Lab 8: Plant Structure and Function
OBJECTIVES:
Calculate rate of water movement in celery stalk
Measure transpirational pull in various environmental conditions and compare how
transpiration is changed in these various environments
Prepare slide to observe stomata function
Differentiate between monocot and eudicot stem and root structures
INTRODUCTION:
Plant tissues, like animal tissues we have already studied, are made up of cells that perform a
common function. Four tissue types are found in plant cells: ground tissue, dermal tissue,
vascular tissue, and meristems.
Ground tissue makes up most of the plant body. It functions in support, protection, and
metabolism. Cells within ground tissue can be parenchyma cells (generalized cells that make up
the soft (and edible) parts of the plant), collenchyma cells (thicker cells that provide support in
stems and roots), or schlerenchyma cells (longer and thicker fibers that are dead at maturity).
Dermal tissue covers the plant body with thin, flat epidermal cells covered in a fatty cuticle that
helps to retain water. Overlying the cuticle in some plants is an additional waxy surface. Dermal
tissue also contains specialized cells such as guard cells, which are found on either side of
stomata, a pore in the leaf that allows for gas and water exchange.
Vascular tissues contain specialized cells that function in transport of water and food materials
around the plant. Xylem form thick walled tubes transporting water from roots to leaves. Phloem
form thinner vessels that conduct food from leaves to other areas of the plant.
Meristems are localized regions of plant growth that produce new cells both at the tips of roots
and shoots, and laterally in woody plants.
The plant body can be divided into the above ground parts (the shoot system) and the below
ground parts (the root system). The shoot system is made up of stems, which provide support for
upright growth and the leaves, which are the primary photosynthetic organ in the plant. The stem
tip contains a terminal bud which contains meristematic tissue, called apical meristem, which
elongates the plant. As a plant grows, leaves emerge from the stems at nodes, which are
separated by internodes. The region between the leaf stalk and stem is known as the axil and
contains an axillary bud. Since some leaves are single blade and others are compound
(composed of small leaflets), the axillary bud can be used to identify a single leaf.
Vascular tissues within stems are arranged in vascular bundles, which contain phloem on the
outside and xylem on the inside. Between the xylem and phloem within the bundles is
meristematic tissue. The arrangement of these vascular bundles varies in different types of
plants. Flowering plants are divided into monocots and eudicots, which have different
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Lab 8: Plant Structure and Function
arrangements of their vascular bundles. Monocots, such as corn, have bundles scattered through
their stem, while eudicots, woody, and herbaceous plants have a ring arrangement. Ground tissue
between the epidermis and vascular bundles is known as the cortex, and the center of the stem is
known as the pith.
Leaves come in a great number of shapes and sizes, usually broad and thin to maximize
photosynthetic area. The flattened portion is called the blade, which is supported by a stalk, the
petiole. Many characteristics of leaves are used in plant identification. For example, the
arrangement of veins is parallel in monocots and branched in eudicots. Dichotomous keys use
characteristics such as simple or compound leaves, alternate or opposite arrangement on stem,
and shape to identify plants. Leaf ground tissue, mesophyll, contains many photosynthetic cells
and is separated into spongy and pallisade layers. The upper epidermis of the leaf often has a
waxy cuticle, while the lower epidermis contains stomata with guard cells. Veins contain xylem
and phloem.
Roots serve to anchor plants and absorb, transport, and store water and nutrients. They can make
up more than half of the plant mass. The two major types of root systems are a taproot system
and fibrous root system. A taproot system is found in most eudicots, in which a single root
grows very thick and deep, with side roots growing off it. A fibrous root system is common in
monocots, in which many roots are very shallow. Grasses tend to have fibrous systems, while a
dandelion is a good example of a taproot system. Roots, like stems, have an apical meristem at
the root tip protected by as root cap. The root epidermis surrounds the entire cortex, which has a
specialized inner endodermis that helps to regulate water and nutrient uptake. The endodermis
surrounds the vascular tissue, xylem and phloem, and the pericycle that produce branch roots
that grow through the cortex and epidermis into the soil.
Plants do not have a heart or any other muscular tissue to move substances around their body.
