MICR221 Exam Questions With Correct
Answers.
Describe the process of binary fission - answer1. Genetic material replicates itself while the
cell elongates
2. Genetic material migrates to either end of the cell and the septum begins to form
3. Septum then completely forms and the cell begins to...
Describe the process of binary fission - answer✔✔1. Genetic material replicates itself while the
cell elongates
2. Genetic material migrates to either end of the cell and the septum begins to form
3. Septum then completely forms and the cell begins to separate
4. Two identical daughter cells are formed
How does population growth occur? - answer✔✔Occurs through binary fission, cell number
increases exponentially
Define the mean generation time - answer✔✔MGT = time it takes for one cell (and therefore the
whole population) to divide
How is the arrangement of a bacterial cell determined? - answer✔✔Determined by the plane of
division in binary fission
Division in one plane - answer✔✔Dipplococcus (chains = streptococcus)
Division in many planes - answer✔✔Cluster
Why are bacterial cells small? - answer✔✔A smaller cell has a larger surface area to volume
ration which is advantageous - especially for diffusion
List the 4 physical factors of growth requirement - answer✔✔Gaseous atmosphere
Temperature
pH
Osmotic pressure
Describe aerobes - answer✔✔Require molecular oxygen
Carry out aerobic respiration, oxygen acts as the terminal electron acceptor (or some other
oxidant)
Describe anaerobes - answer✔✔Prefer the absence of oxygen
Uses the ETC but terminal electron is exogenous eg. Nitrate or Sulphate
Describe fermentation - answer✔✔Absence of oxygen
There is no electron transport chain, no generation of PMF
ATP is synthesised through substrate level phosphorylation, electron acceptor is endogenous
Describe facultative aerobes - answer✔✔Grow with or without oxygen
Describe microaerophiles - answer✔✔Require a little oxygen but not too much
2-10% ideal - less than atmospheric
>10% - harmful
Describe capnophiles - answer✔✔Capnophiles required increased amounts of oxygen
What microorganisms would be found at the very top of a tube? - answer✔✔Obligate aerobes,
require O2
+SOD, +catalase
What microorganisms would be found mostly at the top but some dispersed throughout the tube?
- answer✔✔Faculative aerobes, prefer O2
+SOD, +catalase
What microorganisms would be dispersed throughout the tube? - answer✔✔Aerotolerant
anaerobes, tolerate O2
+SOD, -catalase
What microorganisms would be found confined to the bottom of the tube? - answer✔✔Strict
anaerobes, toxic O2
-SOD, -catalase
What microorganisms would be found in a band near but not at the top of the tube? -
answer✔✔Microaerophiles, 2-10% O2
+SOD, low levels of catalase
Why is oxygen toxic to some microorganisms? - answer✔✔Oxygen can be converted to highly
reactive derivatives such as superoxide free radical = damaging to cells.
Why is oxygen not toxic to aerobes and facultative organisms? - answer✔✔These organisms can
convert the superoxide free radical to hydrogen peroxide (by superoxidedismutase) which is then
further broken down to HARMLESS PRODUCTS (by catalase or peroxidase).
Why is oxygen toxic to anaerobes? - answer✔✔Anaerobes do not possess the superoxidismutase
(SOD), catalase or peroxidase enzymes therefore cannot break down the DAMAGING
superoxide free radical to harmless products therefore they cannot tolerate oxygen.
Equations for the breakdown superoxide free radical - answer✔✔See book
Name 5 types of bacteria based on their temperature preference - answer✔✔-5 - 20 =
psychrophiles
-2.5 - 35 = psychrotrophs
15 - 45 = mesophiles
42 - 80 = thermophiles
68 - 108 = hyperthermophiles
Explain the effect of temperature on microbial growth - answer✔✔Cardinal temperatures = due
to the heat stability of proteins inside the cell, specific to each organism
Min temp = Growth no longer occurs, enter protective dormant phase, only some cell death,
transport of essential nutrients and enzyme reactions slow down
Optimum temp = MGT is shortest, fastest growth time, exponential increase in population
Max temp = Growth is no longer possible, enzymes denature resulting in cell death
What is the optimum pH range for bacterial growth? - answer✔✔6-9
Organisms found in extreme pH environments are most likely to be archaea
What is the significance of osmotic pressure as a physical growth factor? - answer✔✔Osmotic
pressure is determined by the number of molecules in solution, optimum when it is isotonic
(same as the surrounding medium)
Define hypertonic - answer✔✔High concentration of sugar or salt in external environment = will
cause water to move out of the cell
This can pull the plasma membrane away from the cell wall resulting in death by plasmolysis
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