Lab_6-Primary_Tissue-Spring2024 (2).pdf

Primary Growth & Plant Cells Introduction All plants have primary growth (growth that originates with the apical meristems). The meristems consist of immature cells that divide and then differentiate into the various plant cell types found in the plant body. The bodies of vascular plants are organiz...

Primary Growth & Plant Cells Introduction All plants have primary growth (growth that originates with the apical meristems). The meristems consist of immature cells that divide and then differentiate into the various plant cell types found in the plant body. The bodies of vascular plants are organized into three tissue systems: dermal, ground, and vascular. These tissues begin their development in the embryo and are continuous throughout the plant roots, stems, and leaves (plant organs). The dermal tissue system is the outermost covering. The ground tissue system typically comprises the bulk of the plant body and often has functions of storage and photosynthesis. The vascular tissue system, composed of xylem and phloem tissues, is important in the transport of water, minerals, and organic molecules. Each of the tissues is composed of one or more cell types. Some cell types, such as vessel elements found in xylem tissue, are only found in one type of tissue. Other cell types, such as parenchyma cells, can be found in several different tissues. A summary table of plant cells appears below and on p. 95 of the recommended text. In this lab, you will learn to recognize different cells of the dermal, ground, and vascular tissue systems. FIGURE 1. Tissue Systems, Tissues, and Cell Types and Flowering Plants TISSUE TISSUES CELL TYPES SYSTEM Parenchyma Tissue Parenchyma Cells Ground Tissue Collenchyma Tissue Collenchyma Cells System Sclerenchyma Tissue Sclerenchyma Cells (Sclereids, Fiber) Xylem Tracheids, Vessel Elements, Parenchyma Cells, and Fibers Vascular Tissue Sieve-Tube Elements, Companion Cells, System Phloem Parenchyma Cells, and Fibers Epidermis Parenchyma Cells, Guard Cells, Root Hairs, and Trichomes Dermal Tissue System Periderm Cork Cells, Cork Cambium Cells, and Parenchyma Cells What you should be able to do after this lab 1. Identify primary meristems (protoderm, ground meristem, and procambium) in root and shoot apical meristems. 2. Identify dermal, vascular, and ground tissue systems in leaves, stems, and roots. 3. Recognize apical meristems and the different cell types they produce. 1 Part I. Early development of roots and shoots: primary meristems At the tip of every root and shoot, new cells are added to the primary plant body. The apices of these regions are called the root apical meristems and the shoot apical meristems. These apical meristems differentiate into three primary meristems that ultimately produce the mature tissues of the primary plant body. Apical Meristem Protoderm Ground Meristem Procambium Tissues & cells of the dermal tissue system Tissues & cells of the ground tissue system vascular tissue system Tissues & cells of the The dermal tissue system creates the outer covering of the plant body. The vascular tissue system conducts water, dissolved minerals, sugars and other organic molecules, and hormones throughout the plant body. The ground tissue system is the tissue system that specializes in storage, photosynthesis, and other functions. Primary meristems of shoot tips EXAMINE the prepared slide of the Coleus sp. shoot tip, and in the space below, SKETCH and LABEL the apical meristem, the ground meristem, the protoderm, and the procambium. The latter three can be found in the region of cell elongation. When the cells of these primary meristems mature, they are part of the tissue systems listed above. LOCATE, SKETCH, and LABEL a leaf and a bud primordium. 2 COMPARE this slide with Fig. 9.29 in your atlas (p. 135) and with p. 106 in your text. QUESTION #1: What does the leaf primordium become? QUESTION #2: What does the bud primordium become? QUESTION #3: What tissue system will the ground meristem become? The protoderm? The procambium? Examination of live plant shoot tip Find the dissection of a living shoot tip on display under a dissecting microscope. LOCATE the apical meristem and the leaf primordia associated with the bud. Root tips In the root tip there are three main regions behind the root cap: the region of cell division, the region of elongation, and the region of maturation (or differentiation). Keep in mind that these regions overlap somewhat and therefore are not sharply defined. The region of cell division is where the root apical meristem is located. The ground meristem, protoderm, and procambium are found just behind that. In the space below, SKETCH a Zea mays root tip like that on the prepared slide, and IDENTIFY and LABEL these three regions. 