65
Q

What is Gram’s stain?

A

A technique used in microbiology to help with the identification of bacteria

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66
Q

What does using the gram’s stain process to identify bacteria rely on?

A

The fact that bacteria have 2 basic cell wall structures, one of which retains a crystal violet stain and the other of which does not

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67
Q

What can bacteria be divided into using their basic cell wall structures?

A

Gram positive
Gram negatives

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68
Q

What colour do gram positives appear at the end of gram’s stain?

A

Purple

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69
Q

What colour do gram negatives appear at the end of gram’s stain?

A

Red/pink

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70
Q

Procedure for gram’s stain

A

1.) place the bacterial sample on a glass microscope slide
2.) stain with crystal violet (purple dye)
3.) apply iodine to fix the stain (iodine = a mordant)
4.) alcohol wash to decolorize
5.) stain with a a counter-stain —> safranin (red)

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71
Q

What is iodine?

A

A mordant

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72
Q

Purpose of the alcohol wash in the gram’s stain technique

A

To decolorize

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73
Q

Counterstain in the gram’s stain technique

A

Safranin

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74
Q

Colour of the safranin counterstain

A

Red

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75
Q

Cell walls of gram-positive bacteria

A

Simple cell walls, composed mainly of peptidoglycan

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76
Q

Cell walls of gram-negative bacteria

A

More complex cell walls which have an outer lipopolysaccharide membrane

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77
Q

What does crystal violet do to gram-positive bacteria?

A

Stains all cells purple

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78
Q

What does crystal violet do to gram-negative bacteria?

A

Stains all cells purple

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79
Q

What does iodine do with gram-positive bacteria?

A

Forms cross bridges with peptidoglycan and binds the crystal violet to the cell wall

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80
Q

What does iodine do with gram negative bacteria?

A

Doesn’t bond to the cell wall upon the addition of iodine. The lipopolysaccharide membrane prevents this.

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81
Q

What does alcohol do to gram-positive bacteria?

A

Doesn’t wash out the crystal violet as it’s binded to the cell wall

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82
Q

What does alcohol do to gram-negative bacteria?

A

Washes out any unbound crystal violet from the cell walls

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83
Q

What does the safranin counter-stain do to gram-positive bacteria?

A

Has no effect

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84
Q

What does the safranin counter-stain do to gram-negative bacteria?

A

Unstained cells are stained red/pink by the safranin

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85
Q

What’s different about the cell walls of gram-negative bacteria to gram-positive bacteria?

A

Gram-positive —> composed mainly of peptidoglycan
Gram-negative —> an outer lipopolysaccharide membrane

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86
Q

Why doesn’t crystal violet bond to the cell wall upon the addition of iodine in gram-negative bacteria?

A

The lipopolysaccharide membrane prevents it

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87
Q

What can the lipopolysaccharide layer in cells do?

A

Protect it from antibiotics

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88
Q

Culturing

A

Growing bacteria in a laboratory to form a bacterial culture

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89
Q

What do we used for culturing micro organisms?

A

Culture media

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90
Q

Solid culture medium

A

Agar plates

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91
Q

What are liquid culture media in?

A

In flasks

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92
Q

How do we prepare agar plates?

A

1.) Heat until liquid
2.) Mix in nutrients that bacteria needs
3.) pour into petri dished when hot

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93
Q

What is agar derived from?

A

Seaweed

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94
Q

How do we grow bacteria on agar?

A

1.) spread sample on surface
2.) dots appear after incubation
3.) form colonies

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95
Q

What does a liquid culture medium include?

A

The nutrients that bacteria needs and water

96
Q

Where does bacteria grow in a liquid culture medium?

A

In the liquid

97
Q

What doesn’t happen in liquid culture media?

A

Colonies aren’t formed

98
Q

Which factors need to be kept at optimum by microorganisms for growth?

A

Nutrients
Growth factors
Temperature
pH

99
Q

Why do bacteria need nutrients?

A

They’re heterotrophic = needs inorganic compounds already formed

100
Q

Where are nutrients supplied to bacteria in laboratories?

A

In the nutrient media

101
Q

What’s a liquid culture medium often called?

