Materials Included In Kit

Additional Materials Required

Safety Precautions

The materials given in this kit are considered relatively nonhazardous. Follow all normal class guidelines.

Disposal

The leaf samples may be saved and used as many times as desired.

Teacher Tips

• The leaf samples provided in this kit may vary from the actual material list due to availability. All materials are reusable.
• All efforts will be made to match the same type of sample (e.g., shape, size) as needed.
• The reproducible Leaf Identification Key, Leaf Master Sheets and Leaf Identification Worksheet may be copied and given to students.
• The leaf samples may be saved and used as many times as needed.
• Two packages of each type of leaf are included.
• Leaf Master Sheets (including each type of leaf sample) are also included and may be given to students for classification of the leaves for homework or if some of the leaf samples are lost or destroyed.
• Have students identify the genus and species names of each leaf.
• Have students write their own classification guides for their collected samples.
• Student-collected leaves may be pressed and saved using a plant press. Flinn Scientific sells a plant press, (FB1115) or one may be constructed in the classroom using the following procedure:
  1. Obtain two pieces of thin plywood approximately 16" x 16" in size.
  2. Obtain a sheet of folded newspaper approximately 11½" x 14" in size.
  3. Place a leaf sample between the folded newspaper sheets.
  4. When pressing multiple leaves, place sheets of corrugated cardboard between each sheet of folded newspaper.
  5. Place a heavy item, such as a brick, on top of the plywood or wrap the plywood sheets with a belt to “press” the leaves.
  6. Leaves should be pressed for approximately one month.
  7. Drying time of the leaves will be accelerated if the press is placed in direct sunlight or next to a fan.
  8. Leaf samples may be mounted on heavy cardstock or leaf collection books after they have dried.

Further Extensions

• A field trip may be set up to identify trees in your area. A tree finder guide is provided for such an activity. Additional Tree Finder Guides may be purchased from Flinn Scientific (Catalog Number FB1278).
• You may wish to have students collect their own leaves outside of class. Have students classify the leaves and what type of tree the leaf came from using tree finder guides.

Sample Data

Leaf Identification

Answers to Questions

1. Other than leaves, what other characteristics could be used to help identify trees?

   Genes, flowers, fruit, branches or twigs, bark and crown form.

2. Many desert plants close their stomata during the day and open them at night. How has this adaptation allowed these plants to thrive in desert conditions?

   By closing the stomata during the day when the temperature is the highest and opening them at night when the temperature is much cooler, desert plants are able to significantly reduce water loss, which enables them to inhabit warmer, dryer climates.

3. Create your own leaf to sketch by choosing one option from each of the characteristics found in Figures 3a through 6 in the Background information. Label and identify each of the five characteristics you selected.

   Answers will vary based on characteristics the student selects.

Introduction

Leaves can be found in a wide variety of sizes, shapes and colors. Each species of tree produces its own variation of leaf. In this activity, thirteen different leaves will be classified and identified.

Concepts

• Identification
• Classification
• Dichotomous key
• Leaf structures
• Photosynthesis

Background

The leaf has often been called the most wonderful factory on Earth. Leaves capture the Sun’s energy and undergo a process known as photosynthesis. Photosynthesis is the chemical process that uses light, carbon dioxide and water to synthesize food and produce oxygen. Leaf tissues are highly specialized and are composed of cells containing various pigments. The most important pigment is chlorophyll. Chlorophyll is the substance that traps energy from sunlight and gives plants a green pigment. Chlorophyll (and the light energy it traps) is contained in structures called chloroplasts.

Besides photosynthesis, leaves also carry out other exchanges with the atmosphere. It is through the leaf that the plant respires (taking in carbon dioxide and expelling oxygen) and transpires (loses water). The tissues of leaves contain specialized structures called stomata. Stomata are kidney-shaped structures that form microscopic openings in the leaf (see Figure 1). These openings work like valves that will open and close depending on the amount of water pressure, or turgor, in the leaves. The amount of water in the leaves determines if the stomata will open or close, permitting or preventing transpiration or water loss through the leaves. In nearly all plants, stomata are primarily located on the undersurface of the leaves and will vary in number depending on the environment surrounding the plant. The cuticle is a waxy protective barrier on the outermost surface of the leaf. It not only prevents excessive transpiration, but it also allows water to run off the surface of a leaf.

Most leaves have a flattened, generally broad portion called a blade and a slender stalk known as a petiole. Petioles generally run into the base of the leaf blade and form the mid-rib or main vein of the leaf. The place where the petiole or leaf stalk attaches to a stem is known as a node (see Figure 2). Leaves have many different shapes, sizes and margins (or edges). Some common leaf shapes and margins are shown in Figures 3a and 3b. Most leaves are arranged on the stem in three different ways—alternate, opposite and whorled (see Figure 4). Alternate leaves are positioned on the stem one per node and will first form on one side of a stem and then on another. Opposite leaves are positioned two per node and grow at an angle of 180 degrees from each other. Whorled leaves are found three or more per node. Leaves are primarily divided into simple and compound groupings (see Figure 5). Simple leaves usually have one leaflet, a stalk and a bud at the base of the stalk. Compound leaves have a stalk that branches into a number of leaflets. Leaves may also be classified by their parallel or pinnate vein structures (see Figure 6). Leaves come from either deciduous or coniferous (evergreen) trees. Deciduous trees have flat broad leaves that are lost every year to ensure a rest period where metabolic functions are greatly reduced. Deciduous trees produce flowers that develop into seeds after they are pollinated. Oaks and maples are examples of deciduous trees. Conifers keep their leaves and remain green year round. They can withstand very cold temperatures and heavy snow. Coniferous trees produce cones instead of the flowers seen on deciduous trees. Examples of conifers are pines and spruces.

Materials

Procedure

Part I—Leaf Identification

1. Obtain a copy of the Leaf Identification Key.
2. Obtain one of the unknown leaf samples. Use the Leaf Identification Key to classify the unknown sample.
3. When looking at the key, there are several options at each step. For example:

   1a. Leaves are scalelike or needlelike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   1b. Leaves are not scalelike or needlelike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   Choose an option at each step (i.e., continue on to step 2 or step 3). Work your way through the key until all of the samples have been identified. Record the identities of the samples in the Leaf Identification Worksheet.

4. Obtain another unknown leaf and repeat steps 2 and 3.
5. Continue classifying until all of the unknown samples have been identified.
6. Answer the Post-Lab Questions.

Student Worksheet PDF

11753_Student1.pdf