Chapter 23

Roots, Stems and Leaves

Learning Targets 23.1

What are the principal organs and tissues of vascular plants?

How is meristematic tissue different from other plant tissues?

What specialized cells make up vascular tissue?

Specialized Tissues in Plants

Three main organs of plants: ROOTS: underground organs that

absorb water and minerals Also anchor the plant and hold it upright

STEMS: supporting structures that connect roots and leaves

Carry water and nutrients Holds leaves up to light

LEAVES: carry out photosynthesis Capture light, flat so cover more surface

area Cuticle and adjustable pores protect leaves

from water loss

Tissue Systems

Within the roots, stems and leaves are FOUR specialized tissue systems: DERMAL TISSUE: forms the skin of a

plant (is the outermost layer of cells) VASCULAR TISSUE: like the plant’s

bloodstream (transports water and nutrients throughout the plant)

GROUND TISSUE: cells between the dermal and vascular tissues

MERISTEMATIC TISSUE: found only in the tips of shoots and roots

Dermal tissue

Vascular tissue

Ground tissue

Stem

Root

Leaf

Three tissues of

plants

Dermal Tissue

Outer covering of a plantConsists of:

Epidermis: outermost layer Cuticle: thick, waxy layer that

protects against water loss and injury (covers epidermis)

On under side of leaves, contains guard cells which regulate water loss and gas exchange

Dermal Tissue

Vascular Tissue Transport system: “bloodstream” Consists of xylem and phloem

Xylem: water-conducting tissue

Transports water to leaves Phloem: food-conducting

tissueTakes sugar to the roots

Ground Tissue

Tissue that lies between dermal and vascular tissue Consists of parenchyma,

collenchyma and sclerenchyma

Ground TissueParenchyma:

Thin cell walls and large vacuoles In leaves, these cells are packed

with chloroplasts and are the site of photosynthesis

Collenchyma Cells with strong, flexible walls

that help to support larger plants This is what makes up the stringy

part of celery

Ground Tissue

Sclerenchyma Cells that have an extremely

thick, ridged, cell wall that makes ground tissue tough and strong.

Meristematic TissueNew growth is produced in cells

that make up meristematic tissueIt is the ONLY plant tissue that

produces new cells by mitosis!! Best place to see this at the tip of

a shoot/root where apical meristem is located

Learning Targets 23.2

What are the two main types of roots?

What are the main tissues in a mature root?

What are the different functions of roots?

Roots

Functions: Absorb water and nutrients Anchor plant

TWO MAIN TYPES OF ROOTS: Taproots: found mainly in dicots

EX: carrot, dandelions, beets, radishes, oak tree

Fibrous Roots: found mainly in monocots

EX: grass

ROOTS

Root Structure

Epidermis of root is covered with tiny projections called root hairs Increase surface area of root to absorb more

water

Roots grow in length as their apical meristem produces new cells near the root tip The fragile new cells are covered by a tough

root cap that protects the root as it forces its way through soil

Learning Targets 23.3

What are the three main functions of stems?

How do monocot and dicot stems differ?

How do primary growth and secondary growth occur in stems?

Stems

FUNCTIONS: Produce Leaves, branches and

flowers Hold leaves up in the sunlight Transport substances between

roots and leavesComposed of dermal, vascular

and ground tissue (like the rest of the plant)

Stem Parts

Nodes: where leaves are attached

Internodes: regions between the nodes

Buds: contain undeveloped tissue that can produce new stems and leaves

Monocot v. Dicot StemsMoncots: vascular bundles are

scattered throughout the stem

Monocot v. Dicot Stems

Dicots: vascular bundles are arranged in a cylinder

Primary Growth

For a plant’s entire life, new cells are produced at the tips of roots and shoots This is called primary growth They increase in length It takes place in all seed plants

Secondary Growth

The pattern of growth in which stems increase in width is called secondary growth In conifers and dicots,

secondary growth takes place in lateral meristematic tissue called the vascular cambium and cork cabium

