Parts of a Bean Seed
Exterior and Interior
Given the right amount of water, oxygen, and warmth, most seeds germinate and develop into mature plants. Seeds vary in physical appearance both on the outside and on the inside.
In this project you will have the opportunity to identify exterior and interior seed parts. The seed parts of two basic seed types, dicotyledons and monocotyledons, will be compared. You will determine why the cotyledon is necessary and investigate the presence of starch in each seed part.
Purpose: To dissect a bean seed and identify its parts.
- 8 to 10 pinto beans
- 1-pint (500-ml) jar distilled water
- Paper towel
- Magnifying lens (handheld type)
- Place the beans into the jar and cover them with distilled water.
- Put the jar of beans in the refrigerator to reduce bacterial contamination.
- Soak the beans for 24 hours.
- Remove the beans from the jar and place them on the paper towel to absorb the excess water.
- Inspect the outside of the beans and identify the seed coat and hilum (see Figure 14.1).
- Use your fingernails to carefully remove the seed coat from one of the beans.
- Very gently pry the rounded side of the bean open like a book with your fingernail.
- Spread open the two halves of the bean.
- Use the magnifying lens to study the inside of each bean half and identify the cotyledon, plumule, epicotyl, hypocotyl, and radicle (see Figure 14.1).
- Open several beans and compare their parts for differences in size, shape, and organization.
The brown seed coat is thin and peels off easily to reveal a white structure with two separate halves connected at the top. Inside is a cylindrical structure with what appears to be folded leaves at the end.
The bean seed consists of three basic parts: a seed coat, an embryo, and two cotyledons. The surface covering of a seed is called the seed coat. This jacket around the seed protects the embryo (an organism in its earliest stage of development) from insects, disease, and other damage. The hilum is the scar on the seed coat of some seeds, such as beans; it is the point where the seed was attached to the plant during development.
A bean has two halves under the seed coat called cotyledons, so it is called a dicotyledon or a dicot (a plant whose seed has two cotyledons). The end of the embryo that develops into the shoot (part of plant that grows above ground) is called the epicotyl. The tip of the epicotyl that looks like folded leaves is called the plumule (embryonic shoot tip that consists of several tiny, immature leaves that at maturity form the first true leaves). Below the epicotyl is the hypocotyl, which attaches the embryo to the cotyledon. The end of the hypocotyl, called the radicle, develops into the root.
Try New Approaches
CAUTION: Adult supervision is needed when cutting with a sharp instrument. Always cut in a direction away from your hands and fingers.
- While dicotyledons have two cotyledons, monocotyledons, also called monocots, have only one cotyledon. How do the seed parts of a monocotyledon compare to those of a dicotyledon? Repeat the experiment replacing the bean seed with corn seed. Note: A corn kernel is a fruit. The corn seed is inside the fruit, but the kernel is often called a corn seed. Corn seed is much more difficult to open and may require the use of a scalpel. As in the original experiment, study and identify seed parts (see the corn kernel diagram in Figure 14.2).
- Seeds vary in size, shape, and color. Science Fair Hint: Collect and display samples of seeds. Organize the seeds to indicate which are angiosperms (flowering seed plants) and which are gymnosperms (a nonflowering seed plant). Further classifications, such as how the seeds are transported, can also be used. For information about seeds see Cynthia Overbeck's How Seeds Travel (Minneapolis: Lerner Publications Company, 1990).
- Use a stereomicroscope (dissecting microscope that allows thick specimens to be observed) to study, identify, and compare the parts of bean seed and corn seed. Science Fair Hint: Diagram the parts of each seed type, label the parts, and display the diagrams.