Topic 12 - Plant Exchange and Transport

water

• 90-95% of the weight of soft tissues

• Present in cell walls, cytoplasm, organelles, cells sap, intracellular spaces and vascular bundles

• High heat storage capacity

• Transmits visible light and absorbs long wave radiation

• excellent solvent

• forms hydrogen bond

water as polar molecule

turgor pressure

a force within the cell that pushes the plasma membrane against the cell wall

1. growth water

2. metabolic water

3. transpiration water

4. transport water

5. excretion and secretion

physiological function to plants:

1. extrafascicular (short distance)

2. fascicular (long distance/vertical)

2 kinds of water conduction:

extrafascicular (short distance)

• Within cell itself (cellular transport)

• Neighboring cells and tissues (radial transport)

  • Diffusion and osmosis along the symplast

symplast

interconnection of cells through plasmodesmata

fascicular (long distance/vertical)

• Occurs only at longitudinal axis via vascular bundles

• E.g. Bulk Flow Transport via the Xylem

cohesion-tension hypothesis

Transpiration provides the pull for the ascent of xylem sap, and the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots

transpiration

• Loss of water vapor from leaves

• Occurs mainly through stomata

• 2 L of water per day corn plant

• 5 L of water per day for sunflower

• 200 liters for large maple tree

• 450 liters for a date palm

• Major force in the global cycling of water

adhesion

• the attractive force between water molecules and other polar substances

• e.g. water and cellulose

cohesion

the attractive force between molecules of the same substance

rhizines

Absorptive surface of the root hairs