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level: Level 1

Questions and Answers List

level questions: Level 1

Question	Answer
1.Lag Phase 2.Log Phase 3.Stationary phase 4.Death phase	Phases of Growth (4)
Bacteria are first introduced and ‘check out’ environment. Cells very metabolically active. Number of cells changes very little. 1 hour to several days.	Lag phase
Rapid cell growth (exponential). Population doubles every generation. Microbes sensitive to adverse conditions.	Log phase
Death rate=death of reproduction. Cells begin to encounter environmental stress (endospores would form now)	Stationary phase
Death rate>rate of reproduction due to limiting factors in environment. Decline phase.	Death phase
Lack of nutrients, water, space. Presence of metabolic waste. Oxygen and pH	Environmental stress conditions
a resistant asexual spore that develops inside some bacteria cells.	Endospores
pH, moisture content, oxidation-reduction potential, nutrient content, antimicrobial constituents, biological structures.	Factors affecting growth (8)
Effects enzymes and nutrients. No know pathogen grows below pH 4.6	pH
Most fresh foods Aw>0.99	Moisture
Remove or bind water	Humectants
thrive in high salt conditions	Halophilic bacteria
tolerate high osmotic pressure	Moderate or facultative halophiles
require high osmotic pressure	Extreme or obligate halophiles
-0.61. Can thrive in low Aw	Xerophilic moulds
-0.83 Adapts to high salinity	Halotolerant (haloduric)
0.61 Adapted to high sugar or high salt conditions	- Osmophilic yeasts
Tolerant of high osmotic pressure	Osmotolerant
0.86	Lowest Aw for pathogen growth
the process in which cells lose water in a hypertonic solution	Plasmolysis
Ease at which the substrate loses of gains electrons	Oxidation/reduction potential
Cold loving. 0C-20C	Psychrotrophs
Moderate temps. 20C-40C	Mesophile
Heat loving. 40C-100C	Thermophiles
Endure cold	Psychroduric
Endure heat	Thermoduric
Needs oxygen for growth	Obligate aerobe
Oxygen required at levels below 0.2atm	Microaerophile
Can’t grow in presences of oxygen	Obligate anaerobe
Oxygen not required for growth but will be utilised if available	Facultative anaerobe
Not required and not utilised	Aerotolerant anaerobe
Binary Fission	Growth and reproduction method