Chapter 7 Homework

The generation time of Mycobacterium tuberculosis is ______.

12 hours

During one cycle, the sodium-potassium pump binds and moves _______.

3 Na+ and 2 K+

Using the equation Nf = Ni (2n), determine how many Staphylococcus aureus cells are present in a custard tart under these circumstances. During preparation, 15 cells were deposited in the custard, and the tart has sat at room temperature for 5 hours. S. aureus has a generation time of 20 minutes.

4.9 x 105 cells

4. You ingest 20 cells of Salmonella. This bacterium has a doubling time of 30 minutes. After 4 hours, how many of these bacteria would be present in the body (assuming no immune system responses or other biological activities affect its growth)?

5,120

2. After six generations, how many bacteria would have formed from the reproduction of one bacterium?

64

Consider the following hypothetical conditions: A population of 10,000 bacteria has a doubling time of 20 minutes under a given set of growth conditions. The culture is allowed to grow for 2 hours. Select the number of bacteria that best predicts the population size at the end of the two hour incubation period. Assume there is no lag phase.

640,000

How many generations does it take for a single bacterial cell to become 256?

8

1. What is a biofilm?

A group of bacteria that accumulate in layers and secrete an protective extracellular material

2. Which of the following is an example of a biofilm commonly found in the human body?

Dental plaque

Choose the phase of the bacterial growth curve during which a bacterial population has the shortest doubling time.

Exponential growth phase

3. During the stationary phase, binary fission stops.

False

4. If you measure turbidity using a spectrophotometer during the death phase, the turbidity will be much lower than it was during the exponential phase.

False

What type of microbial association is depicted in this figure?

Parasitism

Move the terms to their correct descriptions to review the various nutritional categories of microbes.

Photoautotroph- Uses sunlight as an energy source and carbon dioxide as a carbon source (example: cyanobacteria) Chemoautotroph- Uses simple inorganic compounds for energy and carbon dioxide for a carbon source (example: methanogens) Photoheterotroph- Uses sunlight as an energy source and an organic carbon source (example: purple photosynthetic bacteria) Chemoheterotroph- Converts nutrients from other organisms into energy and uses an organic carbon source (example: protozoa) Saprobe- Metabolizes organic matter of dead organisms for energy and uses an organic carbon source (example: fungi) Parasite- Utilizes the tissues of a live host and an organic carbon source (example: pathogens)

3. What type of bacteria will grow in the refrigerator, and why is this usually not a concern?

Psychrophiles; very few are pathogenic to humans

3. Which enzyme is NOT involved in DNA replication?

RNA polymerase

Which of the following will pass through a cell membrane most easily?

Small nonpolar molecules

2. What factors can affect the doubling time of a bacterial cell?

Temperature Moisture pH Oxygen levels

The rate of diffusion is affected by which of the following?

Temperature, size of molecules, and steepness of the concentration gradient

Which of the following statements are not true about the sodium-potassium pump?

The ions in the extracellular fluid bind to the carrier protein, and the potassium attached to the carrier protein is released.

2. When you inoculate a fresh tube of broth medium, it doesn't instantly turn cloudy. Why is this?

There is lag phase before growth occurs at a level that is visible in the broth.

Select the statement that most accurately reflects biofilms.

They are associated with chronic ear infections.

1. If the doubling time of a bacterium is short, the x-axis of a population growth curve will have smaller numbers.

True

1. Most cultured bacteria tend to multiply by ______.

binary fission

Most bacteria increase their numbers by _____.

binary fission

1. Both human and bacterial cells divide by mitosis.

false

2. Cell division is triggered exclusively when cells attain a threshold mass.

false

3. DNA helicase is responsible for adding nucleotides to the growing end of the DNA.

false

3. Environmental factors control microbial growth through their influence on enzyme activity.

false

4. Cells cannot begin a new round of replication until they have completely finished dividing.

false

1. Most bacteria reproduce by _____.

fission

3. Individual bacteria (such as Salmonella) _______.

grow best at an optimum temperature and a range above and below it

2. The presence of microbes in food can be ______.

harmful beneficial neutral

A cell exposed to a hypertonic environment will _____ by osmosis.

