Transport in Plants part 2 Chapter 7

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.

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

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

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

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

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

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.

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.

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

Loading sucrose into phloem