The transpiration stream Flashcards
What is the function of root hair cells?
Long extensions that increase SA for more absorption of minerals and water absorbed
What happens to the water in the roots?
The water moves through the root cortex down the water potential gradient to the endodermis of the vascular bundle.
It can go through the apoplast pathway but because of the Casparian strip it moves to the symplast pathway
Where is the endodermis?
A layer of cells surrounding the medulla and xylem and blocks the apoplast pathway between the cortex and medulla
What is another name of the endodermis?
Starch sheath because of its starch granules that show that energy is being used
Why does the endodermis block the apoplast pathway between the cortex and medulla?
Makes sure that the water and dissolved minerals go into the cell cytoplasm so that the proteins on the plasma membrane can pump the mineral ions from the cytoplasm of the cortex cells into the medulla and xylem
What happens between the cortex cells and medulla with water potential after the ions enter the medulla?
The medulla decreases in water potential so the water goes in by osmosis
What is the function of the casparian strip with the medulla?
It stops the water from flowing back out into the cortex cells by the apoplast pathway
What is root pressure?
Pressure in the root medulla builds up because of the active transport and osmosis happening and forces the water up into the xylem.
What happens in the transpiration pull?
Water molecules stick to each other in cohesion so they form a long column in the xylem.
As molecules are lost at the top the rest of the column goes up as one chain, which creates tension in the water.
How is lignin used in the transpiration pull?
Because of the tension in the water it could cause the cells to break but the lignin strengthens the wall so that it doesn’t collapse in the tension
What is the cohesion tension theory?
The mechanism that involves the tension and cohesion of the column of water.
What is capillary action?
The water sticks to the xylem wall by adhesion which can help in pulling up the water up the sides of the vessel because it is narrow.
What happens to water in the leaf?
Water evaporates from the cell lining the cavity to above the guard cells, causing water to enter them by osmosis so that water is taken from the xylem. It can also reach the cell by the apoplast pathway.
