Title: STRUCTURE AND FUNCTION OF PLANT LEAVES
Author: Daniel Bondgren, Jordan-Elbridge High School, Jordan, NY
Overview:
Students will familiarize themselves with the internal and external structures of
angiosperm leaves and relate these structures to the overall function of a plant.
Cross-reference to NYS Learning Standards:
Standard 1. Key idea 2 Performance indicators: 2.3
Standard 4. Key idea 5 Performance indicators: 5.1a, 5.1b
Estimated time:
This activity should take approximately 3, 40-minute class periods to complete the
physical activity, plus 1 additional period if you wish for the students to work through the
questions at the end together.
Objectives:
a. Study the structure and function of the different tissues in a plant leaf.
b. Examine the structure of plant stomata.
c. Investigate the response of a plant leaf to different amounts of light.
d. Hypothesize about the type of climate different plants might inhabit based
upon leaf structure.
Background information:
Leaves are the main photosynthetic organs of a plant. Leaf shape and structure vary
from plant to plant depending upon their requirements and the type of ecosystem the
plant lives in. Regardless of the plant, all leaves share certain basic features. The flat
part of the leaf is called the blade. In some plants, the blade is attached directly to the
stem; in others, the blade is attached to the main stem by a thin stalk, or petiole. A leaf
is composed of three types of tissues, epidermis, mesophyll, and vascular tissue. Leaves
have an upper and lower epidermis, which protect the internal tissues. Covering the
epidermis is a waxy cuticle, which helps conserve water. Most of the photosynthesis of
the plant takes place in the mesophyll. The xylem and phloem are found in the vascular
bundles in the veins of the leaf. They are continuous with the xylem and phloem of the
stems and roots.
Materials needed:
 One handout per student, lab notebook (or lined paper to record student answers
on)
 An area to gather leaves from school grounds or several live plants provided by
the teacher
 Several bottles of clear nail polish (approximately 1 bottle for every 6 students)
 Plastic baggies (for storing leaves overnight if you don’t have time to do the
stomata peel the same day)
 Prepared slide of lilac leaf cross section (1 per group of two students)
 Drawing paper (2 or 3 per student, copy paper works well)
 Dissecting probes (1 per group of two students)
 Forceps (1 per group)
 Microscope slides (1 per student)
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Distilled water
Several permanent markers for marking microscope slides
Compound light microscopes (1 per group)
Plastic cutouts (four per group of two- plastic cover slips or overhead
transparencies cut into small squares would work)
Paper cutouts (2 per group of students)
Sharp knives for cutting out pieces from the plastic squares (a couple per classthe teacher could control distribution of these)
Lugol’s iodine (approximately 1 reagent bottle for every three groups of students)
Aluminum foil (approximately 1 box per year)
Paper clips (4 per group)
Safety glasses
Latex or other gloves when handling iodine
Paper towels
Hot plates
Ethanol
Vocabulary :
Venation, stomata, blade, petiole, epidermis, mesophyll, vascular tissue, cuticle, xylem,
phloem, guard cells, biome, annual, perennial, deciduous, tundra, polysaccharide.
Activity:
Part 1: Stomata peels
1. With your partner, obtain a leaf from a plant found on the school grounds. Try to
find a plant that is unique to your class so you can compare your lab results with
other members of your class.
2. In your lab notebook, or on a separate sheet of paper, make a drawing of
your leaf and make a brief description of leaf size, shape, structure, and
where you found it. Include things like venation, where the plant was
growing, sun/shade conditions, etc.
3. Once you have returned to the lab, obtain a bottle of clear nail polish from your
instructor.
4. Each partner will make a stomata peel of the leaf that you have obtained. One
partner will use the top part of the leaf and the other partner will use the bottom
part of the leaf. In order to do so, paint a one-centimeter square on each side of
your leaf with the nail polish. Make sure that you have covered the entire square
with the nail polish. Don’t be afraid of putting too much nail polish on, you want
to make sure that your peel doesn’t rip!
5. Put your leaf aside in a place where it will not be disturbed while it dries and go on
to the next part of the lab.
Part 2: Leaf structures under the microscope
6. Observe a prepared slide of a lilac leaf cross-section under low power. This slide
has been stained to make structures easier for you to see. Focus first on the
upper epidermis, then on the lower epidermis. (For those classes that do not have
lilac leaf cross sections readily available, you may substitute ANY Dicot leaf cross
section.)
a. What is the function of the epidermis? In humans, what is a
comparable structure? Based on this, what other functions might
the epidermis also have?
b. Are the cells of the upper epidermis and the lower epidermis the
same? Describe any differences that you see.
