Class Rules
1.
Punctuality
a.
The last person to come into the class later than me will teach the class for
2 minutes on a selected topic by yours truly.
b.
Homework to be returned during the first Theory lesson of the week.
2.
Cleanliness
3.
Courtesy
a. If you need to speak, raise your hands.
b. If someone is speaking, open your ears, and not your mouth.
4.
Consistency
a. You must always have your notes with you.
5.
Commitment
a. If you are tasked to do something, I expect it to be done with all your
effort.
The Way Up
• Watch Video (Growing, 11:00min)
Topic Overview
Transport in Plant Nutrition
6.1 Stem & Root
Structure & Function
6.1.1 Vascular Bundle
Structure &
Function
6.1.2 Stem Internal
Structure
6.1.3 Root Internal
Structure
6.1.4 Leaf Internal
Structure in
Relation to
Vascular Bundle
Arrangements
6.2 Transport of Water
& Minerals
6.3 Transports
in Phloem
6.2.1 Water Potential
6.2.2 Overview of Water Movement
6.2.3 Water Movement in Roots
6.2.4 Mechanism of Water & Mineral
Transport in Stems
i) Root Pressure
ii) Capillary Action
iii) Transpiration & Transpiration
Pull
6.2.5 Water Movement in Leaves
6.2.6 Factors Influencing Water
Movement and Water Loss
6.2.7 Wilting
6.4 Water Relations &
Leaf Adaptation
6.3.1 Pressure Flow
Hypothesis
6.3.2 Evidence for
Sucrose
Translocation
6.4.1 Hydrophytic
Leaves
6.4.2 Xerophytic
Leaves
The Xylem
• Comprises of 2 types of
substructure:
(1) Vessel Elements
(2) Tracheids
The Xylem
• 5 Main Characteristics
(1)
(2)
(3)
(4)
(5)
Dead, lack protoplasm
Hollow, Lack Cross Walls
Narrow
Laid with Lignin
Pits
The Xylem
Characteristics
Function
1. Dead and lack Protoplasm
Reduce resistance to water flow
2. Hollow, Lack Cross-walls
Reduce resistance to water flow
3. Narrow
↑ Capillary Action
4. Lignin
5. Pits
a) Impermeable to water
Prevent escape of water en route
b) Mechanically strong
Mechanical support
c) High tensile strength
Withstand hydrostatic pressure
Allow lateral transfer of water
The Phloem
• Comprises of 2
types of
substructure:
(1) Sieve Tube
Elements
(2) Companion
Cells
The Phloem
Main Characteristics
Sieve Tube Elements
(1) Thin cytoplasm/ degenerate protoplasm
(2) Pores in Sieve plate
(3) Callose forms at sieve plates
Companion Cells
(1) Prominent Nucleus
(2) Abundant Mitochondria
The Phloem
Characteristics
Function
1. Degenerate protoplasm
Reduce resistance to phloem sap flow
2. Sieve Plates with pores
Reduce resistance to phloem sap flow
3. Callose formation
Prevent wastage of organic compounds
4. Prominent nucleus
in companion cells
Coordinate activities in sieve tube
elements
5. Abundant mitochondria
in companion cells
Provide energy for phloem loading
in sieve tube elements
Water Transport - An Overview
1. Pathways of Water
Movement
2. Water Movement in Roots
-
Root Anatomy (Radial)
Casparian Strip
3. Water Movement up Stems
- Mechanisms of Water
Transport
4. Water Movement in the
Leaves
Water Potential, Ψ
•
•
A measure of the potential energy of water relative to pure
water.
Water’s interaction with other particles, gravity and air
pressure attributes it with potential energy.
Air
Pressure
Inter-molecular Forces
GRAVITATIONAL
POTENTIAL ENERGY
Pure water has a water
potential of 0 Pa.
Water Potential, Ψ
•
Food-for-thought:
•
Why use Water Potential when you can use
Water Concentration?
Water Potential, Ψ
•
Differences in water potential creates a water
potential gradient.
•
Water moves by osmosis down the water potential
gradient, from a region of less negative water
potential to a region of more negative water
potential.
•
Solutes on the other hand, moves by diffusion from
a region of more negative water potential to a
region of less negative water potential.
Pathways of Water Movement
There are 3 ways where water may move
in plant tissues (with the exception of the
endodermis):
1) Apoplastic pathway (via cell wall)
2) Symplastic pathway (via cytoplasm)
3) Vacuolar pathway (via vacuoles)
Plasmodesmata
Water Movement in Roots
• Watch Animation:
http://yorkcountyschools.org/yhs/teac
hers/Holtschneider/media/36_09Trans
portInRoots_A.swf
http://www.biologymad.com/resource
s/transpiration.swf
• What is the Casparian Strip?
