1. Transport in Plants part 2
Chapter 7

2. Factors affecting transpiration
Humidity: low humidity = more transpiration
Wind and temperature: more wind = more transpiration higher temperature = more transpiration
Light intensity: more light intensity = more transpiration
Very dry conditions: This may lead to a reduction in photosynthesis as the stomata might need to close to prevent excessive water loss.

3. Xerophytes
Xerophytes are plants that live in arid conditions like deserts.

4. From xylem across the leaf
As water evaporates from the cell walls of mesophyll cells, more water is drawn in from xylem vessels in the leaf through two possible pathways
Symplastic & apoplastic pathways

5. Symplastic & apoplastic pathways
Symplastic: water moves from cell to cell via the plasmodesmata
Apoplastic: water moves through the cell walls

6. Xylem tissue They are made from cells joined end to end to form tubes
Cells are dead
Walls of cells thickened by lignin
Lumen is the inside of the xylem tubes

7. Plasmodesmata
A narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them.

8. Root pressure
Transpiration reduces water pressure at the top of the xylem vessel.
This causes water to flow up the vessel
Plants also increase the pressure difference by raising the water pressure at the base of the vessel.
Pressure is raised by active secretion of solutes
Mineral ions secreted into the water in the xylem vessels in the root.

9. Cells surrounding xylem
Cells surrounding xylem use energy to pump solutes across their membranes and into the xylem by active transport.
The presence of the solutes lowers the water potential
This brings in more water increasing water pressure
This process is minimal in it’s effects
Water continues to move up the xylem in dead plants due to transpiration.

10. Translocation
Translocation is the moving of substances from one place to another.
Usually refers to sugar movement
Transport is through sieve elements (Phloem)
Translocation uses energy to create pressure differences
Any place where sucrose is loaded into phloem is called source and where it is taken out is called a sink

11. Loading sucrose into phloem