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Seed Germination on Gelatin Experiments
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This experiment is courtesy of 
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GERMINATING SEEDS ON GELATIN
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Developers:
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Jean Miller
Tredyffrin/Easttown Middle School
Tredyffrin/Easttown School District
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Diane Antes
Rohm and Haas Company
Spring House, PA
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The following experiments with plants can be used
progressively through the plant units in the K-6 science
curriculum. They are all based upon growing seeds in a
sterilized baby food or Snapple � jar filled with 3/4
inch of unflavored gelatin to which a few drops of liquid
house plant fertilizer has been added for nutrients. This
set-up provides an amazing environment for seed growth
because:
1. It doesn't need to be watered.
2. All parts of the plant can be very easily observed.
3. Many conditions for growth can be tested simply by
wrapping the jar in foil or plastic wrap, or turning the jar
upside down.
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TABLE OF CONTENTS:
PART I. Basic Gelatin Jar Preparation
PART II. Experiments
1. Observing Germination
2. Hairy Roots
3. Conditions for Growth
A. Light vs. Dark
B. Temperature
C. Fresh Air vs. Stale Air
D. Amount of Fertilizer
E. Crowded vs. Roomy
4. Growth and Conservation of Matter
5. Upside Down Plants
6. Crooked Plants
7. Colored Lights
8. The Point of Light
9. Monocots and Dicots or Corn and Beans
PART III. Helpful Hints
PART IV. Problem: Using Household Disinfectants to
Eliminate
Microorganisms on Seeds
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Part 1:
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BASIC GELATIN JAR PREPARATION
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Goal:
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Students will germinate seeds free of mold on a simple
gelatin culture media using a modified sterile technique and
observe the growth of plants under varying conditions.
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Specific
Objectives:
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- Germinate a seed on gelatin so all parts of it can
easily be seen as it grows.
- Use this controlled environment to test the
conditions necessary for a seed to germinate.
- Perform a controlled experiment changing only one
variable.
- Have a chance to practice a simplified sterile
technique in performing a scientific experiment.
- Gain an awareness of the responsibility one must take
in clean-up and disposal of contaminated materials when
doing research.
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Background:
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In industry, plant tissues are grown
on a culture medium, usually agar, with all the necessary
nutrients added. This is one way to greatly increase the
number of plants with exactly the same genetic makeup in a
very short time. In using this technique called tissue
culture, the scientist must take every precaution to use
absolutely sterile procedures, since only one mold spore or
bacterium is all it takes to destroy a culture and with it
perhaps many months of work.
In a science classroom where we are
germinating seeds to watch them grow, we do not need to be
quite so extreme in our sterile techniques. This method is a
science room adaptation of industrial sterile tissue
culture. The adaptations are noted as follows.
In industry, agar is used as a source
of food and water as well as a solid substrate to support
the seed or plant, instead of soil, but we will be using
unflavored gelatin. In industry, agar can be made with many
different combinations of nutrients added, but we will be
using household liquid fertilizer added to the gelatin. In
industry, the glassware, all apparatus and the agar must be
sterilized underpressure in an autoclave for 15 minutes at
121 � C. We will sterilize baby food, Snapple � or other
jars in a dishwasher on the sanitary cycle and dry with
heat. We will make unflavored gelatin (which is purchased at
the grocery store instead of from a biological supply
company) in the microwave but it can also be made in a pot
on a stove or in a pot on a hot plate. Bean seeds need to
have the seed coat softened by soaking in either sterilized
water or tap water to stretch the coat so the disinfectant
will reach all the crevices. In industry the seeds are then
sterilized using a bleach solution and a rinse of autoclaved
water, but we will sterilize the seeds in 3% hydrogen
peroxide . Typically in industry, before each use, the
forceps and stirring apparatus are dipped in 91% alcohol and
passed through an open flame to burn off the excess alcohol.
We will just soak the forceps or spoon in 91% alcohol.
Industry would use a disinfected work area under a
ventilated hood to provide germ-free air. We can wash our
hands and the tables and cover containers with plastic wrap
or replace a lid quickly to prevent microbial contamination.
Since we are not protecting months of work from
contamination, our methods can be more user-friendly.
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Vocabulary:
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Agar - a polysaccharide made from algae, which is
dissolved in hot water and then forms a gel when it cools.
It is used as a support for culturing organisms such as
bacteria and plants.
Germination - the beginning of growth in a seed.
Medium- a gelatinous substance containing the nutrients
for the,culture of microorganisms and the germination of
seeds.
Microorganism - a general term for any microscopic organism,
including bacteria and fungi such as mold.
Sterile Technique -
procedures used to prepare
cultures of plants while excluding other unwanted organisms
such as mold or bacteria.
Toxin- a poisonous substance given off by certain
organisms.