Radial Root Anatomy
The Casparian Strip
•
The Casparian Strip is a thin band on the radial and lateral walls of
endodermal cells, that contains a deposit of fatty material known as
suberin.
•
It restricts the passage of water and solutes, forcing water and
solutes to pass through the cell membrane of the endodermal cells.
Water Transport - An Overview
1. Pathways of Water
Movement
MECHANISMS OF
WATER TRANSPORT
a. Transpiration Pull
b. Root Pressure
c. Capillary Action
2. Water Movement in Roots
-
Root Anatomy (Radial)
Casparian Strip
3. Water Movement up Stems
- Mechanisms of Water
Transport
4. Water Movement in the
Leaves
Mechanisms of Water Transport
How can water be moved up a plant as huge as the
Sycamore Tree?
TRANSPIRATION PULL
1. Driving Force
Transpiration
Hydrostatic
Pressure
Gradient
Root Pressure
2. Medium for transmitting the force
Cohesion and Surface
tension of water
Transpiration
Where does water go after it
ends up in the leaves?
1. Evaporate from thin film of
water on mesophyll cells.
2. Small amount evaporate from
the cuticle
3. Photosynthesis
Transpiration is the process involving the
loss of water from the aerial parts of a
plant, especially via the stomata.
Root Pressure
Root Pressure is the osmotic
pressure in the roots of vascular
plants, which arises as a consequent of
water undergoing osmosis into the
xylem of the root.
This results from mineral salts being
actively pumped into the xylem of
the roots.
Watch Animation:
•
http://www.yteach.co.uk/page.php/resources/view_all?id
=apoplast_cambium_plasmodesmata_root_pressure_sym
plast_transpiration_acceptors_donors_phloem_proton_pu
mp_translocation_apoplast_symplast_hydathodes_osmosi
s_xylem_transpiration_cohesion_vacuoles_epidermis_end
odermis_t_page_17&from=search
Root Pressure and Guttation
Hydrostatic Pressure Gradient
Transpiration  LOW HYDROSTATIC PRESSURE in
the LEAVES
Root pressure HIGH HYDROSTATIC PRESSURE in
the ROOTS.
Difference in hydrostatic gradient provides the
driving force to move water upwards.
Cohesion-Tension
Water moving from the
roots, through the stem,
and finally to the leaves,
form a continuously
flowing stream, known
as TRANSPIRATION
STREAM.
Cohesion-Tension
The TRANSPIRATION STREAM is
critical in transmitting the
upward pulling force arising from
the hydrostatic pressure gradient.
• Cohesion forces between
water molecules.
• As water evaporates from the
leaves, cohesion causes water
molecules to “pull” on each
other.
Cohesion-Tension
Surface tension
Water seeping into the minute
pores in the cell wall has high
surface tension.
This pulls on more water to move
into the cell wall, then to the thin
film of water lining the mesophyll
cells.
Cohesion-Tension
Transpiration Pull
Driving force
Means of mediating
force
Hydrostatic Pressure
Gradient
Transpiration Stream
Transpiration in
Leaves
Root Pressure
Cohesion
Tension
Factors Affecting Transpiration
Factors Affecting
Transpiration
External
1. Light
2. Humidity
3. Wind Speed
4. Temperature
5. Water Availability
Internal
1. Leaf Area
2. Thickness of Cuticle
3. Number of Stomata
4. Distribution of
Stomata
Factors Affecting Transpiration
1. Light
Light affects size of stomata.
More light causes guard cells to
photosynthesize.
Guard cells becomes turgid.
Stomata opens and higher transpiration
rates.
Factors Affecting Transpiration
2. Humidity
Increased water content in atmospheric
air.
Decreases water concentration gradient
between intercellular air spaces and
atmosphere.
Lower rates of diffusion into atmospheric
air, thus lower transpiration rates.
Factors Affecting Transpiration
3. Wind Speed
Increased in wind speed.
Diffuses water vapour just external of the
stomata, allowing .
Lower rates of diffusion into atmospheric
air, thus lower transpiration rates.
External Factors Influecing Transpiration
Factor
Influence
Light
Stomata open in the presence of light
and closes in the dark.
Humidity
Affects diffusion gradient between the
air spaces in the leaf and the
atmosphere.
Wind Speed
Changes the diffusion gradient by
altering the rate at which most air is
removed from around the leaf.
Temperature
Affects the kinetic energy of the water
molecules and the humidity of the air.
Water Availability
Influences water potential gradient
between soil and the leaf.
Evaporation in Leaves
Wilting
http://academic.kellogg.cc.mi.us/herbrandsonc/bio111/animations/0032.swf
http://bcs.whfreeman.com/thelifewire/content/chp36/36020.html
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter38/animation__phloem_loading.html