Topic: ALL ABOUT LEAVES

Source: A seminar presented in Central Illinois Saturday Science Education Seminars for Elementary Teachers

Presenter: Donald Schmidt Biology Horticulturist Illinois State University Normal, IL 61790

Funded by: Scientific Literacy Center Illinois State Board of Education 1990-1993

Abstract: All About Leaves was a seminar that focused teachers on activities that could be conducted with children using various types of leaves. Teachers learned about collecting leaves, growing plants with specific types of leaves, and developing leaf activities which taught children how to collect, record, and interpret data with leaves.

ALL ABOUT LEAVES (Teacher Copy)

INTRODUCTION

All About Leaves is a set of activities that focus on interesting studies children can do with leaves. Too often teachers use the excuse they can't do hands-on science because they lack classroom materials and equipment. Yet, leaves can be found in the school dooryard and study equipment is minimal. Here students use process skills to collect and classify various kinds of leaves, study the importance of various leaf shapes, and recognize the importance of the relationship between water and leaves. Students from k-12 can do activities from this collection of activities.

What is a leaf? A leaf is a lateral stem outgrowth that is usually the primary photosynthetic organ of the plant. How do we know if something is a leaf?

Rule #1 Leaves will branch from stems and have a bud at the point of attachment to the stem.

Rule #2 There will be no buds on a leaf; buds are only on stems.

ALL ABOUT LEAVES (Teacher Copy)

TABLE OF CONTENTS

Lesson 1 Leaf Collections......................................4

Lesson 2 Leaf Arrangement......................................5

Lesson 3 Leaf Venation.........................................7

Lesson 4 Special Leaves........................................8

Lesson 5 Leaves and Water......................................9

Appendix 1 Sample Data...................................11

Appendix 2 Jesse Fell....................................13

ALL ABOUT LEAVES (Teacher Copy)

LESSON 1 LEAF COLLECTIONS

Background Information

Objectives: Plants are an extremely diverse group of organisms and this great diversity makes them wonderful organisms to study and observe. Observation and measurement are the two most basic skills of science and it is essential that students begin to practice these at an early age. The diversity of plants that exist around you is a resource that can be used to practice these activities.

Ability Level: 1, 2, 3.

Prerequisite Process Skills: Observation, Measurement

Procedure

1. Students will be asked to make a leaf collection, but unlike many other exercises like this they don't have to try to identify what kind of plant it is (i.e. genus and species). Rather, they will be asked to collect, observe, and organize the leaves into categories based on their skill levels.

2. For younger students this can be turned into a simple contest. Give them a list of categories of leaves to try and find. Some of the categories can be quantitative such as the biggest leaf, the smallest leaf, the heaviest leaf, while others can be more qualitative like heart-shaped, hairy, smelly, skinny--Anything else you or the students can think of will work fine.

3. Tracing an assortment of leaves and leaf shapes is a good exercise for demonstrating diversity to young students.

4. For older students you can ask them to make a collections based on leaf morphology and then organize their collection into groups or sets. Collect leaves that are pinnately compound, palmately compound, and an assortment of simple leaves. Find monocot leaves and compare them to the other leaves. Look at evergreens. Collect ones with needles in bundles of two and five. Look for ones that have leaves that are not needles. Look for ones that have needles not in groups. This exercise is a way to teach students plant morphology and to practice observation skills. You can take this one step further by using this exercise to demonstrate how to organize a complex set of information so that the information can be stored and retrieved.

5. Nested Sets, a way to organize information. The most important part of this kind of exercise is to get the students to observe, not to learn how to identify trees. You need to encourage them to look carefully at the biological diversity around them and really see it.

ALL ABOUT LEAVES (Teacher Copy)

LESSON 2 LEAF ARRANGEMENT

Background Information

Objective: To learn to make accurate observations and then communicate these observations by drawing. We will do this by constructing a figure of how the leaves of two different types of plant are arranged on the stem from two different perspectives.

Ability Level: 2, 3

Prerequisite Process Skills: Observation, Measurement, and Communication

Materials Chrysanthemum plant (alternate) 1 Vinca plant (opposite) 1 Styrofoam cup marking pen

Procedure

1. Tape the cup upside down on the table. Punch a small hole in the center of the cup with a pencil. Make marks in a "clock-like" manner at 12, 3, 6, and 9 around the cup with the pen. Remove about a 4 inch piece of one of the plants (do the opposite-leaf plant first) and place it in the hole.

Observation and Communication

2. Side View. Look carefully at the stem in the cup. Draw a horizontal line to represent the top of the cup. Measure the length of the stem from the cup to the top. Draw a line coming from the "cup" that long to represent the stem. Measure the distance from the cup to the first leaf. Draw a line at a right angle to the "stem" at this distance to represent the leaf. Just draw the lines at right angles to the stem and do not worry about whether they go forward or back. Measure to the next set of leaves and then draw them. Repeat this until you can't measure any more.

