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. ( ) Water potential of a plant cell = The osmotic potential + pressure potential

If the soil is desiccated then there will be no net movement into the plant cells and the plant will die. Osmosis

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.

1. Turgor and pressure 2. Photosynthesis 3. Regulation of internal temperature Water is necessary for:

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 its "honeydew' secretion. Plant Hormones. Long-distance auxin transport, also occurs in the xylem. 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?