Microbiology Chapter 4 Part 1 HW

Place the nine steps of the dilution streaking technique in the correct order. - Remove a sample of bacteria from the culture flask (of plate) using the sterile loop. - Flame the loop a third time and allow it to cool. - Inoculate a section of your agar petri dish by sweeping the loop back and forth across the surface. - Using the loop, draw cells from the second area onto another fresh section of agar. - Sterilize the loop (an allow it to cool) before using it to obtain the bacterial inoculum. - Sterilize the loop for a final time. - Using the loop, streak cells from the first area onto a fresh section of agar. - Place the petri plate in the appropriate incubator. - Flame the loop a second time and allow it to cool.

1. sterilize the loop ( & allow to cool), use it to obtain bacterial inoculum 2. remove sample bacteria from culture flask/plate using sterile loop 3. inoculate section of agar petri dish by sweeping loop back & forth across surface 4. flame loop 2nd time & allow to cool 5. using loop, streak cells from 1st area onto fresh section of agar 6. flame loop 3rd time & allow to cool 7. using loop, draw cells from 2nd area onto another fresh section of agar 8. sterilize loop final time 9. place correct petri dish plate in incubator

Which of the following statements is true? Choose one: A. All organisms require carbon as a macronutrient. B. Most bacterial species can be cultured in the lab. C. Bacterial species use a limited number of nutrient sources. D. All bacterial species require the same nutrients for growth.

A Bacteria have evolved to be able to use a wide variety of different compounds as nutrient sources and may have different essential nutrient requirements. Many bacteria are unculturable if their specific requirements are not met in the laboratory or if their niche cannot be readily recreated, such as in the case of intracellular parasites. Carbon is the basis of organic compounds and is a macronutrient for all life forms.

Cellular synthesis of which of the following would be directly affected by nitrogen limitation? Choose one or more: A. Amino acids B. Nucleotides C. Fatty acids D. Simple sugars

A & B Because amino acids each have a nitrogen-containing amine group (-NH2), and nucleotides each contain a nitrogenous base joined to a 5-carbon sugar and phosphate group, these both require nitrogen for synthesis. Thus, they would be directly affected by nitrogen limitation.

Which of the following are characteristics of facilitated diffusion?Choose one or more: A. It involves substrate-specific carrier proteins. B. It only operates unidirectionally (to move solutes into the cell). C. It represents an important uptake system for bacteria living in dilute aquatic environments. D. Solutes are chemically modified (such as by addition of a phosphate group) as they enter the cell. E. It cannot internally concentrate a solute relative to the external environment. F. It does not require energy expenditure by the cell.

A, E, & F Facilitated diffusion contributes to the selective permeability of the membrane by allowing entry of substrates that would not otherwise freely move across the lipid bilayer. Specific carrier proteins are needed that facilitate the bidirectional movement of solutes along its concentration gradient.

Bacteria as a group are incredibly metabolically diverse, but individual species are often highly specialized to reduce competition in their natural environment. This results in these species being unculturable because Choose one: A. trace elements in the water used in the laboratory prevent their growth. B. their growth may depend on necessary growth factors provided by other organisms in their natural environment. C. components in laboratory media are toxic to them. D. they cannot tolerate oxygen.

B Growth factors are specific nutrients required by a species but not by others; they may be products of other organisms' metabolism and thus would not be provided in the laboratory. Meanwhile, anaerobes can be cultured under proper conditions. And though some media can have toxins present either from the media or the water used to produce them, it is possible to tailor recipes for fastidious microbes.

The major factor limiting bacterial growth in nature is Choose one: A. space. B. nutrients. C. antibacterial agents. D. temperature extremes. E. oxygen.

B The ability to find and acquire sufficient nutrients for growth is the major challenge faced by microorganisms.

Organisms that need to ingest reduced carbon are called Choose one: A. autotrophs. B. heterotrophs. C. lithotrophs. D. phototrophs.

B While autotrophs are self-feeding (meaning they assimilate CO2 as a carbon source, reducing it to make cell constituents), heterotrophs need to ingest reduced carbon. Lithotrophs generate ATP from reduced inorganic compounds, and phototrophs generate ATP using light. Lithotrophs and phototrophs may be either autotrophs or heterotrophs.

The dilution streaking technique can take a bit of practice to master. Which of the following represent sources of error that would likely result in failure to obtain isolated colonies? Choose one or more: A.forgetting to sterilize the loop prior to obtaining the inoculum B. flaming the loop immediately after obtaining the bacterial sample C. forgetting to flame the loop before streaking sequential sections of the plate D. allowing the loop to cool for too long before proceeding E.not creating a small section of overlap across sequential sections

B, C, & E It is important to remember to flame your loop between sections and allow it to cool sufficiently before contacting the cells again. Also, a small amount of overlap between sequential sections is necessary if the cells are to be "diluted" onto a fresh secton of agar. Finally, always remember to incubate your plate at the appropriate temperature for the cells to grow into colonies.

