Plant Structure

Hierarchy of a Plant BodyExtreme developmental

plasticity in plantsStructurally change

morphology, external form, to better suit environmentGenetic factors play small

role tooMore variety within plant

species than animal speciesPlants have organs that

are composed of tissues that are made of cells

Basic organs are roots, stems, and leaves

Cabomba caroliniana, a fanwort

Hierarchy of a Plant BodyPlants aquires resources

from 2 different environmentsCO2 and light from above

groundWater and nutrients from soil

Plants have organs that are composed of tissues that are made of cells to facilitateBasic organs are roots,

stems, and leavesForm root system and

stem systemSystems rely on each other

for materials

RootsAn organ that anchors, absorbs, and store3 types

Taproot system has 1 main vertical root that produces small lateral, or branched, rootsMost eudicots and gymnosperms; i.e. carrots and beetsStore sugars and starches for flowering; why root crops harvested before

floweringAdventitious roots arise from stems or leaves, with each forming

separate lateral rootsCan be modified to provide more support of anchorage; fig. 35.4

Fibrous roots form a mat of thin roots that don’t penetrate deeplySeedless vascular plants and most monocots; i.e. grasses

Root hairs found near the tips aid in absorption and increase SAShort lived and constantly replaced, not to be confused with lateral

roots

StemsAlternating nodes where leaves attach and

internodes, the segments in betweenUpper angle of each leaf contains an axillary bud

which can form a lateral shoot, but are normally dormant

Near the shoot tips are apical buds which inhibit axillary bud growth via apical dominanceConcentration of resources so plant can grow tallerIf apical bud is gone then axillary buds can develop

into lateral shoots and become their own apical budReason for pruning bushes and trimming house plants

LeavesMain photosynthetic part of the plantConsist of a flattened blade and a petiole or

stalk to join to stem at nodeVeins, the vascular tissue, differ in arrangement

between eudicots and monocotsMonocots with parallel veinsEudicots with branched veins

Angiosperms classified by vein branching (floral morphology too)Simple have single undivided bladesCompound blades of multiple leaflets (apical at base of

blade only)

Adaptations for support, reproduction, or storage

Leave Patterns and Deviations

Tissue SystemsDermal tissue system is the outer protective covering

Nonwoody plants have an have an single layer of epidermis that covers and protects young parts of a plantSecretes a waxy cuticle covering to help retain water

Woody plants have a periderm to protect older regions of plant

Vascular tissue system runs throughout the plantXylem transports water and minerals upPhloem transports food down to where its neededCollectively know as stele

Angiosperms have solid central vascular cylinder, leaves and stems have vascular bundles, separate strands of vascular tissue

Ground tissue systemInternal to vascular is called pith, external is cortex

Plant Cell TypesParenchyma cells: thin and flexible primary walls, lack

secondary‘Typical’ plant cells because they are least specializedPerform most of the cell’s metabolic functionsCan regenerate a whole plant from one cell

Collenchyma cells: thicker primary walls, but unevenly thickenedGrouped as strands or cylinders to support young parts of shootsi.e. strings of celeryNo secondary walls or lignin

Sclerenchyma cells: thick secondary walls strengthened by ligninCan’t elongate and reside in parts of plants no longer growingMost dead at maturity, but produce the secondary cell wall before for

supportFibers are long and slender; hemp fibers to make rope and flax fibers wove

into linenSclereids irregular in shape and are shorter; impart hardness to nutshells and

seed coatsXylemPhloem