what’s on my skin
TRANSCRIPT
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According to Nathan Wolfe, microbiologist
at Stanford University, the microbes in your
body outnumber your own cells by ten toone and can weigh as much as or more
than your brainabout three pounds in an
average adult.
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For the most part, the microbes inhabiting
our bodies are either beneficial ones or
unobtrusive freeloaders. They help us digest
our food, absorb nutrients, and manufacture
vitamins. They also train our immune
systems to combat infectious intruders.
Bacteria living on our skin secrete a natural
moisturizer, preventing cracks that could
allow pathogens to penetrate.
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If the idea of microbes living on your skin
makes you want to go home and take a
shower, consider this advice from
researcher Julia Serge, "We should think
about proper sanitation with the skin, but
not sterilization. There are good bacteria
that really promote healthy skin."
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Life On Our Skin
What lives on our skin? In this video segment
from Science Friday, Dr. Martin Blaser, the
chairman of the department of medicine at
New York University (NYU) School of Medicine,
is trying to find out. After swabbing the arms
of six people, Blaser and his lab found 182
different species of bacteria--thirty of whichhad never been seen before.
http://aptv.pbslearningmedia.org/resource/sf10.sci.lsci.living.lifeskin/life-on-our-skin/http://aptv.pbslearningmedia.org/resource/sf10.sci.lsci.living.lifeskin/life-on-our-skin/ -
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Predictions
On which area of skin on your body do you
think you will find the most bacteria?
The least bacteria?
Why would one skin area have more bacteriathan another area?
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Materials
Agar prepared Petri dishes
Agar: a gelatinous substance (usually
derived from seaweed extract) used as a
nutrient for growing microorganisms.
Cotton swabs
Latex gloves Distilled water
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Vocabulary
Bacterial Culture: the growing of bacteria ina nutrient substance in specially controlledconditions for scientific, medical or
commercial purposes
Colonymillions of bacterial cells grouped
together that can be observed with thenaked eye
Under favorable conditions, bacteria can
multiply rapidly and form a colony.
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Whats Happening?
Bacteria are single-celled microorganisms that canonly be seen through a microscope. There are many
different kinds of bacteria, and they are found
everywhere, in almost any type of environment,including extreme environments like hot springs.
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Whats Happening?
Just like any other organism, bacteria neednutrients to survive. The agar in the Petri dish is
composed of nutrients usually derived fromseaweed extract and other possible components,
depending on the source. The nutrients areconverted into energy and used to help the
bacterium grow and reproduce. Under favorableconditions, a single cell can turn into millions of
cells within a few hours, and into a billion cellswithin a few days. The grouping of millions ofbacterial cells is called a colony. Often a colony can
be seen without a microscope.
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Whats Happening: Phases of
Bacterial Growth
1. LAG PHASE: Bacteria are adapting to a new environment.The number of cells does not change during this time.
2. EXPONENTIAL PHASE of growth: Binary division occurs. The
number of cells doubles approximately every 20 minutes.
3. STATIONARY PHASE: The number of bacteria remains nearlyconstant, because the dividing rate = the rate of cell death.Cells begin to die due to the build up of waste and thedepletion of nutrients.
4. DEATH or DECLINE PHASE: The death rate is greater than thedividing rate, and the number of cells decreases.
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Whats Happening: Phases of
Bacterial Growth
Stationary
Phase
Number Exponential Death Phase
of Cells Phase
Lag Phase
Time
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Whats Happening?
Samples collected from human skin may contain
other types of microorganisms. Most bacteria
have one of three basic shapesrod, spherical,
or spiral. Colonies that exhibit fuzzy hair-like
growth are most likely fungus or mold.
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Topics for Discussion
What variables could have caused different
types of bacteria to grow?
Why do you think that bacteria can become
resistant to antibiotics or antibacterial agents
such as household cleaners?
How do bacteria reproduce?
Why would scientists want to grow and study
bacteria?