Download Lab 7: Plant Structure

Lab #7: Kingdom Plantae: Vascular Seed Plant Structure
Objectives:
• Identify the structure and function of the major plant cell and tissue types
• Describe the organization of tissues and cells in a plant organ and relate this organization to the
function of the organ
• Describe the major differences that distinguish the roots, stems, and leaves of “typical”
monocots from “typical” eudicots.
• Become familiar with some terms used in plant identification.
General Procedures
Examine the slides and live materials for the organisms in each section.
For the slides:
• start with a low magnification and make a drawing of the overall structure
• increase the magnification and make close-up drawings of the “structures to identify” as noted in
each section.
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You may work individually or in groups of two but all students will complete their own notebook
drawings and questions.
There are often limits to the number of slides/specimens available. Please take only the
slides/specimens to your desk that you are currently working on and leave the rest for other students.
Use the pictures in the photo atlas and your textbook to guide you through the slides and specimens.
Some of these slides may be difficult to interpret. Do your best and ask me if you have
questions.
Introduction:
The vegetative plant organs we will focus on in this lab are the results of adaptations to the
terrestrial lifestyle. Specifically, we will focus on three organs: stems, roots, and leaves. Think about the
challenges plants face in terrestrial environments that we have discussed in lecture and consider how the
structures you view today help vascular plants meet those challenges.
Part 1: Internal Structures
I. Roots
A. Examine the following cross sections to familiarize yourself with internal root structure. You need
to be able to identify structures in both types of roots.
Slides:
Eudicot root: Ranunculus mature root
Monocot root: Root (typical) monocot and dicot (observe monocot root on this slide)
Structures/Regions to Identify: epidermis, cortex, vascular cylinder (stele), endodermis, pericycle, xylem
tissue, vessels/tracheids, phloem tissue
The epidermis is the layer of cells that forms the outer surface of the roots and protects the roots.
Root hairs may be visible, and are an extension of the epidermal cell. The vascular cylinder (or stele) is
located in the center of the root and is defined by a ring of cells called the endodermis. All the cells
between the epidermis and the endodermis are cells of the cortex region. The vascular cylinder contains
the vascular tissue. The endodermal cells are lined with the Casparian strip, a waxy barrier (often stained
red) that prevents the flow of water through the cell wall pathway (more on this later in lecture). Just
inside the endodermis is a single layer of cells that makes up the pericycle, which may or may not be
visible. Cells of the pericycle are meristematic cells that produce other cell types to produce branch
roots.
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In the eudicot root, the xylem tissue is observable as a large cross shaped portion in the middle of the
vascular cylinder. The large red stained cells are the vessels and tracheids. Smaller red stained cells are
sclerenchyma cells. In between the xylem tissue (in the open regions between each section of the “cross”)
is phloem tissue, which is often stained bluish-green. Other cells in the region are parenchyma cells.
In the monocot root, the xylem tissue and phloem tissue look like bundles of cells that alternate in a
circle within the vascular cylinder. The larger (typically red stained) cells are the vessels and tracheids
of the xylem tissue. The phloem tissue is in between the bundles of xylem tissue.
II. Stems
B. Examine the following cross sections to familiarize yourself with internal stem structure. You need
to be able to identify structures in both types of stems.
Slides:
Eudicot stem: Helianthus old stem
Monocot stem: Zea mays stem
Structures/Regions to Identify: epidermis, cuticle, cortex, pith, vascular bundles, xylem tissue, phloem
tissue, vessels/tracheids, phloem fibers, vascular cambium, ground tissue
The epidermis is the layer of cells that forms the outer surface of the stems and protects the stems.
Epidermal cells also secrete the cuticle, a waxy layer that sits on top of the epidermal cells and helps
reduce water loss. The cortex is the region between the epidermis and the vascular bundles, and the pith
is the region that makes up the center of the stem, extending out to the vascular bundles.
The vascular bundles of eudicots are arranged in a circle around the edge of the stem. The
vessels/tracheids of the xylem tissue are visible as large, thick walled, red stained cells on the portion of
the vascular bundle closest to the center of the stem. Moving outward, the phloem tissue is visible as
smaller, typically bluish-green stained cells (the sieve and companion cells). Part of the phloem tissue is
made up of phloem fibers, small, red stained sclerenchyma cells that are the part of the vascular bundle
that is closest to the outside of the stem. Lying between the xylem tissue and the phloem tissue is a
region of small cells, the vascular cambium (which may or may not be clearly visible). The vascular
cambium is the meristematic cells that produce the new cells of the growing xylem and phloem tissues.
