Water Movement In Plants Flashcards
What is the definition of Water Potential?
Water potential definition
• Water potential (Ψ) : The energy available in a solution to cause the movement of water, by osmosis, across a
selectively permeable membrane.
• As a reference the Ψ of pure water is zero
and the more concentrated solutes dissolved in it are the more negative Ψ becomes. So water will move from a region of high water potential (less negative)
to a region of low water potential (more negative)
What is Cohesion Tension Theory ?
Cohesion-Tension Theory
• Most plants secure the water and minerals they need from the roots. The path taken is
soil→roots→stems→leaves→atmosphere • which is referred to as the:
soil, plant, atmosphere continuum (SPAC).
Movement Of Water In Plants
Movement of water in plants
• Water movement in stems – Once absorbed by root hairs:
• moves through symplastic (cytoplasmic network) and apoplastic space (non-cytoplasmic space, interconnected cell walls)
• to vascular tissue across endodermis to xylem
• along the pressure gradients upward to leaves
• diffuses from xylem into mesophyll cells.
• a column of water from the leaves to the roots
What is Transpiration?
Transpiration
• Tension cohesion theory
– transpiration through stomata
– tension produced at the top of the plant
– tension transmitted down the plant along xylem (column
of water)
• Water is pulled up
• Cohesion of water to xylem walls
– Unbroken column of water
Water potential is lower at the top than at the bottom. Water moves from bottom to top!!
What is Vapour Pressure Deficit (VPD) ?
Vapour Pressure Deficit (VPD)
• Vapour Pressure Deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated.
• OnahotdrywindydayVPDwillbehighso plants will transpire rapidly
• On a cold wet still (no wind) day VPD will be low and plant transpiration will be lower