3. Questions. How does it look? Does this accurately represent the stem? How are the leaves arranged? Are they always the same? Look at some other people's drawings. Are the leaves always the same distance apart? Can you see any pattern? Can you attempt to explain this pattern?

4. Top View. Don't remove the stem from the cup. Look down on the stem from above. Using another cup draw a circle to represent the bottom of the cup. Place marks around the

Continued

LESSON 2 Continued

circle in the clock positions the same as on the cup. In the center of the circle place a dot to represent the stem. Looking from position coming off the stem with a "lollipop" to represent the leaf. Number the leaves starting with the 1 to help keep track. Move up the stem and draw the position of as many leaves as possible before it gets too confusing. Can you see a pattern?

5. Repeat parts 2 and 4 using the alternate plant.

6. Compare the two patterns. What is different? Which do you think might work better? Think about shade.

ALL ABOUT LEAVES (Teacher Copy)

LESSON 3 LEAF VENATION

Background Information

Objective: Students will recognize that all leaves of a certain species have leaf veins that are alike. Activities will center around the development of this understanding.

Ability Level: 1, 2, 3

Prerequisite Process Skills: Observation

Materials monocot leaves dicot leaves cardboard box map pins pin

Procedure

1. Remove a leaf from a monocot plant and tape it to the cardboard box. Now take a map pin and start punching holes along the veins of the leaf. Punch holes at short intervals and follow as much of the pattern as you can. Now remove the leaf and use the pen to connect the dots. Repeat the procedure using a dicot leaf.

Observation

2. Do the venation patterns of the two leaves look alike? How are they different?

ALL ABOUT LEAVES (Teacher Copy)

LESSON 4 SPECIAL LEAVES

Background Information

Objectives: To learn about some of the diversity of leave modifications that occur and to look at some of these differences and to try to explain (guess) how they might be important to the plant's survival.

Ability Level: 1, 2, 3

Prerequisite Process Skills: Observation and Hypothesis Formation

Materials This exercise requires as many different types of leaf modifications as you can find. This will require a little searching, but many of these can be acquired and some can be grown easily. You need to keep your eyes out for good examples for this exercise.

Procedure

1. Show the class a plant with a modified leave. Let them look at it carefully. Give them some information about where this plant grows. Ask them what that kind of place might be like. What would be important for survival in that kind of place? Have the leaves somehow been modified (change over time when compared to an "ordinary leaf") to help this plant grow in that environment?

2. Specialized leaves to observe--unmodified leaf:

a. Sundew

b. Venus Fly Traps

c. Kalanchoe, Mother of 1000

d. Haworthia

e. Water Lettuce

f. Lithops

g. Sensitive Plant

ALL ABOUT LEAVES (Teacher Copy)

LESSON 5 LEAVES AND WATER

Background Information

Objective: to help students develop an understanding of how we can go about testing an hypothesis like the ones we made in the previous exercise. We will do this by looking at leaves that may be modified to help conserve water and make some hypotheses about this aspect of their structure. We will then conduct some experiments to test the predictions of our hypothesis. We are only going to test two hypotheses today but there are many others you could try.

Ability Level: 2, 3

Prerequisite Process Skills: Observation, Measurement, Hypothesis Formation, and Hypothesis Testing.

Materials 1 Coleus or bean plant with healthy foliage 1 Haworthia (or other leaf succulent) 1 rubber plant assortment of containers triple-beam balance graduated cylinder Windex

Procedure Part I

Observations

1. Remove three leaves from each of the plants. Individually label the leaves with a marking pen.

2. After they are marked, weigh the leaves to the nearest 1/10 gram and record the data in a chart like the attached sample. Then place the leaves on a rack of some kind to dry. You can place them in the sun but just be sure to do the same thing to all of the leaves.

3. Weigh the leaves everyday and record the new weights. How much of a leave is water? Compare the percent change in weight of all three plants.

4. Try making a graph to represent the percent change in weight. Do all the leaves lose water at about the same rate? Which ones lose water the fastest and which the slowest? What is different about these leaves?

Continued

LESSON 5 Continued Part II

Testing the Succulent Theory (Surface to Volume Ratio)

5. Definitions: Surface Area is the amount of space exposed to the air. Volume is the total amount of space filled.

6. How does shape affect evaporation rates? To answer this question we will use Tupperware
containers as models of leaves. Measure the opening on all the containers and calculate the surface area. Now place an equal volume of water in each container. Each day measure the volume of water remaining in the containers using a graduated cylinder. Does the water evaporate at the same rate in all cases? Which ones evaporate more quickly? Can you see a pattern? If you wanted to conserve water what would be the best shape?