7. Throughout the lower epidermis are tiny openings called stomata. Each stomata
is surrounded by a pair of guard cells that regulate its opening and closing.
a. What is the function of the stomata?
b. What three things necessary for or produced by photosynthesis
move through the stomata?
8. Most photosynthesis in the leaf occurs in the mesophyll. The mesophyll is made
up of two layers. The palisade mesophyll consists of tall, closely packed cells.
The spongy mesophyll consists of irregularly shaped, loosely packed cells. The
spongy mesophyll layer contains many air spaces. Focus on the mesophyll layer
under low, then high power. Identify the palisade and the spongy layer. Ask for
help if you can’t find them.
a. What organelle would you expect to find a lot of in the mesophyll?
(Hint: reread the information in the paragraph above.)
b. Which layer of the mesophyll would you expect to find more of this
organelle?
c. What color is this organelle normally?
d. Why are these organelles not the color that you would expect them
to be?
e. What might be the reason for the air spaces in the spongy
mesophyll?
9. Find a vascular bundle on your slide. The vascular bundle will look different from
the other tissues that you have observed so far. The cells will be more rounded
and will be smaller in diameter than the others on the cross section.
a. What two tissues are found in the vascular bundle?
b. What material necessary for photosynthesis is the xylem bringing to
the leaf?
c. What material is the phloem transporting away from the leaf?
10.Make a drawing of the cross section of the leaf that you are looking at. Label the
cuticle, epidermis (upper and lower), palisade layer, spongy layer,
vascular bundle, stomata, and the guard cells. (Hint: You may have to
move the slide so you can see all of these tissues in the same field of view.)
Part 1 (cont.)
11.By this time the nail polish on your leaf should be completely dry. Using a
dissecting probe, GENTLY tease the edge of the nail polish square lifting it away
from the leaf surface. Continue to do this along the edge of the square until you
have lifted about 5 millimeters of the square away from the leaf. Then, using
forceps, remove the rest of the nail polish square from the leaf.
12.Put a drop of distilled water onto a clean microscope slide. Place the stomata peel
onto the drop of water with the side that was touching the leaf facing up.
Using the side of the probe, gently smooth out the peel so that it is flat against
the slide. Label your slide with your name, the side of the leaf that the peel is
from, the type of leaf (if known), and the year that you made the slide. (Ask your
teacher for a marker to do the label.)
13.Observe your stomata peel under the microscope. Focus first under low power,
then switch to high power.
a. Was this leaf taking in carbon dioxide when you made this peel?
How can you tell?
b. Was this leaf releasing water when you made this peel? How can
you tell?
c. Count how many stomata you can see in your field of view. Record
how many you can see in your lab notebook. Move the field of view
and repeat this step a total of three times then average the number
of stomata on your peel.
d. Compare your average to other student’s averages. If the averages
are different, what might be the reason? If you wanted to get an
accurate stomata count what would be a better number, the
average number from one leaf or the average number from many
leaves? Why?
e. Record the average number of stomata that your partner observed
on their peel.
f. Were there more, less, or about the same number of stomata on the
top and bottom side of the leaf? Why do you think this is so? (Think
about which side had more and the purpose of the stomata.)
g. Make a drawing of your leaf stomata peel. Label the epidermal
cells, the stomata, and the guard cells.
Name_________________________________Date_____________
STRUCTURE AND FUNCTION OF PLANT LEAVES
Leaves are the main photosynthetic organs of a plant. Leaf shape and structure vary
from plant to plant depending upon their requirements and the type of ecosystem the
plant lives in. Regardless of the plant, all leaves share certain basic features. The flat
part of the leaf is called the blade. In some plants, the blade is attached directly to the
stem; in others, the blade is attached to the main stem by a thin stalk, or petiole. A
leaf is composed of three types of tissues, epidermis, mesophyll, and vascular tissue.
Leaves have an upper and lower epidermis, which protect the internal tissues. Covering
the epidermis is a waxy cuticle, which helps conserve water. Most of the photosynthesis
of the plant takes place in the mesophyll. The xylem and phloem are found in the
vascular bundles in the veins of the leaf. They are continuous with the xylem and
phloem of the stems and roots.
Lab objectives:
a. Study the structure and function of the different tissues in a plant leaf.
b. Examine the structure of plant stomata.
Materials needed:
 Live plants
 Bottles of clear nail polish
 Plastic baggies
 Prepared slide of leaf cross section
 Dissecting probes
 Forceps
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

Microscope slide
Distilled water
Several permanent markers for
marking microscope slides
Compound light microscopes
Protocol:
LEAF DRAWING:
Part 1: Stomata peels
1. With your partner, obtain a leaf from a plant
found on the school grounds.