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Materials:
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unflavored gelatin (such as Knox
Unflavored Gelatine �) 3% hydrogen peroxide (usual
strength right from the bottle),91% isopropyl alcohol
liquid house plant food (such as
Miracle-Gro �),disinfecting hand soap
household disinfectant
tap water
seeds (such as radish, mung bean, lima
bean, green bean, alfalfa, and corn)
clear, tall jars with lids (baby food,
Snapple � or other taller jars)
2 or 4 cup measuring cup
forceps or tweezers
spoon, glass rod, or other stirring
instrument
lid opener (bottle opener)
transparent tape
clear plastic wrap
paper towels
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Optional
Materials:
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plastic bags, 12" x 12"
rubber bands
aluminum foil
colored plastic wrap - red, blue, green, yellow, and
clear (made by Reynolds)
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Procedure:
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TEACHER PROCEDURE: (Try "Recommendations" first!)
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Preparation:
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Sterilize Jars:
1. Sterilize jars and lids open end
down in dishwasher on sanitary cycle and use heated cycle to
dry. Wait until cool before opening door.
2. Transfer lids only to a cookie
sheet face down and cover with a sheet of aluminum foil.
Place in oven at 350 o F for 20
minutes to complete drying and sterilizing. Leave jars in
dishwasher.
3. After they cool, quickly put lids
on jars as they are removed from the rack to minimize the
possibility of microbial contamination (i.e. mold). If you
use baby food jars make sure jars and lids are cool or the
gasket will form too tight of a seal.
4. Also if you use baby food jars, use
a lid opener to pry out one side of the lid so it does not
make an air tight seal.
5. Put tape across the middle of the
jar for label. Fold one end of the tape over on itself ~1/2
inch to make a tab for easy removal.
Prepare Gelatin:
1. Put 3/4 cup cold tap water in a 2
cup glass measuring cup.
2. Sprinkle one 1/4 oz envelope of
unflavored gelatin over the water.
3. Cover loosely with plastic wrap to
prevent microbial contamination.
4. Let sit for about 2 minutes.
5. Microwave on high until it has
fully boiled for about 1 1/2 minutes, watching constantly
because it boils over very easily. Times will vary with the
power of the microwave, but try about 3 1/2 minutes.
6. Wait until it cools so condensation
doesn't form in the jars when you pour. You can speed up
cooling by putting the measuring cup in the refrigerator for
about 30 minutes with the cover on it.
7. Use a spoon or glass stirring rod
to stir the gelatin before pouring. Wipe a clean spoon or
other stirring instrument with a paper towel moistened with
alcohol. Wiping helps remove microorganisms. Then give a
final rinse, pouring the alcohol over the spoon and air
drying. You can also soak the stirrer in a jar of alcohol.
Or you can place a cleaned glass stirring rod or smooth heat
resistant plastic spoon in the measuring cup when you
microwave it.
(Four envelopes of gelatin can be made
at once using 3 cups of water in a 4 cup measuring cup. Time
will vary but try heating on high for 7 minutes, again
letting it boil for about 1 1/2 minutes.
If a microwave is not available,
gelatin can also be made in a pot over a stove or hot plate,
although this provides more chances for contamination. First
sterilize the pot and a metal spoon by boiling water in the
pot. Then prepare gelatin in the same proportions as in the
microwave. Gelatin has more of a tendency to erupt as it
cooks on the stove so stir it often. Safety glasses may need
to be worn since the liquid tends to erupt as it boils. Let
it boil for about 2 minutes on medium heat to kill any
microorganisms. Caution: It will burn on high heat. Cover
with plastic wrap while it cools.)
8. Carefully lift up lids from sterile
jars just long enough to pour in gelatin to a level of about
3/4 inch. (Three fourths cup of gelatin will make about 6
tall baby food jars or 4 Snapple � jars.)
9. Quickly replace lid.
10. Put 3 drops of liquid house plant
fertilizer in each baby food jar or 5 drops in Snapple �
jars. If you are doing an experiment without fertilizer,
skip this step.
11. Replace lid, being careful not to
contaminate and gently swirl to mix.
12. Let gelatin set up at room
temperature until firm enough to turn jar upside down
without it falling out. Time will vary with temperature of
room and amount of water in mixture but it will set up
eventually. Using 1 cup of water may take several days to
set up in the summer. Using 1/2 cup water may take 6 hours
to set up firm, but it will not provide as much water for
the plant. Jars with larger diameters and more gelatin also
take longer to set up. Many other size jars will work but
keep in mind they will take more gelatin. Do not place seeds
on gelatin until it has gelled since they will sink below
the surface and get stuck.
You may want to make the jars up 2 or
3 days ahead of time in warm weather. The reason is to allow
plenty of time for the gelatin to gel and to make sure the
gelatin was not contaminated when it was prepared,
especially if you are doing an experiment to test for
contamination.
