Plant Tissues and the Multicellular Plant Body Chapter 5

LEARNING OBJECTIVE 1 Discuss the plant body, including the root system and shoot system

The Plant Body 1 Root system generally underground obtains water and dissolved minerals for plant usually anchors the plant firmly in place

The Plant Body 2 Shoot system Shoot system consists of generally aerial obtains sunlight and carbon dioxide for plant Shoot system consists of a vertical stem bearing leaves (main organs of photosynthesis) flowers and fruits (reproductive structures)

The Plant Body 3 Buds (undeveloped embryonic shoots) develop on stems Although separate organs (roots, stems, and leaves) exist in the plant, many tissues are integrated throughout the plant body, providing continuity from organ to organ

The Plant Body

Nodes (areas of leaf and axillary bud attachment) Developing fruit Nodes (areas of leaf and axillary bud attachment) Flower Shoot system Axillary bud Internode (area between adjacent nodes) Petiole Blade Leaf Stem Figure 5.1: The primary plant body. A plant body consists of a root system, usually underground, and a shoot system, usually aboveground. Shown is mouse-ear cress (Arabidopsis thaliana), a small plant in the mustard family that is a model plant for biological research. Arabidopsis is native to North Africa and Eurasia and has been naturalized (was introduced and is now growing in the wild) in California and the eastern half of the United States. Rosette of basal leaves Root system Taproot Branch roots Fig. 5-1, p. 92

Rosette of basal leaves Shoot system Developing fruit Nodes (areas of leaf and axillary bud attachment) Axillary bud Internode (area between adjacent nodes) Flower Petiole Blade Leaf Figure 5.1: The primary plant body. A plant body consists of a root system, usually underground, and a shoot system, usually aboveground. Shown is mouse-ear cress (Arabidopsis thaliana), a small plant in the mustard family that is a model plant for biological research. Arabidopsis is native to North Africa and Eurasia and has been naturalized (was introduced and is now growing in the wild) in California and the eastern half of the United States. Taproot Branch roots Root system Stepped Art Fig. 5-1, p. 92

KEY TERMS GROUND TISSUE SYSTEM VASCULAR TISSUE SYSTEM All tissues of the plant body other than vascular tissues and dermal tissues VASCULAR TISSUE SYSTEM Tissue system that conducts materials throughout the plant body DERMAL TISSUE SYSTEM Tissue system that provides an outer covering for the plant body

3 Tissue Systems in Plant Body

Vascular tissue system Dermal tissue system Vascular tissue system Ground tissue system (a) Leaf Dermal tissue system Vascular tissue system Ground tissue system (b) Stem Figure 5.2: The three tissue systems in the plant body. This illustration shows the distribution of the ground tissue system, vascular tissue system, and dermal tissue system in the (a) leaves, (b) stems, and (c) roots of an herbaceous plant such as Arabidopsis. Dermal tissue system Vascular tissue system Ground tissue system (c) Root Fig. 5-2, p. 94

LEARNING OBJECTIVE 2 Describe the ground tissue system (parenchyma tissue, collenchyma tissue, and sclerenchyma tissue) of plants

KEY TERMS PARENCHYMA CELL COLLENCHYMA CELL SCLERENCHYMA CELL Relatively unspecialized plant cell; thin walled, may contain chlorophyll, loosely packed COLLENCHYMA CELL Living plant cell with moderately but unevenly thickened primary walls SCLERENCHYMA CELL Plant cell with extremely thick walls; provides strength and support to plant body

Ground Tissue System 1 Parenchyma tissue Composed of living parenchyma cells with thin primary cell walls Functions include photosynthesis, storage, and secretion

Parenchyma Cells

Parenchyma Cells

Vacuole Nucleus Onion (a) Parenchyma cells from an epidermal peel of red onion (Allium cepa). The large vacuole contains pigmented material and occupies most of the cell. The nucleus and cytoplasmic strands are positioned under and on top of the vacuole, between it and the plasma membrane. Figure 5.3: Parenchyma cells. Fig. 5-3a, p. 96

Chloroplasts Figure 5.3: Parenchyma cells. (b) Some parenchyma cells contain chloroplasts, and their primary function is photosynthesis. These parenchyma cells are from a waterweed (Elodea) leaf. Elodea Fig. 5-3b, p. 96

Buttercup Starch grains Figure 5.3: Parenchyma cells. Buttercup (c) Parenchyma cells often function in storage. These parenchyma cells are from a buttercup (Ranunculus) root. Note the starch grains filling the cells. Fig. 5-3c, p. 96

Ground Tissue System 2 Collenchyma tissue Composed of collenchyma cells with unevenly thickened primary cell walls Provides flexible structural support

