Green Chris
Christopher is in his last year of his degree in Agrobiology. He needs to complete a 6 months internship
with the Agri-food and Veterinary Authority AVA of Singapore.
He has prior experience in growing crops of tomato and achieving at least a 95% yield.
In the lab, his supervisor Dr Ong decided to challenge him.
Dr Ong said: “Hi Christopher, welcome to our AVA laboratory. We are
pleased to have you here. We have some problems growing
Rhododendron.”
Christopher replied: “Thank you for your warm welcome. While working
with tomato, I realized that they grow best at around pH 7. Perhaps, it
might work well with Rhododendron too!”
“Oh, you might be right, I’ve read that pH affects the intake of the
nutrients of plants,” Dr Ong exclaimed.
“I think I have to agree with you,” replied Christopher.
“I forgot to mention that the plot of land is on one of the roof top garden of Institute of Chemical and
Engineering Sciences (ICES) at Jurong Island,” mentioned Dr Ong.
As Christopher made his way to Jurong Island, he thought to himself “ I hope this is not as boring as
growing tomato.”
CASE ANALYSIS SHEET
1.
Recognize potential issues and major topics in the case What is this case about?
Underline and list terms or phrases that seem to be important.
Then, list 3-4 biology-related topics or issues in the case.
2. What specific questions do you have about these topics? By yourself, or better yet in a group, list
what you already know about this case in the ”What Do I Know?” column. List questions you would like
to learn more about in the “What Do I Need to Know?” column.
What Do I Know?
What Do I Need to Know?
3. Put a check mark by 1-3 questions or issues in the “What do I need to know?” list that you think are
most important to explore.
4. What kinds of references or resources will help you answer or explore these questions? Identify two
different resources and explain what information each resource is likely to give that will help you answer
the question(s). Choose specific resources or types of resources.
MOE current objective
Theme: Science and technology
Knowledge:

Awareness that science is not confined to the laboratory but is manifested in all aspects of
the world
Skills and processes:

Use scientific inquiry skills such as posing questions, designing investigations, evaluating
results and communicating learning
Ethics and Attitudes:


Show concern for Man’s impact on the environment
Value individual effort and teamwork.
Knowledge:

Discuss how one can change, optimise and define the terms and conditions for tomorrow's food
production for the benefit of future generations.
Resources:
Doyle’s Soil Simulation: http://puzzling.caret.cam.ac.uk/game.php?game=17&age=1
Condition for plant growth: http://www.youtube.com/watch?v=qQfBBRsJovo
Laboratory experiment: Appendix I
Teachers’ note:
Optimum pH for agriculture: http://soil.gsfc.nasa.gov/soil_pH/plant_pH.htm
Appendix I: Laboratory Experiment
Laboratory writeup obtained from:
www.chem.indiana.edu/community/demos
Red Cabbage Juice pH Indicator
Sources: Prof. George Ewing's C100 Demonstration Notes; Prof. Carolyn Huffman's Fall '93
C100 lecture; B. Z. Shakhashiri, 1989, Chemical Demonstrations: A Handbook for Teachers of
Chemistry, vol. 3, pp 162-166.
Description and Concept: Red cabbage juice will change to a variety of colors when added to
solutions of various pH. Red cabbage juice is a pH indicator.
Materials:
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red cabbage*
blender
hot or boiling water
filter paper (coffee filters work well)
1 liter beaker
Six 250 mL beakers
Professors/Instructors please specify which chemicals you wish to use. Some that we
may have on hand are:

household ammonia (NH3)

baking soda (sodium bicarbonate, NaHCO3)

washing soda (sodium carbonate, Na2CO3)

lemon juice (citric acid, C6H8O7)

vinegar (acetic acid, CH3COOH)

