Chapter 29 Plant Tissue. Overview of the Plant Body Although no one species of the 295,000 species of plants can be considered typical, the focus here.

Chapter 29Plant Tissue

Overview of the Plant Body

• Although no one species of the 295,000 species of plants can be considered typical, the focus here is on angiosperms

Shoots and Roots (Figure 29.2)

• Shoots consist of stems, leaves, and flowers (reproductive structures)– Water, minerals, and organic substances are

transported – Stems are frameworks for upright growth and

to display flowers– Parts of the system store food.

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• Root system absorbs water and minerals from soil and conducts them upward

• Root store food

• Anchor and support the plant

Three plant tissue system

• 1- Ground Tissue: makes up the bulk of the plant body (food and water storage)

• 2- Vascular tissue system: contains two kinds of conducting tissues that distribute water and solutes through the plant body.

• 3- Dermal Tissue system: covers and protects the plant’s surfaces.

Where Do Plant Tissues Originate?

• Meristems are localized regions of self-perpetuating, embryonic cells.

• Two kinds of meristems– 1- Apical meristems: at tips of roots and

stems is responsible for growth and elongation

• Growth originating at the root and shoot tips is labeled primary growth

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• Lateral meristem: are responsible for the increase in diameter of older roots and stems.– Vascular Cambium and cork cambium are two

kinds of lateral meristems– These are responsible for secondary growth

which adds to wood parts of the trees.

Types of Plant Tissues

• Simple Tissues:– 1- Parenchyma makes up most of the soft,

moist primary growth of plants• Thin walled pliable cells stay alive and retain the

capacity to divide• Various types of participate in photosynthesis

(mesophyll), storage, secretion, and other tasks.

– 2. Collenchyma: cells are thickened and help strengthen the palnt (e.g. strings of celery)

• It commonly arranged at strands or cylinders beneath the dermal tissue of stems and stalks

• The primary cells walls of collenchyma become thickened with cellulose and pectin at maturity.

– 3. Sclerenchyma: cells provide mechanical support and protection for mature plants

• Secondary walls are thick and often impregnated with lignin, which strengths and waterproofs the cell walls

• Form fibers such as hemp and flax– Sclereids form strong coats around seeds as in a peach

pit

Complex Tissues

• Vascular tissues function in the distribution of substances throughout the plant– Xylem uses two kinds of cells (dead at

maturity) to conduct water and minerals absorbed from the soil

• Vessel members: are shorter cells joined end to end to form a vessel with perforation plates at the end of each member

• Tracheids are long cells with tapered, overlapping ends

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– Phloem: transports sugar and other solutes throughout the plant body.

• Phloem contains living conducting cells called sieve tube members which bear clusters of pores in the walls through which the cytoplasm of adjacent cells is connected

• Companion cells: adjacent to the sieve tubes members, help to load sugars produced in leaves and unload them in storage and growth regions

Continue…• Dermal Tissue System: called the

epidermis covers all primary plant parts– Waxy Cuticle covers the external surfaces of

the plant to restrict water loss and resist microbial attack.

– Stomata openings between pairs of guard cells permit water and gaseous exchange with the air

– Periderm replaces the epidermis when roots and stems increase in diameter and become woody.

Monocots and Dicots

• Through the rest of chapter we will be talking about monocots and dicots

• Moncots have one cotelydons (seed leaf) and Dicots have two cotelydons (seed leaf)

• Common monocots include: grasses, lilies, irises and palms.

• Common dicots include: trees and shrubs

Primary Structure of Shoots

• Leaves develop from leaf primordia along the apical meristems of stems– A node is the point where a leaf or leaves

attach to the stems– Internode is the region on the stem between

the two nodes.

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• Buds develop in the leaf axils (the upper angle where leaves attach to the stem)– A bud is underdeveloped shoot of mostly

meristematic tissue covered by modified leaves (bud scales)

– Buds give rise to stems, leaves, and flowers

Internal Structure of Stems

• A vascular bundle is a multistranded cord of primary xylem and phloem running lengthwise through the ground tissue of shoots.

Similarities and Differences Among Leaves

• Leaves are metabolic factories equipped with photosynthetic cells.

