Plant Tissues and the Multicellular Plant Body

Learning Objectives

• Discuss the plant body, root system, and shoot system.

  • Plants have a basic body plan with a root system and a shoot system.

• Describe the ground tissue system (parenchyma, collenchyma, and sclerenchyma tissue).

  • Ground tissue system supports the plant body.

• Outline the structure and function of the vascular tissue system (xylem and phloem).

  • Vascular tissue system transports water and nutrients.

• Describe the dermal tissue system (epidermis and periderm).

  • Dermal tissue system protects the plant.

• Discuss growth in plants and its differences from growth in animals.

  • Plants exhibit flexible growth patterns to adapt to the environment.

• Distinguish between primary and secondary growth.

  • Primary growth occurs at the tips of branches, while secondary growth increases girth.

Plant Structure and Life Span

• All flowering plants, despite their diversity, share a basic body plan.

  • From desert cacti to giant sequoias, plants have recognizable structures.

• The plant body consists of a root system and a shoot system.

  • Roots anchor the plant and absorb water and minerals, while shoots bear leaves for photosynthesis.

• Plants adapt to different environments with roots in soil and shoots in the air.

• Plants can be herbaceous or woody.

  • Herbaceous plants do not have persistent woody parts, while woody plants include trees and shrubs.

• Annuals, biennials, and perennials have different life cycles.

  • Annuals complete their life cycle in one year, biennials in two years, and perennials live for more than two years.

Evolution of Plant Systems

• Root and shoot systems specialized to obtain resources from soil and air.

• Flowering plants, with flowers and seeds enclosed in fruits, are the largest group of plants.

  • They are the focus of many studies due to their prevalence in the plant kingdom.

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• Plant Life History Strategies

  • Woody perennials can live for hundreds or thousands of years.

  • Herbaceous annuals may only live for a few weeks or months.

  • Longevity of a species depends on environmental conditions.

  • Advantages of long-lived vs. short-lived species.

  • Competition in favorable environments favors long-lived perennials.

  • Short-lived plants thrive in less crowded or disturbed environments.

  • Each species has its own life history strategy based on adaptation to the environment.

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• Plant Tissue Systems

  • Three main tissue systems in plants: dermal, vascular, and ground tissue systems.

  • Organs like roots, stems, leaves, flower parts, and fruits are composed of all three tissue systems.

  • Interconnected network of tissue systems throughout the plant.

• Ground Tissue System

  • Composed of three simple tissues: parenchyma, collenchyma, and sclerenchyma.

  • Cell wall structures differentiate these tissues.

  • Primary and secondary cell walls provide structural support to plant cells.

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Parenchyma Cells

• Thin primary cell walls

• Found throughout the plant body

• Common type of cell and tissue

• Functions: photosynthesis, storage, secretion

  • Photosynthetic parenchyma cells contain chloroplasts

  • Nonphotosynthetic parenchyma cells lack chloroplasts

  • Store materials like starch grains, oil droplets, water, salts

  • Secrete substances like resins, tannins, hormones, enzymes, nectar

• Ability to differentiate into other cell types

• Example: adjacent parenchyma cells can differentiate into xylem cells when needed

Collenchyma Cells

• Unevenly thickened primary cell walls

• Provide support in soft, nonwoody plant organs

• Crucial for plant growth and competition for sunlight

• Usually elongated with thickened corners

• Found near stem surfaces and leaf veins

• Example: strings in celery stalk consist of collenchyma

Sclerenchyma Cells

• Have both primary and thick secondary cell walls

• Provide structural support

• Cells become hard and strong due to extreme thickening

• Types: sclereids and fibers

• Sclereids common in nut shells, fruit stones

• Fibers abundant in wood, inner bark, leaf ribs

Vascular Tissue System

• Consists of xylem and phloem

• Transport materials throughout the plant

• Xylem: tracheids, vessel elements, parenchyma cells, fibers

• Phloem: sieve-tube elements, companion cells, parenchyma cells, fibers

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Parenchyma Cells in Action

• Function in storage

• Examples from buttercup root and red onion

• Some contain chloroplasts for photosynthesis

• Example from waterweed leaf

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Collenchyma Cells and Sclerenchyma Cells

• Collenchyma cells with thickened walls at corners

• Example from water lily petiole

• Sclereids from cherry stone and fibers from bamboo stem

• Sclereids provide structural support with thick, hard walls

• Fibers abundant in various plant parts

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Xylem Tissue

• Conducting cells for water and minerals

• Types: tracheids and vessel elements

• Tracheids transport water and minerals, with pits in cell walls

• Vessel elements have perforation plates for water passage

Overall, the plant body consists of various cell types and tissues like parenchyma, collenchyma, sclerenchyma, xylem, and phloem, each with specific functions in supporting plant growth, storage, and transport of materials.

