Transcript plant_structure__function_ch._29

Plant Structure & Function (ch. 29)
Three Types of Plant Cells
Parenchyma cells:
Sclerenchyma cells:
Collenchyma
cells:
thin, flexible cell walls
thick, even, rigid cell walls
thicker
cell
walls
usually loosely packed
support and strengthen areas
support
regions
of
the
plant
that are
cube-shaped or elongated cells with a
where growth is no longer
large central vacuole still lengthening
occurring
Celery
stalks
have
lots
of
involved in metabolic functions
Woody plants have lots of
collenchyma
cells
Nonwoody plants have mostly
sclerenchyma
parenchyma
Plant tissues are arranged into systems:

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
Dermal System – outermost layer on leaves and stems;
protection, control of water & CO2
Ground System – “in-between” tissues; support,
photosynthesis, food storage
Vascular System– transport/conduction
 Xylem – transports water & minerals; made of dead
cells that form a tube.
 Phloem – transports sugars made by photosynthesis;
made of living cells.
The systems are arranged into the main organs: roots,
stems, leaves
Longitudinal & Cross Section of Root
(ground)
Longitudinal & Cross Section of Leaf
Pallisade mesophyl
Spongy mesophyl
ROOT TYPES & STRUCTURES
Dicots have…
Microscopic
root hairs
absorb…
A hard root
cap digs
into…
Monocots have…
Food storage in
ground tissue
Root Structure – Dicot & Monocot
(lab #4)
Root Structure – Monocot
ID Tissues (Dermal, Vascular, Ground) & Cortex
Lab:
1. Find good
picture in
slide;
2. Get teacher
initials;
3. Sketch
showing
tissues;
4. Label using
book.
Mature
cells
Longitudinal Section
of Root Tip (Lab #5)
Zone of
mitosis
Zone of
Elongation
Root Cap
While doing your root lab…



You must TAP into your resources and ROOT
out any unproductive behaviors…
If you can’t find the info… The ROOT of the
problem usually lies in not PENETRATING
deeply enough into the FERTILE soil of your
textbook or not ABSORBING enough of the
contents…
Watch out for WEEDS… they just sit there and
absorb the nutrients that should be used to
GROW more productive plants… (They think
they can get it all by OSMOSIS.)
Leaf Structure
Monocot
Dicot
Leaf Structure – Venation Pattern in
Dicots and Monocots
Pinnate or
palmate venation
Parallel venation
Leaf Structure – Cross Sections
ID tissues: Dermal, Vascular, Ground
Monocot
Dicot
Leaf Epidermis with Stomata
Guard Cells
Stoma
(pore)
What happens if guard cells
Lose water?
Gain water?
Transport in Plants
Water & Minerals:
Transpiration through leaves provides force for movement;
Cohesion between water molecules ensures flow of water.

Water absorbed by osmosis:
root hairs  cortex  endodermis  xylem

Xylem cells (dead):
tracheids, vessel elements (angiosperms only)

Fast transport in xylem, one direction, up to 75 cm/min.:
roots  stems and leaves
Mature Xylem = Cell Walls Only
(dead sclerenchyma cells)
Tracheids: less efficient
transport
* all vascular plants *
Mature Vessel Member: no
plates between cells  more
efficient transport
* angiosperms only *
Transport in Plants
Sugar Transport :
Pressure-Flow Model
Transport in Plants
Sugars - Pressure-Flow model:
1.
2.
3.
4.
Sugars actively transported (energy used) from source
cells (mesophyll in leaves) into sieve tube elements
(phloem cells, alive);
High sugar concentration in phloem causes water to
diffuse (osmosis) into sieve tube elements;
Water pressure causes sap (sugar water) to flow through
phloem;
Sugars actively transported from phloem to sink cells;
lower sugar concentration in phloem  water diffuses
back into xylem.
*Sugars move more slowly than water: fastest rate ~2m/hour.*
Phloem
Sieve tube members contain cytoplasm only; companion cells
have nuclei (parenchyma cells)
Sugars are
actively
transported
into and out of
phloem:
Source cells 
phloem 
sink cells
STEM TYPES & STRUCTURE
Dicot & Monocot Stem Comparison
Stem Structure - Monocot
Monocot stem has scattered vascular bundles.
Stem Structure – Dicot (Young)
Dicot stem has vascular bundles arranged in a circle.
Cross Section of (Young) Dicot Stem
Modified Stems
Plant
Growth
Plant Growth

Meristems – growing tissues

Primary Growth – all plants:
Apical meristems at tips of roots and branches add
length by producing new cells.
Axillary meristems at joints (axils) between leaves
and stems  side branches.

Secondary Growth - woody plants only:
Lateral meristems (vascular & cork cambium) add
width by producing new xylem, phloem, and cork
cells.
Apical Meristems  Increase in Length
(Textbook picture – not in notes)
Secondary Growth of a
Woody Stem
(notes picture – shows better detail)
Dicot Stem Showing Secondary Growth
Where is the…
Xylem?
Phloem?
Pith? (dicot only)
Heartwood?
Sapwood?
How old is the
tree?
Woodiness
comes from
secondary
growth,
which gives
plants
strength to
grow bigger.
Wood


Sap wood – still
transporting water
Heart wood – old
xylem, clogged 
support only, no longer
transports water
Dendrochronology – Tree-Ring Dating
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Spring wood – xylem has wider
tubes, more water to transport,
more growth
Summer wood – xylem has
narrower tubes, less water, less
growth
Each tree ring represents a year
of growth (spring + summer) 
count rings, calculate age of tree;
measure width of rings, infer
weather conditions in past years