3 Also look for root hairs (extensions of the epidermal cells)—they occur only in the region of cell maturation and can be used to identify the beginning of this region. LABEL at least one root hair in your sketch of the Zea mays root tip. COMPARE what you see with Fig. 9.18 on p. 132 of your atlas and p. 105 of your text. Part II. Tissues and cells of the primary plant body Dermal Tissue The epidermis is the tissue covering the primary plant body. It is made of a layer or layers of parenchyma cells. Photosynthetic leaves and stems often secrete a waxy layer on the outer walls of the parenchyma cells, called a cuticle. These organs also have guard cells, which occur in pairs and function to create and control openings called stomata (singular = stomate). EXAMINE a prepared slide of a Ligustrum sp. (privet) leaf and IDENTIFY the upper and lower epidermis, associated cuticle(s), guard cells, and stomata. The cuticle is waterproof and stains pink in the prepared slide. COMPARE with Fig. 9.75 on p. 144 of your atlas and Fig. 8-6 (p. 158) of your text. QUESTION #4: Do both the parenchyma cells and guard cells of the epidermis have chloroplasts? QUESTION #5: Do the stomata (created by the guard cells) occur primarily on the upper or lower epidermis of this leaf? Your instructor will demonstrate how to sample the lower epidermis of a Zebrina or Tradescantia leaf. EXAMINE this “epidermal peel” under the microscope and look for epidermal cells, guard cells (and their chloroplasts), and stomata. SKETCH a small section of the epidermal peel in the space below. LABEL some parenchyma cells, guard cells, chloroplasts, and stomata. (See Figs. 9.94-9.95 on p. 148 in your atlas.) 4 QUESTION #6: Which is the dominant (most abundant) cell type? QUESTION #7: Are there any spaces between the parenchyma cells of the epidermis? (not including the stomata) QUESTION #8: What three important gases move into or out of the leaf through the stomata? Ground Tissues Most ground tissue is made of parenchyma tissue (made of parenchyma cells). Associated with this is collenchyma tissue (made of collenchyma cells) and sclerenchyma tissue (made of sclereids and fibers). Cells of the parenchyma tissue EXAMINE the Ligustrum sp. leaf. When located within leaves, as in this slide, the parenchyma tissue is distinguished as mesophyll (“middle leaf”) tissue. In mesophyll tissue, the parenchyma cells are specialized for photosynthesis. Notice that these parenchyma cells are green and have multiple chloroplasts. In the Ligustrum sp. leaf some of the mesophyll cells are made up of columnshaped cells (palisade mesophyll) and other mesophyll cells have a more round, irregular shape, with large spaces between them (spongy mesophyll). LOCATE both the palisade and the spongy mesophyll tissues. QUESTION #9: Which of the two types of mesophyll is on the top side of the leaf? QUESTION #10: What might be the function of the spaces in the spongy mesophyll? 5 QUESTION #11: The shape and arrangement of the palisade mesophyll serves to maximize photosynthesis—how would you describe the palisade mesophyll relative to the spongy mesophyll? EXAMINE a prepared slide of a cross section of a Helianthus COMPARE your slide with Fig. 9.36 on p. 136 of your atlas. sp. (sunflower)stem. The bulk of the Helianthus stem is occupied by rather large, round parenchyma cells of the parenchyma tissue, composing the pith. These cells are thin-walled storage cells. QUESTION #12: Do these parenchyma cells also function in photosynthesis? How can you tell? Cells of the collenchyma tissue EXAMINE the layers of cells just inside the epidermis. These are collenchyma cells of the collenchyma tissue. Their unevenly thickened primary cell walls distinguish them. These cells are brick shaped but appear oval because the walls are thickest at their corners. Collenchyma cells are the principal supporting cells in organs with only primary growth. (See p. 6 in your atlas.) Your instructor will demonstrate how to use a razor blade to make a very thin slice of a celery petiole in order to see living collenchyma tissue and cells. These cells are in clusters along the epidermis. Position the tissue on a microscope slide, add a drop of water and a coverslip, and look for clusters of collenchyma cells. SKETCH what you see below. LABEL collenchyma cells and their thick primary cell walls. 