9.2 Water Transport In Multicellular Plants Flashcards
Why is water important for plants?
Turgor pressure provides a hydrostatic skeleton to support the stems and leaves
Turgor allows cell expansion, so roots can force through tarmac and concrete
Loss of water by evaporation keeps plants cool
Mineral ions and products of photosynthesis are transported in aqueous solutions
Water is a raw material for photosynthesis
What type of cell is a root hair cell?
A specialised epidermal cell
Why are root hair cells well adapted as exchange surfaces?
Microscopic size means they can penetrate easily between soil particles
Large SA:V ratio, many on each growing root tip
Each hair has a thin surface layer, through which osmosis and diffusion occurs
Concentration of solutes in the cytoplasm maintains a water potential gradient between the soil water and the cell
Why does water move into root hair cells by osmosis?
Soil water has a low concentration of dissolved minerals, so has a high water potential
Cytoplasm and vacuolar sap of the root hair cell contain many different solvents including sugars, mineral ions and amino acids, so has a lower water potential
Therefore, water moves into the cell by osmosis
3 different pathways for water to move across root hair cells into the xylem
Symplast pathway
Apoplast pathway
Vacuolar pathway
The symplast pathway
Water moves through the symplast by osmosis
Root hair cell has higher WP than the next cell along, so water moves by osmosis into the next cell
Process continues until xylem is reached
What is the symplast?
The continuous cytoplasm of living plant cells that is connected through the plasmodesmata
What is the apoplast pathway?
Movement of water through the apoplast
Water fills the spaces between the loose, open network of fibres in the cellulose cell wall
As water moves into the xylem, more water is pulled through the apoplast behind them, due to cohesive forces between water molecules
The pull from water moving into the xylem and up the plant along with water’s cohesive properties creates a tension that creates a flow of water
Vacuolar pathway
Water moves thorough the cell walls, plasma membranes, cytoplasm, tonoplast and vacuole
What is the endodermis?
Layer of cells surrounding the vascular tissue
What is the Casparian strip?
Band of waxy material called Suberin that runs around each of the endodermal cells forming a waterproof layer
What does the Casparian strip cause?
Water in the apoplast pathway can’t go further and is forced into the cytoplasm, joining water in the symplast pathway
Why is it important that water from the apoplast pathway is diverted into the cytoplasm?
Water must pass through the selectively permeable cell surface membrane - prevents toxic substances passing through, as carrier proteins aren’t present
What is the solute concentration in the endodermal cells compared to the cells in the xylem?
Solute concentration in the endodermal cells is more dilute compared to cells in the xylem
What happens to water once inside the vascular bundle?
Water returns to the apoplast pathway to enter the xylem and travel up the plant