Collenchyma Cells

Thick cell walls at corners of 4 cells Cell's interior Figure 5.4: Collenchyma cells. Note the unevenly thickened cell walls that are especially thick in the corners, making the cell contents appear spherical in cross section. These collenchyma cells are from a water lily (Nymphaea) petiole. Water lily Fig. 5-4, p. 97

Ground Tissue System 3 Sclerenchyma tissue Composed of sclerenchyma cells with both primary and secondary cell walls Sclerenchyma cells are often dead at maturity, but provide structural support

Sclerenchyma Cells

Cherry Bamboo Fiber cells Parenchyma cell Figure 5.5: Sclerenchyma cells. (a) Sclereids from a cherry (Prunus avium) stone. The cell walls are extremely thick and hard, providing structural support. (b) Long, tapering fibers and shorter parenchyma cells from a bamboo (Bambusa) stem. The stem was treated with acid to separate the cells. Fig. 5-5, p. 97

LEARNING OBJECTIVE 3 Outline the structure and function of the vascular tissue system (xylem and phloem) of plants

Vascular Tissue System Conducts materials throughout the plant body and provides strength and support Xylem Phloem

KEY TERMS XYLEM A complex vascular tissue that conducts water and dissolved minerals throughout the plant body Actual conducting cells of xylem are tracheids and vessel elements

Xylem

Pits Tracheids White pine tree Figure 5.6: Conducting cells in xylem tissue. White pine tree (a) Tracheids from a white pine (Pinus strobus) stem in longitudinal section (that is, cut lengthwise). These cells, which occur in clumps, transport water and dissolved minerals. Water passes readily from tracheid to tracheid through pits, thin places in the cell wall. Fig. 5-6a, p. 98

Vessel elements Pumpkin plant Figure 5.6: Conducting cells in xylem tissue. Pumpkin plant (b) Vessel elements from a pumpkin (Cucurbita mixta) stem in longitudinal section. The blue-stained regions are various patterns of the secondary walls in the vessel elements. Perforation plates are not visible in this micrograph. Fig. 5-6b, p. 98

Adjacent perforation plates Southern magnolia Figure 5.6: Conducting cells in xylem tissue. Southern magnolia (c) The end walls of vessel elements, called perforation plates, have large holes. Water passes through the perforation plate from one vessel element to the next. Shown are adjacent perforation plates from a southern magnolia (Magnolia grandiflora) stem; in this species, the perforation plates are at an angle in longitudinal section. Fig. 5-6c, p. 98

Pit Pairs

Pit Pairs

Pit Pairs

Pits Middle lamella Primary cell walls Permeable primary cell wall pair Tracheid Simple pit Figure 5.7: Pit pairs. Impermeable secondary cell walls Cell A Cell B (a) A simple pit pair has an interruption in the secondary cell wall. The primary cell wall in a simple pit pair is permeable to water. Fig. 5-7a, p. 101

(a) A simple pit pair has an interruption in the secondary cell Primary cell walls Bordered pit Torus Pit borders Secondary cell walls Figure 5.7: Pit pairs. Cell A Cell B (a) A simple pit pair has an interruption in the secondary cell wall. The primary cell wall in a simple pit pair is permeable to water. Fig. 5-7b, p. 101

(c) (Left ) When water pressure is equal between the two closes pit Water H2O Cell A Cell B Cell A Cell B Figure 5.7: Pit pairs. (c) (Left ) When water pressure is equal between the two cells (A and B), the bordered pit is open, and water flow is unrestricted. (Right ) When the pressure is greater in cell A than in cell B, the torus, a thickening in the primary cell walls, blocks the opening, restricting water movement through the pit pair. Fig. 5-7c, p. 101

KEY TERMS PHLOEM A complex vascular tissue that conducts food (carbohydrate) throughout the plant body Conducting cells of phloem are sieve-tube elements assisted by companion cells

Phloem

at the end walls. The smaller cells are companion cells. Sieve-tube elements Cross section Sieve plate Companion cell Squash leaves Figure 5.8: Phloem tissue. (a) Phloem tissue from a squash (Cucurbita) petiole in cross section. Note the sieve plates, the end walls of the sieve-tube elements. Most sieve-tube elements appear empty because they were sectioned in the middle of the cells rather than at the end walls. The smaller cells are companion cells. Fig. 5-8a, p. 102

Companion cell Sieve-tube element Longitudinal section Squash leaves Figure 5.8: Phloem tissue. Squash leaves Sieve plate (b) Phloem tissue from a squash (Cucurbita) petiole in longitudinal section. Fig. 5-8b, p. 102

LEARNING OBJECTIVE 4 Describe the dermal tissue system (epidermis and periderm) of plants

Dermal Tissue System Outer protective covering of the plant body Epidermis Periderm