Plant Tissues and Structures

Xylem

• Function: Conducts water and minerals throughout the plant body.

• Components: Tracheids, vessel elements, parenchyma cells, and fibers.

  • Tracheids and vessel elements conduct water and minerals.

  • Parenchyma cells store functions.

  • Fibers provide support.

• Specialization: Tracheids and vessel elements are specialized for water conduction.

• Characteristics: Tracheids are long, tapering cells with pits for water movement.

• Flowering Plants: Vessel elements are efficient water-conducting cells with perforations for water transport.

Phloem

• Function: Conducts food (carbohydrates) throughout the plant body.

• Components: Sieve-tube elements, companion cells, phloem fibers, and phloem parenchyma cells.

  • Sieve-tube elements are specialized for food conduction.

  • Companion cells assist in sieve-tube element functioning.

• Characteristics: Sieve-tube elements form long tubes with sieve plates for cytoplasmic extension.

• Longevity: Sieve-tube elements typically live less than a year, but some palms have elements that survive for about 100 years.

• Companion Cells: Living cells with nuclei that aid in loading food materials into sieve-tube elements.

Dermal Tissue System

• Components: Epidermis and periderm.

• Function: Provides a protective covering over plant parts.

• Epidermis: Outermost layer of herbaceous plants composed of unspecialized living cells.

• Periderm: Replaces epidermis in older woody plants, forming the outer bark.

In summary, plant tissues like xylem and phloem play crucial roles in conducting water, minerals, and food throughout the plant body, while the dermal tissue system, including epidermis and periderm, provides protection and support to plant parts. Each tissue type has specialized components and functions that contribute to the overall health and growth of the plant.

PLANTS AND PEOPLE | Fibers and Textiles

Fibers from Plant Fibers

• Textile fabrics are made from plant fibers found in stems, leaves, seeds, or fruits of flowering plants.

• Plant fibers are divided into three groups: bast fibers, leaf fibers, and surface fibers.

Bast Fibers

• Bast fibers, also known as soft fibers, include flax (linen), hemp, jute, and ramie.

• These fibers come from stem tissues located outside the xylem.

• Bast fiber cells are true fibers and are often spun into thread for fabric.

Leaf Fibers

• Leaf fibers, also called hard fibers, consist of xylem cells, phloem cells, and fibers clustered together in a leaf or stem of monocot plants.

• Less durable than bast fibers, used for cordage fibers like Manila hemp and sisal.

Surface Fibers

• Surface fibers occur on seeds and fruits, with cotton being the most important.

• Cotton fibers are trichomes attached to seeds, not true fibers.

Importance of Cotton and Flax

• Cotton and flax are the two most important textile fibers.

• Cotton has been cultivated for thousands of years, becoming important in Europe after the Moors introduced it.

• Flax, grown since prehistoric times, produces linen cloth of high quality.

• Cotton overtook linen as the fabric of choice in the 19th century.

Cotton and Flax Cultivation

• Cotton was supplied to Europe by the southern United States based on slave labor.

• The American Civil War disrupted the cotton supply, leading Great Britain to grow cotton in its colonies.

• Flax is grown in cool climates, with Ireland known for its linen products.

Description of Cotton and Flax Plants

• Cotton plants are shrubs producing white, yellow, or red flowers followed by seed pods containing fibers and seeds.

• Flax is a slender annual plant with small, narrow leaves and blue flowers.

Economic Importance of Fiber Plants

• Fiber plants like cotton and flax have been economically important throughout history.

