Plant Structure

Three main organs:

Roots

Stems (shoots)

Leaves (shoots)

RootsFibrous

Mat of thin roots

Tap

One long, vertical root

Root Hairs= increase surface area —> increases absorption

StemsNodes: leaf attachment

Internodes: stem segment

Axillary bud: often dormant; vegetative potential

Terminal buds: apex of young shoot

Apical dominance: inhibits axillary buds

LeavesBlades

Absorption of light

Veins

Xylem and phloem

Petiole

Attachment to stem

Life Cycles

Annuals= 1 year

Biennials= 2 years

Perennials= many years

Plant CellsParenchyma

Typical plant cell

Least specialized

Thin primary walls

Site of metabolism (photosynthesis)

Don’t divide unless special conditions

Plant Cells

Collenchyma

Thick primary walls

Help support young plants

Remain flexible to allow growth

Plant CellsSclerenchyma

Secondary walls (lignin)

Don’t elongate

Occur when growth has stopped

Two types:

Fibers: long, slender, occur in bundles (hemp, flax)

Sclerids: short, irregular shape (nutshells, seeds)

Plant CellsTracheids (xylem)

Long, thin

Hard secondary walls

Dead

Transport water & support

Common in “softwoods”

Plant CellsVessel Elements (xylem)

Wider, shorter

Aligned end-to-end

Dead

Transport water

Common in “hardwoods”

Plant CellsSieve-tube Members (phloem)

Transport organic compounds and materials

Alive

Lack organelles

Plant Cells

Companion Cells (phloem)

Connect to stem through channels (plasmodesmata)

Load sugar into stem

Contain organelles

Plant Growth

Meristem

Tissue capable of cell division (growth)

Maybe apical= growth in height/length (primary)

or lateral= growth in width (secondary)

Primary Plant GrowthApical Meristem

- Found in tips of roots, in buds of shoots

- Produces all growth in herbaceous plants

Secondary Plant GrowthLateral Meristem

Causes growth in girth

Occurs in plants where primary growth has stopped

Occurs in woody plants

Layers:

Vascular cambium = secondary xylem and phloem

Cork cambium = thick periderm

TransportProton Pumps

Used to drive transport of potassium and nitrates

ATP is used to force H+ out of membrane (membrane potential)

TransportWater

Water moves from regions of high water potential to regions of low water potential

Transpiration causes water to leave plant

Water moves into plant by osmosis through roots

Cohesion and adhesion help molecules move

Transport

Sugar

Moves from source to sink

From leaves to roots

From leaves to fruit

From stem to roots (rare)