Sub-Concept: Process of Seed Development
Agricultural Context: Many agricultural crops are propagated by seeds
Exercise: Seed Anatomy
Applied Principle: Monocot and dicot seeds are different in anatomy, and in appearance.
Goals:
Preparation Time: 1 day
Materials:
References: Trudeau, M. (1994). Plant morphology and taxonomy. Ithaca, NY: Cornell University Instructional Materials Service.
2. Provide each pair with a set of instructions and materials.
3. Remind the students to exercise caution when using the razor blades, and to be careful with the iodine, which can permanently stain clothing.
4. Allow the students to proceed through the activity, carefully supervising their work.
5. After all groups have completed the exercise and put away their materials, lead the class in a
discussion of the questions from their data sheets.
AGRISCIENCE EXERCISE
PART ONE: LIMA BEAN EXAMINATION
1. Using Figure A as a reference, examine a lima bean that has been soaked in water for several
hours. Take note of the small, scar-like marking on one edge called the hilum, This is the point
where the seed was attached to the pod. At one end of the hilum, you will find a tiny opening
called the micropyle; this is the hole through which the pollen tube entered the ovule.
2. Now carefully remove the seed-coats by rubbing the seed between your fingers. Was this coat
thick or thin? _____________________________ What do you think is the function of the seed
coat? _______________________________
3. The rest of the seed should now split into two pieces, or cotyledons. A cotyledon is actually the embryonic leaf; this structure "modified" in many types of plants.
Compared to a leaf, are the cotyledons thick or thin? _________________
What do you think is their function? ____________________________________
_________________________________________________________________
4. Next, scrape the surface of one of the cotyledons with a razor blade, and add a drop of iodine. Wait a minute or so. What did you observe? _________________________________________________________________
_________________________________________________________________
What do you think this indicates?________________________________________
5. one of the cotyledons, you will find a small structure, the tip of which projects toward the
micropyle. This, along with the cotyledons, makes up the embryo. Also note the stalk-like part
pointing toward the micropyle; this is the embryonic stem, called the hypocotyl.
6. At the lowermost end of the hypocotyl is the embryonic root, called the radicle. At the
opposite end, above the attachment of the cotyledons, look for two small, leaf-like structures;
together these form the embryonic bud, or plumule, at the end of a short stem called the epicotyl.
The plumule and epicotyl make up the shoot of the embryo.
7. Add one drop of iodine to the seed coat, cotyledon, epicotyl and hypocotyl. Wait a few minutes. What happened? ________________________________________
__________________________________________________________________
8. Which structure do you think contains the most starch? ____________________ On what did you base this opinion? _____________________________________
_________________________________________________________________
PART TWO: CORN EXAMINATION
1. Look at a grain of corn that has been soaked in water for several hours. At one end, you will
find the point of attachment to the corn cob. Another bump at the top of the grain, is called the
silk scar. This is where the silk (or style) was attached to the grain when the plant was flowering.
2. Look for a white oval area on one of the flat sides of the corn. The embryo lies inside this area.
Using a razor blade, cut the seed in half through the long axis of the embryo. Add a drop of
iodine to the cut surface. What did you observe?
________________________________________________________________ What do you
think this indicates? _______________________________________
3. Using Figure B as a reference, identify the corn embryo and the region of the endosperm.
What kind of material makes up the endosperm? ________________ What do you think is the
function of the endosperm? ________________________
4. Now use a hand lens or dissecting microscope to find two small cavities; within each of which
there is a very small stalk-like structure. The upper one (away from the point of attachment), is
the plumule; the lower one is the hypocotyl. The unstained area around the cavities is the
cotyledon.
5. Which makes up most of the grain in corn, the embryo or the endosperm?
______________________________ Is the cotyledon single or is it a two-part structure?
_____________________________________
6. How does the "seed coat" of the corn compare in thickness with that of the bean? ______________________________________
The "seed coat" in corn actually consists of the ovary wall and the seed coat proper. Since the corn grain really consists of the ripened ovary and its contents, is it really correct to speak of it as a seed? Why or why not?__________________________ ________________________________________________________________
7. Would you expect to find a micropyle near the point of attachment, as in the lima bean? _____ Why or why not? _______________________________________
_________________________________________________________________
8. If the three main parts of a seed are considered the seed coat, the embryo and the endosperm, where is the endosperm in the bean? ________________________
_________________________________________________________________
Note: Remember to put away all materials and clean up your work area when you have finished
the activity.
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