CH7 Flashcards
(91 cards)
Media containing some ingredients of unknown chemical composition are called __________ media.
complex
A growth medium that distinguishes among different groups of bacteria on the basis of colony appearance or changes is called a __________ medium.
differential
Organisms that grow well at 0°C and have optimum growth temperatures of 15°C or lower are called
psychrophiles
All fastidious microorganisms require what growth?
extra nutrients (such as vitamins and amino acids)
What reasons for the occurrence of a lag phase in a bacterial growth curve?
- The medium may be different from the previous growth medium so that the cells must synthesize new enzymes to use different nutrients.
- The cells may be old and depleted of ATP, essential cofactors, and ribosomes that must be synthesized before growth can begin.
- The organisms may have been injured and require time to recover.
Given a log phase bacterial culture with 1 x 10^6 cells per ml and a generation time of 30 minutes, how long does it take the culture to reach a density of 6.4 × 10^7 cells per ml?
3 hours
Microorganisms are most nearly uniform in terms of chemical and physiological properties during __________ phase.
exponential
Media in which all components and their concentration are known are called __________ media.
defined
For surface cultivation of microorganisms, a sulfated polymer called agar can be extracted from __________ and added to liquid media in order to cause it to solidify.
algae
Organisms that do not require oxygen for growth but grow better in its presence are called
facultative anaerobes.
The total number of viable microorganisms remains constant in stationary phase because
either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active.
can be used to isolate pure cultures of bacteria from mixtures
streak plate, pour plate and spread plates
regarding tolerance of microbes to osmotic stress
cell walls help protect some organisms placed into hypotonic environments
Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2–10% for growth are called
microaerophiles
Most microorganisms maintain their internal pH
near neutral (pH 7 or 7.5)
Organisms that require high levels of sodium chloride in order to grow are called __________ organisms.
halophilic
What method can be used to determine the number of viable microorganisms in a sample?
measuring colony forming units per ml
At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has a population of 65 million cells. The mean generation time is approximately
20 minutes.
Agar is an excellent solidifying agent for microbiological media because
- it is not degraded by most microorganisms.
- solid agar remains solid until the temperature is raised to 90°C, and liquid agar remains liquid if the temperature is lowered to 45°C.
Cells may enter stationary phase because of
- the depletion of an essential nutrient.
- the accumulation of toxic waste products.
- a lack of available oxygen.
What is considered a cardinal growth temperature?
minimum, maximum, and optimum temperature
A growth medium that favors the growth of some microorganisms but inhibits the growth of other microorganisms is a __________ medium.
selective
Organisms that grow near deep-sea volcanic vents are likely to be
thermophilic.
Organisms that grow in the mud under relatively non-turbulent bodies of water are likely to be
anaerobes.
