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Micro Chapter 6
Terms in this set (56)
A cell duplicates its components and divides into two cells
A partition that grows between two daughter cells and they separate at this location
Unequal cell division
Cell division in yeast and few bacteria
A small new cell develops from surface of existing cell and separates from parent cell.
Bacterial Growth Curve
includes: lag phase, log phase, stationary phase, decline or death phase
Organisms do not increase significantly in number.
They are metabolically active.
Grow in size, synthesize enzymes and incorporate molecules from medium.
Produce large quantities of energy in form of ATP
Organisms have adapted to a growth medium
Growth occurs at an exponential (log) rate.
ORganisms divide at their most rapid rate
A regular, genetically determined interval (generation time)
Cell division decreases to a point that new cells are produced at the same rate as old cells die
The number of live cells stay constant
Condition in the medium become less and less supportive of cell division
Cells lose their ability to divide and die
Number of live cells decreases at a logarithmic rate.
The standard measurement used to describe bacterial growth is the number of ________ organisms per _________ of culture
Used to dilute the original bacterial culture before you transfer known volume of culture onto agar plate
A hypothetical situation in which the number of cells in a culture would increase in a stair-step pattern, dividing together at the same rate
A natural situation in which an actual culture has cell dividing at one rate and other cells dividing at a slightly slower rate.
Pour Plate Method
Made by first adding 1.0 ml of a diluted culture from a serial dilution to 9ml of melted nutrient agar
After the medium is mixed, it is poured into an empty petri plate
Once the agar medium cools, solidifies, and is incubated colonies will develop with in the medium and on its surface.
Cells suspended in the melted agar during prep may be heat damaged and then they will not form colonies
Those that do grow inside the agar will form smaller colonies than those growing on the surface.
The spread plate method eliminates problems like that because all cells remain on the surface of the solid medium.
A petri plate with a countable number of bacterial colonies should have between ___ and ___ colonies
30 and 300
Most Probable Number Method (MPN)
Method to estimate number of cells.
Used when samples contain too few organisms to give reliable measures of population size by standard plate count
Series of progressively greater dilutions.
Typical MPN test consists of 5 tubes of each of three volumes (eg. 10, 1, and 0.1 ml)
Instrument used to measure the turbidity in a bacterial culture.
This method is particularly useful in monitoring the rate of growth without disturbing the culture
Do all bacteria grow at same pH or temp?
No, according to their tolerance for acidity/alkalinity bacteria are classified as either acidophiles, neutrophils, and alkaliphiles which affects the growth and how they act in bacteria
Optimal pH 0.1-5.4
Lactobacillus- produces lactic acid but tolerates only mild acidity
Optimal pH 5.4-8.0
Optimal pH 7.0-11.5
Temperature - Obligate
Organism must have specified environmental condition
Temperature - Facultative
Organism is able to adjust to and tolerate environmental condition, but can also live in other conditions
Organism must have specified environmental conditions
The organism is able to adjust to and tolerate the environmental condition, but it can also live in other conditions (15-20*)
Include most bacteria
Grow best at temperatures between 25
Can grow only at temperatures above 37*
Can grow both above and below 37*
True or False most bacteria that live in the human body are psychrophiles
Killed by free oxygen (bacteria at bottom of tube)
Must have free oxygen for aerobic respiration
(bacteria top of tube)
Grow best in presence of small amount of free oxygen (small amount of bacteria in middle of tube)
Carry on aerobic metabolism when oxygen is present but shift to anaerobic metabolism when oxygen is present, but shift to anaerobic metabolism when oxygen is absent (bacteria all over tube)
Salt-loving organisms which require moderate to large quantities of salt (sodium chloride)
Membrane transport systems actively transport sodium ions out of cells and concentrate potassium ions inside
Found in great salt lake in utah and the dead sea
Cells need sodium to maintain a high intracellular potassium concentration for enzyme function- also to maintain in integrity of cell wall
Microbes that have special nutritional needs that can be difficult to meet in the lab.
Some including those that cause gonorrhea grow quite well in the human body but still cannot be easily grown in a lab on nutrient media
Ex: copper, iron, zinc, cobalt
often serve as cofactors in enzymatic reactions
potassium, zinc, magnesium, and maganese are used to activate certain enzymes.
Cobalt is required by organisms that synthesize vitamin B12
The formation of endospores in bacillus, clostridium and a few other gram positive genera
It is protective or survival mechanism, not a means of reproduction
As this begins DNA is replicated and forms a long, compact, axial nucleoid
Pure Culture Methods
Pure culture of a single species is needed to study an organisms characteristics
Water in oceans and lakes exrts pressure exerted by standing water, in proportion to its depth
Pressure doubles with every 10 meter increase in depth
Bacteria that live at high pressures, but die if left in lab at standard atmospheric pressure
Environments that contain dissolved substances exert osmotic pressure, and pressure can exceed that exerted by dissolved substances in cells
Cells lose water and undergo plasmolysis (shrinking of cell)
Cells gain water and swell and burst
Production of enzymes that are released through cell or plasma membrane
Usually produced by gram-prositive rods, which act in the medium around the organism
Usually produced by gram-negative organisms, which act in the periplasmic space
Streak Plate Method
Bacteria are picked up on a sterile wire look and the wire is moved lightly along the agar surface depositing streaks of bacteria on the surface.
The inoculating loop is flamed and a few bacteria are picked from the region already deposited and streaked onto a new region.
Fewer and fewer bacteria are deposited as the streaking continues and the loop is flamed after each streaking
Encourages growth of some organisms but suppresses growth of others
ex: antibiotics, clostridium botulinium
Contains a constituent that causes an observable change
ex: clostridium botulinium
Contains special nutrients that allow growth of a particular organism that might not otherwise be present in sufficient numbers to allow it to be isolated and identified
Ex: salmonella typhi
How Obligate Anaerobes can be cultured
All molecular oxygen must be removed and kept out of medium.
Agar plates are incubated in sealed jars containing chemical substances that remove oxygen and generate carbon dioxide or water
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