Materials Included In Kit

Additional Materials Required

Safety Precautions

The materials given in this kit are considered non-hazardous. Follow all normal safety guidelines.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The seed samples may be saved and used as many times as desired. All items in this kit may be disposed of according to Flinn Suggested Disposal Method #26a.

Teacher Tips

• The seeds provided in this kit may vary from the actual material list due to availability. All efforts will be made to match the same type of sample (e.g., shape, size) as needed.

• The reproducible Seed Identification Key, data tables and Post-Lab Questions should be copied and given to students.
• The tree seed samples may be saved and used as many times as needed.
• Two packages of each type of seed are included.
• Have students identify the genus and species names of each seed.

Further Extensions

• As an extension, have students predict the dispersal method for each seed. Have students drop several seeds from the same height and see which seeds travel the farthest. Repeat the experiment again on a windy day or drop the seeds in front of a fan.
• You may wish to have students collect their own seeds outside of class. Have students classify the seeds and what type of plant or tree the seed came from using seed or tree identification guides.
• Have students write their own classification guides for their collected samples.

Sample Data

Part I. Seed Identification

Part II. Forms of Fruits

Answers to Questions

Part I. Seed Identification

1. What are some identifiable features that are used to classify the unknown samples?

Size of seeds and fruit, color, shape, etc.

2. What other features could be used to classify seeds and fruits?

Method of dispersal, the type of tree the seed came from and the tree’s associated features (e.g., leaf shape, tree height, type of bark).

3. Which of the samples tested in this lab do trees in your area produce?

Answers will vary.

4. How is a fruit produced?

When an egg is fertilized by a pollen grain (the male spore of a plant), a seed forms within the ovary. As nutrients enter into the flowers of an angiosperm, the nutrients are obtained by the endosperm tissue (the food source of the growing seed). Many nutrients are also used in the wall of the ovary that surrounds the seed. Over time, the wall of the ovary thickens and combines with parts of the plant, such as the sepals, petals and the stem, to collectively form a fruit.

5. What is the difference between an angiosperm and a gymnosperm?

Angiosperms are flowering plants whose seeds develop within a ripened ovary (fruit). Gymnosperms have exposed seeds that are usually in a cone type shape.

6. What fruit type was most prevalent in the unknown samples?

Nut-shaped fruits were the most prevalent.

7. Why are some types of trees genetically engineered to produce no seeds or fruit?

Seedless fruits are produced commercially for supermarkets. Also, certain trees may be genetically engineered to be seedless for lawn cleanup purposes.

Teacher Handouts

10363_Teacher1.pdf

References

Gotfried. S.; Hampton, C. D.; Hampton, C. H.; Leibel, W.; Madrazo, G.; LaMoine, M.; Motz, L.; Sinclair, D.; Skoog, G. Prentice-Hall Biology; Prentice-Hall, New Jersey, 1990; Chapter 23.

Introduction

Seeds are found in a tremendous variety of sizes, shapes and colors. Each species of tree produces its own unique seeds. In this activity, various tree seeds will be classified and identified.

Concepts

• Seed identification

• Angiosperms
• Dispersal of seeds
• Gymnosperms

Background

Seeds are reproductive packages that contain a plant embryo and a stored supply of food all within a protective seed coat. Many seeds can withstand adverse environmental conditions, such as intense heat or extreme cold. Seeds do not need a supply of standing water to reproduce. This means that seed-bearing plants may reproduce anywhere at almost any time (unlike mosses and ferns which require standing water to reproduce).

There are two main types of live seed bearing plants—Gymnosperms and Angiosperms. Gymnosperms are seed plants that have exposed seeds (the seeds are not formed in a fruit) that are usually in a cone-shaped structure. Angiosperms, on the other hand, are flowering plants or trees whose seeds develop within an ovary that becomes a fruit.

Gymnosperms, which include conifers, usually have two types of cones—male cones and female cones. Male cones produce pollen and female cones produce eggs. When the pollen is blown from the male cone and enters the female cone, fertilization may occur. If the female cones become fertilized and produce seeds, they are known as seed cones. When the seeds become fully mature, the scales of the cone eventually open and the seeds are dispersed by the wind (see Figure 1).

