Transcript 23-1 Specialized Tissues in Plants

Plant Structures
Roots, Stems, and Leaves
Chapter 23
23-1 Specialized Tissues in Plants
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Plants are as successful
if not more successful
than animals
Seed plants have three
main structures:
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Roots
Stems
Leaves
Linked together by
various means
23-1 Specialized Tissues in Plants
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Roots
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Absorbs water and
nutrients
Anchor plant to the
ground
Hold soil in place and
prevent erosion
Protect from soil bacteria
Transport water and
nutrients
Provide upright support
23-1 Specialized Tissues in Plants
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Stems
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Support for the plant
body
Carries nutrients
throughout plant
Defense system to
protect against predators
and infection
Few millimeters to 100
meters
23-1 Specialized Tissues in Plants
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Leaves
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Main photosynthetic
systems
Suseptable to extreme
drying
Sight of oxygen/carbon
dioxide intake and
release
23-1 Specialized Tissues in Plants
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Plant tissue
systems
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Exist within the
root, stems, and
leaves
Dermal tissue
 Vascular tissue
 Ground tissue
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23-1 Specialized Tissues in Plants
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Dermal Tissue
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Outer covering
Single layer of cells
Cuticle – waxy coating
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Roots have dermal tissue
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Trichomes – Spiny
projections on the leaf
Root hairs
Guard Cells
23-1 Specialized Tissues in Plants
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Vascular Tissue
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Transport System
Subsystems
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Xylem
Phloem
Subsystems are used to carry fluids
throughout plant
23-1 Specialized Tissues in Plants
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Xylem
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Two types
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Seed plants
Angiosperms
Tracheid – long narrow
cells
Walls are connected to
neighboring cells
Will eventually die
Vessel Element – wider
that tracheids
23-1 Specialized Tissues in Plants
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Phloem
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Sieve Tube Elements
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Cells arranged end to end
Pump sugars and other foods
Companion Cells
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Surround sieve tube elements
Support phloem cells
23-1 Specialized Tissues in Plants
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Ground Tissue
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Cells between dermal
and vascular tissue
Parenchyma
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Collenchyma
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Thin cell walls, large
vacuoules
Strong, flexible cell walls
Sclerenchyma
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Extremely thick, rigid cell
walls
23-1 Specialized Tissues in Plants
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Plant Growth
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Meristems – tissues
responsible for growth
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Apical Meristem
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Produce growth increased
length
Differentiation
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Undifferentiated cells
Cells will assume roles in
the plant
Flower Development
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Starts in the meristem
23-2 Roots
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Types of Roots
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Taproots
Found in dicots
 Long, thick root
 Hickory and oak trees
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Fibrous roots
Found in monocots
 No single root larger than any other
 Many thin roots
 Help prevent erosion
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Root Structure and Growth
Outside layer = epidermis
 Central cylinder = vascular tissue
 Between these two = ground tissue
 Roots important in water and mineral
transport
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23-2 Roots
Root Structure
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Epidermis – outside
layer
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Root hairs
Cortex – spongy layer of
ground tissue inside
epidermis
Endodermis – layer
inside cortex
Vascular cylinder –
central vascular system
Root Cap – the tip,
cellular production
Root Growth
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Roots grow by producing new cells near
the tip!
Root lubricates its path
 New cells are added at the root cap
 Behind the meristematic tissue, cells grow
longer
 These cells specialize and take on different
functions (process of differentiation)
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Root Functions
Anchor a plant in the ground
 Absorb water and dissolved nutrients
from the soil
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Water and nutrients do not just soak
into the root from the soil
The plant requires energy to absorb
water
23-2 Roots
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Plant Nutrient Uptake
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Soil includes sand, silt, clay, air, bits of decaying
organic matter
Soil type determines plant type!
Plant requirements
- Oxygen, CO2
- Nitrogen
- Phosphorus
- Postassium
- Magnesium
- Calcium
- Trace elements
Types of soil
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Sandy soil is made up of mostly grains
of sand. Water passes through this
type of soil quickly.
Clay soil is mostly made of fine clay
particles. Water poured on clay soil
sinks slowly.
Loamy soil contains decaying plant
and animal matter along with clay and
sand.
Essential Nutrients
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Nitrogen is important for leaf growth and
color. A plant that lacks nitrogen will
have yellow leaves.
Phosphorous is needed for roots, stems
and flower growth as well as seeds. A
plant lacking phosphorous will have
stunted growth and few flowers.
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Potassium is important in root, stem
and flower development as well. It
helps the plants live in the cold and
fight disease. Plants with too little
potassium have stunted roots.
Potassium is sometimes called potash.
Calcium is needed for cell growth and
for strong cell walls.
Magnesium is needed to make
chlorophyll. Plants will die without
chlorophyll.
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Plants also need very small amounts of
what are called trace elements. The
plant will not grow well if these trace
elements are not present, but if there is
too much of the trace elements in the
soil they are poisonous to the plant.
