Plant-Water Relations Flashcards
How is water transported through a plant?
Passively, no metabolic processes are needed. Transpiration regulates water transport.
What % of water uptake is lost to transpiration?
97%.
What causes water to be absorbed from the soil at the roots?
Negative pressure/ surface tension at menisci.
Describe bulk flow.
Water flows from regions of high water content to regions of lower water content.
Soil pores are interconnected allowing bulk flow of water down the pressure gradient
Describe permanent wilting point.
In very dry soils, water potential is so low that plant can not regain turgor pressure.
What 3 factors affect soil hydraulic conductivity?
Soil type,
Soil water content,
Diffusion of water vapour.
Describe water absorption by roots in 3 steps.
Roots absorb ions from the soil solution and concentrate them in the xylem.
The multicellular root tissue behaves as an osmotic membrane.
This generates positive hydrostatic pressure in the xylem.
What are the three transport pathways for water within a plant?
Apoplast,
Symplast,
Transmembrane.
What is the apoplast pathway?
Water travels from cell wall to cell wall, not entering the cytoplasm at any point.
What is the symplast pathway?
Water and solute move along the cytosol, crossing plasma membranes via the plasmodesmata.
What is the transmembrane pathway?
Water and solute move from cell to cell by crossing cell walls.
Describe the xylem (4 points).
The longest part of the pathway for water transport.
Hollow tubes formed by lignified cells.
A simple pathway of little resistance.
Requires less pressure than water movement through living cells.
Name 2 long-distance transport mechanisms through the xylem.
Tracheids (long and thin), Vessel elements (short and fat).
Describe transpirational water loss in 4 steps.
Transpiration causes a pressure gradient.
Tension pulls the water column into the xylem of the veins in the leaves.
Tension pulls water into the veins of the apoplast of the mesophyll cells.
Water vapour diffuses out of the stomata.
What comes with the risk of dehydration through transpiration?
CO2 uptake, a reverse pathway. The concentration gradient for CO2 is smaller than the concentration gradient driving water loss.
