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

Movement of water depends in:

Volume of water (solvent) Amount of solutes Gravity Membranes Capillarity

Molecular Movement

Diffusion

Concentration gradient

Rates of diffusion are affected by • Temperature • Density

In the leaves, water diffuses out via the stomata into the atmosphere.

Movement of water

Fluid statics = hydrostatics

Hydrostatic pressure is the pressure required to stop the movement of water.

Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or surface tension.

Osmosis

Osmotic potential: minimum pressure required to prevent fluid from moving as a result of osmosis.

The pressure potential: 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

Regulation of Transpiration. Turgor pressure.

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 is high.

• light intensity • carbon dioxide concentration • water concentration • Intake of K+

• Osmosis

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 increases 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 movement of substances against an electrical gradient. 1. Hydrogen pumps

• H+ out into the soil water.

2. H+ 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 Cohesion- Tension 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

Menon the different kinds of transportaon in The Cohesion-Tension Theory and the The Pressure-Flow Hypothesis

Define apoplast and symplast

What is an hydathode?