BCHM 4360 EXAM 2 CHAPTER 9 2026
LATEST UPDATE QUESTIONS AND
CORRECT VERIFIED ANSWERS ALREADY
GRADED A+
For the protein target, what are effect of agents and examples of agents
used? - ANS-- effect of agents: capable of denaturing proteins,
agents may attach to active site, preventing interaction with
substrate
- ex: moist heat, alcohol, phenolics
What are the 2 methods of physical control: heat and cold? - ANS-1.
elevated temps are microbicidal
- moist heat: hot water, boiling water, steam between 60-135 C
- dry heat: hot air/open flame, 160-1000 C
2. lower temps are microbiostatic
- 4 C refrigerator temp
- o C freezer temp
What is the effectiveness of 2 different kinds of heat? What are some
examples? - ANS-DENATURATION OF PROTEINS
1. moist heat: microbicidal effect is the coagulation and
denaturation of proteins (ex: autoclaving, boiling water,
pasteurization, etc)
2. dry heat: dehydrates the cell, removing water necessary for
metabolic reactions (ex: incineration, hot-air oven)
What are bacterial endospores and vegetative cells in terms of heat
resistance and thermal death? - ANS-- bacterial endospores: exhibit
greatest resistance, destruction of spores usually requires
, temperatures above boiling, resistance varies, 15-20 mins, 121 C
under pressure
- vegetative cells: vary in sensitivity to heat, death times vary
from 50 C for 3 minutes to 60 C for 60 minutes, will die before
endospores
What is thermal death time (TDT) and thermal death point (TDP)? - ANS--
thermal death time (TDT): least time required to kill all cells of a
culture at specified temp
- thermal death point (TDP): lowest temp that achieves
sterilization in a given quantity of broth culture upon a 10 minute
exposure
What are the effects of cold and desiccation (drying)? - ANS-- principal
benefit of cold treatment is to slow growth of cultures and
microbes in food during processing and storage (cold slows
growth)
- most microbes are not affected by gradual cooling, long-term
refrigeration, or deep freezing (best way of preserving stock
culture)
- temps from -70 C to -135 C can preserve cultures of bacteria,
viruses, + fungi for months and years (long periods)
What is desiccation? How do these cells become desiccated? - ANS--
vegetative cells directly exposed to normal room temp gradually
become dehydrated
- some microbes are killed by desiccation; others not
What is lyophilization? - ANS-- combination of freezing and drying
- preserves microorganisms in a viable state for many years
- pure cultures are frozen instantly + exposed to vacuum to
remove water (drying), avoiding formation of ice crystals
LATEST UPDATE QUESTIONS AND
CORRECT VERIFIED ANSWERS ALREADY
GRADED A+
For the protein target, what are effect of agents and examples of agents
used? - ANS-- effect of agents: capable of denaturing proteins,
agents may attach to active site, preventing interaction with
substrate
- ex: moist heat, alcohol, phenolics
What are the 2 methods of physical control: heat and cold? - ANS-1.
elevated temps are microbicidal
- moist heat: hot water, boiling water, steam between 60-135 C
- dry heat: hot air/open flame, 160-1000 C
2. lower temps are microbiostatic
- 4 C refrigerator temp
- o C freezer temp
What is the effectiveness of 2 different kinds of heat? What are some
examples? - ANS-DENATURATION OF PROTEINS
1. moist heat: microbicidal effect is the coagulation and
denaturation of proteins (ex: autoclaving, boiling water,
pasteurization, etc)
2. dry heat: dehydrates the cell, removing water necessary for
metabolic reactions (ex: incineration, hot-air oven)
What are bacterial endospores and vegetative cells in terms of heat
resistance and thermal death? - ANS-- bacterial endospores: exhibit
greatest resistance, destruction of spores usually requires
, temperatures above boiling, resistance varies, 15-20 mins, 121 C
under pressure
- vegetative cells: vary in sensitivity to heat, death times vary
from 50 C for 3 minutes to 60 C for 60 minutes, will die before
endospores
What is thermal death time (TDT) and thermal death point (TDP)? - ANS--
thermal death time (TDT): least time required to kill all cells of a
culture at specified temp
- thermal death point (TDP): lowest temp that achieves
sterilization in a given quantity of broth culture upon a 10 minute
exposure
What are the effects of cold and desiccation (drying)? - ANS-- principal
benefit of cold treatment is to slow growth of cultures and
microbes in food during processing and storage (cold slows
growth)
- most microbes are not affected by gradual cooling, long-term
refrigeration, or deep freezing (best way of preserving stock
culture)
- temps from -70 C to -135 C can preserve cultures of bacteria,
viruses, + fungi for months and years (long periods)
What is desiccation? How do these cells become desiccated? - ANS--
vegetative cells directly exposed to normal room temp gradually
become dehydrated
- some microbes are killed by desiccation; others not
What is lyophilization? - ANS-- combination of freezing and drying
- preserves microorganisms in a viable state for many years
- pure cultures are frozen instantly + exposed to vacuum to
remove water (drying), avoiding formation of ice crystals