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Prepare
Seeds:
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To stretch the seed coat before disinfecting the seeds,
soak them in tap water in a clean, covered baby food jar,
according to the following schedule:
Lima Beans-
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7 hours or until seed coat is smooth
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Mung Beans-
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2 hours or until seed coat is smooth
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Green Beans-
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2 hours or until seed coat is smooth
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Corn-
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does not need to be soaked
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Radishes-
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do not need to be soaked
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Alfalfa Sprouts-
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do not need to be soaked
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If these soaking times are difficult to meet, an alternative
method for lima beans, mung beans and green beans will also
work. Instead of soaking in water and then disinfecting,
put lima beans, mung beans, or green beans in 3% hydrogen
peroxide for 12 to 16 hours or overnight. Then the
students can use the seeds right from this jar without
additional treatment.
With these soaking times, most seeds will germinate in
less than 24 hours after being placed on gelatin. But there
is usually a certain percentage, about 20%, that do not
germinate.
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STUDENT PROCEDURE:
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Preparation:
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(For best results)
1. Students should wash their hands with a disinfecting
soap.
2. Disinfect desks with a household disinfectant or 91%
isopropyl alcohol before working with the seeds.
3. Tie back long hair.
4. Close windows and turn off any fans, if possible, to
prevent movement of microorganisms.
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Materials:
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Disinfect Seeds:
1. Disinfect seeds in a
fresh 3% solution of hydrogen peroxide in a clean
baby food jar with a lid according to the following time
chart:
Lima Beans-
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15 minutes
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Mung Beans-
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15 minutes
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Green Beans-
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15 minutes
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Corn-
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16 hour or overnight
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Radishes-
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15 minutes
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Alfalfa Sprouts-
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15 minutes
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2. Swirl jar frequently so all of the seed surfaces get
treated.
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Transfer Seeds:
1. To transfer seeds to gelatin jars,
use clean forceps that have been soaking in a baby food jar
of 91% isopropyl alcohol and will be re-dipped in that jar
after each seed is touched. Gently tap the forceps against
the edge of the jar to remove all excess alcohol before
picking up the next seed. Alcohol contaminating the gelatin
will dissolve it.
2. Lift lids and take seeds out of the
jar of hydrogen peroxide one at a time and allow any excess
liquid to drip back into the jar before dropping seed onto
gelatin surface. Note: A few radish seeds may pop and shoot
out of the jar as the seed coat splits open after soaking in
fresh hydrogen peroxide about 12 minutes. You may want to
have students use safety goggles, caution them not to get
their eyes too close to the jar, or leave seeds in the
disinfectant for 20 minutes before they get them.
3. Open and close gelatin jar lid
briefly after each time a seed is dropped in to minimize the
possibility of microbial contamination. Holding the lid over
the jar at an angle like a roof will help. Do not breathe on
the jar. Avoid touching the gelatin with the forceps.
4. When all seeds are placed on the
gelatin surface, check jar lid to make sure it is on
securely but that there is a crack for air exchange. Since
baby food jars have a rubber gasket, the edge needs to be
pried up just a little so the seal is not complete. Other
jars without the gasket just need to be screwed on half way
for air exchange and for this reason may be better to work
with than baby food jars.
5. Place a piece of transparent tape
over the lid and down the sides about one inch to keep the
lid on while still allowing gas exchange.
6. Seeds that do not germinate tend to
contaminate the gelatin. If you discover this soon enough,
you can try to remove them quickly with forceps sterilized
in alcohol.
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TEACHER PROCEDURE:
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Procedure:
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Disposal of Contaminated
Material:
If gelatin gets microbial growth,
precautions must be taken to dispose of the contaminated
material in a responsible way, just as must be done in
industry.
1. Pour 1 to 2 teaspoons of a diluted
bleach solution (made with 1/4 cup bleach and 1 cup of
water) into each contaminated jar and replace the lid. You
can also use 1 or 2 teaspoons of 91% isopropyl alcohol
instead of bleach.
2. Gently swirl jar and let sit
overnight.
3. Pour the contents of the jar
through a strainer in the sink. A coffee can with holes in
the bottom will work.
4. Wrap the solid, now disinfected,
material in a paper towel or plastic bag, and place it in
the trash, since it is harmless.
5. Wash hands after completion of the
experiment.
6. Jars and lids can now be
re-sterilized in the dishwasher on the sanitary cycle and
used again. You may want to put them through twice or soak
the empty jars in a 20% bleach solution overnight before
washing to be sure all the microbial contamination is
killed.
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Recommendation:
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First try this quick setup!
1. Clean 6 or 8 baby food or Snapple � jars. For this
quick setup you can wash jars and lids by hand with soap and
water. Then swirl 91% alcohol around in the jar and wipe jar
and lid with a clean, alcohol moistened paper towel. Let jar
air dry upside down on the lid. You may get some microbial
contamination, but you will also see how quickly you will
get results with the seeds.
2. Mix 2 packages of gelatin with 1 1/2 cups of water in
a 2 cupmeasuring cup and microwave it for 30 seconds after
it starts to boil.
3. Let cool slightly and swirl the measuring cup to
finish mixing.
4. Pour gelatin into 6 or 8 jars to a level of about 3/4
inch.
5. Add 3 drops of liquid fertilizer to each jar and swirl
to mix it.