Which of the following is true of complex media? Choose one: A. Complex media can help determine the metabolic capacity of an organism. B. All the components and their concentrations are known. C. Bacteria grow faster on complex media than on synthetic media. D. Complex media are the most difficult of all to prepare.

C Complex media provide many of the chemical building blocks that a cell would otherwise have to synthesize on its own. Hence, they grow faster on complex media. Complex media are poorly defined, nutrient-rich media. They are usually easier to prepare than precisely defined synthetic media. Defined synthetic media can be used to help determine the metabolic capacity of an organism. For example, a specific amino acid or vitamin can be added to synthetic media to support the growth of organisms that lack the ability to produce it.

A complex medium is one that Choose one: A. is designed to specifically inhibit the growth of either Gram-negative or Gram-positive cells. B. contains specified amounts of five to ten known chemical components. C. is nutrient-rich, but the amounts and identity of specific nutrients are unknown. D. distinguishes among microorganisms based on some enzymatic or metabolic ability. E. is difficult and time consuming to make.

C Ingredients in complex media may include digests of yeast cells, animal proteins or tissues, and so on.

While adding nutrients to a culture medium in a glass container, which of the following would LEAST likely need to be added?Choose one: A. Nitrogen B. Magnesium C. Zinc D. Phosphorous

C Magnesium, nitrogen, and phosphorous are all macronutrients and would be needed in larger quantities than the micronutrient zinc.

The dilution streaking technique is probably the most common procedure performed by microbiologists on a daily basis. It is not, however, particularly useful for Choose one: A. isolating colonies from a mixed culture containing different bacterial species. B. transferring bacteria from a petri plate (as opposed to liquid culture as shown in the video). C. calculating the concentration of viable cells in a culture. D. culturing bacteria that stick together or grow as chains or clusters (such as Streptococcus and Staphylococcus).

C This technique is not quantitative.

Which of the following would not be included in the formulation of a defined medium? Choose one: A. potassium phosphate B. glucose C. tryptone D. magnesium sulfate E. sodium chloride

C Tryptone is a pancreatic digest of milk proteins. It provides a good source of amino acids and peptides for bacterial growth. The exact composition is unknown.

The composition and health effects of the human microbiome are currently topics of extensive interest and research. For example, it is becoming increasingly apparent that the initial development of a robust intestinal microflora is dependent on many factors in a newborn's life, beginning with the mode of delivery (vaginal vs. cesarean section). Other potential influences include premature birth, exposure to antibiotics, and even mode of feeding. Suppose you were interested in the effect of breastfeeding versus formula feeding on the composition of gut flora in newborns. As part of your experiment, stool samples from healthy babies in the study get plated on various agar media. You notice that greater numbers of colonies are recovered when samples are plated on blood agar compared to Luria Bertani (LB) agar. After some diligent subculturing, you isolate several bacterial species capable of slow growth on the blood but not on the LB agar. You correctly surmise that these organisms Choose one: A. should be classified as beta-hemolytic. B. are Gram-positive and, thus, inhibited by the ingredients in LB agar. C. are opportunistic blood pathogens. D. have extensive and complex nutritional requirements not met by LB agar. E. grow because the blood agar suppresses the growth of faster-growing bacteria.

D Blood agar is an example of an enriched medium and is useful for cultivating certain bacteria (especially those that have become dependent upon a host organism) that are unable to grow on a regular complex medium such as LB.

An essential nutrient is one that Choose one: A. is not needed by the bacteria for proper growth. B. is always plentiful in the environment. C. bacteria need for proper growth and can make themselves. D. bacteria need for proper growth but cannot make themselves.

D Essential nutrients are needed for proper bacterial growth and must be acquired from the environment, where they may or may not be plentiful.

Why are elements such as cobalt, copper, manganese, molybdenum, nickel, and zinc referred to as micronutrients? Choose one: A. They are required by microscopic organisms but not by most macroscopic organisms. B. If present, these will enhance growth, but they are not required. C. Care must be taken to add each of these elements to bacterial growth media. D. All cells require these elements in trace amounts. E. Their atomic numbers are lesser than those of most other nutrients.

D Yes, these elements are required by all cells, but they needn't be added to culture formulations; sufficient levels are found in the water and glassware used to prepare media.