• Deciduous trees drop their leaves as winter approaches– Evergreen retain their leaves

• Leaves vary enormously in shape, size, texture, and surface features.– Monocots leaves tend to have a flat surface – like a knife

blade, the base of which encircles and sheaths the stems– Dicots leaves have broad blade attached by a petiole to the

stem; the blade may be lobed or composed of leaflets– Simple leaves: undivided leaves

• Oak – Compound leaves: divided leaflets

• Locust• Leaves represent a large surface area that is exposed to

sunlight and carbon dioxide

Leaf Fine Structure

• Epidermis covers every leaf surface exposed to air (waxy layer)– A cuticle layer minimizes water loss.– Stomata are located mostly on the lower

epidermis

Continue…• Mesophyll consisting of photosynthetic parenchyma

cells extends throughout the interior of the leaf– Air spaces, which connect to the stomata,

participate in gaseous exchange– Palisade mesophyll cells lies closer to the epidermis

and are columnar in shape compared to the spongy mesophyll below them

• Leaf veins are vascular bundles of xylem and phloem that form a network for movement of water , solutes, and photosynthetic products

Primary Structure of Roots

• Taproots and Fibrous Root Systems– In most dicots, the primary root emerges from

the seedling, increases in diameter, and grows downward.

• Lateral roots emerge sideways along its length• Primary root plus lateral roots form from the

taproot system

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– Monocots: the taproot is replaced by adventitious roots that arise from the stem

• The roots and their branching form a fibrous root system

• Fibrous roots do not penetrate as deeply.

Internal Structure of Roots

• Cells in the apical meristem divide and then differentiate into root epidermis, ground tissues, and vascular tissues behind the meristematic region– The root cap protects the apical meristem and

pushes through the soil– Cells are torn loose as the root grows

Continue…• Protoderm gives rise to the root epidermis with

its extensions called root hairs for the outer absorptive interface with the environment

• Vascular tissues form a vascular cylinder arranged as a central column– The column is surrounded by root cortex (ground

tissue), which has abundant air spaces– The endodermis- the innermost layer of the cortex

–surrounds the vascular cylinder and helps control water movement into it

Woody and Nonwoody Plants• Seasonal growth cycles proceed from

germination, to seed formation to death.– Annuals complete life cycle in one season,

they are nonwoody , or herbaceous plants such as corn.

– Biennials such as carrots, live two seasons: vegetative growth first , flower and seed formation second season

• Perennials live many years and have secondary growth (roses, grape vines, and apple trees)

• Woody plants such as dicots and gymnosperms show secondary growth by producing large amounts of secondary xylem

Vascular Cambium

• Vascular Cambium is a cylinderlike lateral meristem.– It produces a secondary xylem on its inner

face and secondary pholem on its outer.– The secondary growth displace the cells of

the vascular cambium toward the stem surface

• Secondary xylem and phloem form at the vascular cambium of the roots

Formation of Bark• In response to rupture of the outer cortex (by

girth expansion), cork cambium produces the periderm – a corky replacement of the epidermis– Periderm and secondary pholoem constitute of

bark– Periderm consist of cork, secondary cortex, and

cork cambium

• Lenticels are small channels through the corky surface of bark that allow for exchange of gases

Heartwood and Sapwood

• Heartwood lies at the center of older stems and roots.– It depository for resins, oils, gums and tannins– It makes tree strong and able to defy gravity/

• Sapwood is secondary growth located between heartwood and the vascular cambium– Wet, pale in color and is not strong– Rich in the sugar-rich fluid of the phloem

Early Wood, Late Wood, and Tree Rings• In regions with cool winters or dry spells, the

vascular cambium is inactive during part of the year– Early wood (start of the growing season) contains

xylem with large diameters and thin walls– Late wood contains xylem with small diameter and

thick walls– Growth rings appear as alternating light bands or

early wood and dark bands of late wood

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• Hardwood: (OAK) has vessels, tracheids, and fibers in its xylem

• Softwood (CONIFERS) have no vessels or fibers

Limits to Secondary Growth

• Some trees live in habitats too harsh and remote for most invaders

• Most trees use a strategy of compartmentalization to wall off invaders, building a fortress of thickened cells walls around wounds or deploying toxic compounds

•The End