Download Movement of water and solutes in plants Chapter 4 and 30

Movement of
water and solutes
in plants
Chapter 4 and 30
Molecular Movement
Diffusion
Molecules or ions moving in the opposite direction = movement against a
diffusion gradient.
Rates of diffusion are affected by
• Temperature
• Density
In the leaves, water diffuses out via the stomata into the atmosphere.
Osmosis
Osmotic potential is the minimum
pressure required to prevent fluid from
moving as a result of osmosis.
The pressure potential is the pressure
that develops against the cell walls as a
result of water entering the cell’s vacuole.
(Ψ) Water potential of a plant cell =
The osmotic potential + pressure
potential
Osmosis
If the soil is desiccated then there
will be no net movement into the
plant cells and the plant will die.
Regulation of Transpiration
The pores of the stomata are closed
when turgor pressure (pressure
potential) in the guard cells is low,
and they are open when turgor
pressure (pressure potential) is
high.
light intensity
carbon dioxide concentration
water concentration change.
The guard cells of the stomata use
energy to take up potassium ions
from adjacent epidermal cells. The
uptake opens the stomata.
Plasmolysis
Plasmolysis is the loss of water via osmosis and accompanying
shrinkage of the protoplasm away from the cell wall. When this occurs,
the cell is said to be plasmolyzed.
Imbibition
Imbibition is the swelling of
tissues, alive or dead, to
several times their original
volume.
This is a result of the
electrical charges on
materials in suspension
attracting highly polar water
molecules which then move
into the cell.
Photographer: Michael Clayton Active Transport
Active transport is the energy assisted movement of substances against a
diffusion or electrical gradient.
1. Hydrogen pumps of the
plasma membrane actively
pump hydrogen ions out into
the soil water.
2. Hydrogen ions combine
with anions or membrane
carriers allow the uptake of
the ion against the
electrochemical gradient (3).
4. H+ displace cations from
the clay particles
Direct method of active mineral absorption
Cations that are free and in solution in the soil water can be taken up
actively by active transport membrane pumps.
Experiments that metabolically poison the root causes all mineral
absorption to stop.
Water and its movement
through the Plant
Roughly 95% of the water that enters a
plant is lost via transpiration.
Water is necessary for:
1.  Turgor and pressure
2.  Photosynthesis
3.  Regulation of internal temperature
The CohesionTension Theory
The difference between
the water potentials of
the soil and the air
around the stomata are
capable of producing
enough force to transport
water through the plant
—from bottom to top and
thus goes the cycle.
Translocation / The Pressure-Flow Hypothesis
Food substances from a source are taken
up by osmosis
destination or a sink
organic solutes are moved along concentration gradients existing
between sources and sinks.
• roots
• food storage tissues (root cortex or rhizomes)
• food producing tissues (mesophyll in leaves)
The Pressure-Flow Hypothesis
Apoplast and symplast pathways
Ernst Münch, separated the plant into two principal compartments, the "dead" apoplast
and the living symplast.
Apoplast
Spaces between the cells
Cells walls
It essentially maintains homeostasis in a plant.
Symplast
The cytoplasm of root cells
Plasma membrane
Plasmodesmata
Apoplast and symplast
Apoplastic and symplastic pathways
The root hair cell provides both
an increase in the cell wall
(apoplastic pathway) and the
cytoplasmic route (symplastic
pathway) for the movement of
water.
Guttation
Appearance of drops of
xylem sap on the tips or
edges of leaves
The water will accumulate
in the plant, creating a
slight root pressure.
The root pressure forces
some water to exude
through hydathodes,
forming drops.
Hydathodes
The hydathodes, that can
often be found at the end of
vascular bundles are
derivatives of stoma
complexes.
They have guard cells, but
they cannot be closed any
more
Phloem Contents
Sucrose
Glutamate or Glutamine and
Aspartate or Asparagine
Plant Hormones. Long-distance
auxin transport, also occurs in the
xylem.
its "honeydew' secretion.
Basic pH
Potassium, Magnesium,
Phospahate and Chloride
Nitrate, Calcium, Sulfur and Iron
may be excluded
Attendance
Men3on the different kinds of transporta3on in The Cohesion-­‐Tension Theory and the The Pressure-­‐Flow Hypothesis Define apoplast and symplast What is an hydathode?