Corny Data
Experiments with corn to demonstrate germination, gravitropism, and etiolation
Janice H. Haldeman, Ph. D.
Professor Emerita of Biology
Department of Biology
Erskine College
P.O. Box 338
Due West, SC, 29639
864-379-8724
[email protected]
Corny Data: Growth and Response in Plants
Introduction:
What if seeds had to be deliberately planted with their future root pointing down and their
future shoot pointing up? Sowing seed by scattering or dropping wouldn't work! Planting fields
and
gardens could be pretty tedious. Fortunately for the farmer and the gardener, the seeds "know"
whch
way is up!
When a seed is planted, it's important for the new plant it contains (embryo) to be able to
quickly anchor itself in the soil. The first part of the embryo to grow out of the seed is the future
root. No matter how the seed lands in the soil, roots grow toward the force of gravity. This
phenomenon is termed a positive gravitropism. The future shoot part of the plant grows away
from the force of gravity, usually in a direction that will get it out of the soil and into the light,
the pIant's vital source of energy. This phenomenon is termed a negative gravitropism. These
responses require the seed parts to grow at different rates in order to "choose" the right direction!
For many years, plant scientists have been fascinated with this "built in" wisdom that enables
plants to move in the right
direction.
Plants also grow and move in response to light. Phototropism is a term for plant growth
movements in response to light. Older plants grow in a way that places their leaves in the best
position to capture light. Houseplants demonstrate this when their leaves turn and bend toward a
window. To keep their fullest, most attractive sides facing the room, houseplants must be turned
periodically. The shoot of a young seedling planted in the soil responds by growing quickly
toward light. If light is not found, the shoot will respond by growing even faster, "stretching up"
to get to vital light before food energy stored in its seed is used up. This process is called
etiolation. Older plants will also etiolate, (elongate, grow spindly and appear yellow) when their
light source is cut off. You may have noticed this response in lawn grass after being covered up
for several days by any piece of equipment that shields plants from light.
Over 100 years ago, Charles Darwin and h s son Francis were two of the first to conduct
experiments to demonstrate plant growth movements like gravitropism and phototropism.
Researchers today are still worlung to explain the mechanisms of motion in plants.
Obiectives:
1. To observe and learn about structure of corn kernels and their responses to stimuli such as
light and gravity.
2. To formulate and test hypotheses about behavior of growing seedlings.
3. To collect and analyze data on plant growth, and response to stimuli.
Materials:
Plastic sandwich baggies
1 % Clorox solution 20 ml syringes or graduated cylinder
Tape
Rulers
Alcohol wipes
Marking pen
Iodine solution
Soaked bean and corn kernels (seed corn)**
Procedures:
1. Seed preparation and study. The corn kernels have been soaked for 48 hours in a one
percent solution of Clorox. Observe the kernels, in the dish and see if you can notice differences
in appearance of their largest flat sides. One side has a shield shaped lighter region with a
vertical swelling running down the middle. The swelling is the embryo axis and the shield
shaped lighter areas is the cotyledon. Corn is a monocot, meaning that its seeds have one
cotyledon (seed leaf), compared to dicots such as soaked beans, also in the dish with the corn
kernels, which have two cotyledons. Remove the seed coat from a bean and separate its two large
halves each of which is a cotyledon. On the inner surface where they attach, you should be able
to see the bean's embryo. Compare the bean and corn. Beans develop inside their fruit which is a
pod that developed from the bean flower's ovary. Maybe you have shelled some lima beans to
remove the seeds which are eaten. With string beans, which you may have "snapped" both fruit
and seed are eaten. A kernel of corn is actually a one seeded fruit called a grain. Each kernel
developed from an ovary on the "ear" of corn, composed of female flowers, and the seed coat
represents ovary remnants. Make a longitudinal section through a corn kernel, cutting the
embryo in half.. Place a drop of iodine solution on the cut surface and note which part turns
black ( the endosperm) , a positive test for starch. This is the food source for a corn seedling
until it begins to make its own food by photosynthesis. Your section should match the diagram of
a longitudinal section of a corn kernel below. You should also be able to distinguish the
cotyledon, a leaf like structure of the embryo which stores some nutrients and is just next to the
endosperm. The embryo is next to the cotyledon. Its structure consists of an epicotvl (future
leafy shoot) and a radicle (future root). A stem develops from the region comnect3ng epicotyl
and radicle and it is called the hypocotyl, Label the diagram with terms above that are in bold
print and underlined .
Fig. 1 Embryo side and longitudinal section of a corn kernel.
2. Planting the seeds. Baggies for seed germination have been prepared in the following manner:
A paper towel is folded so that they form a lining for the plastic bag. A marker is used to draw a
line across the bag, 3 inches from the top of the bag, where the kernels of corn will be "planted".