The flowers of angiosperms are composed of female and male structures. The female structure of a flower is known as the pistil. The pistil is composed of a stigma, style and ovary (see Figure 2). The male organs of a flower are known as stamens. Stamens are composed of two parts—a filament and an anther. The filament is the stalk-like structure, which gives rise to the anther (see Figure 2).

When the anthers of a flower mature, they open up and release pollen (the sperm cell of a plant). If and when a pollen grain lands on the sticky surface of the stigma, pollination occurs. The pollen grain begins to form a structure known as a pollen tube. The pollen tube grows downward through the stigma and style and eventually reaches the ovary (the reproductive organ of a flower that contains egg cells). Once the pollen tube reaches the ovary, the egg and sperm cells unite and fertilization occurs. The fertilization process eventually produces an embryo (seed) and an endosperm.

As nutrients enter into the flowers of an angiosperm, the nutrients are used by the endosperm tissue (the food source of the growing seed). Many nutrients are also absorbed in the wall of the ovary that surrounds the seed. Over time, the wall of the ovary thickens and combines with parts of the plant, such as the sepals, petals and stem, to collectively form a fruit (see Figure 3).

Fruits come in various shapes and sizes and can be broken down into six generic categories: winged, nut, pod, berry, cone and capsule.

Winged—fruit contains an elongated “fan”-like structure
Nut—fruit has a hardened ovary wall that forms a protective outer shell
Pod—fruit splits open on two sides; seeds are exposed when pods are opened
Berry—fruit has soft outer shell and generally contains a large amount of seeds
Cone—fruits have seeds that are exposed; seeds form in a scale-like form
Capsule—fruit usually contains small seeds that are surrounded by a hardened seed coat

The way a seed is dispersed from a fruit is important for species survival. The chances of survival of an individual tree or plant species increases if the seed can be carried away from the plant to a variety of environments. Four different methods of seed dispersal are common: water, wind, animal and mechanical dispersal.

Water is used as a dispersal agent for fruits such as water lilies or coconuts. Both of these fruits have membranes that allow the seed from the fruits to float on water. The seeds are usually dispersed through waterways, such as lakes, rivers or oceans.

Wind is a major dispersal agent for many types of seeds. Seeds such as the ash or maple are flattened and tend to be caught by the wind as they fall through the air. Seeds that are in the form of tufts of hair can also be propelled for long distances by the wind.

Dispersal of seeds by animals is done in various ways. First of all, seeds of fruits can be eaten by animals and deposited in different areas after the seeds travel through their digestive tract. Fruits that are brightly colored tend to attract animals and birds and are good candidates for this type of dispersal. Many seeds also need to be exposed to the digestive juices in the animal in order to help break down the tough seed coat before germination can occur. Secondly, some plants have developed mechanical adaptations, such as hooks or burrs that catch onto the fur of animals. The seeds are then carried away, fall off the animal’s fur and are deposited in other locations.

Materials

Procedure

Part I. Seed Identification

1. Obtain a copy of the Seed Identification Key.
2. Obtain one of the unknown samples. Use the Seed Identification Key to classify the unknown sample.
3. When looking at the key, you will have options at each step. For example:

1a. Fruit is a woody cone, ½" to 2" long . . . . . . . . . . . . . . . . . . . . . . Scotch pine
1b. Fruit is not a cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

You will choose an option at each step (i.e., if the fruit is not a cone, continue on to step 2). Work your way through the key until all of the samples have been identified. Record the identities of the samples in the Seed Identification Data Table.

4. Obtain another unknown seed and repeat step 2.
5. Continue classifying until all of the unknown samples have been identified.
6. Answer the questions for Part I in the Post-Lab section.

Part II. Forms of Fruit

7. Obtain one of the 12 identified samples.
8. Record the seed name next to its number in Part II of the data table.
9. Classify each sample as an angiosperm or gymnosperm in Part II of the data table.
10. Identify the fruit type of the sample. Use the fruit classifications from the Background section.
11. Repeat steps 5–8 with the remaining seed samples.
12. Answer the questions for Part II in the Post-Lab section.

Student Worksheet PDF

10363_Student1.pdf