Exam 1 Flashcards
We wished to determine the abundance of bacteria in a sample of milk. To do this ten-fold serial dilutions of a one milliliter milk sample were prepared. One milliliter of the fourth dilution was plated in a pour plate. After incubation, the plate had 32 colonies. How many bacteria were in the original milk sample?
320,000 cells per ml
Which of the following statements is/are correct?
A. Flagella allow bacteria to glide on surfaces
B. Flagella allow bacteria to swim
C. The directed movement of bacterial cells in response to a gradient of a chemical, is called chemotaxis
Flagella allow bacteria to swim and The directed movement of bacterial cells in response to a gradient of a chemical, is called chemotaxis
Bacteriostatic compounds
are biological or chemical agents that stop bacteria from reproducting
An isolated colony on a streak plate typically contains millions of cells that are the progeny of a single cell
this is a true statement
Toxic hydrogen peroxide produced in some bacteria can be broken down into water and oxygen by which enzyme
catalase
Which of the following is NOT likely to be a reason for why exponential growth stops in bacterial cultures grown in a lab? A. accumulation of waste products B. exhaustion of nutrients C. harmful changes in pH D. Bacteria becoming dormant
bacteria becoming dormant
which of the following are required for microbial cell growth?
A. Reduced cofactors
B. anabolic intermediates
C. Energy conserved in chemical bonds.
all,
A. Reduced cofactors
B. anabolic intermediates
C. Energy conserved in chemical bonds.
The growth of almost all bacteria in the environment
is typically limited by the availability of one or more nutrients
Antoni can Leeuwenhoek developed and used
a microscope with a single lens to view bacteria
the cell membrane of bacteria
is semi permeable and is usually a lipid bilayer
prokaryotes and eukaryotes
have many things in common because they share a common ancestor
Penicillin interferes with bacterial cell growth by
inhibiting the formation of shor polypeptide crosslinks between strands of polysaccharide in peptioglycan that re made of repeated units of Nacetylglucosamine (NAG) linked to N-acetylmuramic acid
Bacterial cells reproduce by binary fission, which results in exponential growth of the population. If the size of a bacterial population at time zero (t0) is 20 cells and the generation time is 30 minutes, how many cells will be in the population after 3 hours of growth?
1280 cells
There are similarities and differences between gram negative and positive bacteria. Which of the following is not true?
A. The cell wall of Gram-negative cells is composed of only one or two layers of peptidoglycan whereas the cell walls of Gram-positive bacteria have many peptidoglycan layers.
B. Only gram positive bacteria have lipopolysaccharide that extends out the cell surface
C. The cell membranes of both Gram-negative and Gram-positive bacteria are lipid bilayers.
D. There is a second membrane (called the outer membrane) just outside the cell wall of Gram-
negative bacteria, but this is absent from Gram-positive bacteria.
Only Gram positive bacterial calls have lipopolysaccharide that extends out the cell surface.
Which of the following statements about phospholipids is true?
a. They are comprised of molecules that are entirely hydrophilic.
b. They are comprised of molecules that are entirely hydrophobic.
c. They are the principle components of bacterial cell membranes.
d. have “heads” and “tails” that both have phosphate groups.
They are the principle components of bacterial cell membranes
Approximately two billion years ago, ______ were primarily responsible for initially oxygenating earth
cyanobacteria
Koch’s postulates
are steps that must be followed to determine the cause of an infectious disease
gram-positive bacteria
- have a thick cell wall which retains crystal violet dye
- contain teichoic acid in their cell walls
- appear purple when gram stained
The cell envelope of Gram negative bacteria
includes both an inner and outer membrane and includes a peptidoglycan layer
Archaea and bacteria are unified as prokaryotes in lacking
nuclei and membrane enclosed organelles
when a bacterial culture contains only one type of organism it is called a _____
pure culture
Which of these are routinely used to obtain a pure culture of bacteria
agar streak plates
pasteurization requires
the use of heat to kill most of the microorgamisms present in liquids
bacterial growth is usually graphed using ____
a semi logarithmic plot
most bacteria reproduced by
binary fission
the lipopolysaccharide (LPS) layer is found ONLY in the cell surface of
gram negative bacteria
what are environmental factors that influence microbial growth?
oxygen, temperature, osmotic pressure, the kinds and concentrations of available nutrient
generation time can best be defined as
the time it takes for a cell to divide
Today the enrichment culture technique developed over a century ago by Martinus Beijerinck remains a feasible approach to obtain bacterial populations that are able to degrade chemicals that are environmental pollutants.
True
The “plate count anomaly” refers to the fact that the number of bacteria seen in a sample using microscopy is less than the actual number of cells in the sample.
False
Aseptic techniques are a collection of practices that prevent contamination of cultures.
True
Not only do some microorganisms tolerate extremely hot temperatures, some actually require high temperatures for optimal growth.
Ture
The largest mass of living material on Earth comes from microorganisms.
True
Gelatin is the solidifying agent that is most widely used in bacteriological growth media.
False
According to our present understanding, each of the three major domains of organisms has what is known as its own universal ancestor.
true
By using swan-necked flasks Pasteur was able to prove the theory of spontaneous generation.
False