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Pit Pairs

• Simple pit pair:

  • Interruption in secondary cell wall

  • Permeable primary cell wall for water

• Bordered pit pair:

  • Small opening in secondary cell wall

  • Functions like a valve

• Pressure difference:

  • Equal pressure: Bordered pit open, water flow unrestricted

  • Greater pressure in cell A: Torus in primary cell wall blocks opening, restricts water movement

Epidermis

• Structure and function:

  • Single layer of cells with thicker walls for protection

  • Transparent to allow light penetration

• Cuticle:

  • Secreted by epidermal cells to prevent water loss

  • Restricts water loss but also carbon dioxide diffusion

• Stomata:

  • Tiny pores for gas exchange

  • Open during the day for photosynthesis, closed at night and during drought

• Trichomes:

  • Outgrowths with various functions like salt removal, cooling, and protection

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Root Epidermis

• Root hairs:

  • Unbranched trichomes increasing surface area for water and mineral absorption

Periderm

• Replaces epidermis in woody plants

• Composition:

  • Cork cells and cork parenchyma cells

  • Cork cells dead at maturity, coated with suberin to reduce water loss

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Guard Cells

• Form stomata for gas exchange

Periderm in Woody Plants

• Forms protective outer bark in older stems and roots

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Summary of Selected Cell Types

• Parenchyma cell:

  • Living with thin primary walls

  • Functions in secretion, storage, and photosynthesis

• Collenchyma cell:

  • Living with unevenly thickened primary walls

  • Provides support

• Sclerenchyma cell (fiber):

  • Often dead at maturity with thick secondary walls

  • Provides support throughout the plant body

• Tracheid and Vessel element:

  • Conduction of water and minerals, support in xylem

• Sieve-tube element and Companion cell:

  • Conduction of dissolved food materials in phloem

• Epidermal cells:

  • Living cells tightly packed together for protective covering

Table 5-2

• Summary of cell types, descriptions, functions, and locations

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• Plant Meristems

  • Plant growth involves cell division, elongation, and differentiation.

  • Cell division increases cell number, followed by elongation due to cytoplasm growth and vacuole water filling.

  • Differentiation leads to various cell types in the mature plant body.

• Meristematic Growth in Plants

  • Plants have meristems for growth, unlike animals where growth occurs throughout the body.

  • Primary growth increases plant length, while secondary growth increases girth.

  • Primary growth at apical meristems, secondary growth at lateral meristems.

• Primary Growth

  • Apical meristems at root and shoot tips drive primary growth.

  • Root tip structure includes root cap, apical meristem, area of cell elongation, and maturation.

• Secondary Growth

  • Lateral meristems like vascular cambium and cork cambium drive secondary growth.

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• Root and Shoot Growth

  • Root tip has areas of cell division, elongation, and maturation.

  • Primary meristems in cell elongation: protoderm, procambium, ground meristem.

  • Protoderm forms epidermis, procambium develops into xylem and phloem, ground meristem gives rise to cortex, pith, and ground tissue.

• Shoot Apex

  • Shoot apical meristem in terminal buds leads to leaf and bud primordia development.

  • Stem tip structure includes apical meristem, leaf primordia, and bud primordia.

• Development in Stem Tip

  • Areas of cell division, elongation, and maturation in the stem tip.

  • Primary meristems in elongation give rise to mature cell types in maturation.

This section provides insights into plant growth processes, focusing on cell division, elongation, and differentiation driven by meristems in roots and shoots. It explains primary and secondary growth in plants, detailing the roles of apical and lateral meristems in length and girth increase. The differentiation of primary meristems into various tissues is crucial for the development of the plant body.

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• Shoot Apical Meristem

  • Leaf primordia protect the shoot apical meristem.

  • Cells elongate, pushing the shoot apical meristem upward.

  • Cell divisions produce stem tissue, new leaf, and bud primordia.

• Secondary Growth

  • Trees and shrubs have secondary growth for girth increase.

  • Lateral meristems (vascular cambium, cork cambium) responsible for secondary growth.

  • Vascular cambium adds cells to wood and inner bark.

  • Cork cambium forms cork cells and cork parenchyma for periderm.

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• Plant Body Overview

  • Root system obtains water and minerals, anchors the plant.

  • Shoot system obtains sunlight and carbon dioxide, consists of stem, leaves, flowers, and fruits.

• Tissue Systems

  • Ground tissue system: parenchyma, collenchyma, sclerenchyma tissues.

  • Vascular tissue system: xylem