Staples across the line form three one inch long chambers in which one kernel of corn is placed
between the towel lining and the bag. Use an alcohol wipe on your hands before "planting" the
corn kernels. Be sure that all kernels are placed with the lighter shield shaped region (embryo)
facing outward. Refer to Figure 2 below, and place one kernel with developing root end
pointing down, one up, and one horizontal Fill a syringe with 10 mL of freshly prepared 1%
Clorox solution and squirt all of it onto the towel, then seal the bag. At the bottom corner mark
bags with your initials, the date, and "dark" or "light" depending upon assignment of conditions
for your bags.
Fig. 2. Corn kernels placed in bag for gravitropism demonstration,
3. Placement of baggie planters. Use the tape to hang the "dark" baggies vertically on the inside
of one of the lab cabinet doors. Hang the "light" baggies vertically on a lighted wall designated
by the instructor.
1. Formulate hypotheses about:
a. When the seed starts to grow, will the shoot or root appear first? What is your hypothesis?
b. Which direction with respect to the force of gravity will roots grow? Which way will shoots
grow?
c. Which condition, light or in the dark will produce the longest shoots?
d. What sort of differences in shoot and root color might occur when grown with and without
light?
2. Observe seed's growth and record information about: . . . . . . a., b., c., and d. above. . . . . . .the structure and function of seeds. Which part of the embryo appears first as the seedling
grows? Refer to the labeled diagram of the corn kernel.
..... responses of roots and shoots to gravity (gravitropism) and light (phototropism and
etiolation) Record on data sheet.
3. Record and analyze data by:
... calculation of germination percentages (Number of seeds planted compared to the number that
grew) Record on data sheet.
... measurement and graphing data ( length of dark-grown and light-grown shoots recorded and
plotted over time ) Record on data sheet and use Excel or graph paper for your lab report.
Data collection:
Examine your corn seedlings according to a schedule provided by the instructor. Note the
direction of shoot and root growth on the gravitropism experiment. Measure the shoot lengths of
the seedlings growing in the light or dark. Record these observations and measurements on the
data sheet. Using Excel or graph paper, produce graphs from your experiment and the averages
from the class’ shoot length data.
Questions:
1. Of what value to plants are the seedling's growth responses to the force of gravity?
2. What would be your prediction about seedling's growth (direction of roots and shoots if the
experiment was performed in a space shuttle?
3. What difference(s) did you observe in dark and light grown seedlings?
-in shoot length?
-in color of shoots?
-in direction of growth of roots?
-in direction of growth of shoots?
-in % germination?
4. Which condition (Light or Dark) stimulated the greatest amount of shoot growth in your
experiment? Did other experiments demonstrate the same results?-
5. Did your data on shoot growth in light vs. dark support or cause you to reject your hypothesis.
Explain.
6. Did class data on shoot growth in light vs. dark support or cause you to reject your hypothesis.
Explain.
References:
Barrett, Paul H., ed. 1977. The Collected Papers of Charles Darwin. Vok. 2, Chicago:
The University of Chicago Press.
Haldeman, Janice H. and M. S. Gray. Experiments with Corn to Demonstrate Plant
Growth and Development American Biology Teacher. 62:No.4. April 2002.
Moore, Randy and W. Dennis Clark. 1995. Botany. Plant Form and Function. Dubuque
IA: Wm. C. Brown Publishers.
Salisbury, Frank B. and Cleon W. Ross. 1992. Plant Physiology, Third Edition.
California: Wadsworth Publishing Company. Simons, Paul. 1992. The Action Plant: Movement
and nervous behavior in plants. Blackwell's.
Simpson, Beryl Brintnall and Molly Conner Ogorzaly. 1995. Economic Botany, Plants in
Our World. McGraw-Hill, Inc.
*cartoon image from page 1 with permission from Food and Nutrition Services, Fairfax County
Public Schools.
* * Any viable corn seed can be used. Garden seed sold in bulk is often treated with pesticide,
indicated by an indelible red powder the kernels. This seed should be washed with soap and
rinsed thoroughly. Liquid dishwashing detergent works well for the wash. Place kernels in a
pint jar and fill with water and 4 or 5 drops of detergent. Cover and shake periodically for 3
minutes, drain and rinse three times with tap or bottled water. Sweet corn kernels are wrinkled,
so starchy corn is preferable. Feed corn works well and is one of the best to demonstrate the pale
yellow oval shield ( cotyledon ) on the embryo side. These seeds will require sorting to remove
any cracked or insect damaged. Insects leave a black spot at the small end of the kernel. In
other words as they say in the South, you'll "look the seeds" just like you "look the beans"!
A. Gravitropism. Direction of shoots and roots with respect to gravity after _______ days.
(+ = toward gravity, - = away from gravity, I = perpendicular to gravity)
Sample
1
Shoots
Roots
2
3
B. Etiolation
Sample
Length light
(Day # ___)
Length dark
(Day # ___)
Length light
(Day # ___)
Length dark
(Day # ___)
Length light
(Day # ___)
Length dark
(Day # ___)
Length light
(Day # ___)
Length dark
(Day # ___)
Length light
(Day # ___)
Length dark
(Day # ___)
Length light
(Day # ___)
Length dark
(Day # ___)
1
2
3
C. Averages
Sample
Your Group
Class
D. Seed Germination Data (for entire class)
Treatment
Dark Treatment
# of seeds
Light Treatment
Total
# of seeds germinated
% germination
The Story of Corn (a corny story?)
