chapter 6 microbial growth

acidophiles

Bacteria that are remarkably tolerant of acidity

physical and chemical

The requirements for microbial growth can be divided into 2 main categories:

true

alkalinity also inhibits microbial growth but is rarely used to preserve foods. true or false?

peptones and amino acids

are some media act as buffers

true

certain bacteria grow well at high temperatures that would kill most bacteria, and a few bacteria can actually grow at temperatures well below freezing. true or false?

maximum growth temperature

is the highest temperature at which growth is possible

minimum growth temperature

is the lowest temperature at which the species will grow.

optimum growth temperature

is the temperature at which the species grows best.

true

low temperatures decrease microbial reproduction rates, which is the basic principle of refrigeration. true or false?

psychrophiles (cold-loving microbes), mesophiles (moderate-temperature-loving microbes) and thermophiles (heat-loving microbes)

microorganisms are classified into three primary groups on the basis of their preferred temperature:

true

microorganisms obtain almost all their nutrients in the solution from the surrounding water. Thus, they require water for growth, and their composition is 80-90% water. true or false?

true

most bacteria grow best in a narrow pH range near neutrality, between pH6.5 and 7.5. true of false?

why is it difficult to define psychrophile, mesophile, and thermophile?

the ranges and maximum growth temperatures that defined bacteria as psychrophile, mesophile, or thermophiles are not rigidly defined. (ex.: psychrophiles were originally considered simply to be organisms capable of growing at 0degrees., however, there seem to be two fairly distinct groups capable of growth at that temperature).

true

to neutralize the acids and maintain the proper pH, chemical buffers are included in the growth medium. true or false?

true

very few bacteria grow at an acidic pH below about pH 4. true or false?

carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements and organic growth factors

what are the chemical aspects/requirements for microbial growth?

temperature, pH, and osmotic pressure

what are the physical aspects/requirements for microbial growth?

plasmolysis or shrinkage of the cell's cytoplasm

when a microbial cell is in a solution whose concentration of solutes is higher than in the cell, the cellular water passes out through the plasma membrane to the high solute concentration. This osmotic loss of water causes,____________________________

true

when bacteria are cultured in the laboratory, they often produce acids that eventually interfere with their own growth. true or false.

soilborne plant pathogen

which bacterium would theoretically be ore likely to grow at refrigerator temperatures: a human intestinal pathogen or a soilborne plant pathogen?

psychrophiles

-cold-loving microbes -originally considered simply to be organisms capable of growing at 0degrees.

thermophiles

-heat-loving microbes -are microorganisms capable of growth at high temperatures -optimum growth temperature of 50-60degrees -about the temperature of water from a hot water tap. -such temperatures can also be reached in sunlit soil and in thermal waters such as hot springs. -remarkably, many thermophiles CANNOT grow at temperatures BELOW about 45degrees.

mesophiles

-moderate-temperature-loving microbes -optimum growth temperature of 25-40degrees -the most common type of microbe -organisms that have adapted to live in the bodies of animals -include most of the common spoilage and disease organisms