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27 Cards in this Set

  • Front
  • Back
Microbial Growth
Refers to an increase in the # of cells, not the size of a cell.
Mother (Parent) Cell
Duplicates its contents and doubles in size

Divides into 2 daughter cells
Cell Division
Occurs by binary fission or budding
Binary Fission
Most bacteria...
- Cell duplicates its components and divides into two cells
- Daughter cells become independent when a septum grows between them and they separate
Mainly in Yeast
- A small new cell develops on the surface of an existing cell and subsequently separates.
Bacterial Cell Division
Prokaryotic cells do not have a cell cycle with a specific period for DNA synthesis
Bacterial Cell Division (2)
Continuously dividing cells replicate the single bacterial chromosome shortly before division

Chromosome is attached to the cell membrane
- Grows and separates the replicated chromosome
Bacterial Cell Division (3)
Cell temporarily may have 2 nucleoids

May have incomplete seperation
- Diplo, strepto, tetrads, sarcinae, staphylo
- Some always form the above shapes, some do so under certain conditions
Phases of Growth (l)
Lag Phase
-organisms do not increase in number, but are metabolically active
Phases of Growth (2)
Log Phase
-Once organisms are adapted, population growth is exponential or logarithmic
-cells are dividing at their most rapid rate
-Best time to identify Bacteria shape
Phases of Growth (3)
Generation Time
- the time it takes to double the population
- can vary from 20 minutes to 20 hrs most are under 1 hr
Phases of Growth (4)
Stationary Phase
- as growth increases exponentially, nutrients are used up, resources get tight, new cells are produced at the same rate as cells die off, numbers stay constant
Phases of Growth (5)
Death Phase
- conditions worsen, the number of live cells decreases at a logarithmic rate

- Cells assume unusual shapes, difficult to identify, pleiomorphic
- Never do stains on an old culture, best to use log phase growth
Serial Dilution
Successive 1:10 dilutions of a liquid culture are made and then transferred to an agar plate to grow and be counted
- Direct microscopic counts
- Most probable number technique
- Filtration
- Measurement of turbidity
- Measurement of metabolic products
- Dry weight
Phases of Growth: Solid Media
- a group of descendants of an original cell
- after growing exponentially, the organisms at the edges continue to divide rapidly while the ones in the middle stop growing or die
Phases of Growth: Solid Media (2)
All phases of the growth curve occur simultaneously in a colony
Physical Requirements for Growth
Hydrostatic pressure
Osmotic pressure
A must for bacteria, only spores survive in a dry environment
Bacteria that must have high pressure in order to live
between pH 5.4-8.5
most pathogens
between pH .1-4
Lactobacillus; Helicobacter pylori (Single most cause of ulcer)
between pH 7.0-11.5
Vibrio Choleraie grows at pH 9
- Minimum, optimum, and maximum temperatures
- Optimum temperature for growth is usually near the maximum temperature
Grow just below 0 degrees Celsius-20 degrees Celsius

Obligate - cannot grow above 20 degrees Celsius
Most bacteria
25-40 degrees Celsius
Grow best at 50-60 degrees Celsius some as high as 110 degrees Celsius

Obligate only about 27 degrees Celsius

Facultative above and below 37 degrees Celsius

More common than psychrophiles

Grow well at refrigerator temperature (Do not actually grow well at the low temp, but grows better than others)

Cause low-temp food spoilage

Over time degrade food
Most microbes survive even subfreezing temps
Food Spoilage
Oxygen Metabolism
Obligate aerobes
Facultative anaerobes
Obligate anaerobes
Facultative Anaeroves
Aerotolerant anaerobes