University of Arkansas - AgriScience Project

AGRISCIENCE EXERCISE

PLANT SCIENCE & BIOTECHNOLOGY

Sub-Concept: Leaf Parts and Functions

Agricultural Context: Different plant parts are used for agricultural purposes, each of which serves an important function. Knowledge of plant parts and functions assists in the development and use of herbicides and fertilizers.

Exercise: Leaf Structure and Function

Applied Principle: Leaves play a vital role in the survival and growth of the plant.

Goals:

1. Identify the parts of a leaf.
2. Explain the functions of a leaf and its parts.
3. Observe the parts of a leaf specimen in the lab.

Materials:

• geranium plant leaves
• microscope
• microscope slide
• razor blade/scalpel
• medicine dropper
• cover slip
• water

References: Green, D.E., Woolley, D.G., and Mullen, R.E. (1981). Agronomy Principles and Practice. Edina, MN: Burgess International Group, Inc. Bellwether Press Division.

Chilson, J., Hehn, D. and Sivertsen, D. (1994). South Dakota Agriscience Lab Manual. Pierre, SD: Office of Adult, Vocational and Technical Education.

Trudeau, M. (1994). Plant Morphology and Taxonomy. Ithaca, NY: Cornell University Instructional Materials Service.

Teacher Preparation Notes:

• This activity requires the use of sharp instruments. You may wish to alter the exercise to make it more appropriate to your classroom situation.
• Several plant species are appropriate for this activity. Geraniums are suggested, since they are readily available and their cells are somewhat easier to view with the microscope. You may also wish to include common agricultural plants or even weeds from your area in this exercise.
• You will need to demonstrate the process of tearing a leaf to obtain a sample of the lower epidermis for your students. Hold a healthy leaf topside up in your hands, folding it over to form a crease. As you tear at an angle from the fold, a transparent layer of tissue should be removed from the bottom side of the leaf. Students must take care to keep this layer from wrinkling as it is placed on the microscope slide.
• In slicing a cross-section of the leaf to view the palisade cells and spongy mesophyll, remind students that very thin slices make the best specimens.

Procedures for Conducting the Activity:

2. Demonstrate proper tearing of a leaf to obtain a sample of the lower epidermis, as outlined in the teacher preparation notes. Answer any questions the students may have at this point.

3. Provide each group with the necessary materials and data sheets.

4. Allow the students to proceed through the activity, as instructed on the data sheets. You will need to monitor their procedures and progress; however, it is recommended that they be allowed as much independence as possible in carrying out the lab.

5. Upon completion of the activity, review the discussion questions from the data sheets as a group.

---

AGRISCIENCE EXERCISE

- Leaf Structure & Function -

Student Data/Instruction Sheet

1. Using the scalpel/razor blade, slice a very thin piece of the leaf to obtain a cross-section.

2. Place the slice carefully onto a microscope slide.

3. Place one drop of water onto the slide, and carefully cover the specimen with a cover slip.

4. Using the microscope, first view the specimen on low power, then high power to locate the various parts of the leaf structure.

5. Locate the following cell layers and parts: upper epidermis, palisade cells, spongy mesophyll tissue, chloroplasts, guard cells, and stoma. Draw and label these parts, as observed from your specimens, on the back of this sheet.

6. Complete the following discussion questions. Be prepared to share your answers with the rest of the class at the end of the activity.

a. What is the major function of leaves?

b. Why do you think the upper epidermis has a somewhat waxy cuticle covering?

c. What part of the leaf contained the most chloroplasts? What do you think this infers?

d. How do you think leaves protect themselves from too much water loss?

e. How can knowledge of the structures and functions of a leaf be used in practical agricultural applications?

TEACHER BACKGROUND SHEET

- Leaf Structure & Function -

Leaves are generally classified as either parallel-veined or netted-veined. Parallel-veined leaves contain veins which run parallel and are of mostly equal size; an example is grass leaves. Netted-veined leaves have a few prominent veins, from which many smaller veins branch out; soybean leaves are an example.

The parts and functions of an individual leaf are as follows:

1. Blade - Flat surface of leaf

2. Petiole - Leaf stem which attaches blade of leaf to the plant

3. Veins - Also called "vascular bundles," the veins contain the translocation tissue of xylem and phloem, which transport food and nutrients.

4. Cell Layers

A. Upper Epidermis - Protective upper layer of cells.

B. Palisade Cells - Layer of cells located inside leaf, which contain most of the plant's chloroplasts, and therefore produce most of the plant's food. Note that dicot leaves contain palisade cells, while monocot leaves do not.

C. Spongy Mesophyll - Irregular layer of cells beneath palisade cells which allow veins and vascular bundle to extend into the leaf. Usually has large spaces between cells, allowing for gas movement within the leaf.

D. Lower Epidermis - Bottom layer of leaf, containing stoma and guard cells, which open and close to allow gas and water exchange.

This activity has been accessed Counts file completly FULL times.