Download Plant Structure

Plant Structure
“Plants have to be exquisite to survive
because they can’t run.”
• Plasticity- ability to mold form to
microenvironment
• Morphology adapted to
environment
Roots
• Anchors plant, stores nutrients, absorbs
minerals and water
• Taproot system (lateral roots)
– Dicots and Gymnosperms
– Stores nutrients
• Fibrous root system
– Many small roots grow from stem
– shallow
– monocots
Root modifications
• Root hairs- extensions of root epidermal cells, increase
surface area
• Prop roots
• Storage roots
• Strangling aerial roots
Pneumatophores- air roots
Stems
• Alternating nodes and internodes
– Nodes=leaf attachment
– Internodes=stem between nodes
• Axillary bud- tissue between leaf and stem
that can turn into a new shoot, most are
dominant
• Terminal bud (apical bud)- developing leaves,
top of plant
Apical dominance
• Terminal bud inhibits axillary buds
• How is elongation an evolutionary advantage?
• Once terminal bud is gone,
axillary buds break dormancy,
and grow into shoots with
their own terminal bud
Modified stems
• Stolons-strawberry runners
• Rhizomes-horizontal stems
• Tubers-enlarged rhizomes,
eyes=axillary buds
Leaves
• Photosynthetic organ
• Stomata facilitate gas
Exchange
• Surface area
– Water loss
– Light collection
Modified Leaves
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Tendrils
Spines
Storage leaves
Reproductive leaves
Plant Cells
• Plant cells differentiate in embryo and at
meristems
• Primary and secondary cell wall,
central vacuole,
Chloroplasts
Three types of
Plant cell
Parenchyma cells
• Thin, flexible primary cell walls, no secondary
cell wall
• Large central vacuole
• Photosynthetic cells in leaves
• Soft parts of plant
Collenchyma cells
• Thick primary cell walls
• Used for support (celery strings)
• Flexible- support without inhibiting growth
Sclerenchyma cells
• Thick Secondary Cell Wall
• Reinforced with lignin
• Can’t grow, only occur in parts of the plant
that are done growing
• Seed coating, nut shells, pear crunchies
Water conducting Xylem cells
• Elongated, dead at functional maturity
– Less resistance
– More volume
• Water moves from roots to
leaves
• Pits allow water to move
laterally
Sugar conducting phloem
• Alive at functional maturity
• Lack organelles or
Nucleus companion cell
controls function in phloem
• Sugar flows from source
to sink
Meristems generate cells for new organs
• Indeterminate growth- plant grows
throughout life
• Determinate growth- period of no growth, set
final size
• Meristem- undifferentiated cells, can grow
into any type of cell
Meristems
• Apical- tips of roots and stems (buds), allow
plant to grow longer (primary growth)
• Lateral meristems- surround stem and roots,
allow plant to grow in girth (secondary
growth)
• Primary and secondary
growth happen each year,
in different areas of
the plant
• Primary growth
lengthens branches
and roots
• Secondary growth thickens
and strengthens previous
years growth
Primary growth
• Roots
– Root cap protects
meristem
– Produces all
three tissues
– Zone of division
– Zone of elongation
– Zone of maturation
Primary growth of stems
Leaf primordia
Apical meristem
Axillary meristem
Apical meristem suppresses lateral growth
Axillary buds develop from leftover meristem
Elongation of shoot comes from growth of internode cells
Secondary Growth
• Occurs in stems and roots, not in leaves
• Vascular cambium
– Produces xylem and phloem
– Last year’s phloem
becomes this year’s
inner bark
• Cork cambium
– Produces cork
(outer bark)
– Waterproofed w/
suberin
???
Maple syrup overview
• Sugar storage (seasonal)
• Phloem
– Source  sink
• Pressure/suction
– Respiration
– Osmosis
• 40:1  sap: syrup ratio
What factors will affect sap
production?