A

Nutrient broth

102
Q

What, as well as nutrients, do culture media supply?

A

Water

103
Q

Which nutrients are required for bacteria?

A

Carbon
Nitrogen

104
Q

Where does the carbon and energy source for bacteria usually come from?

A

Glucose

105
Q

Why do bacteria need nitrogen?

A

For amino acid synthesis

106
Q

How do bacteria obtain nitrogen?

A

In organic molecules
In inorganic form, such as nitrate ions

107
Q

What are bacteria good at synthesising and from what?

A

Their own amino acids from carbon and nitrogen

108
Q

At which concentrations are the growth factors of bacteria?

A

Low concentrations

109
Q

Growth factors needed by bacteria

A

Vitamins
Mineral salts

110
Q

Example of a vitamin needed by bacteria

A

Biotin

111
Q

Examples of mineral salts needed by bacteria

A

Sodium
Magnesium
Chloride
Sulphate
Phosphate

112
Q

Why do bacteria need sulphate salts?

A

For some amino acids

113
Q

Why do mineral salts need phosphate salts?

A

To synthesise phospholipids and nucleic acids

114
Q

Nucleic acids synthesised with phosphate

A

DNA
RNA
ATP

115
Q

How do we keep bacteria, when culturing it, at the right temperature?

A

Incubate it

116
Q

What is bacterial metabolism regulated by?

A

Enzymes

117
Q

Which temperature is suitable for most bacteria and why?

A

25 - 45 degrees Celsius
As bacterial metabolism is regulated by enzymes, and this is optimum for them

118
Q

Optimal temperature for mammalian pathogens

A

37 degrees Celsius

119
Q

Which bacteria have an optimum temperature of 37 degrees Celsius and why?

A

Mammalian pathogens
Human body temperature

120
Q

Name for bacteria that have about 37 degrees Celsius as their optimum temperature

A

Mesophiles

121
Q

Optimum temperatures for psychrophiles

A

Very low temperatures, even below 0 degrees Celsius

122
Q

What type of bacteria have an optimum temperature that can be below zero degrees?

A

Psychrophiles

123
Q

Where could psychrophiles live?

A

In deep oceans

124
Q

Optimum temperature of hyperthermophiles

A

Very high

125
Q

What type of bacteria have very high optimal temperatures?

A

Hyperthermophiles

126
Q

Where could hyperthermophiles live?

A

Volcanic springs

127
Q

List 4 biological problems which Psychrophiles must overcome to carry out cellular processes

A

Transport proteins inactive
Inflexibility of cellular membranes
Freezing of cell contents
Less energy for enzyme activity

128
Q

Which pH conditions do most bacteria grow best in?

A

Slightly alkaline conditions (pH 7.4)

129
Q

Which pH conditions do fungi grow best in?

A

Neural or slightly acidic

130
Q

What grow best in neutral or slightly acidic conditions?

A

Fungi

131
Q

How do we maintain the pH of a growth medium?

A

Use buffers

132
Q

3 classifications of bacteria in terms of oxygen requirements

A

Obligate aerobes
Obligate anaerobes
Facultative anaerobes

133
Q

Obligate aerobes

A

Will only grow in the presence of oxygen, respire aerobically

134
Q

Bacteria that will only grow in the presence of oxygen and respire aerobically

A

Obligate aerobes

135
Q

Obligate anaerobes

A

Will only grow when oxygen is absent, respire anaerobically

136
Q

Bacteria that will only grow when oxygen is absent and respire anaerobically

A

Obligate anaerobes

137
Q

Facultative anaerobes

A

Will grow in the absence of oxygen, although they do grow best in aerobic conditions with oxygen

138
Q

Bacteria that will grow in the absence of oxygen, although they do grow best in aerobic conditions with oxygen

A

Facultative anaerobes

139
Q

What is oxygen to obligate anaerobes?

A

Toxic

140
Q

2 examples of obligate anaerobes

A

Clostridium tetani
Clostridium botulinum

141
Q

What does clostridium tetani cause?

A

Tetanus

142
Q

What causes tetani?