Sugars can flow from the leaves down to the roots with the assistance of gravity, but what
mechanism drives water from the roots, against gravity, to the leaves? You will recall that water
will move in response to solute differences into and out of cells through osmosis. Roots take
water (and minerals) into their cells primarily by diffusion. The water travels into the xylem in
the roots and is transported up, against gravity into the leaves, driven by transpiration, the
evaporation of water from the leaves. Water vapor diffuses from the moist air spaces of the leaf
to drier air outside through the stomata. Because water molecules tend to stick together by their
hydrogen bonds as molecules evaporate, cohesion draws water in a column from the roots,
through the stems in a process called transpirational pull. The flow of water to the top of the
tree is solar powered.
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Lab 8: Plant Structure and Function
8.1 MOVEMENT OF WATER THROUGH CELERY STALK
1. Prior to your arriving to lab, celery stalks were either cut and IMMEDIATELY placed in
water or cut and placed in air.
2. Grab two beakers (400 mL) and place about 100 mL of water plus some nice food coloring (a
dark, visible one) in each beaker.
3. Transfer a celery stalk that had been cut and placed immediately in water prior to your arrival
in one of the beakers. Make a note of which beaker.
4. Transfer a celery stalk that had been cut and placed in air prior to your arrival in the other
beaker. Make a note of which beaker.
5. With scissors, cut off the top end of each stalk.
6. Look at the celery stalks every 5 minutes to check for movement of dye. Record results in
the table below.
7. Once the dye has reached the top of a celery stalk, remove that stalk.
Table 1. Movement of water in celery stalk.
Time Dye reach top Dye reach top Time Dye reach top Dye reach top
(min) yet? yet? (min) yet? yet?
Beaker with Beaker with air Beaker with Beaker with air
soaked stalk stalk soaked stalk stalk
5 35
10 40
15 45
20 50
25 55
30 60
GENERAL QUESTIONS:
1. Cut your celery stalks to the point where you begin to see the dye. Measure (in mm) how
much the dye moved up from the bottom. Divide by the minutes it took for dye to move up.
Record the rate of dye movement in mm/min for each stalk.
2. Which celery stalk had the faster dye movement? Explain why.
3. Which vascular tissue does water use to move up a stem?
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Lab 8: Plant Structure and Function
8.2 TRANSPIRATIONAL PULL
1. The potometer is also called a transpirometer.
2. The leafy shoot will be cut for you prior to your arrival in lab. The shoot was
IMMEDIATELY placed in water.
3. Slowly SUBMERGE the tip of the tube into a sink full of water. Begin pushing the rest of
the tube slowly into the water until eventually submerging the pipette portion in the water as
well. LEAVE the tube and pipette submerged while doing the next step.
4. Put the stem of the shoot in the sink of water also. Make sure the leaves are dry. WHILE IN
THE WATER, cut about 1.5 cm off the end and place the cut end inside the open tube.
AGAIN, ALL THIS IS DONE IN THE WATER IN THE SINK.
5. Remove the entire apparatus from the sink and place onto ring stand and clamps available.
Use modeling clay to make a nice seal between the plant and tube.
6. Let apparatus stand for 5 minutes before beginning to read measurements every 10 minutes.
7. Record results in Table 2.
8. One group will set up normal conditions; another will set up windy conditions; another will
set up bright light conditions; and another will set up humid conditions.
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Lab 8: Plant Structure and Function
Table 2. Transpirational pull in various environmental conditions. Record the values as how
many mL are lost or gained.
Time (min) Normal Windy Bright light Humid
0 min (Initial mL _________ mL _________ mL _________ mL _________ mL
reading)
10 min
20 min
30 min
40 min
50 min
60 min
Total volume
change (mL)
GENERAL QUESTIONS:
1. Which of the three conditions (windy, bright light, humid) showed a higher rate of
transpiration than normal? Explain why.
2. Which of the three conditions (windy, bright light, humid) showed a slower rate of
transpiration than normal? Explain why.
3. Based on the results above, which environmental habitat (in the real world) has the lowest
rate of transpiration?
4. If you could test another environmental condition for rate of transpiration, describe that
condition. In the real world, where would you find such a condition?
