January 24, 2010

• Mycrorrhizae are roots associated with symbiotic fungi. These absorb water and minerals in the root cortex must pass through the endodermis in order to enter the rest of the plant. Endodermis surrounds the stele
• The endodermis contains the Casparian Strip which prevents substances from going around the cells. Water and minerals must therefore pass through an endodermal cell to enter the vascular tissue

Turgor/Root Pressure- water and minerals forcing in the strip to reach vascular tissue

• Transpiration- is the loss of water vapor from leaves and other parts of the plant in contact with air
• Two ways substances pulled through plant

1. Root Pressure occurs when water flowing in from the root cortex generates a

positive pressure that forces fluid up through the xylemà positive pressure

2. Transpiration- Cohesion- Tension Mechanism- water is lost through transpiration at the leaves of the plat, and this creates a negative pressure, which draws water up through the plant. The cohesion of water due to hydrogen ions bonding (groups of 4) enables it to form a column, which is drawn up through the xylem with the help of adhesion (the fact that water molecules are attracted to the plant cell walls

• Guard cells control size of the opening in the stomata by changing shape and this regulates plant water intake
• increase size by taking up water thus swelling and sealing off the stomata opening
• influence stomata opening and closing

1. Light

2. Depletion of carbon dioxide in air spaces in leaf

3. Internal clock of guard cells

• Phloem transports organic products of photosynthesis from the leaves throughout the plant
• Sieve tubes carry food from a sugar source (leaf) to a sugar sink (all organs)
• Flow through the phloem occurs mainly as a result of bulk flow-loading sugar into cells create a high solute concentration at the source end of the sieve tube, and this lowers the water potential and causes the water to flow in the tube
• Roots can be a source in fallà summer
• Leaves can be a source in summerà fall