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PLANT STRUCTURE,
GROWTH &
DEVELOPMENT;
RESOURCE
ACQUISITION AND
TRANSPORT
Chapter 35
What you should know:
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Plants grow only at meristems
How leaf anatomy relates to photosynthesis
The role of root hairs and mycorrhizae in resource acquisition
Roots, stems, and leaves interact in essential plant life functions
YOU MUST KNOW
 How passive transport, active transport, and cotransport function to
move materials across plant cell membranes
 The role of water potential in predicting movement of water in plants
 How the transpiration cohesion-tension mechanism explains water
movement in plants
 How bulk flow affects movement of solutes in plants
 Mechanisms by which plant cells communicate with other distant
cells
I. Plant organization
A. Root system – multicellular organ beneath the ground to
anchor plant, absorb water and minerals, and store sugars
and starches
1. Root hairs – at the tips, extensions of root cells that
increase surface area for absorption
2. Mycorrhizae – fungi in a symbiotic relationship with
roots that help with absorption
B. Shoot System – multicellular organ above the ground
consisting of stems and leaves
1. Stems – display the leaves
2. Leaves – main photosynthetic organs of the plants
C. Tissue types – compose roots and shoots
1. Dermal tissue – single layer of closely packed cells that
cover the entire plant to protect and prevent water loss
and prevent pathogen invasion
a. Cuticle – particularly waxy dermal tissue around
leaves
2. Vascular tissue – transports materials between the roots and
shoots
a. Xylem – transport water and minerals up from the
roots, dead at maturity
b. Phloem – transports sugars and other organic
compounds from the leaves to other parts of the plant
II. Plant growth
A. Meristems – where cell division occurs for plant growth
1. Apical meristems –primary growth (elongating roots
and shoots), located at the tips of roots and buds of shoots
Height of bicycle
will not change –
growth only occurs
at the meristems
2. Lateral meristems – secondary growth (adding thickness)
a. Vascular cambium tissue – located between xylem and
phloem, produces secondary xylem (wood)
b. Cork cambium tissue – produces tough covering that
replaces epidermis early in secondary growth
c. Bark – all tissues outside
vascular cambium, includes
living phloem from vascular
cambium
1. The wood (xylem) of
large trees is dead when
its functional
2. The living part of the
tree is almost entirely bark
(injuries to bark may kill
tree if it interferes with
movement of materials
through phloem)
Plant version of cell differentiation and
specialization
III. Organization of leaves
III. Organization of leaves
Large
number of
chloroplasts
Lightly
packed for
gas
exchange
Xylem – transports water
from roots
Phloem – transports
sugars to rest of plant
Stomata – pores for gas
exchange (CO2 enters, O2
and water vapor exit)
Guard cells – open and
close stomata
IV. Transport
A. Electrochemical gradients –
combined effects of
concentration gradient and
voltage differential across
membrane
B. Cotransport – using a steep
concentration gradient of
one solute to transport
another solute along with it
1. Drop in potential energy
of the first pays for the
transport of the second
C. Water potential – combined effects of solute concentration
and physical pressure
*Remember
-water potential of pure water in an open container = 0
-solute potential is always negative (-)
-turgor pressure – contents of cell press against the cell wall
Sample Problem:
Calculate the solute potential of the potato cores in the
figure below if the temperature is 21 degrees C. Express
your answer in bars, round to the nearest one-hundredth.
Calculate the solute potential of the potato cores in the figure below if the
temperature is 21 degrees C. Express your answer in bars, round to the
nearest one-hundredth
= -(1)(0.35M)(0.0831 liter bar/mole K) (273 +21)
= -8.55 bars
D. Aquaporins – transport protein channels for the passage of
water
E. Bulk flow – long-distance transport, movement of liquid in
response to a pressure gradient
1. From regions of high pressure to low pressure
V. Transpiration
A. Water and minerals from the soil enter through the root
epidermis, cross the body of the root, and flow up the
xylem (xylem sap) through the shoot and exit the plant
through the leaves
B. Transpiration is the loss of water vapor from the plant
C. 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
*Remember
the
importance
of hydrogen
bonds!
4. Water is pulled from root cortex
into xylem cells
5. Water is pulled from the soil into
the roots
D. Rate of transpiration
1. Regulated by stomata
2. Large leaf surface area
increases rate of
photosynthesis AND water
loss by transpiration
3. Guard cells – open and close
stomata (reducing water loss
also reduces amount of CO2
uptake)
4. Inverse relationship between
K+ concentration and water
potential
Guard cells –
stimulated to
open by light,
loss of CO2,
circadian
rhythms.
Triggers K+
pumps.
When guard cells
take in K+ causes
decrease in water
potential causing
water to enter the
guard cell, cells
bulge and open
stomata
When guard cells lose
K+, also lose water,
pore closes
VI. Sugar Transport
A. Translocation – movement of sugar from photosynthesis
from leaves to rest of plant through phloem using
pressure flow
B. Sugar source = net producer of sugars (leaves)
Sugar sink = net consumer or storer of sugar (fruit, roots)
1. Loading of sugar at source –
reduces water potential, causing
uptake of water by osmosis
2. Uptake of water creates positive
pressure, forcing sap to flow
4. Xylem
recycles
water from
sink to
source
3. Pressure is relieved by unloading of
sugars (and water) to sink
VII. Symplast
A. Network of living phloem cells that connects all parts of a
plant
B. Plasmodesmata – allow for movement of informational
molecules (RNA, proteins) that coordinate development
between cells
1. Respond to changes in turgor pressure, pH, ion levels
C. Long-distance electrical
signaling – can regulate
transcription, respiration,
photosynthesis, etc. in distant
locations in the plant