5. Through which structure in the leaf does the water leave?
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Lab 8: Plant Structure and Function
8.3 OBSERVING STOMATA
1. Grab a celery leaf. Turn the leaf so that the lower epidermis is facing up.
2. Bend the leaf so that it breaks a little along a vein.
3. Take a forceps and gentle peel off the lower epidermis. Place this lower epidermis on a slide
that has a drop of distilled water on it. Put cover slip on top.
4. Using proper scope procedures, observe the lower epidermis under high power (400X total
magnification). Find stomata. Draw below.
5. Take a forceps and gentle peel off the lower epidermis. Place this lower epidermis on a slide
that has a drop of saline solution on it. Put cover slip on top.
6. Using proper scope procedures, observe the lower epidermis under high power (400X total
magnification). Find stomata. Draw below.
Stomata, in water, 400 X total mag Stomata, in saline, 400 X total mag
GENERAL QUESTIONS:
1. In saline solution, are stomata open or closed? Explain why.
2. If you forgot to water your plants for a few days, and the plant started to wilt, would you
expect stomata to be open or closed? Explain why.
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Lab 8: Plant Structure and Function
8.4 PLANT STRUCTURE
1. Obtain a slide of corn stem (cross-section). Observe at 40 X total magnification first to get
an overall picture. Refer to figure 77c-d in the Photo Atlas and p. 445 of your text to help
locate structures.
a. Locate vascular bundle and focus first under scanning power objective (red objective), go
to low power objective (yellow) and fine focus, go to high power objective and fine focus
to view 400 X total magnification.
b. Draw and label vessel element of xylem, sieve and companion cells of phloem.
c. Show to the instructor (on the scope) the above parts.
2. Obtain a slide of Ranunculus root (cross-section). Observe under scanning power objective
first to get an overall picture. Refer to figure 75 a, c in the Photo Atlas and p. 440 of your
text to help locate structures.
a. Locate vascular cylinder and fine focus under low power and then high power to view
400 X total magnification.
b. Draw and label xylem, phloem, and endodermis.
c. Show to the instructor (on the scope) the above parts.
3. Obtain a slide of Allium root tip (longitudinal section). Observe at 100X magnification.
Refer to figure 74b in the Photo Atlas and p. 440 of your text to help locate structures.
a. Locate the root cap, apical meristem, zone of cell division, and zone of elongation.
b. Draw and label above structures.
c. Turn to high power (400 X total mag). Identify at least one cell in metaphase, anaphase,
OR telophase. Show the instructor.
4. Obtain a slide of privet leaf (Ligustrum) (cross-section). Observe at 400 X total
magnification. Refer to figure 81a-b in the Photo Atlas to help locate structures.
a. Locate the stomata and draw a portion of the leaf with stomata and label stomata.
b. Show the instructor (on the scope) the stomata.
demonstration ___ ____
[400 X for
both]
Corn stem vascular bundle Ranunculus root vascular cylinder
(label vessel element of xylem, (label xylem, phloem, and
sieve and companion cells of phloem) endodermis)
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Lab 8: Plant Structure and Function
Metaphase, Anaphase, OR Telophase ___ ____
Allium root [100 X total] privet leaf stomata [400 X total]
(label root cap, apical meristem, (label stomata)
zone of cell division, and zone of elongation)
GENERAL QUESTIONS:
1. Identify the following plants as monocots or eudicots: corn, Ranunculus, Allium (i.e.,onion)
[hint: parallel leaf veins], privet
Monocots:
Dicots:
2. In a monocot stem, are the vascular bundles arranged in a ring or scattered throughout the
stem?
3. In dicot root, the shape of the xylem reminds you of a __________.
8.5 SET UP EXPERIMENTS FOR NEXT WEEK
1. Obtain 2 seed trays, each with four smaller compartments.
2. There may be 2-4 types of seeds available. Select the type of seeds you wish to plant in the 2
trays. Just make sure that the number and type in each compartment are identical in both
trays.
3. Label each seed tray with your names.
4. Place seed tray in the designated lighted area and one in the designated dark area. Leave
them until next week.
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