lose water

Carbon, nitrogen, oxygen and hydrogen are considered _______ because they are required in relatively large quantities, whereas manganese, zinc, and copper are considered ______ because they are required in very small quantities.

macronutrients; micronutrients

1. Most of the microbiota in the human body are classified as _______.

mesophiles

A majority of medically important microbes are classified as ______.

mesophiles

Simple diffusion is defined as the movement of _______.

molecules from areas of higher concentration to areas of lower concentration

Diffusion of water through a selectively permeable membrane is referred to as ______.

osmosis

2. Cells must ______ their DNA prior to cell division.

replicate

A _____ derives its nutrients and energy from the organic matter of dead organisms, whereas a _____ lives in or on another living organism and derives its nutrients and energy from that living organism.

saprobe; parasite

1. The FtsZ protein is needed to form the _______.

septum

1. In the United States, the CDC estimates that ______ people suffer each year from some form of food-borne infection.

several million

3. Pathogens usually have ______ doubling times.

short

A red blood cell placed in a hypertonic medium will ______.

shrink

When sugar is mixed with water, equilibrium is reached when _______.

the dissolved sugar molecules are evenly distributed throughout the solution

2. The energy source for contraction of the FtsZ ring during cell division comes from _______.

the hydrolysis of GTP

3. The safe temperature ranges for the storage of foods are determined by _______.

the low temperature where microbes stop multiplying and the high temperature where they physically die.

If human red blood cells are placed in a vial of pure water, _______.

the net water movement is into the cell

4. The type of food-borne infection known as an intoxication is caused by _______.

toxins produced by microbes as they grow in the food

Another two-word term for micronutrients is ______.

trace elements

1. During binary fission, one bacterial cell becomes _______ cells.

two genetically identical

Osmosis is best defined as the movement of _______.

water molecules across a membrane from an area of high water concentration to an area of lower concentration

6. What is the effect of cold on a population of bacteria?

Cells survive but do not divide at temperatures below the minimum.

7. What food product is least likely to contain viable vegetative pathogens?

Chicken cooked to 170 degrees F

3. Bacteria that grow in oxygenated environments are referred to as ______.

aerobes

4. Bacteria that thrive in environments with a pH of greater than 7 are classified as ______.

alkalinophiles

Antibiosis is a form of ______.

antagonism

Which of the following statements are not true about the sodium potassium pump?

ATP is broken down into ADP and potassium to supply the energy.

3. Why are biofilms important in infectious disease?

Bacteria in biofilms are often protected from antibiotics.

What is the source of energy used to power the sodium-potassium pump?

Breakdown of ATP

5. What is the effect of heat on a population of bacteria?

Cells begin to die at a temperature slightly above the maximum.

Which of the following is true of passive transport?

It requires a gradient

What term describes an organism that lacks superoxide dismutase and catalase enzymes?

Obligate anaerobe

4. You leave your potato salad out on the table at the company picnic. When you made it, you unknowingly introduced 100 cells of Salmonella. How much time will it take for the population of Salmonella to reach at least one million if its doubling time is 20 minutes at picnic conditions?

Over 4 hours

Select the term that refers to a microbe able to survive very low pH conditions.

acidophile

The sodium-potassium exchange pump is an example of ______.

active transport

1. If conditions are favorable, the generation time of bacteria _______.

can be as short as 30 minutes

In terms of energy and carbon sources, deep-sea vent microorganisms and methanogens are most specifically classified as ______.

chemoautotrophs

In a viable count, each _______ represents a _______ from the sample population.

colony; CFU

The structure that divides the bacterial cell in two is termed the ______.

cross septum

The time required for one complete cycle of binary fission is known as the ______, or generation time.

doubling

2. Refrigeration will ______ the doubling time of most pathogens.

increase

A pathogen would most accurately be described as a ______.

parasite

An organism that can synthesize all its required organic components from CO2 using energy from the sun is a _______.

photoautotroph

The sodium-potassium pump functions to pump _______.

sodium ions out of the cell and potassium ions into the cell

2. The environmental factor that influences bacterial growth the most is ______.

temperature