6. The gelatin will set up at room temperature in about 6
hours or overnight.
7. Disinfect radish seeds in 3% hydrogen peroxide for 15
minutes and place on the gelatin with forceps rinsed with
alcohol.
8. Remember to open the jars only briefly for each seed
as described earlier.
Seeds will germinate in less than 24 hours and stems will
grow 1 inch in 2 or 3 days at a warm room temperature. After
using this simplified setup to get a feel for the process,
the detailed directions for the sterile technique described
earlier will be easier to follow. They can be used to
perform many different kinds of experiments on seeds and
plant growth. Some are described below, but the
possibilities are endless.
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Part 2:
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EXPERIMENTS
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Experiment:
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Experiment 1: OBSERVING GERMINATION
What Do Seeds Look Like As They Germinate?
- Place 6 or more seeds on the gelatin surface in a jar
using the sterile transfer technique.
- Observe the seeds every day to see the stages of
growth, step by step.
- Draw pictures of what appears first, second, etc.,
until students have a complete set of drawings, showing
all the stages in the germination process. Have them
identify the following parts: root, root hairs
(especially in radishes), stem, seed coat, seed leaves or
cotyledons (were originally inside the seed), and true
leaves (first new leaves formed). Then give the students
a set of drawings showing the plant at different stages
and have them put the drawings in the correct sequence.
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Questions:
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- What is the order of the
appearance of the plant parts? (Roots, stem, leaves.)
- What do the root hairs in radishes
look like? (White fuzz.)
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Experiment:
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EXPERIMENT 2: HAIRY ROOTS
How Fast Do Roots Grow?
- Germinate 6 or more radish seeds to observe the
location of root hairs (they look like white fuzz) and
how fast the roots grow.
- Make a mark on the jar each day to mark the tip of
the root so a comparison can be made the next day. Also
point out that new growth in the root occurs at the tip,
so try to observe that the older part of the root is in
the same location it was in the day before. (Radishes
will germinate in less than 24 hours in this setup and
sometimes roots will grow 1/2 inch in 6 hours during the
school day, so results can be seen very quickly. Root
hairs will appear the second or third day.)
- Older students can measure the daily growth of the
root and graph the results. Y= length of root and X=
number of days. If there are several plants, they can
take an average, or pick one plant.
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Questions:
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- Where does growth occur in the root? (At the
tip.)
- What is the function of root hairs? (Taking in water
and minerals.)
- Where do these plant get water and minerals? (From
the gelatin.)
- What is the average daily root growth? (Answers will
vary.)
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Experiment:
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EXPERIMENT 3: CONDITIONS FOR GROWTH
What Conditions Are Necessary For the Germination and
Growth of Seeds?
Test the conditions for germination of seeds using a
control and a single variable or factor to be tested. Have
students make predictions before they perform the
experiment. Let the students try to design a way to test
their hypothesis. Have them make sure, in the design of
their experiment, that there is only one variable so if they
observe a difference, they know it is because of the tested
variable and not because they set up the 2 jars differently.
Here are some suggestions.
A. Light vs. Dark
- Set up 2 jars with 6 seeds each on the gelatin.
- Wrap 1 jar in aluminum foil but do not cover the lid
with foil so air can be exchanged.
- Do not wrap the other jar.
- Place them side by side where they will have a warm
temperature and indirect sunlight.
- Check them each day to compare how and when they
germinate. Make a chart to write in the daily
observations or draw a picture. Radishes (and most of the
other seeds listed) germinatein less than 24 hours so
they will get results very quickly.
Once they have determined whether or not light is
necessary for germination, they can continue to make
observations for several days to see if the new plant needs
light to continue to grow and make food. They should make
daily observations of leaf color as well as stem length in
each jar every day. Then record the results and take an
average. They can make a graph of the data, Y= height of
stem and X= number of days.
Questions:
- Do seeds need light to germinate?
(No.)
- How can they germinate in the
dark?
- (They use the food stored in the
seed for energy to germinate. Keep in mind, it is dark
where seeds are planted in the ground.)
- Do seeds in the light and dark
germinate at the same time? (Yes.)
- Which stems grew the tallest? (The
ones in the dark.)
- Why do the plants in the dark grow
faster than the ones in the light? (Plant cells that are
in the dark are stimulated to grow fast to find light in
a hurry, so they tend to grow taller faster and look
lanky.)
- Which plant had greener leaves?
(The one in the light.)
- Which plant can continue to grow
well under its present conditions and why? (The one in
the light because it can make its own food from
light.)
- Do plants need light to grow
healthy? (Yes, without it, they cannot make food.)
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B. Temperature
- Set up 3 to 5 jars with 6 seeds in
each.
- Wrap each jar in aluminum foil
(this is part of the identical treatment in a single
variable experiment.)
- Since temperature will be the only
variable and all other conditions must be identical,
place each jar in a location with a different
temperature. Try to find places with temperature
differences, such as 40� F (a refrigerator),
50� F (a refrigerator with the temperature turned up
warmer), 60� F, 70� F, and 80� F,
depending on what is available.
