Water Flashcards
What is the result of more free water molecules?
Compared to suite, the higher the water potential
Why is water important?
A key substance for plants both metabolism and structure
What does water provide?
Turgor (hydrostatic) pressure
What is the result of turgor?
It provides a hydrostatic skeleton to support stems and leaves
What is water vital for?
Cell expansion
How is water vital for cell expansion?
The force allows roots to push through soil and shoots to grow through concrete and tarmac
What are other uses of water?
Keep plants cool, transport and photosynthesis
How is water used to keep plants cool?
Loss of water by evaporation from the stomata in leaves
How is water used in transport?
Mineral ions and products of photosynthesis are transport in aqueous solutions
How is water used in photosynthesis?
It is one of the raw materials
What is the function of the root?
To anchor plant and provide surface for uptake of water from soil
How does the root increase SA for water uptake?
Present of root hairs just behind root tip
How are root hairs a well adapted exchange surface?
Microscopic size, large SA:V, thin SA for diffusion and osmosis, and cytoplasm solute
What is the function of the microscopic size of a root hair?
It can penetrate between soil particles
How do root hairs have a large SA?
1000s grow on root tips
What is the function of cytoplasm solute?
It maintains water potential gradient between soil, water and cell as ions can be moved into the root hair cell by active transport
How does water move into the root?
Through cytoplasm and sap in root hair cell and from soil water
What is the cytoplasm and sap in root hair cell?
Sugar, mineral ions and amino acids with low water potential
What is soil water?
A very low concentration of mineral ions with high water potential
How do mineral ions and water move into root hair cells?
By active transport when in short supply and then water follows by osmosis
What are the 2 ways water moves across the root?
The apoplast or symplast pathway
What is the apoplast pathway?
Water moves through the open network of cellulose fibres in the cell walls through intercellular spaces
What is the resistance in apoplast pathway?
Little resistance to the movement
How does water move into the xylem?
As water moves into the xylem, other water molecules are pulled along behind across the movement in a continuous flow
What allows the continuous flow of water?
Cohesive forces joining water molecules together
What is the symplast pathway?
Water moves through the cytoplasm from one cell to the next through the plasmodesmata
How does water move from cells?
It moves by osmosis from one cell to the next across the root until it reaches the endodermis
What happens when water leaves a cell?
The water potential gets lower, maintaining the water potential for the next water molecules to come into cell
What is the effect of plasmodesmata?
The cytoplasm is continuous
What is the endodermis?
A ring of cells surrounding xylem and phloem
What is the casparian strip?
A strip of wax (suberin) embedded in the cell walls of the endodermis and is impermeable to water
What is the function of the casparian strip?
It blocks to apoplast pathway
How does water move from the apoplast pathway to the symplast pathway?
The water in the apoplast pathway is diverted across the plasma membrane and into the cytoplasm where it travels through the symplast pathway
What does water cross when it moves pathway?
A partially permeable membrane which has selective carrier proteins to prevent toxins reaching other parts of the plant
What is the function of the endodermis?
It moves minerals by active transport from the cortex into the xylem
What is the result of the endodermis?
Water potential in xylem becomes more negative and water passes into the xylem from cortex by osmosis down water potential gradient
How is the water potential set up from soil to xylem?
Water potential in cells outside the endodermis goes down and water i pulled in from the next layer of cells right away across the root so water enters root hairs by osmosis
What is the result of active transport of minerals?
Resulting movement of water by osmosis into the xylem results in root pressure
What is root pressure?
A positive hydrostatic pressure which in independent of transpiration
What is the result of root pressure?
Water is pushes a little way up the xylem
What is evidence for root pressure?
If the shoot of a plant is cut off, sap exudes from the stump, guttation, mitochondrial poisons, lack of oxygen and increased temperature
What is guttation?
Leave tips exude sap overnight
How is mitochondrial poisons evidence for root pressure?
Mitochondrial poisons such as cyanide which prevents production of ATP, result in loss of root pressure
What happens due to a lack of oxygen?
Loss of root pressure
How does temperature affect root pressure?
Root pressure rises, suggesting chemical reactions
