Plant NotesPlant NotesRoots, Stems, and LeavesRoots, Stems, and Leaves

qwetqwetChapter 23Chapter 23

Roots, Stems, and LeavesRoots, Stems, and Leaves

• Three of the principal organs of seed Three of the principal organs of seed plants are roots, stems. and leavesplants are roots, stems. and leaves..

Function in:Function in:1. Transport

2. Protection

3. Coordination of plant activities

Plant Tissue SystemsPlant Tissue Systems

Plants consist of Plants consist of threethree

main tissue systemsmain tissue systems::1. Dermal tissue

2. Vascular tissue

3. Ground tissue

Dermal TissueDermal Tissue

• The “skin” of a plantThe “skin” of a plant• Contains a waxy Contains a waxy

cuticlecuticle to prevent to prevent water losswater loss

Vascular TissueVascular Tissue• Plants “bloodstream”Plants “bloodstream”• Transports water and nutrients throughout the Transports water and nutrients throughout the

plant.plant.• Made of Made of XylemXylem and and PhloemPhloem

PhloemXylem Phloem

XylemXylem

• Water conducting Water conducting tissuetissue

PhloemPhloem

• Food conducting tissueFood conducting tissue. .

RootsRoots

Two main types:Two main types:

1.1. TaprootsTaproots – found mainly in dicots – found mainly in dicots

2.2. Fibrous rootsFibrous roots found mainly in monocotsfound mainly in monocots

Root Structure and GrowthRoot Structure and Growth• The root’s surface is The root’s surface is

covered with cellular covered with cellular projections called projections called root hairsroot hairs. . Root Root hairs provide a large hairs provide a large surface area through surface area through which water can which water can enter the plantenter the plant..

Root hairs

Root FunctionRoot Function

• Anchor a plantAnchor a plant• Absorb waterAbsorb water• Absorb dissolved nutrientsAbsorb dissolved nutrients

Stems- FunctionsStems- Functions

• Produce leaves, branches and Produce leaves, branches and flowersflowers

• Hold leaves up in the sunlightHold leaves up in the sunlight

• Transport various substances Transport various substances between roots and leavesbetween roots and leaves

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Monocot and Dicot StemsMonocot and Dicot Stems

•Monocot and Dicot StemsMonocot and Dicot Stems–The arrangement of tissues in a stem differs among seed plants.–How do monocot and dicot stems differ?

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Monocot and Dicot StemsMonocot and Dicot Stems• Monocot Stems

• Vascular bundles are scattered throughout the ground tissue.

Monocot

Vascular bundles

Epidermis

Ground tissue

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Monocot and Dicot StemsMonocot and Dicot Stems

–Dicot Stems• Dicot stems have

vascular bundles arranged in a ring-like pattern.

Dicot

Cortex

Pith

Vascular bundles Epidermis

LeavesLeaves

• The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

Leaf FunctionsLeaf Functions•The air spaces connect with the exterior The air spaces connect with the exterior through stomata.through stomata.

•Stomata are porelike openings in the underside Stomata are porelike openings in the underside of the leaf that allow carbon dioxide and oxygen of the leaf that allow carbon dioxide and oxygen to diffuse into and out of the leafto diffuse into and out of the leaf..

Stoma

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Leaf FunctionsLeaf Functions•Each stoma consists Each stoma consists of two guard cells.of two guard cells.

•Guard cells are Guard cells are specialized cells that specialized cells that control the opening control the opening and closing of stomata and closing of stomata by responding to by responding to changes in water changes in water pressure.pressure. Guard cells

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Leaf FunctionsLeaf Functions

•When water pressure within guard cells is When water pressure within guard cells is high, the stoma open.high, the stoma open.

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Leaf FunctionsLeaf Functions

•When water pressure within guard cells When water pressure within guard cells decreases, the stoma closes.decreases, the stoma closes.

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Leaf FunctionsLeaf Functions

•Plants regulate the opening and closing of Plants regulate the opening and closing of their stomata to balance water loss with their stomata to balance water loss with rates of photosynthesis.rates of photosynthesis.

•Stomata are open in daytime, when Stomata are open in daytime, when photosynthesis is active, and closed at night, photosynthesis is active, and closed at night, to prevent water loss. to prevent water loss.

•In hot, dry conditions stomata may close In hot, dry conditions stomata may close even in bright sunlight, to conserve water.even in bright sunlight, to conserve water.