Lab 10: Angiosperm Plant Structure PDF

BIOL 227 (Fall 2024) Lab 10: Angiosperm plant structure Written by: Catherine Calogeropoulos © Edited by Dr. Jin Suk Lee Learning outcomes 1. Review plant anatomy, the organs, tissues and cells that make up the body...

BIOL 227 (Fall 2024) Lab 10: Angiosperm plant structure Written by: Catherine Calogeropoulos © Edited by Dr. Jin Suk Lee Learning outcomes 1. Review plant anatomy, the organs, tissues and cells that make up the body of angiosperms, covering both monocots and eudicots 2. Understand how plants grow throughout their lives and locate different tissues generated by meristems 3. Differentiate between primary and secondary growth This lab reviews the basic structure of the largest group of plants, the angiosperms (flowering plants) within the Anthophyta Phylum. With about 435,000 species, angiosperms are by far the most abundant, species rich, and widespread plant group today. There are four organs that make up the angiosperm plant body: roots, stems, leaves, and flowers. The structures and functions of flowers (a major distinguishing feature of angiosperms) were reviewed in lab 9. We will focus on the vegetative organs that angiosperms possess: roots, stems, and leaves and each of these organs will be reviewed in terms of its structure (overall form/morphology of the organ and the arrangement of its cells and tissues). Plant cells: parenchyma, collenchyma & sclerenchyma Plants are remarkably simple in form. Their tissues and organs are built up from just three types of cells: parenchyma, collenchyma, and sclerenchyma cells. Parenchyma cells are thin cells with flexible primary cell walls. They lack secondary cell walls and are the least specialized of all types of cells. They perform, however, most of the metabolic functions of the plant, including photosynthesis and the storage of photosynthates. The cells of the ground tissue in stems and roots are mostly examples of parenchyma cells functioning in storage and support. The palisade and spongy mesophyll cells of leaves are parenchyma cells functioning in photosynthesis. Parenchyma cells demarcate themselves from other cells by retaining the ability to divide and differentiate. Collenchyma cells have thickened, uneven cell walls. Like parenchyma cells, they too lack secondary cell walls. Unlike parenchyma cells, collenchyma cells are generally elongated and grouped together in strands to help support the young plant. The uneven thickening of cell walls offers structural support in stems without restraining growth. We typically find collenchyma cells on the underside of the epidermal layer in monocot stems. Unlike parenchyma and collenchyma cells, sclerenchyma cells have lignified secondary cell walls. This lignification renders sclerenchyma cells dead at functional maturity. There are two types of sclerenchyma cells: sclereids and fibers. Sclereids are short and irregularly shaped cells. We find them in nutshell and seed coats where they serve to protect the embryonic plant. Sclerenchyma fibers, on the other hand, are long and 1 BIOL 227 (Fall 2024) slender with tapered ends and arranged in threads. In stems and leaves, sclerenchyma fibers help to reinforce vascular bundles. Tracheids and vessel elements are specialized sclerenchyma cells of the xylem that function in the long-distance transport of water and minerals. Cells and tissue arrangements of plant organs: roots, stems & leaves Cells come together to form three types of tissues: dermal, vascular and ground tissue. All three tissue systems are continuous throughout the entire body of a plant, but the arrangement of these tissues differs between roots, stems and leaves. The arrangement also differs between monocot and eudicot plants. The dermal tissue covers the entire outside surface of the plant with almost no interruptions. Dermal tissue functions in defense against physical damage, pathogens, and water loss. In monocots and non-woody eudicot plants, the dermal tissue is made up entirely of the epidermis. The epidermal cells of leaves and young stems are responsible for producing the cuticle –a hydrophobic extension of the primary cell wall that renders leaves and stems impervious to water. The dermal layer of leaves also includes specialized cells that flank openings through which gas exchange occurs. These specialized epidermal cells are called the guard cells and the openings are the stomates. The guard cells mediate the opening and closing of the apertures to control gas exchange and minimize water loss. Trichomes are another class of specialized epidermal cells found in leaves. In roots, the specialized epidermal cells include the root