- Record the temperature at each
location.
- Record observations by noting day
or hour of germination.
- Students can make a graph of their
results, Y=temperature and X=number of days or hours to
germinate. (The germination time difference will be in
hours, near 24, for most temperatures except cold ones
such as the refrigerator which takes about seven
days.
The effects of temperature on
germination and on plant growth after germination can also
be tested in the presence of light. Place the plants in
locations with different temperatures that also have light.
Omit the aluminum foil. Take the temperature at each
location. Record the day or hour of germination of each
plant. Measure the height of the stem each day, since the
plants have light. Make graphs of the average stem growth at
various temperatures, Y= height of stem and X= number of
days.
Questions:
- As the temperature gets colder, what happens to the
length of time it takes the seeds to germinate? (It takes
longer.)
- What effect does temperature have on stem growth of
the plant? (The growth of the stem slows down as the
temperature gets colder.)
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C. Fresh Air vs. Stale Air
- Set up 2 small jars with 6 seeds each on the gelatin.
Results may be better with mung beans which are larger
than radishes.
- Seal the lid tight on one jar.
- Adjust the lid on the other jar, either by prying a
gap in the lid as in a baby food jar or screwing a loose
lid down just slightly, so air can be exchanged.
- Put tape across the lid to keep it from coming off
when the jar is picked up.
- Set both jars side by side at room temperature in
indirect light.
- Make daily measurements and observations of both
plants andrecord them on a chart.
After a while in the jar that is sealed, one of the gases
will be usedup and there will be an excess of another. This
can be tested at theend of the experiment by the teacher
using a flame test. Light acandle, then quickly insert the
candle into the jar as you open the jarand hold the jar
upside down or sideways to prevent the gas frommixing with
fresh air. If oxygen is the main gas present, the flame
should glow brighter. If carbon dioxide is the main gas
present, the candle should go out. Caution: Use safety
goggles when performing this test.
Questions:
- What do plants use carbon dioxide for? (Plants use a
lot of carbon dioxide for making food during
photosynthesis.)
- What do plants use oxygen for? (Plants use a small
amount of oxygen to burn the food they make which
supplies the energy for growth.)
- When do plants give off oxygen? (During
photosynthesis.)
- Do plants give off carbon dioxide? (Yes, when they
burn food to get energy, just like animals do.)
- Which gas was there more of in the jar at the end of
the experiment and why? (Oxygen, because plants make more
food than they burn. The food that they do not burn, they
store. They give off more oxygen from photosynthesis than
they do carbon dioxide from respiration.)
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D. Amount of Fertilizer
1. Liquid house plant fertilizer is added to the gelatin
when it is made up. To test for the need of fertilizer, make
up some jars without adding any fertilizer.
2. Then make up some jars with different amounts of
fertilizer, such as 1 drop, 2 drops, 3 drops, etc., or a lot
more.
3. Add the same number and kind of seeds, disinfected the
same way.
4. Place the jars in the same location so they have the
same growing conditions.
5. Record the daily length of the stem and observe the
color of the leaves. The average stem length can be graphed
for each number of drops of fertilizer, Y= height of stem
and X= number of days.
Questions:
- What is the reason for putting the same number of
seeds in each jar? (So each jar has the same number of
plants using the fertilizer.)
- Is the volume of gelatin important to consider in
this experiment? Why? (Yes, because different volumes of
gelatin provide differentamounts of nutrients and
water.)
- How much fertilizer is the optimum amount to add to
the gelatin? (Answers will vary.)
- What nutrients are in the liquid fertilizer? (See
label on fertilizer container.)
- Why is fertilizer added to the gelatin? (To provide
nutrients for the plant.)
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E. Crowded vs. Roomy
- Take 2 jars with gelatin.
- In 1 jar give the seeds plenty of room to grow. If
seeds are large, just use 1 seed.
- In the other jar, place many seeds.
- Have the students observe the size and shape of the
plants as well as how fast the level of the gelatin goes
down. This can be difficult to observe, but look at the
gelatin from different angles.
- You can also try different sized jars as the variable
and use the same number of seeds.
Questions:
- Does the level of the gelatin stay the same? Why?
(No, the plants use the water and nutrients in the
gelatin forgrowing.)
- What happens to the plants when they are crowded?
(The roots grow close to each other and they compete for
space and nutrients. The stems and leaves compete for
light.)
- What happens when the plants grow in larger jars?
(They have more room and their shapes are not affected by
the closeness of other plants. They also grow larger
because there is more food and space.)
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Experiment:
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EXPERIMENT 4: GROWTH AND CONSERVATION OF MATTER
Where Does the Plant Get the Materials to Make It Grow
so Big?
- Weigh the jar with seeds on the day it is set up.
- Then weigh it each day as it grows to see if there is
any change in mass of the system.
