Water transport in roots Flashcards
Why is water key in the structure of plants?
turgor pressure as a result of osmosis in plant cells provides a hydrostatic skeleton to support the stems and leaves
turgor also drives cell expansion - it is the force that enables plant roots to force their way through concreate
Why is water key in the metabolic activities of plants?
water evaporation helps keep the plant cool
mineral ions and the products of photosynthesis are transported in aqueous solution
water is a raw material for photosynthesis
How are root hair well adapted as exchange surfaces?
microscopic size - easily penetrate between soil particles
each microscopic hair has a large SA:V ratio and there are thousands on each growing root tip
each hair has a thin surface layer (just the cell wall and surface membrane) through which diffusion and osmosis can quickly take place
the concentration of solutes in the cytoplasm maintains a water potential gradient between the soil and cell
What makes it difficult for minerals to enter the roots and how do the roots overcome this?
soil has a very low concentration of dissolved minerals so it has a high water potential
the cytoplasm and vacuolar sap of the root hair cell contain many different solvents e,g, sugars and ions, so water moves in
they actively pump minerals from the soil into the cytoplasm in order to lower the water potential
What is the symplast pathway? How does water move across it?
water moves through the symplast - via cytoplasms through the plasmodesmata of cells
the root hair cell has a higher water potential than next cell, so water moves to the next cell by osmosis, this process continues until the xylem is reached
as water leaves the root hair cell the water potential falls, this maintains a steep water potential gradient
What is the apoplast pathway?
movement of water through the apoplast - the cell walls and intercellular spaces
water fills the spaces between the loose open network of fibres in the cellulose cell wall
as water molecules move into the xylem , more water molecules behind them due to the cohesive forces between water molecules
creates tension and means there is a continuous flow through the apoplast
