Microbiology

What method do bacteria use to reproduce?

Binary fission

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List some positive uses of bacteria (2 marks)

1) Mutualistic bacteria in herbivores 2) Insulin making bacteria 3) Blue cheese production

2 of 25

List some negative effects of bacteria (2 marks)

1) Spoil food 2) Can cause disease

3 of 25

What is the plasmid and what is its function?

Small circular DNA which is used for antibiotic resistance

4 of 25

Name and describe the three shapes of bacteria (3 marks) MUST LEARN!!!

1) Spiral :-Corkscrew 2)Bacillus;- Rod Shaped 3) Coccus :- Spherical

5 of 25

List the four steps of the gram stain technique.

1) Application of crystal violet (a purple dye) 2) Application of grams iodine solution 3) Alcohol wash 4) Application of safranin (a counter-dye which is red)

6 of 25

At what stage of the gram stain technique do gram + and gram - bacteria differentiate?

At the alcohol wash stage: gram +ve remain purple but gram -ve turns colourless and is then made red by the counter-dye

7 of 25

Give an example of a gram positive bacteria

Staphylococcus aureus

8 of 25

Give an example of a gram negative bacteria

E.coli

9 of 25

Describe the structure of gram +ve bacterial cell walls (2 marks)

1) A thick peptidoglycan cell wall 2)No outer lipopolysaccharide layer.

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Describe the structure of gram -ve bacterial cell walls (2 marks)

1) A thin peptidoglycan cell wall 2) Has an outer lipopolysaccharide layer

11 of 25

Suggest Why don't gram negative bacteria retain the purple dye

The alcohol wash dissolves the outer LipoPolyS layer which had the purple dye on it and take on the counter stain which appears red.

12 of 25

What's the difference between antibiotic susceptibility in gram +ve and gram -ve bacteria and why (2 marks)

1) Gram -ve isnt as susceptible to penicillin because penicillin attacks the peptidoglycan cell wall 2) Gram -ve bacteria, this is protected by the LPS layer

13 of 25

What are the conditions required for bacterial growth?

1) Temperature at range of 25-40°C 2)O2 requirement based on type of microorganism they are 3) pH: bacteria a bit alkaline and fungi a bit acidic 4)Nutrients: nutrient agar or broth providing glucose for C and N for nucleic acid synthesis

14 of 25

Suggest why should microorganisms not be kept at 37°?

Thats body temperature so it might lead to the development of pathogens

15 of 25

What are the aseptic techniques to prevent the contamination of pure culture?

1) Sterilise all media and equipment before use 2) Disinfect work benches 3) Light a bunsen burner for a convection current 4) Handle cultures carefully and flame the neck od the bottle before opening and closing

16 of 25

What are the aseptic techniques to prevent the contamination of an environment?

1) Seal agar dish with adhesive tape but not all the way around 2) Flame the neck of the culture bottle and don't place the lid on the work surface 3) Lift the lid of the agar dish to 45° 4) Sterilise work surface before and after use

17 of 25

Suggest why should you not tape the agar dish all the way around?

Anaerobic conditions may lead to pathogens being developed

18 of 25

How would you sterilise glass and metal equipment?

Place the equipment in an autoclave for 15 minutes under high pressure and heated to 121° in steam

19 of 25

How are plastic equipment sterilised?

Using gamma rays before use and after use, autoclave for 15 mins at 121°C under high pressure and then discard

20 of 25

Name two real life scenarios that require estimating the growth of a bacterial population

1. Checking water supplies 2. Food manufacturers checking the safety of their food

21 of 25

Define total cell count and total viable count

Total cell: living and dead cells in a bacterial sample Total viable: living cells in a known volume of liquid medium

22 of 25

What inaccuracies might occur if the original bacterial culture is under diluted in a serial dilution?

Colonies might merge and clump together so counting would be inaccurate and lead to an underestimate

23 of 25

What inaccuracies might occur if the bacterial culture is over diluted in a serial dilution?

There will be too few colonies on each plate so it's not statistically good

24 of 25

What is the assumption for a serial dilution?

A single bacterial cell will reproduce asexually to form a single colony of cells that can be seen on an agar plate and counted

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Microbiology

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