- After the experiment is finished, weigh a seed and
the grown plant with the gelatin removed, Compare the
mass.
Questions:
- Is there any change in the mass of the closed jar
from day to day? (No.)
- Does the plant grow in size? (Yes.)
- Where does the plant get the materials to increase
its size? (It used the materials in the gelatin and the
air to make a new product, the plant.)
- What happens to the volume of the gelatin? (It
decreases.)
- Does the difference in the mass of the seed and the
plant equal the mass of the gelatin that is used up?
(Yes, approximately, since the air used has very little
mass. According to the Law of Conservation of Matter,
matter is neither created nor destroyed during a chemical
change.)
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Experiment:
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EXPERIMENT 5: UPSIDE DOWN PLANTS
What Effect Does Gravity Have on Germination of a
Seed?
- Turn a jar upside down as soon as the seeds stick to
the gelatin surface to see if the roots grow up towards
the gelatin or down with the force of gravity.
- Also observe which way the stem grows.
Questions:
- Which way do the roots grow? (They grow down toward
the pull of gravity.)
- Which way does the stem grow? (Up.)
- Can the plant can grow for very long this way?
(No.)
- What will make it stop growing? (It will not be able
to get water or nutrients.)
- Is the stem able to penetrate the gelatin to grow
into it? (Sometimes, but it can't grow as tall as it
normally does.)
- How can you be sure the results were due to gravity
and not light? (You can't without doing a similar
experiment to test the reaction to being upside down in
the dark.) Since light and gravity are both variables in
this experiment, you may want to do the experiment a
second way and try wrapping both jars in foil to test the
effect of gravity in the dark.
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Experiment:
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EXPERIMENT 6: CROOKED PLANTS
What Effect Does Changing the Position of the Plant
Several Times Have on the Growth of the Plant?
- After a stem (radish works well) has grown about 3/4
inch, turn the jar on its side to see which direction the
stem grows. Make sure the gelatin is from a firm batch
(3/4 cup of water or less per envelope.)
- Make a mark on the tape label on the side of the jar
to indicate the side that is down so it can be returned
to the same position if it is moved.
- The next day put the jar right side up and keep
alternating these positions each day.
- Draw the plant each day.
Questions:
- How does the stem grow each time the position is
changed? (Up.)
- What makes the stem change the direction it is
growing each time its position is changed? (Either
gravity or light.)
- What test can you do to determine if the reaction is
due to gravity or light? (Perform the same experiment
with the jars wrapped in aluminum foil to eliminate light
as a variable.)
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Experiment:
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EXPERIMENT 7: COLORED LIGHTS
What Color of Light Is Best for Growing Plants?
- Set up five tall jars with seeds and wrap each jar
twice around in a different color of plastic wrap (red,
green, blue, yellow, and clear).
- Place them in the same location and observe for about
10 days.
- Determine which of these colors of light plants need
for photosynthesis by observing the height and color of
the plants grown in the different colors of light.
Questions:
- Which color of plastic wrap represents the control?
(Clear.)
- Plants grown under which color of light are the
greenest? (Results will vary depending on the type of
plant and it's most active type of chlorophyll. The color
of plastic wrap is the color of light the plant receives.
All other colors are filtered out by the plastic.)
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Experiment:
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EXPERIMENT 8: THE POINT OF LIGHT
How Does a Plant Respond to Light from Only One
Direction?
- Wrap a jar with radish seeds in aluminum foil.
- Cut a circle about 3/4" in the foil on one side of
the jar and draw this circle on the jar with a marker to
mark the location of the hole.
- Face this side of the jar towards light to observe
the reaction of a plant to light coming from only one
direction instead of from all around.
- Remove the foil for observations but replace it
making sure that the hole in the foil is lined up with
the mark on the jar.
Questions:
- How does the plant respond to the direction of light?
(It grows towards the light. The side of the stem away
from the light grows faster than the side of the stem
facing the light. This makes the stem curve and grow
towards the light.)
- How does a plant grown this way compare to one grown
on a window sill? (Both stems curve and grow towards the
source of light.)
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Experiment:
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EXPERIMENT 9: MONOCOTS AND DICOTS OR
CORN AND BEANS
What Is the Difference in the Germination and Growth
of Monocots and Dicots?
- Germinate Monocot seeds (such as corn which has only
one embryonic leaf in the seed) and Dicot seeds (such as
beans and radishes which have two embryonic leaves in the
seed and the seed splits into two halves).
- Observe their growth for several days.
- Make a table comparing observations of the two types
of seeds as they grow. Include shape of leaves, number of
leaves, location of seed as the plant grows, shape of
roots, and appearance of stem.
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Part 3:
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HELPFUL HINTS
- Radish seeds are the easiest and quickest to
germinate.
- Putting the gelatin jars in the refrigerator makes
them set up faster but it does not help this technique
because they only melt again when put at room
temperature. They set up when they would have anyway.
- Direct sunlight or heat source will melt the gelatin
in the jars.
- Mung bean and alfalfa seeds can be purchased at
nutrition stores.