2. Record a drawing of your leaf and a brief
description of leaf size and shape.
3. Each partner will make a stomata peel of the
leaf that you have obtained. One partner will
use the top part of the leaf and the other
partner will use the bottom part of the leaf. In
order to do so, paint a one-centimeter square
on each side of your leaf with the nail polish.
Make sure that you have covered the entire
square with the nail polish. Don’t be afraid of LEAF DESCRIPTION:
putting too much nail polish on, you want to
make sure that your peel doesn’t rip!
4. Put your leaf aside in a place where it will not
be disturbed while it dries and go on to the
next part of the lab.
Part 2: Leaf structures under the microscope
5. Observe a prepared slide of a dicot leaf cross-section under low power. This slide
has been stained to make structures easier for you to see. Focus first on the
upper epidermis, then on the lower epidermis.
a. What is the function of the epidermis? In humans, what is a
comparable structure?
b. Are the cells of the upper epidermis and the lower epidermis the
same? Describe any differences that you see.
6. Throughout the lower epidermis are tiny openings called stomata. Each stomata
is surrounded by a pair of guard cells that regulate its opening and closing.
c. What is the function of the stomata?
d. What molecules related to photosynthesis move through the
stomata?
7. Most photosynthesis in the leaf occurs in the mesophyll. The mesophyll is made
up of two layers. The palisade mesophyll consists of tall, closely packed cells.
The spongy mesophyll consists of irregularly shaped, loosely packed cells. The
spongy mesophyll layer contains many air spaces. Focus on the mesophyll layer
under low, then high power. Identify the palisade and the spongy layer. Ask for
help if you can’t find them.
e. What organelle would you expect to find a lot of in the mesophyll?
(Hint: reread the information in the introduction to the lab.)
f. What color is this organelle normally?
g. Why are these organelles not the color that you would expect them
to be?
h. What might be the reason for the air spaces in the spongy
mesophyll?
8. Find a vascular bundle on your slide. The vascular bundle will look different from
the other tissues that you have observed so far. The cells will be more rounded
and will be smaller in diameter than the others on the cross section.
i. What two tissues are found in the vascular bundle?
j. What material necessary for photosynthesis is the xylem bringing to
the leaf?
k. What material is the phloem transporting away from the leaf?
9. Make a drawing of the cross section of the leaf that you are looking at. Label
the cuticle, epidermis (upper and lower), palisade layer, spongy layer,
vascular bundle, stomata, and the guard cells. (Hint: You may have to
move the slide so you can see all of these tissues in the same field of view.)
LABELED DRAWING OF A LEAF IN CROSS-SECTION:
Part 1 (cont.)
10.By this time the nail polish on your leaf should be completely dry. Using a
dissecting probe, GENTLY tease the edge of the nail polish square lifting it away
from the leaf surface. Continue to do this along the edge of the square until you
have lifted about 5 millimeters of the square away from the leaf. Then, using
forceps, remove the rest of the nail polish square from the leaf.
11.Put a drop of distilled water onto a clean microscope slide. Place the stomata peel
onto the drop of water with the side that was touching the leaf facing up.
Using the side of the probe, gently smooth out the peel so that it is flat against
the slide. Label your slide with your name, the side of the leaf that the peel is
from, the type of leaf (if known), and the year that you made the slide. (Ask your
teacher for a marker to do the label.)
12.Observe your stomata peel under the microscope. Focus first under low power,
then switch to high power.
l. Was this leaf taking in carbon dioxide when you made this peel?
How can you tell?
m. Was this leaf releasing water when you made this peel? How can
you tell?
n. Count how many stomata you can see in your field of view. Record
this number in the table below. Move the slide and repeat two more
times. Determine the average the number of stomata on your peel.
Top Side of Leaf
Bottom Side of Leaf
Field of view
# Stomata
Field of View
# Stomata
1
1
2
2
3
3
Average:
Average:
o. Record the average number of stomata that your partner observed
on their peel.
p. Compare your average to other student’s averages. If the averages
are different, what might be the reason?
q. If you wanted to get an accurate stomata count what would be a
better number, the average number from one leaf or the average
number from many leaves? Why?
r. Were there more, less, or about the same number of stomata on the
top and bottom side of the leaf? Why do you think this is so? (Think
about which side had more and the purpose of the stomata.)
s. Make a drawing of your leaf stomata peel. Label the epidermal
cells, the stomata, and the guard cells.
LABELED DRAWING OF LEAF STOMATA PEEL: