Lab Quiz 5: Bacterial Growth Curve, Environmental Conditions, and Anaerobes (Bio 286 - Microbiology)

Question 1

spectrophotometry

Answer 1

measuring the turbidity (cloudiness) of a bacterial suspension

Question 2

beer’s law

Answer 2

absorbance = E x l x c

Question 3

factors of absorbance (amount of light scattered)

Answer 3

molar extinction coefficient (E) is a constant that describes how much light is scattered per mole of cells (this value is affected by size, shape, arrangement, and other optical qualities of culture)… path length (l) is a constant that refers to the diameter of the spectrophotometer tubes… concentration (c) is the only variable – as the number of cells increases, the absorbance will also increase

Question 4

limitations to spectrophotometry

Answer 4

only concentrations within a certain range are capable of being accurately measured; both live and dead bacteria scatter light (as do nonbacterial particles) so turbidity can overestimate viable cell numbers

Question 5

number of cells in a culture growing by binary fission

Answer 5

X = 2^Y x X0 (X is number of cells, Y is number of doublings, X0 is initial number of cells)

Question 6

number of doublings

Answer 6

Y = t/g (t is time elapsed, g is the doubling time or the amount of time necessary per each doubling)

Question 7

growth rate

Answer 7

k = 1/g (reciprocal of generation/doubling time)

Question 8

the y = mx+b format of the plot of the log of cell numbers versus time, which can yield the slope (which can be used to calculate for Y or g or k)

Answer 8

log(X) = log(2)/g x t + log(X0)

Question 9

lag phase

Answer 9

(A) intense activity preparing for population growth, but no increase in population

Question 10

log phase

Answer 10

(C) The period of exponential growth of bacterial population

Question 11

stationary phase

Answer 11

(D) period of equilibrium; microbial deaths balance production of new cells

Question 12

death phase

Answer 12

(B) interval in which # of dying cells exceeds # of new cells formed; so there is a decline in overall # of cells

Question 13

binary fission

Answer 13

asexual reproduction in bacteria

Question 14

psychrophiles

Answer 14

microbes that grow optimally under cool conditions (0-15 degrees Celsius)

Question 15

psychrotrophs

Answer 15

microbes that tolerate cool conditions but grow best around room temperature (20 degrees Celsius)

Question 16

mesophiles

Answer 16

microbes that grow best between room temperature and body temperature (20-40 degrees Celsius)

Question 17

thermophiles

Answer 17

microbes with optimal growth under high temperatures (>40 degrees Celsius)

Question 18

acidophiles

Answer 18

microbes that grow best at low pH (1-5)

Question 19

neutrophiles

Answer 19

microbes that grow best at neutral pH (6-8)

Question 20

alkalinophiles

Answer 20

microbes that grow best at alkaline or high pH (9-14)

Question 21

nonhalotolerant

Answer 21

microbes that are inhibited by moderate levels of salt (1-5% NaCl)

Question 22

halotolerant

Answer 22

microbes that can tolerate higher concentrations of salt (1-15% NaCl)

Question 23

halophiles

Answer 23

microbes requiring elevated salt concentrations for growth

Question 24

halophiles cannot grow without

Answer 24

added salt (whereas halotolerant microbes can grow without added salt)

Question 25

obligate aerobes

Answer 25

organisms that require oxygen to live

Question 26

obligate anaerobes

Answer 26

organisms that are unable to use molecular oxygen to obtain energy and are usually killed or inhibited by its presence

Question 27

facultative anaerobes

Answer 27

organisms that can use oxygen if it is available but can also grow when oxygen is absent

Question 28

aerotolerant anaerobes

Answer 28

organisms that cannot use oxygen for growth but they can tolerate its presence well

Question 29

microaerophilic

Answer 29

organisms that require a lower oxygen concentration than what is in the air

Question 30

thioglycolate broth

Answer 30

contains sodium thioglycolate and cysteine that act as reducing agents to create anaerobic conditions when they convert molecular oxygen to water; resazurin is used as the color indicator– where strict aerobes will grow only it the pink band, microaerophiles growing near the bottom of the band (in lower concentrations of oxygen), and anaerobes growing in areas without pink (indicating absence of oxygen)

Question 31

oxygen indicators

Answer 31

resaxurin is pink when oxidized and colorless when reduced and methylene blue is blue when oxidized and colorless when reduced

Question 32

anaerobic jar

Answer 32

chamber from which oxygen is removed to be replaced with a carbon dioxide atmosphere

Question 33

brewers anaerobic agar plates

Answer 33

contain methylene blue as oxygen indicator; culture anaerobes when placed inside an anaerobe jar