- Label all the jars from each batch of gelatin in case
it needs to be identified as a source of microbial
contamination. Make a gelatin control for each batch by
putting a small amount of media in a jar and labeling it
control, no seeds.
- 6. 91% isopropyl alcohol dries faster than 70%
isopropyl alcohol because it has less water in it. Either
can be used, but 91% may reduce contamination better.
- Lima beans purchased from the grocery store food
shelf do not germinate as well as lima beans from seed
packages.
- When plants grow too tall for the container, you can
remove the lid and cover the top of the jar with a 12" x
12" clear plastic food storage bag secured with a rubber
band. This will give them about 10 inches of space to
grow taller. They will eventually die when the gelatin is
consumed or overcome with microbial contamination.
- The plants can be transplanted to soil. All the
gelatin must be gently rinsed off the roots with warm
water and pulled off between your fingers. Be careful not
to pull off the roots! If any gelatin is left,
microorganisms in the soil will have a feast and
eventually destroy the plants.
- Although plastic jars are great for safety with
younger students, some brands of jars may warp on even
the top shelf of the dishwasher. They may also warp if
the gelatin is too hot when poured. Jars which are not
affected by the heat have a PETE 1 recycling symbol on
them.
- Students will be more successful when they transfer
the seeds to the gelatin if they have had a chance to
practice the sterile technique first. They can simply use
seeds soaked in water, forceps standing in a jar of water
and a jar with water, instead of gelatin. Make sure they
also practice with lids on what would be the gelatin jar
and the disinfectant jar. The forceps jar does not get a
lid.
- If mold contamination appears in the gelatin, it is
from the preparation process if it is below the
surface. It is airborne contamination if it is on the
surface.
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Part 4:
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SOLVING A PROBLEM
Using Household Disinfectants to Eliminate Microorganisms
on Seeds.
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Grade Level:
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Sixth
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Goal:
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The student will have an opportunity to test the effects
of various disinfectants on microorganisms and observe the
results.
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Objectives:
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- Observe the effect of a disinfectant on the growth of
microorganisms on a seed germinating in a gelatin culture
medium.
- Learn to read product labels to obtain information
about a product's ability to disinfect.
- Develop an appreciation for sterile technique and for
how easy it is for contamination to occur in a culture
medium.
- Gain an awareness of the responsibility one must take
in toxicityof materials used in an experiment.
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Background:
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In designing this technique for germinating seeds on
gelatin, one of the major obstacles to overcome was the
problem of microorganisms contaminating the system. They
would either kill the plant or turn the gelatin into a
liquid, due to the toxins given off by the microorganisms.
Many different household disinfecting products were tested
for varying times and at varying concentrations, both with
and without soaking the seeds, as in the case of the beans.
Some of the products killed all the microorganisms but
stunted the growth of the plant. Some required that the
seeds be treated for a long period of time to be effective,
and some containing alcohol reacted with the gelatin,
turning it into a liquid. To be an effective disinfectant
for the seeds, the product must prevent contamination of
microorganisms without affecting the growth of the plant or
the consistency of the gelatin. To be suitable for young
children to use, it should not contain bleach or other
strong chemical.
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Problem:
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Which household disinfecting agent is the best product to
use to disinfect radish seeds in 15 minutes of treatment
time without killing the seed or stunting the growth of the
plant?
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Discussion:
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- Discuss with the students the problem involved in
growing radish seeds in the jar of gelatin. Since the
gelatin medium contains nutrients for growth, if any mold
spores or other microorganisms contaminate the gelatin,
they will grow very rapidly and quickly outgrow the seed
and kill it. In setting up the gelatin jar there are many
opportunities for contamination (cleaning the jars,
making the gelatin, pouring the gelatin into the jar)
which have to be controlled using a sterile technique. If
a scientist were doing a project involving months of work
growing a plant on a culture medium, one mold spore could
contaminate the culture and destroy months of work. So
scientists are extremely precise in how they perform
sterile technique. Most science classrooms do not have
the equipment required for industrial sterile techniques,
but we can make use of some of their practices in solving
our problem.
- Describe or demonstrate the preparation of the
gelatin jars, emphasizing the precautions that were taken
to prevent contamination. Show a jar with gelatin in
which radish seeds were planted without being treated to
illustrate the problem with microbial contamination.
- The students now have the problem of figuring out how
to treat the seeds to kill the microorganisms and not the
seed. Have them search their shelves at home for
disinfecting products. Have them look at the labels for
words to identify the product as a disinfecting agent,
such as, antibacterial, mold or mildew control,
disinfectant, antiseptic, anti-infective, and germicidal.
Also have them read the labels to see if the products
have any ingredients which would be harmful to the
environment if they were used on a large scale and then
required special disposal. Two examples are mercury
(Mercurochrome " ) and petroleum distillates (Lestoil "
). This is an important consideration in responsible
product evaluation in industry. One resource for this
information is the software package on hazardous
materials listed in the references.
