Unit 7Plants

Chapter 23

Roots, Stems, and Leaves

Plant tissue types:

• Dermal: – epidermis (outer skin) with

waxy cuticle lining made of cutin

• Vascular: – xylem and phloem cells for

transport

• Ground: – tissues between the dermal

and vascular

• Meristem: – growth cells

dermalvascularground

Ground tissues

• Parenchyma: – primary wall (soft)

• Collenchyma:– unevenly thickened primary wall

(flexible)

• Sclerenchyma: – primary wall + thick secondary wall

(rigid)

Vascular tissue: xylem cells

• Conducts (transports) water and minerals from roots to leaves

• Tracheids: – long and thin

(mostly in gymnosperms)

• Vessel elements: – short and wide

(mostly in angiosperms)– Dead when mature!

Xylem cells are arranged like a bunch of straws.

Vascular tissue: phloem cells

• Sieve tube elements:– anucleated (no nucleus)

when mature, “empty” cell to conduct sugars

• Companion cell:– nucleated, controls the

activities of the sieve tube cell

• Sieve plate: – separates sieve tube

elements in the sieve tubes

Roots

Types of Root Systems (p.584)

• Fibrous =– many, spreading,

branching roots– good for binding

soil to prevent erosion

Types of Root systems

• Taproot =– one long, main

root from which all others branch

– good for growing toward water source

Types of Root systems

• Adventitious =– specialized roots

that grow above ground

– Ex: aerial rootsor prop roots

Regions of the Root Tip

• Root Cap = – covers and protects the

delicate cells in the meristematic region

• Meristem Region (region of cell division) – area where new cells are

created by mitosis

Regions of the Root Tip

• Region of Elongation – area where cells grow in length

• Region of Differentiation (maturation) – area where cells become specialized for different jobs,

I.e. storage, protection, transport, etc.

Root hairs for increasing surface area may be found in maturation region

Inner Layers of Roots• Epidermis = outer

layer of cells, for protection and absorption

• Cortex = inside epidermis, main storage area of roots

• Endodermis = single layer of cells that controls flow of water into the vascular cylinder

Vascular Cylinder

• Xylem = innermost star-shaped cells for transporting water upward

• Phloem = small bundles between rays of star, for transporting food down to cortex for storage

• Pericycle = cells between others that give rise to secondary (lateral) roots

Monocot root

Dicot root

Stems

Types of Stems (p.590)

Herbacious = soft, green & short-lived Ex: tomato plants

Woody = hard, brown & long-lived Ex: trees & shrubs

Parts of a twig

• Node = point of growth along a twig

• Internode = spaces between nodes

• Lateral buds = buds along the side of the twig; may be for new leaves, flowers or branches

• Terminal buds = buds at the end of the twig; only for extending length of stem

• Bud-scale scar (determines age of twig)

Herbacious Stems• Epidermis = outer layer, for

protection• Cortex = below epidermis, for

storage• vascular bundles =

contain phloem (outside) & xylem

(inside) • Arrangement: radially around

cambium in dicots & randomly scattered in monocots

• Pith = innermost; for storage

Woody Stems

• BARK consists of four layers:

• 1) CORK = rough, outermost; for insulation

• 2) CORTEX = below cork; for storage

• 3) PHLOEM= “arching” through cortex; for carrying food downward

• 4) CAMBIUM = inner layer; gives rise to secondary growth (outward)

Woody Stems

• WOOD consists of only XYLEM = transports water upward

• 1) Sapwood = outer, lighter, still active(the “sap” is still flowing)

• 2) Heartwood = inner, darker, inactive(this area is “dead” & may only provide support)

• PITH (young stems) for storage

Annual Rings

• *determine age of stem because texture of spring and summer cells is different

Leaves

Types of Leaves (p. 595)

• Simple leaf – single blade

• Compound leaf – blade divided

into leaflets

4

5 6

External features of leaf

• Blade =– flat green portion

• Petiole =– supporting stalk

(dicots)

• Veins = – vascular tissue

(parallel in monocots & branching in dicots)

Internal features of leaf (p. 596)• Cuticle =

– waxy covering to prevent water loss (not a cell layer)• Epidermis =

– single protective layer without chloroplasts for sun to shine through

• Mesophyll = – central layers where photosynthesis occurs

Mesophyll layers

• Palisade = – elongated tightly

packed cells near top of dicot leaf where most of photosynthesis occurs

• Spongy = – irregularly packed cells

with air spaces for gas exchange to occur

Vascular tissue within veins

• Xylem = – transports water & minerals upward from the

roots to the leaves (to be used during photosynthesis)

• Phloem =– transports food downward from the leaves to

the roots (for storage)

Electron microphotograph of Leaf vein

• Guard cells = – kidney-shaped cells in lower epidermis that

regulate the opening and closing of the stomata (only epidermal cells with chloroplasts)

(p. 596)

• Stomata = – openings for the exit of water & oxygen and the

entrance of carbon dioxide

Transpiration (p.600)

• Water absorbed by roots by osmosis

• Water sticks to other molecules by cohesion & adhesion

• Water moves up xylem by capillary action

• Water is pulled out of leaf by evaporation process called transpiration

Transpiration =

evaporation of water from the leaf

100%

?%95%

5%

Translocation (p.602)• Food (mainly

carbohydrates) move down from leaf (SOURCE) to be delivered to (SINK)

• Food may be stored in parenchyma cells of cortex or pith of stems and roots

• Food may be sent to fruits (or away from fruits during hard times)