23-2 Roots
Active Transport in Plants
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Root hairs use ATP
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Pump minerals from
soil
Causes water molecules
to follow by osmosis
Vascular Cylinder
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Casparian Strip –
waterproof strip
surrounding endodermal
cells: H20 retention
Osmosis and Root Pressure
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Water moves into the vascular cylinder by
osmosis (diffusion through semipermeable
membrane)
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Water and minerals can’t pass through the
Casparian strip, so they’re trapped once inside the
vascular cylinder!
Root Pressure
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One-way movement creates pressure
Forces water up into the plant
If pressure didn’t build up, roots would swell up!
23-3 Stems
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Stem Structure
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Like other plant parts, stems have
vascular, dermal, and ground
tissue!
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Produce leaves, branches,
and flowers
Hold leaves up to sunlight
Transport substance
between roots and leaves
Essential part of transport
system
Function in storage and
photosynthesis
23-3 Stems
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Xylem and phloem – major
tubule systems
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Transport water and nutrients
Composed of 3 tissue layers
Contain nodes – attachment
for leaves
Internodes – regions
between the nodes
Buds – undeveloped tissue
23-3 Stem Types
Monocot – vascular bundles
are scattered throughout
- Distinct epidermis
Dicot – vascular tissue
arranged in a cylinder
- Pith – parenchyma cells
inside the ring (ground
tissue with thin cell wall,
large vacuole)
23-3 Stem Growth
Primary growth – new
cells produced at the root
tips and shoots
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Increases the length
Secondary growth –
increase in stem width
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Vascular cambium –
meristematic tissue that
produces vascular tissue
and increases thickness
Cork cambium – produces
outer covering of stems
23-3 Stems
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Formation of Vascular
Cambium
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Xylem and phloem
bundles present in a ring
Secondary growth
initiates production of a
thin layer
The vascular cambium
divides
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Produces new xylem and
phloem
23-3 Stems
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Formation of wood
Wood – layers of xylem
 Produced year after year
 Results from the older xylem not
conducting water – heartwood
 Becomes darker with age
 Sapwood – surrounds
heartwood
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Annual Rings
In spring, growth happens
quickly, producing lightcolored xylem cells with thin
cell walls
At the end of the season, the
cells become darker with
thicker cell walls (late wood)
Each season, a ring with light
and dark is produced
By counting rings in a tree,
you can estimate age!
23-3 Roots
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Formation of Bark
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All the tissues
outside the vascular
cambium
Consists of outermost
layers of dead cork
Water proof
23-4 Leaves
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Main site of
photosynthesis
Consist of:
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Blade – thin flattened
section
Petiole – stalk that
attaches stem to blade
Covered by epidermis
and cuticle (waxy
covering)
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Create water proof
barrier
23-4 Leaves
Leaf Functions
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Photosynthesis – occurs in the
mesophyll (specialized ground tissue in
leaf)
Palisade mesophyll – absorb light
 Spongy mesophyll – beneath palisade
level
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Stomata
Stomata – pores in the
underside of the leaf
Singular: stoma
Guard Cells – epidermal
cells surrounding the
stomata, specialized to
open and close
23-4 Leaves
Transpiration
Loss of water
through its leaves
 Replaced by water
drawn into the leaf
through xylem
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Gas Exchange
Take in CO2 and release
O2
 Can do the opposite –
when using food, take
in oxygen and release
CO2
Gas exchange takes
place at the stomata
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Not open all the time
Stomata is controlled
by water pressure in
guard cells
Gas Exchange & Homeostasis
Plants keep stomata open just enough to
allow photosynthesis to occur, but not to
lose too much water!
When water pressure is high, guard cells
pulled away and stoma opens!
When water pressure is low, inner walls
pull together and stoma closes!
Usually: stomata open in daytime, closed at
night… why?
23-5 Transport in Plants
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Water Transport
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Active transport and root
pressure
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Cause water to move from
soil to roots
Capillary action
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Combined with active
transport and root
pressure, moves materials
throughout the plant
23-5 Transport in Plants
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Capillary Transport
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Capillary transport
results from both
cohesive and adhesive
forces
Water molecules
attracted to one another
Water is also attracted to
the xylem tubes in the
plant
Causes water to move
from roots to the stem
and upward
23-5 Transport in Plants
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Transpiration
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Evaporation is the major
moving force
As water is lost, osmotic
pressure moves water out
of vascular tissue
This pulls water up from
the stem to the leaves
Affected by heat,
humidity, and wind
23-5 Transport in Plants
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Controlling
Transpiration
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Open the stomata –
increase water loss
Close the stomata –
decrease water loss
23-5 Transport in Plants
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Transpiration and
Wilting
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Osmotic pressure –
keeps plants semi-rigid
Wilting is a result of
high transpiration rates
Loss of water causes a
drop in osmotic pressure
Loss of rigidity
Conserves water
23-5 Transport in Plants
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Nutrient Transport
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Most nutrients are
pushed through plant
Nutrient movement takes
place in phloem
Source to Sink
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Source – any cell that
produces sugars
Sink – any cell where
sugars are used
Pressure-flow
Hypothesis