Identification and growth of bacteria

Question 1

Which method is used to detect only viable bacteria in a sample?

A) Direct microscopic count
B) Plate count
C) Spectrophotometry
D) Turbidity measurement

Answer 1

B

Question 2

What does a direct microscopic count measure?

A) Only living cells
B) Total number of cells
C) Metabolic activity
D) Optical density

Answer 2

B

Question 2

Which instrument is used to measure turbidity in a bacterial culture?

A) Haemocytometer
B) Spectrophotometer
C) pH meter
D) Microscope

Answer 2

B

Question 2

What is the principle of the plate count method?

A) Detects both living and dead bacteria
B) Each bacterial cell forms a visible colony
C) Measures absorbance at 600 nm
D) Measures cell weight

Answer 2

B

Question 3

Which of the following methods can count both living and dead bacteria?

A) Direct microscopic count
B) Agar plate count
C) Filtration
D) Pour plate method

Answer 3

A

Question 4

Filtration is commonly used to:

A) Separate bacterial cells from liquids
B) Count bacterial colonies
C) Measure bacterial weight
D) Detect intracellular components

Answer 4

A

Question 5

Bacteria typically grow at:
A) 25°C
B) 30°C
C) 37°C
D) 50°C

Answer 5

C

Question 5

In the death phase, bacteria:
A) Grow at an accelerated rate
B) Remain in equilibrium
C) Die faster than they reproduce
D) Form endospores

Answer 5

C

Question 6

Mycobacteria have a slow growth rate because:
A) They require oxygen
B) They reproduce by budding
C) They grow in acidic environments
D) They have a thick cell wall

Answer 6

D

Question 7

Which medium is commonly used to culture bacteria?
A) Nutrient broth
B) Gelatin
C) Peptone water
D) Thioglycollate broth

Answer 7

A

Question 7

Which type of bacteria can grow in both aerobic and anaerobic conditions?
A) Obligate aerobes
B) Obligate anaerobes
C) Facultative anaerobes
D) Microaerophiles

Answer 7

C

Question 8

Which of the following factors can cause an underestimation in a plate count assay?

A) Presence of dead bacterial cells
B) Use of a high dilution factor
C) Overcrowding of colonies
D) All of the above

Answer 8

D

Question 9

Which method is best for isolating pure bacterial colonies?
A) Streak plate method
B) Pour plate method
C) Spread plate method
D) Filtration

Answer 9

A

Question 10

What is the main purpose of using agar in bacterial cultures?
A) As a nutrient source
B) To solidify the medium
C) To inhibit growth
D) To enhance bacterial motility

Answer 10

B

Question 11

What is the primary use of thioglycollate broth?
A) Growing fungi
B) Detecting motility
C) Identifying Gram-positive bacteria
D) Culturing anaerobic bacteria

Answer 11

D

Question 12

What structure allows bacteria to adhere to surfaces in biofilms?
A) Capsule
B) Flagella
C) Glycocalyx
D) Pili

Answer 12

C

Question 13

If a bacterial culture in the log phase is diluted into fresh medium, what happens?

A) Cells enter the lag phase again
B) Cells immediately resume logarithmic growth
C) Cell growth stops completely
D) All cells lyse

Answer 13

B

Question 13

In a continuous culture system (chemostat), what is primarily controlled to maintain bacteria in the log phase?

A) pH and osmotic pressure
B) Rate of nutrient input and waste removal
C) Amount of dissolved oxygen
D) Light intensity

Answer 13

B

Question 14

Why does turbidity measurement sometimes fail to give an accurate estimate of viable cell count?

A) It cannot differentiate between live and dead cells
B) It is affected by bacterial motility
C) It only works for anaerobic bacteria
D) It requires a large sample size

Answer 14

A

Question 14

What is the main limitation of using optical density (OD600) measurement for bacterial growth monitoring?

