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A-Level EDUQUAS Biology > Component 1: Microbiology > Flashcards

Component 1: Microbiology Flashcards

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1
Q

Draw and label the structure of a prokaryotic cell

A 
Flagellum
Pilus
Circular DNA
Plasma Membrane
70s Ribosome
Murein Cell Wall
Slime Capsule
Plasmid
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2
Q

What is the function of the plasma membrane in a prokaryote?

A
  • barrier between the environment and the cytoplasm

- controls entry and exit of substances into and out of the cell

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3
Q

What is the function of the murein cell wall in a prokaryote?

A
  • prevents osmotic lysis
  • limits pressure inside cell
  • rigidity and cell structure
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4
Q

What is the function of the circular DNA in a prokaryote?

A

contains genes necessary for protein synthesis of the prokaryote

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5
Q

What is the function of the slime capsule in a prokaryote?

A
  • can glue bacterium together
  • allows bacterium to stick to surfaces
  • protect against other cell attack
  • prevents cell drying out
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6
Q

What is the function of 70s ribosomes in a prokaryote?

A

synthesis of proteins

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7
Q

What is the function of pili in a prokaryote?

A
  • attaching to surfaces

- transferring plasmids (genetic information) by conjugation

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8
Q

What is the function of the flagellum in a prokaryote?

A

for motility (movement)

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9
Q

What is the function of the plasmic in a prokaryote?

A
  • contains extra bacterial genes, e.g. bacterial resistance

- can be exchanged between bacteria during conjugation allowing spread of resistance

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10
Q

What are the 3 bacterial shapes?

A
  1. Bacillus (Rod)
  2. Coccus (sphere)
  3. Spirillum (Spiral)
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11
Q

What are the 4 bacterial arrangements?

A
  1. Diplo (cells are attached in pairs)
  2. Strepto (cells are attached in chains)
  3. Tetrads (cells are arranged in square)
  4. Staphylo (sheets and clumps)
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12
Q

What are prokaryotes?

A
  • no membrane bound nucleus
  • no membrane bound organelles
  • small ribosomes (70s)
  • cell wall made up of peptidoglycan
  • small cells, 0.5-5um
  • reproduce by binary fission
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13
Q

What is the structure of gram positive bacteria?

A
  • cell wall has a thick layer of peptidoglycan and a plasma membrane
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14
Q

What happens to gram positive bacterium in the Gram stain?

A
  • peptidoglycan holds onto crystal violet dye

- dye is not washed out by ethanol and therefore appears purple in the Gram stain

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15
Q

What are some examples of Gram positive bacterium?

A
  • Staphylococcus (MRSA)

- Streptococcus

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16
Q

What is the structure of Gram negative bacterium?

A
  • thick outer layer of lipopolysaccharides with a thin layer of peptidoglycan
  • plasma membrane beneath
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17
Q

What happens to Gram negative bacterium in the Gram stain?

A
  • crystal violet dye is removed when rinsed with ethanol (dissolves the stained lipopolysaccharide layer)
  • peptidoglycan is stained with the counter-stain and therefore appears pink in the gram stain test
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18
Q

What are some examples of Gram negative bacterium?

A

Salmonella and E.coli

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19
Q

What antibiotics interfere with Gram positive bacterium?

A
  • Penicillin
  • prevents bonds interlinking peptidoglycan forming
  • when the bacteria divide, the cell walls are weak and collapse
  • water uptake by osmosis bursts the cell
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20
Q

What antibiotics interfere with Gram negative bacterium?

A
  • Require antibiotics that interfere with the cell’s metabolism/protein synthesis
  • e.g. vancomycin
  • penicillin is not effective as the outer layer protects the peptidoglycan
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21
Q

Why are animal cells not damaged by penicillin?

A

Animal cells do not have a cell wall, not damaged by penicillin

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22
Q

Definition of the Gram Stain?

A

A method of staining the cell walls of bacteria as an aid to their identification

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23
Q

What is the method for the Gram-stain test?

A
  1. create a flame-fixed emulsion of bacterial samples on a slide
  2. flood with crystal violet, leave for 1 min then rinse of excess with sterile distilled water
  3. Add lugol’s iodine solution, leave for 1 min then rinse
  4. Flood with decolouriser (ethanol) for 30 seconds until run-off is clear
  5. Counter-stain with Safranin, leave for 1 min then rinse
  6. Gently blot dry slide
  7. Observe slide under oil immersion on a microscope
24
Q

How do you make a heat-fixed emulsion?

A

sample of a culture added to water on a microscope slide and passed through a flame to fix

25
Q

Why is a heat-fixed smear prepared?

A
  • kills cells in a life-like position

- attached bacteria to the slide and not rinsed away

26
Q

Why do you flood the smear with crystal violet?

A
  • able to identify Gram-positive bacterium

- stains/binds to peptidoglycan in gram-positive bacterium

27
Q

Why do you add lugol’s iodine?

A

Binds the crystal violet to the peptidoglycan more strongly

28
Q

Why do you add alcohol/ethanol?

A
  • washes out unbound crystal violet and lipopolysaccharide

- declourises gram-negative bacteria

29
Q

Why is the counterstain/safranin added?