6 Cells of the sclerenchyma tissue EXAMINE a prepared slide of a cross section of a Helianthus sp. stem. LOCATE a vascular bundle. Notice the red “cap” of tissue located on the outside of the bundle (i.e., the bundle cap). This cap is made of fiber cells of the sclerenchyma tissue. The lignin in the very thick secondary cell walls of fiber cells stains bright red, helping us identify them. These fibers give the stem mechanical support. COMPARE your slide with Fig. 1.22 on p. 8 of your atlas. Your instructor will demonstrate how to sample pear flesh to look at under the microscope. When you do this, look for sclereid cells amongst the parenchyma cells. These sclereids are typically clumped, so scan the slide for clusters of darkcolored cells and when you find one, zoom in and notice the thick cell wall. You might also be able to see the lines running through the cell wall—these are pits—areas where there is no secondary cell wall. Sclereids provide mechanical support or protection. COMPARE your slide with Fig. 1.24 on p. 8 of your atlas. SKETCH a sclereid cell below. LABEL the primary cell wall, secondary cell wall, and pits. Vascular tissues Phloem and xylem Return to your Helianthus sp. slide to examine the vascular tissue of a stem. LOCATE the sclerenchyma fibers that make up the bundle cap. Next to this you will find the phloem tissue (green or blue-green), and then the xylem tissue (red). The xylem tissue occurs closest to the stem interior. COMPARE your slide with Fig. 9.36 on p. 136 of your atlas. 7 EXAMINE the prepared slides of Zea mays (corn) stem starting with the cross section (c.s.). LOCATE a vascular bundle. Refer to Fig. 9.31 on p.135 of your atlas or p.134 in your text. SKETCH a vascular bundle below. Be sure to note the relative positions of cells within the bundle and recognize the bundle sheath. LABEL the primary xylem, primary phloem, and bundle sheath. QUESTION #13: What is the major function of the xylem? Of the phloem? EXAMINE the longitudinal section (l.s.) of the Zea mays stem. IDENTIFY the parenchyma cells of the ground tissue and compare them to the cells of the vascular bundle. QUESTION #14: What is the major difference in shape between these two tissues (in the longitudinal section)? LOCATE the fibers of the bundle sheath, then the vessel elements within a vascular bundle. They will both be stained red. The vessel elements will be wider and full of pits. QUESTION #15: Which of these cells types is wider? Which is longer? 8 Refer back to the cross section of a bundle (that you drew earlier) frequently to check on relative locations of cell types. Bundle sheath cells (fibers) also stain red but can be differentiated from tracheids by their lack of visible pits. QUESTION 15: What is the function of pits? The sieve tube elements and companion cells are roughly the same shape and size as tracheids but stain blue. LOCATE these cells in the phloem tissue. QUESTION #16: In this view, how does the shape of the sieve tube elements compare to the shape of tracheids? Isolated cells of xylem tissue There are three main cell types that make up the xylem tissue. On display are prepared slides of each. They are slides of tracheids, fibers, and vessel elements. Vessel elements are found only in angiosperms and gnetophytes, while tracheids are found in the xylem of all vascular plants. (See Fig 1.14 and 1.15 on p. 6 of your atlas.) View each slide and IDENTIFY each cell type. NOTE distinguishing characteristics for each cell type and SKETCH them in the table below. FIBER TRACHEID VESSEL ELEMENT -Long, with tapered ends -No pits present -Long, with tapered ends -Pits present -Larger diameter, short -End-plate missing -Very large pits 9 Primary Growth & Plant Cells: Terms you should know Procambium Spongy mesophyll Ground meristem Pith Protoderm Cortex Dermal tissue system Vascular bundle Ground tissue system Parenchyma Vascular tissue system Collenchyma Apical meristem Sclerenchyma Leaf primordia Fiber Bud primordial (= axillary bud) Sclereid Region of cell division Xylem Region of elongation Phloem Region of maturation Tracheid Epidermis Vessel element Palisade mesophyll Sieve tube element 10