Stem Structure
Bud
Stem
Petriole
Internode
Node
Leaf Structure
Cuticle
Protects from water loss,
insect invasion, UV light
Upper
epidermis
Additional
protection
Palisade Mesophyll
Large number
chloroplast
Spongy Mesophyll
Xylem
Transport
water
from
Vein/
rootsVascular
Lightly packed
– allows for
gas exchange
bundle
Phloem
Transport
sugar to rest
of plant
Lower epidermis
Guard Cells
Open/Close stomata
Stomata
Gas exchange
CO2(g)
H2O(g)
Xylem Cells
Dead Cells
Thickened cellulose,
lignified 2⁰ walls
Strengthens cell walls
Waterproofs plant
Protects against
pathogens
Tapered to form
continuous
column
Most modern plants
Allows water to
mover laterally
Ancient plants
Stomata Operations
Open/close due to
cell turgor of
guard cell
Bulge to outside
 opens
Blue light triggers
ATP powered
pumps
Causes K+ to
move into guard
cells
Higher solute =
osmosis
Cell wall
thickness uneven
K+
Caused by absisic
acid (plant
hormone)
Produced in root
during water
definicency
CO2 levels
circadian
rhythms
Cells sag due to
water loss (close)
Transpiration
Cohesion-Tension Theory
2. Water lost by transpiration is
replaced by water from xylem
1. Water moves down concentration
gradient (out of plant)
Creates negative pressure
3. Vessel water column is maintained
by cohesion/adhesion
4. Water is pulled from root cortex
into xylem cells
5. Water is pulled from the soil into
the roots
Root Structure
Fully differentiated
 functional cells
Root Hairs: increase surface
area = more absorption of
water/minerals x3
Enlarging cells
(G1 phase)
Start differentiating
Zone of cell
division (M phase)
‘Stem’ cells –
undifferentiated cells
Protects apical meristem
Cross Section of Root
Water movement: due to osmosis
(higher solute concentration inside root)
Root Hair
Epidermis
Endodermis
Xylem
Vascular
Bundle
Pericycle
Phloem
Cortex
Mineral Ion Movement
Fungal Hyphae: symbiotic relationship
Increases surface area for absorption
Active Transport: high
concentration of solute in root
Need more or ion cannot
pass lipid bilayer 
hypertonic situation
Diffusion of mineral ions by
mass flow of water
Passively flow due to
low solute
concentration in root
Movement within roots
All particles need to go symplastic at
endodermis to get to xylem
Water
and
Minerals
Movement between cell walls
Movement within cells – water/minerals
pass through plasmodesmata
Factors that affect transpiration
Increase evaporation
Reduces difference in
water concentration
gradient
Removes humidity from
stomata
Less soil water, water
stream stopped at roots,
stomata close
Increase kinetic
energy - evaporation
Cause guard cells
to lose turgor –
close stomata
Xerophytes
thickened
Crypt/pit –
increases humidity
Reduced
number
Trap water vapor,
increases humidity
Decreases surface
area for transpiration
Go dormant in dry months
Succulents – fleshy
stems
Alternative photosynthetic
pathway
CAM: stomata open at
night
C4: rapid uptake of
CO2
Halophytes: high levels of salinity
Sunken stomata
Leaf surface area reduced
Succulents: dilute salt concentration
Compartmentalize Na+ and Cl- in
vacuoles
Prevents salt toxicity
Salt glands: secrete salt
In your groups
• Read transpiration lab
• Design how you want to conduct the
experiment.
• Rough draft write up
• Friday you will conduct this experiment.
• P 392 in your book will help. You need to copy
that chart in your results.