A

Anything that causes a deep penetrating wound (e.g - dog bites)

143
Q

What happens during tetanus and why?

A

Can grow deep in the tissue where there’s low oxygen levels
Releases a powerful neurotoxin that causes paralysis of the body muscles = all contract at the same time
Deadly pathogen since is can paralyse breathing muscles

144
Q

What are both clostridium tetani and clostridium botulinum?

A

Deadly pathogens

145
Q

What does clostridium botulinum cause?

A

Botulism food poisoning

146
Q

What causes botulism food poisoning?

A

Canned foods that haven’t been properly treated
For example, air got in or it wasn’t cooked at a high enough temperature

147
Q

What happens during botulism food poisoning and why?

A

Clostridium botulinum produces a powerful neurotoxin
Causes all muscles to relax as the toxin blocks the nerve impulse form crossing the synapses = can’t move
Can be fatal is breathing muscles all relax

148
Q

Which less dangerous thing is C.botulinum used in? Why?

A

Botox
In small amounts, it can relax the muscles in the skin that cause wrinkles

149
Q

Liquid culture name

A

Nutrient broth

150
Q

Which 2 methods can be used to count bacteria in liquid culture?

A

Directly (by counting each cell)
Indirectly (by measuring turbidity - cloudiness - of the culture medium with a colorimeter)

151
Q

Turbidity of a culture medium

A

Cloudiness

152
Q

What do we measure the turbidity of a culture medium with?

A

A colourimeter

153
Q

2 types of direct counts for counting bacteria

A

Total counts
Viable counts

154
Q

Total counts of bacteria

A

Include both living and dead cells

155
Q

Viable counts of bacteria

A

Only count living or actively growing cells
= underestimates population size

156
Q

2 examples of total counts methods for counting bacteria

A

Direct counting with a counting chamber
Indirect counting by measuring bacteria numbers by optical density

157
Q

What type of total counts counting is using a counting chamber?

A

Direct counting

158
Q

What type of total counts counting is measuring bacteria numbers by optical density?

A

Indirect counting

159
Q

Which device is used to measure optical density by total counts?

A

Spectrophotometer

160
Q

What happens with a spectrophotometer with a bacterial suspension with low bacterial numbers?

A

High transmission and high level of light detected

161
Q

What can we do with the data collected with a spectrophotometer when completing a total count of bacteria and what does this tell us?

A

Produce a calibration curve
Can work out a certain number of cells from the light transmission

162
Q

How can we work out the number of bacterial cell in a suspension when measuring by optical density?

A

Produce a calibration curve

163
Q

On what are viable counts completed and what are we counting?

A

On agar plates
Count cells which are able to grow into visible colonies

164
Q

Procedure of completing viable counts on an agar plate

A

1.) put sample of culture onto agar plate
2.) incubate at optimum temperature
3.) count the number of colonies growing on the plate
We assume that each colony grow from a single cell

165
Q

What do we assume when doing viable counts of bacteria?

A

That each colony grows from a single cell

166
Q

When would a dilution technique be used on a bacterial sample?

A

If the population density of the sample is too high to count

167
Q

What do we do if the population density of a sample of bacteria is too high to count?

A

A dilution technique is used

168
Q

Name for the process of diluting bacterial samples

A

Serial dilution or dilution plating

169
Q

Method for serial dilution

A

1.) fill 5 test tubes with 9cm^3 sterile water using a sterile pipette
2.) add 1cm^3 of your sample to the first tube. This is a 1 in 10 dilution or 10^-1
3.) mix the 10^-1 dilution thoroughly and pipette 1ml into the second test tube. This is a 1 in 100 or 10^-2 dilution.
4.) repeat this process until you reach a 1 in 10,000 dilution (10^-4)
5.) plate each dilution on nutrient agar using aseptic techniques
6.) incubate the plates at 25 degrees Celsius for 48 hours

170
Q

Why is serial dilution done?

A

When placing a sample that isn’t very diluted onto an agar plate, all of the individual colonies could be merged together. Therefore, we can’t count them.
When it’s diluted, the colonies are clearly separate and are easier to count.

171
Q

Which dilution factor are colonies the most clearly separated?

