Chapter 24PLANT

STRUCTURE and

FUNCTION

Overview of PLANT

STRUCTURE

Reproductive shoot (flower)

Terminal bud

Node

Internode

Terminalbud

Vegetativeshoot

BladePetiole

Stem

Leaf

Taproot

Lateral roots Rootsystem

Shootsystem

Axillarybud

• Vegetative organs are concerned with growth and nutrition

• Flowers, seeds, and fruits are structures involved in reproduction.

10

Flowering Plants: Monocots or Eudicots

Stem LeafSeed Root Flower

Monoco

tsEud

icots

One cotyledon in seedRoot xylem andphloem in a ring

Leaf veins forma parallel pattern

Flower parts in threesand multiples of three

Root phloem betweenarms of xylem

Leaf veins forma net pattern

Flower parts in fours orfives and their multiples

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Two cotyledons in seedVascular bundlesin a distinct ring

Vascular bundlesscattered in stem

4

• Roots

– Generally, the root system is at least equivalent in size and extent to the shoot system

• Anchors plant in soil

• Absorbs water and minerals

• Produces hormones

– Root hairs:

• Projections from epidermal root hair cells

• Greatly increase absorptive capacity of root

ROOTS

Roots • Roots anchor plant in soil, absorb

minerals & water, & store food– fibrous roots (1)

• mat of thin roots that spread out• monocots

– tap roots (2)• 1 large vertical root • also produces many small lateral,

or branch roots • dicots

– root hairs (3)• increase absorptive

surface area

2

1

3

Shoots

• Shoots consist of stems, leaves & buds

• Stems– nodes = points at which

leaves are attached– internodes = stem

segments between nodes

• Buds– growth of shoot

• terminal or apical bud = at tip of plant• axillary bud = in nodes on stem

STEMS

– Support for the plant bodySupport for the plant body– Carries nutrients Carries nutrients

throughout plantthroughout plant– Defense system to protect Defense system to protect

against predators and against predators and infectioninfection

– Few millimeters to 100 Few millimeters to 100 metersmeters

8

• Leaves are the major part of the plant that carries on photosynthesis– Foliage leaves are

usually broad and thin• Blade - Wide portion of

foliage leaf• Petiole - Stalk attaches

blade to stem• Leaf Axil - Axillary bud

originates– Tendrils - Leaves that

attach to objects– Bulbs - Leaves that store

food

LEAVES

succulent leaves

Modified leavestendrils (peas) spines (cacti)

colored leaves (poinsetta)

• Both systems depend on the other– roots receive

sugars & other nutrients from photosynthetic parts

– shoot system depends on water & minerals absorbed from the soil by roots

Interdependent systems

water

sugars

Putting it all together • Obtaining raw materials

– sunlight• leaves = solar collectors

– CO2

• stomates = gas exchange

– H2O• uptake from roots

– nutrients• uptake from roots

TISSUES OF FLOWERING PLANTS• Dermal

– “skin” of plant– single layer of tightly

packed cells that covers & protects plant

• Vascular– transport materials

between roots & shoots– xylem & phloem

• Ground– everything else:

storage, photosynthetic– bulk of plant tissue

DERMAL TISSUE• Dermal TissueDermal Tissue

– Outer covering Outer covering

– Single layer of cells Single layer of cells consisting ofconsisting of

• CuticleCuticle – waxy coating – waxy coating

• HairsHairs• Guard Cells that Guard Cells that

surround stomatasurround stomata

Cells of GROUND TISSUE

• Parenchyma– “typical” plant cells = least specialized– photosynthetic cells, storage cells– tissue of leaves, stem, fruit, storage roots

• Collenchyma– unevenly thickened primary walls = support

• Sclerenchyma – very thick, “woody” secondary walls (lignin) = support– Fibers (rope); Schlereids (grittiness, hardness of nuts,

peach pit)– rigid cells that can’t elongate– dead at functional maturity

Those would’vebeen great names

for my kids!

VASCULAR TISSUE• Transports materials in roots, stems &

leaves• Xylem

– carry water & minerals up from roots

– tube-shaped dead cells• only their walls provide a system

of microscopic water pipes

• Phloem – carry nutrients throughout plant

• sugars (sucrose), amino acids…

– tube-shaped living cells

Xylem• Dead at functional maturity • Cell elongated into tubes

– tracheids• long, thin cells with tapered ends• walls reinforced with lignin =

support• thinner pits in end walls allows

water flow

– vessel elements• wider, shorter, thinner walled &

less tapered• perforated ends walls allows free

water flow from one hole to the next

Aaaaah…Structure-Function

again!

Phloem• Living cells at functional

maturity– lack nucleus, ribosomes & vacuole

• more room: specialized for liquid food (sucrose) transport

• Cells – sieve tubes

• end walls, sieve plates, have pores to facilitate flow of fluid between cells, pump sugars

– companion cells• nucleated cells connected to the

sieve-tube • Surround sieve tubes; support phloem

cells

Aaaaah…Structure-Function

again!

Phloem: food-conducting cells

sieve tube elements & companion cells

Vascular tissue in herbaceous stems

dicottrees & shrubs

monocotgrasses & lilies

What I actually eat….

• What I should eat….

Root structure: dicot

xylemphloem

Root structure: monocot