Summer Research Program for Science Teachers
Bergen Academies, New Jersey
2000
Activity #3 Related to Natural Products
Activity 1: Operation of the Microwave Oven for Chemistry Experiments
Activity 2: Extraction of Caffeine from Tea Leaves
Introduction to Activity 3: Natural products are substances produced in living systems that may be useful to humankind, especially in the field of medicine. For example, taxol is a substance derived from Pacific yew trees that has been shown to be effective against certain types of cancer. The extraction of such substances is necessary before their therapeutic value can be evaluated.
This action plan presents three activities related to natural products. One of these is the extraction of a natural product, caffeine, from tea leaves. This has been chosen since the starting ingredients are relatively easy to come by, and the student will still find a reasonable level of challenge. The microwave oven was chosen to provide energy for heating the tea bags, to emphasize the importance of the microwave oven in the field of organic chemistry. Microwave-assisted chemical reactions are increasingly important, especially for organic chemistry. Many chemical reactions that used to take hours now take minutes or seconds with the use of microwave techniques. A simple demonstration of the microwave is included in the action plan. A third activity is the growing of barley under controlled conditions, since it is often necessary to grow plants (or animals) to provide raw material from which natural products can be extracted. The growing of plants offers ample opportunity for open-ended activities
III.
Growing Barley and Detecting the Presence of Amino Acids
Barley is fairly easy to grow in a classroom. It
has even been grown in a windowless classroom under fluorescent
light! The teacher will designate a particular part of the
plant, such as the roots or the shoots, as the target material,
and students will try to grow this target material to the
greatest extent possible for a given amount of starting
materials. Students will conduct experiments in which
conditions will be varied from one setup to another to determine
which conditions are most favorable to plant growth. The
plants grown will be judged not just on the sheer mass of the
roots or shoots produced, but on how free of fungus they are
(fungal growth is one of the major drawbacks when barley is grown
in these conditions).
Objectives:
1. To produce the greatest mass of plant material possible
for 100 seeds of barley.
2. To detect amino acids in barley plant material.
Materials and Equipment
barley seeds (obtainable from grocers
with food of India)
250-mL beakers
10-cm petri dishes
paper towels (various brands)
scissors (for separating target material)
distilled water
bleach (such as Clorox)
balance (preferably electronic)
autoclave
hairdryer
forceps or crucible tongs
Na2HPO4
ninhydrin
2-propanol
notebook and pen
graph paper
round marbles
goggles
glass stirring rod
[Teaching Standard D- Make accessible science materials]
1. Put on goggles.
2. Every student will maintain a notebook for this
activity which will include hypotheses to be tested, plans for
testing hypotheses, data, and results.
3. At the outset, 100 seeds of barley are counted
out by a designated student, and these seeds are massed to
establish the mass of 100 seeds. By doing this, it will be
unnecessary for every student to count out 100 seeds. Instead,
each student will use a mass of seeds equal to that of the
original 100-seed batch. In this way everyone will have
approximately 100 seeds.
4. Autoclave the beakers, petri dishes and marbles
to be used for 15 minutes.
5. Students are to plant seeds in a glass
container (petri dish or a beaker), with nothing but paper towel,
marbles (marbles may be omitted), and water present in the
container with the seeds themselves.
6. Students may water the plants as often as they
wish, but all activities, including watering, must be recorded in
the notebook.
7. Among the variables students may choose are the
frequency of watering, the type of container to be used (beaker
or petri dish), the amount of paper toweling to use, the number
of marbles (if any) to be placed in the container, the way the
paper towel is situated in the container, and the extent to which
seeds are soaked in bleach before being planted (this may be
varied from a condition of no soaking at all to overnight
soaking).
8. Germination may be aided by soaking the barley
seeds in water, usually overnight. Students may modify this
step as follows:
(1) The step may be omitted entirely.
(2) The duration of soaking may be extended or reduced.
(3) The liquid in which the seeds are soaked may have a certain
percentage of bleach included, but
if this is done, the seeds must be thoroughly rinsed before
planting.
(4) Treatment with bleach and soaking in water may be
accomplished in separate steps. The seeds may for example
be soaked for 5 minutes in 30% Clorox, then rinsed. Then,
the seeds may be soaked in ordinary distilled water for a predetermined
duration.
9. A committee of five students will set ground
rules for the investigation. For example, conditions for a
control setup for the class will be specified, and criteria
for disqualifying plantings will be established. The
committee will decide criteria for excessive fungus, which will
result in the “farmer” having to start over again, with
a new harvest date specified by the committee. (The
committee may want to limit replantings to one time, to allow the
class investigation to be completed on schedule.)
10. Seeds may be planted in various settings.
For example, the control planting may be set up close to a
window, while one of the experimental plantings may be set up
away from sunlight but under fluorescent light, to compare the
effect of sunlight with that of artificial light on growth.
11. Plants are harvested 10 school days from when
they were planted, or earlier, if the student so chooses, and the
target material is massed to determine how well the student
did. [Teaching Standard D- Structure time for extended
investigations] Each student has his
or her own container. The committee will have to establish
some means of monitoring the growth of the plants; for example,
students might measure and record the height of the tallest plant
each day, and record this in a table. A graph based on this
table will be required of each student to show the progress of
the plant growth as a function of time. [9-12 Content Standard A- Use mathematics to improve scientific
communication] Each student will prepare a
computer spreadsheet of the table, and computer-generated
graphs will be made. Each student will take a turn
describing his or her results to the class, using charts and
computer generated graphs to illustrate the presentation.
12. Students will take the harvested plants,
separate the target material, and place this material in a
solution of Na2HPO4 (10 grams per 100 mL of
solution should be sufficient) to soak overnight and break up
proteins into amino acids.
Note: Ninhydrin is poisonous and the ninhydrin
solution can cause skin to turn purple. Be sure to
wear gloves for this step.
13. After putting on gloves, prepare a ninhydrin
solution as follows:
(1) Mass 0.10 g of ninhydrin and place it in a test tube.
(2) Add 10 mL of 2-propanol.
(3) Seal the end of the test tube with Parafilm and shake.
(4) Place in a test tube rack. Be sure to label this ninhydrin
solution so that it may be saved for future use.
14. Using a clean capillary tube, transfer a small
amount of the liquid from the Na2HPO4
solution the barley has been soaking in, to a clean piece of
filter paper. Then use a stirring rod to transfer a small
drop of ninhydrin solution to the same spot on the filter paper.
Wash and dry the stirring rod.
15. While holding the filter paper with a forceps
or crucible tongs, heat the spot with a hairdryer. If amino
acids are present, the spot will eventually turn purple.
16. Clean up. Save the ninhydrin solution
for future experiments.
Students will report their results to the class. Based
on these results, students will make hypotheses predicting the
heights of plants grown in a subsequent cycle, and will then grow
plants again, to test the hypotheses.