The vascular bundles of monocots are scattered throughout the stem. The location of the xylem and
phloem tissue within each bundle are similar to the eudicots.
III. Leaves
C. Examine the following cross sections of leaves to familiarize yourself with internal leaf structure.
You need to be able to identify structures in both types of leaves.
Slides:
Eudicot leaf: Privit leaf
Monocot leaf: Leaf - monocot & dicot (observe monocot only in this slide)
Structures/Regions to Identify: upper epidermis, cuticle, guard cells of stomata, mesophyll, palisade
mesophyll, spongy mesophyll, chloroplasts, xylem tissue, phloem tissue, lower epidermis
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The epidermis is the layer of cells that forms the outer surface of the leaves and protects the leaves.
Epidermal cells also secrete the cuticle, a waxy layer that sits on top of the epidermal cells and helps
reduce water loss. Within the epidermal layer are the guard cells of the stomata. The guard cells
surround a pore, and control whether the pore is open or closed. To locate guard cells, scan along the
epidemeris (examine both upper and lower epidermis) for areas where there are open spaces (no cells)
just interior to the epidermal cells. These are air spaces and usually lead to a pore in the epidermis. The
layer of cells interior to the epidermis, and not including the vascular tissue, is called the mesophyll.
In the eudicot leaf, the layer of cells just beneath the upper epidermis is called the palisade
mesophyll, made up of rectangular shaped parenchyma cells. Many chloroplasts should be visible
within these cells, whose primary function is photosynthesis. Beneath the palisade mesophyll is a layer
of more irregular shaped parenchyma cells, the spongy mesophyll, which also contain some
chloroplasts. These cells also do photosynthesis. These cells are more spread out, and allow for air space
between them, which assists in gas exchange. Eudicot leaves often have one large central vascular
bundle (the main vein of the leaf) and then many smaller vascular bundles spread out along the leaf.
Xylem tissue is located near the top of the vascular bundle (large, thick walled and typically stained red),
and phloem tissue (smaller, typically stained bluish-green) lies just below them.
The monocot leaf mesophyll is structured differently and does not have cells clearly separated into a
palisade and spongy mesophyll layer. The vascular bundles are spread across the leaf in a regular
pattern, but do not have the large central vascular bundle seen in the eudicot leaves.
Questions for Lab Notebook:
1. On the eudcot leaf, where were the most stomata found (on top or bottom of leaf?) What is the
advantage to a plant of having more stomata on the bottom of the leaf rather than on the top?
D. Examine the following cross section to familiarize yourself with internal leaf structure of a typical
gymnosperm.
Slide:
Gymnosperm leaf Pinus leaf needle type
Structures/Regions to Identify: epidermis, guard cells of stomata, mesophyll, endodermis, xylem tissue,
phloem tissue
The layer of cells interior to the epidermis, and not including the vascular tissue, is called the
mesophyll. The endodermis of the Pinus leaf is a ring of cells located in the center of the leaf, and is
somewhat oblong, rather than round, in shape. Inside the endodermis are vascular bundles. Xylem
tissue is a collection of red stained cells located towards the bottom of the vascular bundles, and the
phloem tissue is located directly above the xylem tissue. Large hollow looking cells located outside of
the endodermis, within the mesophyll are resin ducts.
Questions for Lab Notebook:
2. Where are the stomata located on the Pinus sp. leaf (needle)?
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Part 2: External Structures
I. Live Material
Use the specimens in the demonstration areas to familiarize yourself with the terms at the station.
A. Choose two specimens to draw and identify the following:
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Identify leaf arrangement (opposite, alternate, whorled) and whether a leaf is simple or compound.
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Identify leaf shape, margin and venation.
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Identify the external structures of a stem (stem, leaf, apical/terminal bud, axillary/lateral bud, axil,
node, internode).
B. Complete the plant identification section. Record your answers in your lab notebook.
Questions for Lab Notebook:
3. What are the major structural differences you saw between monocot and eudicot roots?
4. What are the major structural differences you saw between monocot and eudicot stems?
5. What types of cells provide support in a plant stem?
6. What are the major structural differences you saw between monocot and eudicot leaves in the lateral
section slides?
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