A
  • counterstains Gram-negative cells pink

- Gram-positive bacteria remain purple

30
Q

Conditions necessary for culturing bacteria: temperature

A
  • bacterial metabolism is regulated by enzymes
  • suitable temperature for enzyme activity is 25ºC-45ºC
  • however optimum temperature for pathogenic bacteria is 37ºC (core human body temperature)
31
Q

Conditions necessary for culturing bacteria: pH

A

optimum pH for bacterial enzymes is slightly alkaline (6.5-7.5)

32
Q

Conditions necessary for culturing bacteria: oxygen

A

must have the right amount of O2 that their metabolism requires (obligate anaerobes etc)

33
Q

Conditions necessary for culturing bacteria: C

A
  • a carbon source (e.g. glucose)

- bacteria are heterotrophs and a carbon source is needed for bacterial respiration

34
Q

Conditions necessary for culturing bacteria: N

A
  • nitrogen source (e.g. amino acids)

- to synthesise proteins and nucleotides

35
Q

Conditions necessary for culturing bacteria: vitamins and minerals

A
  • E.g. Ca2+, Na+, Fe2+, Mg2+ and Cl-

- vitamins and minerals are essential for growth and enzyme activity

36
Q

What are the two problems when working with bacteria?

A
  1. contamination of cultures from the environment

2. contamination of the environment from the cultures

37
Q

What is the aseptic technique for using glassware?

A
  • Autoclave all glassware at 121ºC for 15 minds
  • prevents contamination to the environment
  • kills bacteria and spores
38
Q

What is the aseptic technique for using any kind of spreaders?

A
  • passing an inoculating loop through a roaring blue flame until red hot and passing glas spreads through a flame after being dipped in ethanol
  • prevents contamination to environment and to the cultures
  • kills bacteria
39
Q

What is the aseptic technique when using a petri dish?

A
  • open petri dish at a small angle
  • prevents contaminations to environment and cultures
  • prevents bacteria entering the petri-dish
40
Q

What is the aseptic technique for all cultures being used?

A
  • have a roaring blue flame on the bench at all times
  • prevents contamination of the culture
  • creates a convection current to uplift air away from cultures
41
Q

What is the aseptic technique when handling bottles and caps?

A
  • keep McCartney caps in hand and flame neck of the bottle (do not put the cap on the bench)
  • prevents contamination of bench and creates a convection current to lift air from the bench
42
Q

Why is sterilisation important?

A

So pure cultures of microorganisms can be grown

43
Q

What happens in an autoclave?

A
  • an autoclave allows a pressure of 15 atmospheres and a temperature of 121ºC to be generatures
  • if this is kept up for 15 mins this kills all bacteria and the spores are boiled
44
Q

What is used commercially to sterilise plastic?

A

gamma radiation as plastic would melt in an autoclave

45
Q

Define Obligate aerobes

A

Bacteria that require oxygen to grow or divide

46
Q

Define obligate anaerobes

A

Bacteria that can only grow/divide in the absence of oxygen

47
Q

Define facultative anaerobes

A

bacteria that can grow/divide in the absence of oxygen but grow faster in the presence of oxygen

48
Q

Why is it important to estimate population growth?

A
  • Environmental Health Monitoring (e.g. to check for E.coli in sea water at bathing beaches)
  • Water supply (to check drinking water is uncontaminated at the end of purification process)
  • Monitoring growth in fermenters (checking for unwanted bacteria)
49
Q

How is the size of a population of microbes measured?

A
  • Directly by counting cells:
    • viable counts describe living cells only
    • total counts describe living and dead cells
  • Indirectly, by measuring the turbidity (cloudiness) of the culture)
50
Q

What is the method for serial dilution?

A
  • 9cm^3 of sterile water is placed in each of a series of 6 sterile tubes
  • using a sterile pipette add 1cm^3 of culture to the first tube and then with another pipette transfer 1cm^3 from the first tube to the second
  • continue until all 6 tubes have been done
  • use sterile pipettes to transfer 0.5cm^3 of sample onto a sterile petri dish for each of the 6 tubes and spread with a glass spreader
  • forms 6 spread/pour plates
  • seal plates with 3 pieces of tape and then incubate at 25ªC for 24-48 hours
51
Q

How to estimate population size from a serial population?

A
  • after the 2 days bacteria will grow
  • a dish containing 20-100 colonies that are distinct and separate is chosen and the colonies counted
  • to find the total viable cell count the number of colonies is multiplied by the appropriate dilution factor
52
Q

What happens if the dilution is too great?

A

There will be too few colonies on each plate for the count

53
Q

What happens if the dilution is insufficient?

A

colonies merge, ‘clumping’ and counting may result in an underestimation of numbers

54
Q

What is the assumption made with serial dilutions and viable counts?

A

separate colonies of bacteria are counted assuming that every colony has originated from one single cell

55
Q

Define viable counts using serial dilution

A

cells in a small sample are used, made in known dilutions of the culture

56
Q

How are total cells counts done?

A
  • using a haemocytometer
  • special type of microscope slide to count individual cells
  • not possible to distinguish between living and dead cells so the result is a total cell count
57
Q

How can growth rate be estimated?

A

by regularly measuring the diameter of a bacterial or fungal colony spreading from a central point over the surface of a solid growth medium

A-Level EDUQUAS Biology (24 decks)

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