Biology Unit 3.4 - Microbiology

Question 1

What are microorganisms?

Answer 1

Organisms including bacteria, fungi, protoctista and viruses, which are important in decaying dead organsism and recycling nutrients

Question 2

What are bacillus bacteria?

Answer 2

Rod-shaped bacteria, that may be straight, curved, or spiral, and may have a flagella, which occur singly or in chains

Question 3

What are cocci bacteria?

Answer 3

Spherical bacteria, which occur singly, in pairs, chains or clusters

Question 4

What are spirillum?

Answer 4

Spiral shaped bacteria i.e., Leptaspira

Question 5

What occurs during staining in Gram positive bacteria?

Answer 5

Bacteria have a thick outer wall made of peptidoglycan and are stained purple

Question 6

What occurs during staining in Gram negative bacteria?

Answer 6

Bacteria have a thin outer wall and an extra outer membrane that includes lipoproteins and lipopolysaccharides, which are stained red following the addition of the counter stain Safranin O

Question 7

Antibiotic resistance in Gram positive bacteria…

Answer 7

More susceptible as the thick cell wall has a greater number of cross-linkages

Question 8

Antibiotic resistance in Gram negative bacteria…

Answer 8

Less susceptible as the outer membrane protects the cell wall, which is also thinner and has fewer cross-linkages

Question 9

Gram staining procedure…

Answer 9

• Smear bacteria on a slide
• Heat fix, then stain with crystal violet and dilute iodine
• Gram positive will retain the stain
• Gram negative will lose the stain as it is washed away
• Gram negative can be counterstained with a stain such as safranin O (red in colour)

Question 10

Nutrition in autotrophic bacteria…

Answer 10

Build up their own organic food by photosynthesis or chemosynthesis

Question 11

Nutrition in heterotrophic bacteria…

Answer 11

Feed like animals and fungi on ready-made organic food, and play a key role in decomposition

Question 12

How do obligate aerobes respire?

Answer 12

Growth is inhibited in the absence of oxygen

Question 13

How do obligate anaerobes respire?

Answer 13

Oxygen inhibits their growth

Question 14

How do facultative anaerobes respire?

Answer 14

Can grow in the absence of oxygen, but grow best with oxygen

Question 15

How will bacteria be classified in the future?

Answer 15

Biochemical analysis and DNA profiling

Question 16

What is the function of carbon, hydrogen and oxygen in bacterial growth?

Answer 16

Manufacture organic molecules

Question 17

What is the function of nitrogen in bacterial growth?

Answer 17

Synthesis of constituents of the cell i.e., amino acids, NAD, etc

Question 18

What is the function of sulfur in bacterial growth?

Answer 18

Manufacture proteins and co-enzymes

Question 19

What is the function of phosphorus in bacterial growth?

Answer 19

Manufacture phospholipids and ATP

Question 20

What factors affect bacterial growth?

Answer 20

pH
Carbon source i.e., glucose or lactose
Nitrogen source i.e., ammonium ions or amino acids
Growth factors
Vitamins and minerals

Question 21

What are the optimum temperature ranges of different types of bacteria?

Answer 21

Psychrophiles - 0
Mesophiles - 25-45
Hyperthermophiles - 45+

Question 22

Why is aseptic technique used?

Answer 22

Prevent contamination of the environment by the microbes being handled and of the bacterial cultures by unwanted microbes from the environment

Question 23

How do you pour an agar plate?

Answer 23

• Sterilise the work station
• Work closely to a Bunsen burner flame, so bacteria will be carried upwards
• Loosen the lid of the molten agar bottle
• Open the lid using your little finger and flame the neck of the bottle
• Open the petri dish at an angle to avoid air born bacteria falling onto the plate
• Pour the agar and close the lid immediately
• Swirl contents to burst air bubbles
• Flame the neck of the agar bottle and close it
• Allow agar to set

Question 24

How do you inoculate an agar plate?

Answer 24

• Sterilise the work station
• Work closely to a Bunsen burner flame, so bacteria is carried upwards
• Sterilise the inoculating loop by flaming it
• Open the petri dish at an angle and place the loop on a clear patch of agar to cool it down
• Close the lid of the agar plate and open a new agar plate at an angle
• Spread the bacterial colony in a zig-zag pattern, rotating the plate 2-3 times
• Close the lid and seal it with maksing tape
• Place it upside down in an incubator at 25 degrees celsius for 48-72 hours

Question 25

How do you conduct a total count using a colorimeter?

Answer 25

• Sample is pipetted into a cuvette and inserted
• Light is passed through each sample
• Amount of light received is indicated via a meter
• Less light reaching the sensor indicates a greater bacterial population

Question 26

Why is dilution plating used when conducting a viable count?

Answer 26

Used when bacterial colonies have merged together or when the number of colonies can be described as too numerous to count

Question 27

How do you conduct a viable count using serial dilution technique?

Answer 27

• Fill test tubes with a ml sterile water using a pipette
• Add b ml of sample to the first tube to form a dilution factor of c
• Mix this dilution and pipete b ml into the subsequent test tube
• Repeat until maximum possible dilution factor is achieved
• Pipette sample from each dilution onto an agar plate and spread using a sterile spreader
• Incubate the plates for between 48-72 hours
• Count the colonies on the pates which have between 30-300 colonies

Question 28

Why do we ignore plates with less than 30 colonies?

Answer 28

This numbered is considered unreliable

Question 29

Why do we ignore plates with more than 300 colonies?

Answer 29

Colonies begin to merge making it impossible to count, and they are deemed as too numerous to count