7. How does our model above relate to the leaves we looked at? Is Haworthia "fatter" than Coleus and if so how much? Calculate the approximate surface area of Haworthia by laying each of the three sides on a piece of paper and then tracing their outline. Cut out these shapes and try to arrange them in something approaching a rectangle. Calculate the approximate area of this rectangle and you will have an estimate of surface area. Do the same thing with the Coleus leaf (it only has two sides). Record your data. Now put about 10 of each kind of leaf in a graduated cylinder of water and see how much water is displaced. Divide this amount by the total surface area and you will have the approximate surface-to-volume ratio.

Part III

Wax Coating Theory

8. Take the four leaves from the Rubber Plant. Take two of them and wash them with Windex to remove any waxy coating. Weigh all of the leaves and place them aside to dry. Weigh all leaves every day. Convert the weight loss to percentages. Do all leaves lose water at the same rate? Which is fastest? Do waxy coatings help conserve water?

9. Remove four Coleus leaves from the plant and weigh all of them and record data. Spray two of them with a coating of clear enamel. Weigh these two again. Place all the leaves on the drying rack and weigh all four each day. Do all the leaves lose water at the same rate? Do artificial waxy coatings help reduce water loss?

ALL ABOUT LEAVES

APPENDIX 1 SAMPLE DATA LEAF WATER LOSS

ALOE

Dates 4/20 4/21 4/22 4/23 4/24

Dish 347.0 347.0 347.0 347.0 347.0

Aloe + Dish 590.3 586.3 583.6 580.8 578.9 Aloe 243.3 239.4 236.6 233.8 231.9 Wt. Loss 0.0 3.9 6.7 9.5 11.4 % Loss 0.0 1.6 2.7 3.9 4.7

COLEUS

Dish 101.2 101.2 101.2 101.2 101.2 Coleus + Dish 125.4 122.9 122.0 120.4 120.0 Coleus 24.2 21.7 20.8 19.2 18.8 Wt. Loss 0.0 10.3 14.0 20.6 22.3

RUBBER TREE LEAF

Leaves 40.4 39.0 38.6 38.2 37.5 Wt. Loss 0.0 1.4 1.8 2.2 2.9 % Loss 0.0 3.4 4.4 5.4 7.2

All weights in grams

THE SUCCULENT LEAF THEORY (a.k.a. fat leaves)

Small Container (16cm X 9.5cm = 152 sq cm)

Dates 4/22 4/23 4/24

Volume 350.0 297.0 255.0 Loss 0.0 53.0 95.0 % Loss 0.0 15.1 27.1

Medium Container (16cm X 26.5cm = 424 sq cm)

Volume 350.0 250.0 155.0 Loss 0.0 100.0 195.0 % Loss 0.0 28.5 55.7

Large Container (24cm X 35cm = 840 sq cm)

Volume 350.0 185.0 45.0 Loss 0.0 165.0 305.0 % Loss 0.0 47.1 87.1

All volumes in milliliters

APPENDIX 1 Continued

WAXY LEAF THEORY

RUBBER TREE LEAF UNWASHED

Dates 4/20 4/21 4/22 4/23 4/24

Leaves 40.4 39.0 38.6 38.2 37.5 Wt. Loss 0.0 1.4 1.8 2.2 2.9 % Loss 0.0 3.4 4.4 5.4 7.2

RUBBER TREE LEAF WASHED

Leaves 43.9 39.0 38.8 37.1 35.5 Wt. Loss 0.0 3.7 5.1 6.8 8.4 % Loss 0.0 8.4 11.6 15.6 19.1

All Weights in grams

ALL ABOUT LEAVES

APPENDIX 2 JESSE FELL

Jesse Fell is best known as one of the founders of Illinois State University and the town of Normal, but he is also remembered as "a planter and lover of trees." He is said to have often quoted the old couplet: He who plants a tree and cares for it does something for posterity. Mr. Fell personally saw to the planting of thousands of trees in the town of Normal before a single home was built. He assumed the responsibility for the care of the grounds around the Normal School he helped establish (ISU) and soon surrounded the new school with trees. It was his hope that on the grounds of the Normal School every kind of tree that would flourish in Central Illinois would be planted so that the studies of botany and forestry could be pursued to their advantage. This ambitious goal has never been realized; however, it is likely that because of his earlier pursuit of this noble goal, we have such a fine collection of trees on campus today.

Trees make the ISU campus and every place else more beautiful. We need to remember that trees are not planted for the present, but are planted for the future. We should be thankful for Jesse Fell and the planters who came after him for the fine collection of trees that we have inherited, and take care to follow their example by leaving a beautiful legacy of trees on the ISU campus for the future.