cream of tartar (Potassium bitartrate, KHC4H4O6)
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Other household items that may be used include:
antacids (calcium carbonate, calcium hydroxide, magnesium hydroxide...),
seltzer water (carbonic acid, H2CO3),
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muriatic acid or masonry's cleaner (hydrochloric acid, HCl),
or lye (potassium hydroxide, KOH or sodium hydroxide, NaOH).
Safety:
Hydrochloric acid and Sodium Hydroxide are strong irritants.
You should wear safety goggles and disposable gloves for this demo, especially if you
choose to use HCl and NaOH.
Procedure:
Chop cabbage into small pieces.
Put cabbage in 5 liter beaker and then cover with boiling water,
let stand for 10 minutes or more (the more you wait the more potent your indicator).
OR
Put about 2 cups of cabbage in a blender, cover with boiling water, and blend.
Filter out the plant material to get the red-purple-bluish colored liquid. This liquid is at
about pH 7.
Pour about 50 - 100 mLs of your red cabbage indicator into each 250 mL beaker.
Add your indicator to various household solutions until you see a color change.
For example: Ammonia will turn your indicator green, NaOH -yellow, vinegar -red, and
HCl - a deep red.
You could do a neutralization experiment with the indicator. First add an acidic solution
such as vinegar or lemon juice to get a reddish color, then add baking soda or
antacids*** to bring the pH back towards a neutral 7.
Clean-Up: All of the chemicals used in this demo can be washed down the drain with water.
Background:
Red cabbage contains a pigment called flavin. This pigment is also found in red poppies,
blue cornflowers, grapes, and apple skin. Depending on the pH of the fruit or plant the pigment
will give a different color. This pigment can be used to indicate pH.
pH is the -log[H+]. Acids increase the concentration of hydrogen ions ([H+]) in a solution
and therefore have a low pH. A base will increase the concentration of hydroxide ions ([OH-])
(decreasing the [H+]) in a solution and will have a high pH.
Notes:
*Another household item from which a pH indicator can be extracted is Ex-Lax.
Phenolphthalein is a commonly used indicator available from most chemical supply companies
in its concentrated form. A small concentration of phenolphthalein is used as a laxative in ExLax. Caution: Never use concentrated phenolphthalein as a laxative. Death may be the result.
Dissolve Ex-Lax tablet in ethanol to make indicator.
Prof. Tim Starn told me that if a physician suspects that a case of diarrhea was caused by
an ExLax prank, they will test for phenolphthalein by exposing the patients "sample" to UV light.
** The blender method of preparation was done Fall '93 in Prof. Huffman's C100 class.
It worked well in class with hot water from the tap. The other method of preparation has been
done by Prof. Ewing. I have prepared the indicator in this way and it works well also.
***Antacid tablets will only neutralize the acid very slightly ( maybe it will bring the pH
up from 1 to 1.2). You will not observe a color change in your indicator. The baking soda will
neutralize more acid and will bring about a color change. This could stimulate a discussion
about the effectiveness of antacids versus baking soda as a treatment for acid indigestion.
It turns out that the antacids are best because you would not want to completely
neutralize your stomach acid. The antacid tablet is really meant to neutralize the stomach acid
that has entered the esophagus (which causes the heart burn). If a person ingested too much
baking soda, they could actually be in danger of changing the pH of their stomach and blood
dramatically. Many chemical processes and enzymes in our bodies require a specific pH. For
example, we would not be able to digest our food properly if our stomach was not at an acidic
pH.
LEVEL 4
LEVEL 3
LEVEL 2
LEVEL 1
Identification of
the Main Issues/
Problems
Identifies four or more
questions pertinent to the case
Identifies three questions
pertinent to the case.
Identifies two questions
pertinent to the case.
Identifies one question pertinent
to the case.
Analysis of the
Issues
Insightful and thorough analysis
of all the problems/questions
Thorough analysis of most of
the problems/questions
Superficial analysis of some
of the problems/ questions
in the case
Incomplete analysis of the
problems/questions
Comments on
effective solutions
Well documented, reasoned and
thorough comments on
solutions to all
problems/questions
Appropriate, well thought out
comments on solutions to most
of the problems/questions
Superficial comments about
solutions to some of the
problems/ questions
Superficial comments and at
times inappropriate solutions to
some of the problems/ questions
Links to Research
Excellent research into the
problems/questions with clearly
documented evidence –ie.
photos, tables, documents
Good research and
documented evidence with
clearly documented evidenceie. Photo, tables, documents
Limited research and
documented evidence or
unclear evidence
Incomplete research and little
documented evidence or
inappropriate evidence
Time on Task
All group members are on task
and actively engaged the
majority of the time.
Most group members are on
task and actively engaged most
of the time
The majority of the time at
least one person is not
engaged or on task.
The majority of the time, more
than one person is not engaged
or on task.
Interaction between members is
respectful and cooperative the
majority of the time.
Interaction between members
is respectful and cooperative
most of the time.
Interaction between
members is disrespectful or
uncooperative more than a
few times.
Interaction between members is
disrespectful or uncooperative
the majority of the time.
Material is presented in an
orderly fashion and
demonstrates a clear point of
view.
Material is presented in an
orderly fashion but point of
view has some ambiguity
Material presented is
somewhat orderly and point
of view is unclear.
Material presented lack order
and point of view is unclear.
(Group work)
Collaboration
(Group work)
Presentation
Case Based Learning rubric: http://www.bioquest.org/myplantit-2010/workshop_forms/icbl_details.php?project_id=284
Angela Turner
Amit Kashi
Elizabeth Torres Rod
Suggestions for deliverable:
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Skit
Posters
Poems
Comics
Songs
Pamphlets etc.
Things to be included:

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Physical condition of plants growth (eg. Soil pH, temperature, lights, water)
Experimental data (eg. pH value over a period of time)
Specify the targeted audience (eg. Peers, gardeners, experts)