- After reading labels, the students can discuss in
groups and select several products they think have the
most potential to be effective in killing the
microorganisms. Suggested products are not limited to the
following:<P>
- 91% isopropyl alcohol
- 3% hydrogen peroxide (usual strength right from the
bottle)
- Lysol " Basin, Tub and Tile Cleaner
- Lysol " Disinfectant (diluted 1/8 tsp. in 1/2 cup
water)
- Lysol " Disinfectant Spray (diluted 1 tsp. in 3 tsp.
water)
- Lysol " Deodorizing Cleaner (diluted 1/8 tsp. in 1/2
cup water)
- Liquid Dial " Antibacterial Soap (diluted 1/4 tsp. in
1/4 cup water)
- Spic and Span " (diluted 1/8 tsp. in 1/2 cup
water)
- Listerene " (diluted 50%)
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Materials:
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disinfecting products to be tested
safety goggles
gelatin jar setup (one per student)
clean baby food jars and lids for seeds (one per product
to be tested)
91% isopropyl alcohol in a jar to soak forceps (one per
team)
forceps (or tweezers)
radish seeds
clock
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Experiment:
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- Divide the class into teams, for example, 6 (four
member) teams. Each member of the team will test the same
product. One student per group will be the control and
just soak their seeds in water. So the experiment does
not get too unmanageable, have the class select the 6
most promising products to test. Seat all members of the
same product team together for testing. (For increased
reliability, the test results from other classes can be
combined if more than 1 class does the experiment)
- Follow the steps for preparation of work conditions
described in the Student Procedure Section of Part I.
- Give each student a jar prepared with gelatin and
fertilizer that has gelled. Be sure to label all jars
made from the same batch so that they can be checked if
batch contamination becomes a possibility.
- Give each team a clean baby food jar with lid and the
product they wish to test. Add to the empty jar the
disinfectant or a dilution of the disinfectant calculated
from the use directions on the container. Caution:
Goggles should be worn while working with these products
since most of their labels warn that they are harmful if
they get in the eyes. Also they may want to wear some
type of protective covering (lab coat or apron or old
shirt).
- When the test solution is prepared, drop enough seeds
in it for all the students on the team to place about 6
seeds in each jar. Cover jar with a lid.
- Time the treatment for 15 minutes.
- Each team should also have one jar of seeds soaked in
water for the control.
- Then to transfer seeds, use forceps that have been
soaking in a jar of 91% isopropyl alcohol and will be
returned to the jar after each time a seed is
touched.
- Take the seeds one by one out of the disinfectant jar
with forceps and allow all excess alcohol to drip
off.
- Briefly open the gelatin jar and close it after each
seed is dropped in. Decide how many seeds each student
should test (about 6-8).
- Each student should label his or her jar with name,
date, product tested, and dilution. The batch number
should already be on the label.
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Observations:
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Decide what observations will be important in determining
the best product. Make daily records of these observations.
Students will want to look for the appearance of
microorganisms (i. e. mold) and when it forms. They should
also look at plant characteristics such as time of
germination, daily growth of stem and roots, leaf color, and
overall health of the plant and roots. They can measure the
stem lengths each day, average the data and graph the
results.
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Analyze
Data:
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Compare the results of each member on the team and then
of all the teams to decide which product was the best. If
several products allow no microorganisms, then graph each
group's stem length data on identical (xeroxed from the same
blank master graph) overhead transparencies, Y=stem length
and X=number of days. They can be laid on top of each other
and compared that way on an overhead projector.
If all jars get microbial contamination, then gather
information on how the jars were prepared to see if the
contamination resulted from sources other than the seed.
At the end of the experiment, the contaminated material
must bedisposed of using a 20% bleach solution or 91%
isopropyl alcohol as described in Part I under Disposal of
Contaminated Material.
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Questions:
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- Is one product clearly the best? (Answers will vary,
depending on products tested.)
- If the experiment gives definite results, does it
seem logical, based on the ingredients or the claims on
the product label?
- Is the most effective product the most efficient to
use?
- Is the best product environmentally friendly, that is
would disposal of it on a large scale harm the
environment?
- Does it harm the growth of the plant?
- What other problems does this experiment lead you to
try to solve?
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References:
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Bottino, P. J. Methods in Plant Tissue Culture,
Kemtec Educational Corporation, Kensington, MD 1981.
Murphy, Terence. Plant Tissue Culture: The Basic
Concepts, Biology Media, Burlington, NC, 1982.
Neyhart, C. J. Hazardous Materials Lurking in Your
Home, Discovery Software, 1830 Old Sumneytown Pike,
Harleysville, PA 19438, (215)234-8450. Mac or PC compatible.
Pogosian, B. Safety in Microbiology Experiments,
EleSec, Vol. 1, No. 1., Jan. 1981. Available from Sister
Helen M. Burke, Ph.D., Chemistry Department, Chestnut Hill
College, Philadelphia, PA 19118, (215)248-7194.
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This experiment is courtesy of 
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