A) It only works for Gram-negative bacteria
B) It can only measure anaerobic bacteria
C) It does not work for motile bacteria
D) It cannot measure bacteria at high cell densities accurately

Answer 14

D

Question 15

Which metabolic pathway is likely absent in obligate anaerobes?
A) Glycolysis
B) Tricarboxylic Acid (TCA) Cycle
C) Fermentation
D) Electron Transport Chain with oxygen as the final acceptor

Answer 15

D

Question 16

If an obligate aerobe is suddenly exposed to an oxygen-free environment, what would most likely happen?
A) It will switch to anaerobic metabolism
B) It will become a facultative anaerobe
C) It will undergo oxidative stress and die
D) It will form endospores for survival

Answer 16

C

Question 17

What happens if you increase the temperature above the maximum growth temperature of a bacterial species?
A) Growth rate increases exponentially
B) Protein denaturation and cell death occur
C) The bacteria form more biofilms
D) The generation time decreases indefinitely

Answer 17

B

Question 18

In a bacterial growth curve, why does the lag phase occur?
A) Cells are adapting to new conditions and synthesizing enzymes
B) Cells are undergoing DNA replication
C) Cells are already in stationary phase
D) Bacterial cells are dying at the same rate as they divide

Answer 18

A

Question 19

What structural component protects biofilm bacteria from antibiotics? A) Capsule B) Peptidoglycan layer C) Extracellular polymeric substances (EPS) D) Flagella

Answer 19

C

Question 19

Bacteria in biofilms exhibit higher antibiotic resistance due to: A) Genetic mutations B) Slower metabolism and reduced penetration of drugs C) Lack of cell walls D) Increased antibiotic efflux

Answer 19

B

Question 20

What is the primary function of enrichment media? A) To isolate a single bacterial colony B) To reduce contamination C) To enhance the growth of specific bacteria D) To measure bacterial motility

Answer 20

C

Question 20

A selective medium is designed to: A) Support the growth of all bacteria equally B) Promote the growth of a specific bacterial group while inhibiting others C) Differentiate bacterial species based on metabolism D) Inactivate all Gram-negative bacteria

Answer 20

B

Question 21

Which of the following is a direct method for measuring bacterial growth? A) Plate count B) Optical density measurement C) Turbidity measurement D) Filtration

Answer 21

A

Question 22

Which method is used to estimate bacterial numbers in water samples with low bacterial concentrations? A) Plate count B) Spectrophotometry C) Membrane filtration D) Microscopic counting

Answer 22

C

Question 23

What is the characteristic of the log phase of bacterial growth? A) No increase in cell number B) Slow adaptation to a new environment C) Rapid and exponential increase in cell number D) Decline in cell population

Answer 23

C

Question 24

Which method provides a rapid but indirect estimate of bacterial growth? A) Microscopic count B) Plate count C) Turbidity measurement D) Membrane filtration

Answer 24

C

Question 25

Which bacterial group thrives at human body temperature (37°C)? A) Psychrophiles B) Mesophiles C) Thermophiles D) Hyperthermophiles

Answer 25

B

Question 26

What is the function of the glycocalyx in bacterial biofilms? A) Provides motility B) Protects bacteria from the immune system C) Inhibits bacterial growth D) Enhances bacterial metabolism

Answer 26

B

Question 27

Which of the following is a selective medium? A) Nutrient agar B) Chocolate agar C) Blood agar D) MacConkey agar

Answer 27

D

Question 28

The streak plate method is primarily used to: A) Measure bacterial motility B) Count bacterial colonies C) Isolate pure bacterial colonies D) Detect antibiotic resistance

Answer 28

C

Question 29

Which of the following best explains why bacterial growth in a closed system eventually enters the stationary phase? A) Accumulation of metabolic waste and depletion of nutrients B) Increase in bacterial size without division C) Continuous exponential growth D) Decrease in environmental temperature

Answer 29

A

Question 30

Which of the following statements about the use of a spectrophotometer for measuring bacterial growth is INCORRECT? A) It measures optical density at 600 nm B) It provides an indirect estimate of cell concentration C) It can distinguish between live and dead bacteria D) It is a rapid and non-invasive method

Answer 30

C

Question 31

What is the key advantage of a chemostat system over batch culture? A) It allows continuous growth by maintaining cells in the log phase B) It promotes the formation of endospores C) It eliminates the need for sterile conditions D) It allows bacteria to complete their entire growth cycle in minutes

Answer 31

A

Question 32

Why do facultative anaerobes grow faster in the presence of oxygen than in anaerobic conditions? A) Oxygen directly stimulates bacterial DNA replication B) Oxygen allows them to use aerobic respiration, which produces more ATP than fermentation C) Oxygen helps them absorb more nutrients from the medium D) Oxygen prevents the formation of endospores

Answer 32

BV