Micro exam 3 Ch. 6

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How do salts and sugars work to preserve foods?

By creating a hypertonic environment. The bacteria/fungi will not be able to reproduce, because the salt/sugar will take the water out of the organism. Loss of water causes PLASMOLYSIS : shrinking of the cytoplasm.

Distinguish between basic and acidic environments

Acidic environments are below 7.5 pH only yeast and mold can grow in acidic env, Basic environments are between 6.5-7.5 pH, which most bacteria grow best in.

How does a buffer affect pH levels?

When bacteria is cultured in the lab many produce acid that interefere with their growth. Buffers are added to neutralize the acid and maintain proper pH for the bacteria to grow.

At what pH levels do bacteria thrive?

betweem 6.5-7.5

At what pH levels do fungi thrive?

pH 5-6

Identify the primary method by which bacteria reproduce by.

binary fission

Binary Fission

type of asexual reproduction in which an organism replicates its DNA and divides in half, producing two identical daughter cells

obligate aerobes

organisms that need oxygen to live

facultative anaerobes

can live with or without oxygen/ concentration at the top/ fermentation cellular resperation- more oxygen you have more atp- can grow in oxygen and with out, better with oxygen more atp. Have catalyst.

obligate anaerobes

organisms that cannot live where molecular oxygen is present

aerotolerant anaerobe

cannot use oxygen for growth but can tolerate it well, ferment carbohydrates to lactic acid


microbes by this name are aerobic but can only grow in places where the oxygen content is lower than in pure air due to their own production of toxins when exposed to atmospheric air. TOO MUCH OXGEN TOXIC/ NO OXYGEN THEY ARE GOING TO DIE.

singlet oxygen

normal molecular oxygen that has been boosted into a higher-energy state and is extremely reactive

superoxide radicals

formed in small amounts during the normal respiration of organisms that use oxygen as a final electron acceptor, forming water; obligate anaerobes form; toxicity caused by great instability, lead them to steal electrons from molecules

superoxide dismutase

an enzyme that catalyzes the conversion of superoxide into hydrogen peroxide and oxygen. **reason why anetolerant anaerobes can tolerate oxygen. neutralized oxygen radicals produce hydrogen peroxide.

peroxide anion

toxic; Hydrogen peroxide produces it; catalase converts it into oxygen and water; when added to colony of bacteria cells producing catalase, oxygen bubbles are released; peroxidase also breaks down but does not produce oxygen.


breaks down hydrogen peroxide, does not produce oxygen

hydroxyl radical

The most reactive of the four toxic forms of oxygen


highly reactive form of oxygen that is generated by passing oxygen through high-voltage electrical discharges. used to supplement chlorine in the disinfection of water bc it helps neutralize tasts and odors.

selective media

suppress growth of unwanted bacteria and encourage growth of desired microbes.

differential media

make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate. The colonies have different colors or cause different changes in the surrounding medium.** mannitol salt selecting ind. that can maintian a salty env.

enrichment culture

designed to increase very small numbers of desired microbes at detectable levels. certain nuetrience to grow better, picky bacteria.

direct measurement of microbial growth


pour plates

isolation technique using a series of serial dilutions to separate CFUs (colony- forming units)

spread plate

A specific volume is placed on the surface of the agar and spread over it to evenly distribute cells. Cells grow up on the surface of agar.


the process of seperating substances in a mixture by trapping larger particles outside the membrane filter and letting the smaller ones get through

direct microscopic count

A method of measuring bacterial growth by counting cells in a known volume of medium.

most probable number

A statistical method of measuring bacterial growth used when samples contain too few organisms to give reliable measures by the plate count method

plate count

a method of determining the number of bacteria in a sample by counting the number of colony-forming units on a solid culture medium

indirect measurement of microbial growth

-uses turbidity to determine microb numbers
- bacteria multiply & liquid becomes turbid
-spectrophotometer measues turbidity\
-bacterial numbers increase, less light will reach the detector
-absorbance = is used to plot bacteria growth
-10-100million cells per mill. are needed to make a suspension turbid enough to read.
-not as acurate as direct method

metobolic activity

the amount of certain metabolic product is a direct porportion to the number of bacteria present

dry weight

not good for most bacteria; useful for filamentous bacteria and fungla molds; growth is removed, dried (dessicated), and weighed

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