Question 1

A medium that inhibits the growth of organisms other than the one being sought is termed a(n)

Accepted Answer

A selective medium is designed to allow the growth of only certain microorganisms, inhibiting the growth of others. This is useful when trying to isolate a specific organism from a mixed culture.

Question 2

Agar replaced gelatin as the gelling (solidifying) agent for media because

Accepted Answer

Agar is preferred over gelatin as the gelling agent for media because much fewer bacteria can break down agar than gelatin, making it more stable for bacterial growth. Additionally, agar is solid at body temperature, which allows for easier handling and transport of bacterial cultures.

Question 3

Agar

Accepted Answer

Agar has chemical and physical properties that make it almost ideal for solidifying media. It stays solid at a wide range of temperatures, is transparent which allows visualization of bacterial growth, and is not metabolized by most bacteria, making it a useful solidifying agent in microbiology.

Question 4

In the cultivation of microaerophilic and anaerobic bacteria,

Accepted Answer

In a candle/anaerobe jar, the candle consumes the atmospheric oxygen and produces carbon dioxide and water by combustion. This results in a reduced oxygen atmosphere that is suitable for the growth of microaerophilic and anaerobic bacteria.

Question 5

Candle jars are usually used to

Accepted Answer

Candle jars are designed to provide an atmosphere with a certain level of carbon dioxide (CO2) which can enhance the burning of candles and create a more pleasant atmosphere for the user. This can also provide a certain mood and feel to the space it is used in. It is not used to stimulate or prevent the growth of any bacterial species.

Question 6

Peptone

Accepted Answer

Peptone is a hydrolysate of proteins that is commonly used in growth media for microorganisms. It is produced by the partial hydrolysis of proteins, usually from animal sources such as beef, casein, or soy. It provides a rich source of amino acids and peptides that can be used as a nutrient source for microorganisms.

Question 7

You are a microbiologist working for a pharmaceutical company and discover a new secreted metabolite that can serve as a medication. Your company asks you to oversee the production of the metabolite. Which of the following is something that is NOT important to consider if you need to grow 5,000 liter cultures of bacteria for the purpose of harvesting the metabolite they secrete?

Accepted Answer

The death rate of the bacteria after stationary phase is complete may not be important for the purpose of harvesting the metabolite they secrete, as long as the cells are still producing the desired compound at that point. However, it may be important to consider for other applications, such as maintaining a sustainable culture for long-term use.

Question 8

A microbe is discovered growing near a deep sea thermal vent. When researchers bring a sample up to the surface and try to grow it in a lab at room temperature in a normal incubator, they are unsuccessful. Why?

Accepted Answer

The answer of A microbe is discovered growing near a...

Question 9

Products which limit pH changes are often incorporated into media and are referred to as

Accepted Answer

Buffer solutions are used to prevent drastic pH changes in a chemical reaction or biological system. These buffers contain a weak acid and its corresponding conjugate base or a weak base and its corresponding conjugate acid. They are designed to resist changes in pH when small amounts of an acid or base are added to the system. Enzymes are biological catalysts, bases are substances that can accept protons (H+) in a reaction, and acids are substances that can donate protons (H+) in a reaction.

Question 10

Secondary metabolites may be antibiotics.

Accepted Answer

Secondary metabolites are often produced by microorganisms as a defense mechanism against other microorganisms or organisms. Some of these compounds can act as antibiotics, inhibiting the growth of bacteria or fungi. Examples include penicillin, produced by the fungus Penicillium, and streptomycin, produced by the bacterium Streptomyces.

Question 11

Medically important bacteria are often

Accepted Answer

Medically important bacteria are often grown on agar containing blood and at 37°C because this temperature mimics the human body temperature, allowing for optimal growth of the bacteria. The addition of blood to the agar provides nutrients for the bacteria and can also help to distinguish between different species based on their ability to hemolyze (break down red blood cells). While agar containing chocolate may also be used for some medically important bacteria, it is not as commonly used as blood agar. Growing bacteria at a pH of 5 is not typical for medically important bacteria, as most prefer a neutral or slightly acidic pH.

Question 12

Prokaryotes are the only organisms able to use atmospheric nitrogen as a nitrogen source.

Accepted Answer

Prokaryotes, specifically nitrogen-fixing bacteria, have the ability to convert atmospheric nitrogen into a form that can be used by themselves and other organisms. Other organisms, including eukaryotes, rely on the nitrogen cycle and the availability of nitrogen compounds in the soil or water.

Question 13

MacConkey agar is

Accepted Answer

MacConkey agar is both selective and differential. It is selective for gram-negative bacteria and differential for lactose fermentation. The agar contains crystal violet and bile salts which inhibit the growth of gram-positive bacteria. Additionally, it contains lactose and neutral red which allow for the differentiation between lactose-fermenting bacteria (pink or red colonies) and non-lactose fermenters (colorless or pale colonies).

Question 14

In microbiology, growth usually refers to an increase in size of the bacteria.

Accepted Answer

In microbiology, growth usually refers to an increase in the number of bacteria, not necessarily their size.

Question 15

Freezing is an effective means of destroying bacteria.

Accepted Answer

Freezing can prevent bacterial growth but it does not necessarily destroy all bacteria present. Some bacteria can survive and become active again once they are thawed.

Question 16

There are 5 stages of growth in an open system of culture.

Accepted Answer

There is no established framework for the stages of growth in an open system of culture. Different models may propose different number of stages, and there may be variations based on the specific cultural context being analyzed.

Question 17

It is assumed that every colony observed on a streak plate arose from a single bacterium.

Accepted Answer

The purpose of streaking a plate is to obtain isolated colonies, which arise from a single bacterium that has undergone multiple rounds of division. It is assumed that each colony on the streak plate originated from a single bacterial cell.

Question 18

Differential media only allows certain bacteria to grow.

Accepted Answer

The answer of Differential media only allows certain bacteria to...

Question 19

A single bacterial cell may multiply to form a visible colony.

Accepted Answer

This is true. Under favorable conditions, a single bacterial cell can go through multiple rounds of cell division and create a visible colony of millions of cells in just a matter of hours or days.

Question 20

One would expect most strict anaerobic organisms to have superoxide dismutase.

Accepted Answer

Strict anaerobic organisms are adapted to survive in oxygen-deprived environments and do not require superoxide dismutase as they do not produce superoxide radicals, which are byproducts of aerobic metabolism. Instead, these organisms often have other enzymes such as ferredoxins and pyruvate:ferredoxin oxidoreductases to deal with the intermediate products of metabolism in anaerobic conditions.

Quiz 4: Dynamics of Prokaryotic Growth