A

At about 10^-5

172
Q

What happens after the dilusion factors of about 10^-5 during serial dilution?

A

The number of colonies can become too small to be statistically significant

173
Q

What happens if we don’t have enough colonies when counting on a bacterial sample?

A

Unreliable estimate

174
Q

What provides the most reliable results when counting the number of colonies in a bacterial sample?

A

When there’s enough colonies but they’re still easy to count

175
Q

What happens if we have too many colonies to count in a bacterial sample?

A

Too many to count reliably

176
Q

What’s the problem when colonies merge when trying to count them?

A

Impossible to distinguish individual colonies, so it’s impossible to count them

177
Q

Equation for estimating bacterial numbers in a culture - total viable count

A

Number of cells in 1cm^3 of original sample =
Number of colonies x 1/dilution factor
—————————————————-
Sample volume

178
Q

Weaknesses of the total viable count method

A

1.) number is usually an underestimate since it doesn’t include dead or non-viable bacteria
2.) cannot be sure that each colony as grown from a single bacterium (bacterial cells may have been clumped together)
3.) Takes time and skill
4.) Lots of steps where contamination can happen

179
Q

When are aseptic techniques used?

A

When transferring bacteria from 1container to another

180
Q

What type of techniques are used when transferring bacteria from 1 container to another?

A

Aseptic techniques

181
Q

What are aseptic techniques used to prevent?

A
  • Contamination of the environment (and ourselves) by the microorganisms being handled
  • contamination of the bacterial cultures by unwanted microorganisms from the environment (and ourselves)
182
Q

What must all equipment and growth media which come into contact with microorganisms bing cultured (grown) be?

A

Sterile

183
Q

5 examples of sterilisation

A
  • use pre-sterilised Petri dishes (sterilised with UV light when manufactured)
  • passing metal transfer tools (such an inoculating loops) through a roaring/blue Bunsen flame until they glow red
  • sterilising any glassware used under high pressure and high temperature (121 degrees) in a special piece of apparatus called an autoclave for 15 minutes
    -heating the nutrient agar used for the plates in an autoclave to sterilise it before pouring into the plates and letting it set
    -disinfect bench
184
Q

How are pre-sterilised Petri dishes pre-sterilised?

A

Using UV light when manufactured

185
Q

Where are glassware and nutrient agar sterilised?

A

In an autoclave

186
Q

How long does glassware go into an autoclave for?

A

15 minutes

187
Q

Temperature of autoclave

A

121 degrees Celsius

188
Q

Process of using an autoclave

A

1.) place the glassware and water in\
2.) seal the lid
3.) put on heat (121 degrees Celsius)
4.) water heats up and forms a steam
5.) steam builds up pressure
6.) high pressure = boiling point of water goes up = bacterial spores are killed

189
Q

How does a liquid culture medium look initially when we produce it?

A

Clear

190
Q

What do we do when initially producing a liquid culture medium? Why?

A

Heat sterilise
To ensure there isn’t anything already living there

191
Q

Why do we heat sterilise culture media before introducing the bacteria?

A

To ensure there isn’t anything already living there

192
Q

What happens to a liquid culture medium when bacteria is introduced?

A

Turns cloudy

193
Q

How much of a bacterial sample is usually placed on an agar plate?

A

0.1cm^3

194
Q

What is meant by bacteria “growing”?

A

Cell division

195
Q

What is the unit of the number of cells in 1cm^3 of a bacterial sample?

A

Cellscm^3

196
Q

Are clumping and merging of bacteria the same?

A

No

197
Q

What does the microbial growth curve involve?

A

4 stages of growth

198
Q

4 stages of growth of the microbial growth curve

A

Lag phase
Exponential (log) phase
Stationary phase
Death phase

199
Q

How does inoculation occur at the beginning of the microbial growth curve?

A

Inoculate a sterile culture medium with bacteria (e.g - inoculating loop + aseptically transfer them)

200
Q

What happens to the number of bacteria during the lag phase?

A

No change

201
Q

Why is there no change in bacterial numbers during the lag phase?

A

Bacteria are becoming accustomed to the new growth medium

202
Q

How do bacteria become accustomed to a new growth medium?

