plant structure - ap biology with mrs. haas€¦ · plant structure three main organs: roots stems...
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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)
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