Corn or maize (Scientific name : Zea mays) is the only cereal ( grain) crop that originated in the
New World. Archeological evidence indicates that corn has been domesticated for at least 5000
years. It formed the basis for civilizations such as Maya, Aztec, and Inca. It was one of the North
American Native's four sacred plants, along with squash, beans and the now infamous tobacco.
Planting corn and beans together was a common practice in both North and South America when
Europeans reached the New World. In grade school we learned that native North Americans
showed Pilgrims how to grow corn and beans. According to one Native American legend, the
growing of corn and beans came about when "man-corn" was looking for a wife. Squash asked to
be considered, but was rejected because she had the habit of wandering lasciviously over the
ground. Bean, however, clasped the corn stalk dearly, demonstrating her fidelity, and so became
the chosen one. In Native American art the theme of corn as a revered plant appears often. The
design* below pictures from top left clockwise, corn, squash, beans and tobacco.
Modem corn is unlike most other members of the grass family. The plants grow a tassel of male
flowers at the top and female flowers along the stem. Female flowers are tightly packed together
and form the cob. Each kernel is botanically a fruit, having developed from an ovary of each
flower. The corn "silks" are remnants of styles of female flowers. A corn stalk produces
specialized supporting prop roots that grow out of its base.
Even though there are thousands of cultivated varieties of corn, there are six main types: pod
corn with husks around each kernel, flint corn with long hard ( starchy) kernels, dent corn with a
dent in the top of each kernel, popcorn with starchy kernels inside a tough coat, flour corn with
soft starchy kernels, and sweet corn with sugars in the kernels. The last is the main variety eaten
in the United States. Diagrams* of these are shown below:
1. pod corn
2. dent corn
3. flint corn
4. popcorn 5. flour corn
6. sweet corn
Corn doesn't have the same nutritional value as other grains, because it lacks the amino acids
(units that make compose proteins) tryptophan and lysine. Corn is also relatively low in total
protein. Whenever people depend upon corn for most of their diet, they run a risk of developing
a deficiency disease called pellagra, with symptoms of dermatitis, diarrhea and dementia. This
disease was a serious health problem of rural North Americans in the first quarter of the 20th
century, because their diet consisted mainly of cornbread, molasses, and a little salt pork. The
problem was largely solved by encouraging them to add yeast, rich in tryptophan and lysine, as a
food supplement.
Generally between 80 and 90 percent of the United States corn crop is used to feed animals,
mainly hogs. Both the grain and silage made from stalks are used for animal feeds. Additional
corn products include: corn syrup, corn starch, grits, corn oil, margarine and alcohol.
*Simpson, Beryl Britnall and Molly Conner Ogorzaly. 1995. Economic Botany: Plants in Our
World. McGraw-Hill, Inc. New York.
GLE’s Corny Data:
IN.1.A.5,6,7,8.a Formulate testable questions and explanations
IN.1.A.5,6,7,8.b Recognize the characteristics of a fair and unbiased test
IN.1.A.5,6,7,8.c Conduct a fair test to answer a question
IN.1.A.5,6,7,8.d Make suggestions for reasonable improvements or extensions of a
fair test
IN.1.B.5,6,7,8.a Make qualitative observations using the five senses
IN.1.B.5,6,7,8.b Determine the appropriate tools and techniques to collect data
IN.1.B.5,6,7,8.c Use a variety of tools and equipment to gather data
IN.1.C.5,6,7,8.a Use quantitative and qualitative data as support for reasonable
explanations
IN.1.C.5,6,7,8.b Use data as support for observed patterns and relationships and
to make predictions to be tested
IN.1.C.5,6,7,8. c Evaluate the reasonableness of an explanation
IN.1.C.5,6,7,8.d Analyze whether evidence supports proposed explanations
IN.1.D.5,6,7,8.a Communicate the procedures and results of investigations and
explanations through oral presentations, drawings and maps, data tables, graphs,
and writings
LO.1.A.6,8.a Describe the common life processes necessary to the survival of
organisms
LO.1.C.6.a Recognize all organisms are composed of cells, the fundamental units
of life, which carry on all life processes
LO.1.D.8.a Identify and contrast the structures of plants and animals that serve
similar functions (e.g., taking in water and oxygen, support, response to stimuli,
obtaining energy, circulation, digestion, excretion, reproduction)
LO.1.E.5.b Distinguish between plants (which use sunlight to make their own food)
and animals (which must consume energy-rich food)
EC.1.D.6.a Describe beneficial and harmful activities of organisms, including
humans (water pollution, restoration of natural environment, river bank/costal
stabilization, recycling, channelization, reintroduction of species, depletion of
resources), and explain how these activities affect organisms within an ecosystem
EC.1.D.6.b Predict the impact (beneficial or harmful) of natural environmental
change in an ecosystem
EC.1.D.6.c Describe possible solutions to potentially harmful environmental
changes within an ecosystem