A

Prepare for cell division + growth by…
Synthesising enzymes
Synthesising proteins
Replicating DNA

203
Q

Exponential growth

A

Doubling per unit time

204
Q

During which phase of the microbial growth curve does exponential growth occur?

A

Exponential (log) phase

205
Q

Describe the rate of cell division against the rate of cell death during the exponential (log) phase

A

Rate of cell division»rate of cell death

206
Q

Why is the rate of cell division much higher than the rate of cell death during the exponential (log) phase?

A

No limiting factors = plenty of nutrients and no competition = grow quickly

207
Q

Which stage of the microbial growth curve does bacteria stay in the longest and how long is this?

A

Stationary phase
A number of hours

208
Q

What does bacteria start doing during the stationary phase of the microbial growth curve and why?

A

Compete
Is comes to the point where there’s so much bacteria that’s grown that the finite number of nutrients won’t be enough for them all

209
Q

What limits the rate of growth in the microbial growth curve and at which phase?

A

The concentration of nutrients
Stationary phase

210
Q

Describe the rate of cell division against the rate of cell death during the stationary phase

A

Rate of cell division = rate of cell death

211
Q

What happens to the absolute number of cells during the stationary phase?

A

Stays constant

212
Q

When has bacteria reached the death phase on the microbial growth curve?

A

Once the numbers of bacteria start to decrease

213
Q

Describe the rate of cell division against the rate of cell death during the death phase of the microbial growth curve

A

Rate of cell division<rate of cell death

214
Q

What happens to the population of the growth culture during the death phase and why?

A

Decreases
The build up of toxic metabolic waste
Nutrients becoming scarce

215
Q

Why do we plot log numbers instead of actual numbers on the microbial growth curve?

A

If we plotted number of cells against time, the line would eventually go vertical due to exponential growth
It’s increasing in steepness due to the rate of growth increasing
This is meaningless, so we plot lot numbers instead of absolute numbers

216
Q

Why would plotting number of cells against time for the microbial growth curve increase in steepness until it becomes a vertical line?

A

The rate of growth is increasing due to exponential growth

217
Q

How do you calculate the % increase in population size of a bacterial culture?

A

Increase (highest value - lowest value)
Answer/lowest value x100

218
Q

How do we know whether a sample has been contaminated?

A

See different types of bacteria

219
Q

How do we confirm bacterial numbers in a sample?

A

Repeat and calculate a mean

220
Q

How many colonies of bacteria is too few counted to be valid?

A

Less than 30

221
Q

What do we need to ensure we mention when describing serial dilution?

A

Aseptic techniques

222
Q

Different ways to describe culture media

A

Defined medium
Undefined medium
Selective medium
Complete medium

223
Q

Defined medium

A

Contains only known ingredients

224
Q

Undefined medium

A

Contains components that are not all known because they include, for example, yeast extract or beer peptone

225
Q

Selective medium

A

Only allows certain bacteria to grow

226
Q

Complete medium

A

Contains all the chemicals needed to support growth

227
Q

Disadvantage of total counts method

A

Can’t identify the death phase

228
Q

Describe the peptidoglycan in the cell walls of gram positive bacteria

A

Thick layer

229
Q

When do bacteria grow fastest?

A

At optimum temperature

230
Q

What does bacteria do at optimum temperature?

A

Grows fastest

231
Q

What does bacteria do to nutrients in the lag phase?

A

Absorbs them

232
Q

What has been reached in the stationary phase of the microbial growth curve?

A

Carrying capacity

233
Q

What has increased by the stationary phase of the microbial growth curve?

A

Environmental resistance

234
Q

Environmental conditions that could affect the rate of bacterial cell division

A

Amount of nutrients
Accumulation of waste products
Temperature
pH
Oxygen

235
Q

Total viable count

A

Total number of bacteria in a known volume of liquid

236
Q

What do we need to use when plotting a graph after a total viable count and why?

A

Logs
Large numbers that are difficult to plot

237
Q

Why is it difficult to count large colony numbers of bacteria?

A

Clumping

A level Biology (26 decks)

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