hairs. The vascular tissue serves as conduits for moving fluids from source to sink. The vascular tissue carries out long distance transport of materials between the root system and the shoot system. There are two types of vascular tissue –the xylem and phloem system. The xylem conveys water and dissolved minerals that are absorbed from the soil solution and transported to the shoot system. The phloem transports organic nutrients, including sugars, amino acids, and plant hormones, from where they are made to where they are needed. There are two types of xylem cells: tracheids and the vessel elements. Tracheids are found in all vascular plants within the plant kingdom. They are long with tapered ends where water flows from one conduit to the next through bordered pits. Vessel elements are common to most angiosperms and few gymnosperms. They are wider than tracheids and stacked end-to-end without any tapering. The specialized cells of the phloem system function to move the products of photosynthesis to locations where chemical energy is needed or stored. The sugar conducting cells of the phloem include the sieve tube elements stacked end-to-end. Gutted of organelles, sieve-tube elements maintain function because of their close association to companion cells. Each sieve-tube element is adjacent to a companion cell that helps to maintain the plasma membrane of the sieve tube element it serves. The xylem and phloem tissues in stems and leaves are grouped together in discrete bundles. In monocot stems, the vascular bundles are dispersed throughout the stem. In eudicot stems, they form a ring just below the epidermis of the stem. 2 BIOL 227 (Fall 2024) In eudicot and monocot roots, the vascular tissue is concentrated within a centrally located vascular cylinder. In eudicots, the xylem tissue has a characteristic X shape. The space in between the arms of the X, is filled with sieve tube elements and their companion cells. Parenchyma cells are also present within the vascular cylinder. The vascular cylinder is bordered by specialized cells called the endodermal cells. Immediately on the inside of the endodermis is where we find the pericycle, where lateral roots will emerge from. In monocots, the xylem and phloem tissues are arranged in a ring near the inside edge of the vascular cylinder. Like the eudicots, the endodermis, borders the vascular cylinder, and the cells of the pericycle are immediately below the endodermis. Lateral roots branch out from the pericycle of eudicots and monocots to exploit a greater range of resources within the soil matrix. The ground tissue has several roles. In stems and roots, ground tissue functions in structural support, and the storage of photosynthates and minerals. In eudicot stems, the ground tissue on the inside of the ring of vascular bundles is called the pith while the ground tissue on the outside of the ring is called the cortex. In monocot stems, there is no distinction between the cortex and pith because the vascular tissue is dispersed in discrete bundles throughout the stem. In monocot and eudicot roots, the ground tissue is confined to the cortex –the space between the epidermis and vascular cylinder. In leaves, ground tissue functions in photosynthesis. In the leaves of most eudicot plants, the cells of the ground tissue include the palisade mesophyll cells that are arranged as columns on the upper side of leaves and the sparsely populated spongy mesophyll cells occupy the bottom half of leaves. Reminiscent of the sponge-like alveoli in mammalian lungs, this spongy arrangement of mesophyll cells is important for increasing the available surface area for gas exchange. In monocots, only one kind of mesophyll cell is observed in cross sections of leaves. Meristems and plant growth: primary & secondary growth Plants are capable of both determinant and indeterminant growth. Leaves have determinant growth because they cease to grow at maturity while stems and roots have indeterminate growth. Indeterminate growth can be of two kinds. We have the indeterminate growth that is confined to the apical meristems concentrated at root and shoot tips, as well as the axillary buds located where the leaf petiole meets the stem. Apical meristems are responsible for what we call primary growth that makes plants grow taller and longer continuously. All plants undergo primary growth. Primary growth in roots: A root has 3 zones: - The zone of cell division: the part where root apical meristem is found. In roots, the apical meristem is protected by a structure called the root cap. - Zone of elongation: the part where the cells elongate. - Zone of differentiation/maturation: the part where the cells mature and differentiate. Epidermal cells in this zone form root hairs, which increase the surface area of dermal tissue. Additionally, lateral roots originate from the pericycle found here. Primary growth in shoots: - The shoot apical meristem is not covered by a cap. - The apical bud contains a shoot apical meristem. 