Microbio Ch. 6 Questions 1-28
14. Which microorganisms tend to grow well in an acidic environment? Which do not?
Acidophiles and chemoautotophic bacteria grow well in an acidic environment, molds and yeasts will to. Most bacteria do not grow well in an acidic environment.
23. What are facultative halophiles?
Do not require high salt concentrations but are able to grow at salt concentrations up to 2%, a concentration that inhibits the growth of many other organisms.
21. What are extreme halophiles?
Organisms that have adapted so well to high salt concentrations that they actually require them for growth.
22. What are obligate halophiles?
Organisms that need high salt concentrations to grow because they have adapted so well to it.
2. What conditions lead to microbial growth? On what does it depend?
Physical and chemical are the two main categories required for microbial growth. Physical aspects include temperature, pH, and osmotic pressure. Chemical requirements include sources of carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements, and organic growth factors.
28. What does nitrogen do in the cell?
Primarily to form the amino group of the amino acids of proteins. Other bacteria use nitrogen from ammonium ions (NH4+), which are already in the reduced form and are usually found in organic cellular material. Still other bacteria are able to derive nitrogen from nitrates (com- pounds that dissociate to give the nitrate ion, NO3−, in solution). Some important bacteria, including many of the photosyn- thesizing cyanobacteria (page 137), use gaseous nitrogen (N2) directly from the atmosphere. This process is called nitrogen fixation. Some organisms that can use this method are free- living, mostly in the soil, but others live cooperatively in symbiosis with the roots of legumes such as clover, soybeans, alfalfa, beans, and peas. The nitrogen fixed in the symbiosis is used by both the plant and the bacterium
4. What are psychrophiles, psychotophs, mesophiles, thermophiles, and hyperthermophiles?
Psychrophiles: cold-loving microbes Psychrotrophs: low-temperature food spoilage, grow well at refrigerator temps Mesophiles: moderate-temperature-loving microbes Thermophiles: heat-loving microbes Hyperthermophiles: Optimum growth temp of 80 degrees Celsius
3. What are the physical requirements for microbial growth?
Temperature—bacteria are able to grow well at the temps. humans favor, however they are able to grow at extreme temperatures that would hinder almost all eukaryotic organisms. pH—most bacteria grow best in a narrow pH range near neutrality, between 6.5 and 7.5. Very few bacteria grow at an acid pH below about pH 4. Osmotic Pressure—Microorganisms obtain almost all their nutrients in solution from the surrounding water. Thus, they require for growth, and their composition is 80-90% water. High osmotic pressures have the effect of removing necessary water from a cell.
18. How does a hypertonic environment affect the growth of a cell?
The cellular water passes out through the plasma membrane to the high solute concentration—causes osmotic loss.
24. What happens if high concentrations of agar are used in media?
The increases osmotic pressure can inhibit the growth of some bacteria.
1. Define microbial growth.
The number of cells, not the size of cells. Microbes that are "growing" are increasing in number, accumulating into colonies of hundreds of thousands of cells or populations of billions of cells.
16. What is osmotic pressure? What is it a measure of?
The pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.
15. What are buffers and why are they important?
They neutralize the acids and maintain the proper pH, chemical buffers are included in the growth medium.
13. Why is an acidic environment important?
Very few bacteria frown at an acidic pH below about pH 4, thus inhibiting their growth.
25. What happens when a cell is in distilled water?
Water tends to enter the cell rather than leave it.
8. What effect does volume have on the cooling rate of food in the refrigerator? Why is that important?
When large amounts of food must be refrigerated, it is important to keep in mind the slow cooling rate of a large quantity of warm food. The larger the volume, the slower the cooling rate. It is important because the less volume there is, the faster it will cool; therefore, it will greatly slow growth of most spoilage and disease organisms.
20. Why is sugar used as a preservative?
It draws water out of any microbial cells that are present, and thus prevents their growth.
19. Why is salt used as a preservative?
It results in increasing osmotic pressure that preserves foods. It draws water out of any microbial cells that are present and thus prevent their growth.
6. How does low temperature affect microbial growth? Why?
Low temperatures decrease microbial reproduction rates, which is the basic principle of refrigeration. There are always some exceptions to the temperature responses shown here; for example, certain bacteria grow well at temperatures that would kill most bacteria, and a few bacteria can actually grow at temperatures well below freezing.
9. How could mesophiles cause disease in food that is refrigerated?
Mesophiles are an organism that has adapted to live at an optimum temperature that is close that that of their hosts. It is able to produce toxins which can contaminate the food.
5. Define minimum growth temperature, optimum growth temperature, and maximum growth temperature?
Minimum growth temperature: the lowest temperature at which the species will grow Optimum growth temperature: the temperature at which the species grows best Maximum growth temperature: the highest temperature at which growth is possible
11. What is pH? What does it represent?
pH stands for possible hydrogen. pH regers to the acidity or alkalinity of a solution.
10. What is special about thermophile endospores?
Are unusually heat resistant and may survive the usual heat treatment given canned goods. Although elevated storage temperatures may cause surviving endospores to germinate and grow, thereby spoiling the food, these thermophilic bacteria are not considered a public health problem.
12. What are acidophiles?
Bacteria that are remarkably tolerant of acidity.
27. What is carbon used for?
Carbon is the structural backbone of living matter; it is needed for all the organic compounds that make up a living cells.
26. Name the elements that are necessary for microorganisms to live
Carbon, Nitrogen, Sulfur, Phosphorus, Trace elements, Oxygen, and organic growth factors.
7. When cooling, why can food have growth some of the time but not all of time?
Depending on the volume(less volume) ; the bacteria will become dormant and not grow. Sometimes bacteria will be able to slowly degrade food, and sometimes some bacteria are able to survive in cooler temperatures. Also, some species decline faster than others.
17. What is plasmolysis?
Shrinkage of the cell's cytoplasm. (This is caused by osmotic loss)