WOOD WOOD is actually

layers of XYLEM Heartwood:

older xylem in center of wood, that no longer conducts water

Darkens with age as it accumulates impurities

Sapwood: surrounds heartwood, active in transport

WOOD Growth Rings Indicate age of tree

and environmental conditions Thick rings

indicate the growing season experienced adequate moisture

Thin rings indicate there was less water (draught)

Wood Bark

Cork

Cork Cambium

Phloem

Vascular Cambium

Xylem: Sapwood

Xylem:HeartwoodContains old, nonfunctioningxylem that helpssupport the tree

Contains active xylem that transports water and minerals

Produces new xylem and phloem, which increase the width of the stem

Transports sugars produced by photosynthesis

Produces protective layer of cork

Contains old, nonfunctioning phloem that protects the tree

Learning Targets 23.4

How does the structure of a leaf enable it to carry out photosynthesis?

How does gas exchange take place in a leaf?

Leaves

Main organs of photosynthesis Makes food for plants (glucose:

C6H12O2)

Structure is optimized for absorbing light and carrying out photosynthesis Blades: thin, flattened to increase

surface area to absorb sunlight Attached to stem by petiole

Epidermis: outer layer Cuticle: waxy, protective layer

Protects tissues and limits water loss

Leaves

Simple and Compound Leaves

Leaf Structure/FunctionPhotosynthesis

Most of photosynthesis carried out in MESOPHYLL layer

Packed with chloroplasts Palisade Mesophyll: column-

shaped cells just under epidermis

Absorb most of light coming into leaf

Leaf Structure/Function

Veins

Xylem

Phloem Vein

Cuticle

Epidermis

Palisademesophyll

Epidermis

Stoma

Guardcells

Spongymesophyll

Leaf Structure/FunctionSpongy Mesophyll:

loose tissue layer beneath palisade with air spaces between cells Air spaces connect

with outside through STOMATA

Leaf Structure/Function

Veins

Xylem

Phloem Vein

Cuticle

Epidermis

Palisademesophyll

Epidermis

Stoma

Guardcells

Spongymesophyll

Leaf Structure/Function

STOMATA: pores in underside of leaf that let carbon dioxide and oxygen diffuse in and out of the leaf Each stoma consists of two

GUARD CELLSGuard Cells: cells in the epidermis

that control the opening and closing of the stomata by responding to water pressure changes

Single stomata Multiple stomata

Leaf Structure/FunctionGas Exchange

Leaves take in CO2 and give off O2 during photosynthesis

Plant leaves allow gas exchange by opening their stomata

If kept open all the time, there would be large amounts of water loss due to transpiration

Plants keep stomata open just enough to allow photosynthesis to take place, not long enough to lose too much water

Leaf Structure/Function

Guard cells regulate opening/closing of the stomata

If water pressure is high, they open the stomata

If water pressure is low, they close the stoma

Stomata/Guard Cells

Stoma Open Stoma Closed

Guard cells

Inner cell wall

Stoma

Guard cellsInner cell wall

Leaf Structure/Function

Veins

Xylem

Phloem Vein

Cuticle

Epidermis

Palisademesophyll

Epidermis

Stoma

Guardcells

Spongymesophyll

Learning Targets 23.5

How is water transported throughout a plant?

How are the products of photosynthesis transported throughout the plan?

Water TransportCombo of root pressure, capillary

action and transpiration provides force to move water through the xylem Root Pressure: pressure created

by water entering the tissues of a root that pushes water upward in a plant stem

Capillary Action: tendency of water to rise in a THIN tube

Water is attracted to the walls of the tube and to other water molecules

Water Transport

Transpiration: loss of water through plant leaves

•When water is lost through transpiration the leaf “pulls” water upward from the roots Moves water from HIGH to

LOW pressure

Water Movement

Evaporation of water molecules out of leaves.

Pull of water molecules upward from the roots.