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This is a prototype lesson plan for "Planet in a Bottle"
yeast experiments intended for 2nd through 4th grade classrooms.
We invite our readers to try the experiments (they are lots of
fun) and we welcome comments from educators and others to improve
our procedures. Please send comments and suggestions to james.a.phillips@earthlink.net.
Objective: The student will measure the viability of yeast
samples and to explore environmental conditions which affect
the health of yeast microbes. The yeast samples may be common
store-bought Baker's yeast, or more exotic forms which have been
exposed to extreme environments as part of the Life on the Edge
program.
Overview: Students mix yeast with a nutrient broth consisting
of warm water and table sugar in a plastic water bottle. A common
9 inch party balloon is used to cap the bottle. As yeast digest
the sugar they produce carbon dioxide and inflate the balloon.
A healthy 1/4 oz sample of baker's yeast can inflate a balloon
to 12 inch circumference in less than 30 minutes. Simple variations
of this experiment may be used to discover environmental factors
that inhibit or promote the health of the yeast colony. Students
can compare these factors to conditions on other planets.
 Materials:
- 1 cup lukewarm water
- 3 cubes sugar
- 1 quarter-oz package of yeast
- 1 empty half-liter plastic water bottle
- 1 nine or ten inch party balloon
- 1 cloth measuring tape
- 1 small funnel (optional)
- OPTIONAL: see variations
Procedure:
- Mix water + sugar in water bottle until the cubes are dissolved.
- Using the funnel add yeast, the gently swirl the mixture.
- Cap the bottle with a balloon.
- Use the cloth measuring tape to measure the circumference
of the balloon every 15 minutes.
 This
basic recipe can be considered an "Earth in a Bottle."
It is a warm, healthy environment for yeast with plenty of nutrients.
The total amount of CO2 in the balloon when it reaches
its greatest volume is proportional to the number of healthy
yeast microbes present in the initial sample. For the procedure
outlined above, the balloon will achieve its maximum volume less
than two hours after the yeast are added to the nutrient mix.
The rate at which the balloon inflates is proportional
to the growth rate of the yeast colony. After the yeast are added
to the nutrient broth they begin to divide and increase in number.
As the colony size increases so does the rate of CO2
production, so long as there is an ample supply of nutrients.
If the environment inside the bottle is conducive to yeast growth,
the maximum rate of CO2 production will be high. Conversely,
if the environment is hostile to yeast, the maximum rate of CO2
production will be low.
Students can begin to explore conditions on other planets with
simple variations to the basic recipe. Although we cannot create
truly accurate extraterrestrial conditions in a grade school
classroom, there are many simple variations that are representative
of conditions on other planets. A few examples are listed below:
Example variations:
- Mercury
-- Mercury's surface is very hot. Mercury in a Bottle: Boil the
water before adding sugar and yeast.
- Venus
-- Venus is very hot, and has an acidic atmosphere. Venus in
a Bottle: Instead of water and sugar, use scalding hot orange
juice as a nutrient mix. Citric acid in the juice represents
sulfuric acid in Venus's hot atmosphere. Lemon juice or vinegar
can also be used to increase the acidity of the nutrient mix.
Venus's atmosphere also has a high pressure, so that the simulation
can be made more realistic by heating the nutrient mix in a pressure
cooker.
- The
Moon -- The moon has no atmosphere, so that yeast on its
surface would be exposed to a strong vacuum and solar radiation.
Moon in a Bottle: Expose the yeast to a vacuum, using a hand
pump bell jar, and to radiation in a microwave oven and/or from
a UV lamp.
- Mars
-- Mars is cold and has a thin atmosphere which allows much solar
UV radiation to penetrate to its surface. Mars in a Bottle: freeze
the yeast, then expose the microbes to ultraviolet radiation
from a UV lamp before adding yeast to the nutrient mix.
- Europa
-- this moon of Jupiter may harbor the largest ocean in the solar
system. The icy surface is a combination of pure water ice, Epsom
salts, and unknown minerals. Europa in a Bottle: Freeze a briny
mixture of water and Epsom salt. Break the ice into chips and
mix the salty ice chips with a cold nutrient solution.
- Callisto
-- this moon of Jupiter may have a salty ocean beneath its frozen
crust. Callisto in a Bottle: Add common table salt or Epsom salts
to the nutrient mix to simulate a salty environment.
- Pluto
-- Pluto is the most distant planet from the sun and is very
cold. Pluto in a Bottle: freeze the yeast in a deep freezer before
adding to the nutrient mix.
For more information about conditions on other
planets, visit Bill Arnett's Nine
Planets web site.
To learn more about yeast click
here.
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