KEY TERMS EPIDERMIS Outermost tissue layer, usually one cell thick Covers the primary plant body (leaves, young stems and roots)

Epidermis Epidermis covering aerial parts secretes a wax layer (cuticle) that reduces water loss Gas is exchanged between interior of shoot system and surrounding atmosphere through stomata

Epidermis

Epidermal cells Guard cells Stoma Spiderwort Fig. 5-9, p. 103 Figure 5.9: Epidermis. This light micrograph shows the leaf epidermis of spiderwort (Tradescantia virginiana). Note the stomata, minute pores formed by guard cells (stained pink). Nuclei of all epidermal cells are stained a dark magenta. Spiderwort Fig. 5-9, p. 103

KEY TERMS PERIDERM Outermost layer of cells covering a woody stem or root (the outer bark that replaces epidermis when it is destroyed during secondary growth)

Periderm

Exterior environment Geranium Remnants of epidermis Cork cells Figure 5.10: Periderm. Formed by the cork cambium, periderm is the secondary plant body replacement for epidermis and makes up the outer bark of woody stems and roots. Some herbaceous eudicots, such as geranium (Pelargonium), form a limited periderm as they age. The cells of periderm are arranged in vertical stacks. Note that the cork cambium produces many layers toward the cell’s exterior but only a few layers toward the cell’s interior. Cork cells Periderm Cork cambium Cork parenchyma Cortex (interior of stem) Fig. 5-10, p. 103

LEARNING OBJECTIVE 5 Discuss what is meant by growth in plants and how it differs from growth in animals

Growth in Plants Involves cell division, cell elongation, and cell differentiation Plants grow only in specific areas (meristems) composed of cells that do not differentiate

Growth in Animals Location of growth differs between plants and animals When a young animal grows, all parts of its body grow, although not necessarily at the same rate

LEARNING OBJECTIVE 6 Distinguish between primary and secondary growth

KEY TERMS PRIMARY GROWTH An increase in stem and root length due to the activity of apical meristems at the tips of roots and at the buds of stems

KEY TERMS APICAL MERISTEM BUD An area of cell division at the tip of a stem or root in a plant; produces primary tissues BUD A dormant embryonic shoot that eventually develops into an apical meristem

Root Tip

Area of cell maturation Root hairs Area of cell Protoderm elongation Ground meristem Figure 5.11: The root tip. A root cap protects the root apical meristem, where cells divide and thus increase in number. Farther from the tip is an area of cell elongation, where cells enlarge and begin to differentiate. The area of cell maturation has fully mature, differentiated cells. Note the root hairs in this area. Procambium Area of cell division Apical meristem Root cap Fig. 5-11, p. 105

Stem Tip

Older leaf Leaf primordia Apical meristem Older leaf Trichome Bud primordium Figure 5.12: The stem tip. This longitudinal section through a terminal bud of coleus (Coleus) shows the stem apical meristem, leaf primordia, and bud primordia. Coleus Fig. 5-12, p. 106

Stem Tip Development

Immature leaf Stem apical meristem Area of cell division Procambium Protoderm Procambium Ground meristem Area of cell elongation Epidermis Figure 5.13: Development in the stem tip. This diagram shows the kinds of cells in the area of cell division, the area of cell elongation, and the area of cell maturation. The three primary meristems (protoderm, procambium, and ground meristem) in the area of cell elongation give rise to the mature cell types in the area of cell maturation. (Procambium cells shown in the area of cell maturation—between the primary xylem and primary phloem—may give rise to vascular cambium later in development.) Area of cell maturation Cortex Procambium Pith Primary xylem Primary phloem Fig. 5-13, p. 106

KEY TERMS SECONDARY GROWTH An increase in a plant’s stem and root girth due to the activity of lateral meristems (the vascular cambium and cork cambium)

Secondary Growth Woody plants have secondary growth In addition to primary growth Secondary growth is localized, typically as long cylinders of active growth throughout the lengths of older stems and roots

KEY TERMS LATERAL MERISTEM An area of cell division on the side of a vascular plant; the two lateral meristems (vascular cambium and cork cambium) give rise to secondary tissues

Lateral Meristems and Secondary Growth

Inner bark (secondary phloem) Outer bark (periderm) Inner bark (secondary phloem) Figure 5.14: Lateral meristems and secondary growth. The vascular cambium, a thin layer of cells sandwiched between the wood and bark, produces secondary vascular tissues: the wood, which is secondary xylem, and inner bark, which is secondary phloem. The cork cambium produces the periderm, the outer bark tissues that replace the epidermis in the secondary plant body. Wood (secondary xylem) Bark Surface of vascular cambium Fig. 5-14, p. 107

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