3 BIOL 227 (Fall 2024) - Leaf primordia and axillary buds develop below the apical bud. Secondary growth is achieved by laterally positioned meristems. There are two types of lateral meristems: the vascular cambium and the cork cambium. In woody plants, the epidermis is replaced by the periderm. The periderm consists of a variety of cells, including meristematic cells, that contribute to the continuous regeneration of the bark. The cells produced by the lateral meristem within the periderm, have secondary cell walls lined with suberin, making the bark impervious to both water and pathogens. Thus, the suberin lined cells of the periderm have the same function as the cuticle-lined epidermal cells of leaves and non-woody stem. Secondary growth increases the diameter of stems and roots in woody plants. Lateral meristems include the vascular cambium and cork cambium. The vascular cambium takes the shape of a cylinder that runs the length of the stem. It is only a single cell layer thick. The meristematic cells that form the vascular cambium are called cambial cells. When a cambial cell divides, one of the cells remains a meristematic cell called an initial. The other cell becomes a derivative. If the derivate cell finds itself on the inside of the vascular cambium it differentiates into a cell of the xylem system. If on the outside, it becomes a cell of the phloem system. Near shoot apical meristems, the newly formed vascular cambium, deposits primary xylem and primary phloem. During subsequent years, when the vascular cambium resumes activity along the older parts of the stem, it deposits secondary xylem and secondary phloem tissue. As the secondary xylem accumulates over the years it pushes the primary xylem towards the center of the stem. Conversely, the secondary phloem does not accumulate. As new secondary phloem is added, the phloem from previous years gets pushed out and flakes off the bark. Within the vascular cambium, we have two different types of meristematic cells. We have elongated initials with their long axis parallel to the main axis of the stem. These elongated initials differentiate into tracheids and vessel elements if they are part of the xylem system or sieve tube elements and companion cells if associated with the phloem. Elongated initials also produce sclerenchyma fibers and axially oriented parenchyma cells. The vascular cambium also produces shorter initials with their long axis perpendicular to the main axis of the plant. These shorter initials produce the vascular rays. These ray cells form the distinct star-like pattern that radiates out from the center of a cut tree. These radial parenchyma cells serve as conduits for the movement of substances from the secondary xylem to the secondary phloem located on the outside of the vascular cambium. Radial parenchyma cells are a lifeline for the transport of substances from the xylem to the phloem and vice versa. Observing the cross-section of a tree trunk, one can estimate the age of the tree by counting the number of rings. The rings are the result of xylem cells with different diameters. In early spring, the xylem conduits produced are much larger in diameter than the xylem cells that are produced in mid to late summer. The need for large conduits in the spring is to supply water for the deployment of new leaves; each cell within the leaf must imbibe a significant volume of water to elongate and become turgid. Thus, for many deciduous tree species, large diameter tracheids and vessel elements are produced in early spring. In mid to late summer, the concern for leaf hydration is replaced with a concern for structural support. Consequently, more narrow and densely 4 BIOL 227 (Fall 2024) packed conduits are produced. Thus, the distinct pattern of light and dark bands that we recognize as tree rings is alternating bands of early wood and late wood. The vascular and cork cambium are located within a very short distance of each other. The layers of the periderm consist of the cork cambium – a lateral meristem that produces cells both on the inside and outside of the cork cambium. The cells that accumulate on the inside of this lateral meristem are called cork parenchyma cells while those that accumulate on the outside are called cork cells. While cork parenchyma cells are metabolically active, cork