Bio310 Microbiology Fall „07 Mock Exam Answers
This “exam” can be turned in for grading until Monday Sept. 24 2007
1.) (6 pts.) What is meant by the term “stellar synthesis” and why is it important to life
Stellar synthesis refers to the process of fusion and stellar core
collapse producing elements heavier than helium. These heavier
elements are essential components to life on Earth, Life would not
have been possible without them.
2.) (12 pts.) What are the four nutritional types for prokaryotes. For each nutritional
type state the primary energy source and carbon source.
Photoautotroph: Energy from sunlight, carbon from CO2
Photoheterotroph: Energy from sunlight, carbon from chemical
Chemoautotroph: Energy from chemicals, carbon from CO2
Chemoheterotroph: Energy from chemicals, carbon from chemical
3.) (8 pts.) Why don‟t we find too many large (Eukaryote sized) bacterial cells? What
force tends to select for smaller cells? Explain.
Prokaryotes rely on diffusion to move materials around within the cell, this limits
cell size. Both diffusion and rapid growth favor smaller cells.
4.) (8 pts.) Explain the principal of phase contrast microscopy.
Phase contrast utilizes the difference in refractive index between the sample and
the background to make the sample easier to see. This is done by breaking the light beam
into two paths, allowing one beam to interact with the sample and then recombining the
beams to allow interference (caused by light interacting with the sample through its
refractive index) to highlight cell edges (changes in refractive index).
5.) (6 pts.) Name two functions of the bacterial cytoskeleton.
The bacterial cytoskeleton is required for cell division and DNA segregation (cell shape
is the 3rd function).
6.) (12 pts.) We talked about several experiments which helped to disprove the idea of
“Spontaneous Generation”. Briefly describe one of these experiments. How does the
experiment serve to suggest that spontaneous generation doesn‟t work?
Redi, Spallazani, Schulze, or Pastuer experiments, must briefly
describe experiment AND connect results to S.P.
7.) ( 3 pts.) What type of microscopy would you use to identify surface features on a
diatom or other eukaryotic cell with a mineralized cell wall?
SEM best, darkfield would work.
8.) ( 4 pts.) What is the point of doing Kohler illumination in light microscopy?
To optimize illumination to make maximum use of available resolution,
also very critical for photomicroscopy. (note: does not increase resolution)
9.) (4 pts.) What important principal (important to modern medicine) did Paul Ehlich
develop while working in Koch‟s lab?
Chemotherapy, the idea that specific molecular toxins could be used to treat
parasitic disease (be careful, he never used the term “antibiotic”, that term was applied
1. ( 6 pts.) Explain the cell structure basis of the Gram stain.
Gram staining differentiates bacterial cells on the basis of the thickness of their
cell wall or peptidoglycan layer. Gram (+) cells have a thick peptidoglycan layer
which retains the purple Crystal Violet stain. Gram (-) cells have a thinner
peptidoglycan layer and lose the purple stain and are stained by the red
2. (8 pts.) Why is a “biased random walk” a reasonable solution to the problem of how
to get around if you are a bacterium (hint: think about bacterial chemotaxis)?
A bacterium has no external senses capable of determining an absolute
position, also due to Brownian motion a bacterium cannot travel in a
straight line for very long. So motion from “here to there” is not really
possible. A biased random walk involves lengthening forward motion in
one direction coupled with random reorientations to achieve net
displacement over time without requiring any knowledge of absolute
position. (there are a number of ways this could be worded, a diagram
with labels could also be used).