Plant structure, growth and development

Chapter 35

Plant Tissues

• There are three categories of plant tissues– Dermal tissues

• form the outer covering of the plant• serve a protective function• herbaceous plants – epidermis• Woody plant – periderm (outer bark)

– Vascular Tissues• Function to transport materials through the plant body and provides support

– Xylem – transport of water and dissolved minerals– Phloem – transport of dissolved sugars

• Arranged into vascular cylinder in the root or vascular bundles in stems and leaves

– Ground Tissues• Neither dermal or vascular • Pith – internal ground tissue (in vascular cylinder or stem)• Cortex – ground tissue located towards the outside of the plants organs• Functions for storage, photosynthesis

Cell types composing plant tissues

• Simple tissues– Collenchyma

• Cell walls of irregular thickness

• Flexible support– Parenchyma

• Cell walls very thin to facilitate movement of particles through cell

• Storage, photosynthesis

– Sclerenchyma• Very thick cell walls

(primary and secondary cell walls made of lignin)

• Dead at maturity• Sclerenchyma fibers

and sclerids• Rigid support

Cell types composing plant tissues

• Complex tissues– Xylem

• Tracheids and vessels– Modified

sclerenchyma fibers– Dead at maturity

(hollow)

– Phloem• Sieve tubes and

companion cells• Companion cells alive• Sieve tubes dead at

maturity (sclerenchymafibers)

Plant organs

• Plant organs may be divided into two systems– Shoot system

• Above ground (usually)

• Stem• Leaf• Flower

– Root system• Taproot

(primary)• Lateral roots

(secondary)• Adventitious

roots (arise from stem)

Growth of plant parts• Plant exhibit localized growth at

meristems– Apical meristems – produce primary

tissues and increase the length of plant parts

• Found at the tips of roots (root apical meristem) and in buds on stems (terminal buds and axillarybuds)

– Lateral meristems are found in woody plants and increase the girth of plant parts

• Vascular cambium – produces secondary xylem and phloem

• Cork cambium – produces cork cells that will form periderm (outer bark)

The root system

• Functions of the root– Absorption of water and nutrients– Anchorage– Storage– Soil erosion– Other root modifications:

• Prop roots– Adventitious

• Storage roots• Aerial roots• Buttress roots• Pneumatophores

– Exchange gases

Root modifications

Root anatomy

• Zone of cell division– Root apical meristem– Protected by root cap

• Zone of elongation• Zone of maturation

– Contains mature tissues

– Root hairs• Cytoplasmic

extension of epidermal cells

• Increase surface area

• Layers of typical root– Epidermis– Cortex– Vascular cylinder

• Be sure to know the difference between monocot and eudicotroots

• Epidermis• Cortex• Vascular cylinder

– Endodermis– Pericycle– Pith (in monocots)– Xylem/phloem

Development of lateral (secondary) roots from pericycle

• Notice that the vascular cylinder of the original root and the lateral root are connected

The stem• Part of shoot system• Functions for support of leaves and flowers• Modifications allow for other functions as well

– Bulbs– Stolons– Rhizomes– tubers

Stem anatomy (external)

• Node• Internode• Axil• Axillary bud• Terminal bud• Bud scale

– Modified leaf to protect apical meristem

• Terminal bud scar

• Leaf scar

Stem anatomy(internal)

• Be sure to note differences between monocots and eudicots

Secondary growth to produce woody tissues

• All woody plants exhibit primary growth to produce new shoots (herbaceous)

• Secondary growth at lateral meristems is responsible for the production of woody tissues and increases the girth of plant– Vascular cambium– Cork cambium

• Wood (secondary xylem)– Heartwood vs.

sapwood• Cork cells form periderm

outer bark• Secondary phloem

forms inner bark

Secondary growth to produce woody tissues

The leaf

• Primary function of photosynthesis

• Form = function– CO2 + H2O C6H12O6 + O2

– Other function of leaves (leaf modifications)

• Tendrils• Spines• Storage• Bracts• Reproductive leaves (asexual)

Leaf anatomy (external)

• Axil• Petiole• Blade• veins

Leaf types

• Simple – one blade per leaf• Compound – blade divided into leaflets

– Palmate– Pinnate (once –pinnate and twice pinnate)

Leaf anatomy(internal)

Epidermiscuticleguard cellsstoma

Mesophyllpalisadespongy

Veinbundle sheathxylemphloem