cells have secondary cell walls lined with suberin. Once suberized, they die. Every growing season the cork cambium adds new cork and parenchyma cells within the outskirts of the trunk. This however contributes only modestly to diameter growth. The cork cambium mainly functions in minimizing water loss and rendering the trunk impervious to both microorganisms and wood boring insects. But this protection comes at the cost of gas exchange. Entry of oxygen, to meet the metabolic demands of the lateral meristems and phloem cells, is through tiny openings called lenticels that stud the entire length of tree trunks. Like stomata, but without guard cells, oxygen diffuses through these apertures a very short distance to find the living cells sequestered at the periphery of the trunk. Finally, the bark of a tree includes both the secondary phloem tissue and all the layers of the periderm. Thus, the gradual shedding of the bark, spares the vascular cambium. 5 BIOL 227 (Fall 2024) Lab 10: Angiosperm plant structure Name: ____________________________________ Tu W Th Bench #: ___________ 1. Identify the following plant cell types based on their distinguishing features. Sketch your observations of the stained slide of Cucurbita stem. Label parenchyma and Collenchyma cells. How do you recognize these cell types? - Total magnification: - Unique trait of parenchyma cells: - Unique trait of collenchyma cells: 2. Sketch your observations of the stained slide of Hoya carnosa stem. Label two sclerenchyma cells, fibers and sclereids. How do you recognize these cell types? 6 BIOL 227 (Fall 2024) - Total magnification: - Unique trait of fibers: - Unique trait of sclereids: 3. Sketch your observations of the stained slide of the monocot root. Label epidermis, cortex, endodermis, pericycle, phloem, xylem, and pith. Total magnification: 4. Sketch your observations of the stained slide of the eudicot root. Label epidermis, cortex, endodermis, pericycle, phloem, xylem, and vascular cambium. Total magnification: 7 BIOL 227 (Fall 2024) 5. State 2 features of plant internal anatomy that distinguishes monocot and eudicot roots. 1) 2) 6. Sketch your observations of the stained slide of the monocot stem. Label epidermis, ground tissue, xylem, and phloem. Total magnification: 7. Sketch your observations of the stained slide of the eudicot stem. Label epidermis, cortex, xylem, phloem, area of the vascular cambium, and pith. Total magnification: 8 BIOL 227 (Fall 2024) 8. State 2 features of plant internal anatomy that distinguishes monocot and eudicot stems. 1) 2) 9. Sketch your observations of the stained slide of the monocot leaf. Label cuticle, upper epidermis, lower epidermis, guard cells, stoma, mesophyll cells, vascular bundle, xylem, and phloem. Total magnification: 10. Sketch your observations of the stained slide of the eudicot leaf. Label cuticle, upper epidermis, lower epidermis, guard cells, stomata, palisade mesophyll cells, spongy mesophyll cells, vascular bundle, xylem, and phloem. Total magnification: 9 BIOL 227 (Fall 2024) 11. State 2 features of plant internal anatomy that distinguishes monocot and eudicot leaves. 1) 2) 12. This is the longitudinal section of Allium root tip. Label root cap, zone of cell division, zone of elongation, zone of differentiation, root apical meristem, and root hair. 13. What is the origin cell type and function of root hair? Origin: Function: 14. What are two major functions of the root cap? 15. What is the origin of lateral roots with respect to the cross-section and development zone? 10 BIOL 227 (Fall 2024) 16. Sketch your observations of the longitudinal section of Coleus shoot apex. Label apical meristem, axillary bud, and leaf primordia. Total magnification: 17. Where are two types of apical meristems found on a plant? 11 BIOL 227 (Fall 2024) 18. The cross section of the Tilia mature stem. Label cork, cork cambium, bark, cortex, secondary phloem, primary phloem, vascular cambium, phloem ray, secondary xylem, primary xylem, spring wood, summer wood and annual rings. 12 BIOL 227 (Fall 2024) 19. From a to d below, circle the correct sequence of the tissues from the center outward: a) Pith, secondary xylem, primary xylem, vascular cambium, secondary phloem, primary phloem, cork cambium, cork b) Pith, primary xylem, secondary xylem, vascular cambium, primary phloem, secondary phloem, cork cambium, cork c) Pith, primary xylem, secondary xylem, cork cambium, secondary phloem, primary phloem, vascular cambium, cork d) Pith, primary xylem, secondary xylem, vascular cambium, secondary phloem, primary phloem, cork cambium, cork 20. From which cambium does the outer bark of a woody stem develop? 13