9.2&9.3 Water Transport In Multicellular Plants&transpiration Flashcards
What takes up water into plants from the soil
Root hair cells
How are root hair cells well adapted for exchange surfaces
Microscopic size
Large SA:V ratio
Think surface layer
How do root hair cells maintain a water potential gradient
Soil had a high water potential whereas root hair cells contain many solvents so has a low water potential therefor osmosis continually takes place
What are the two movements of water across roots
The symplast pathway
The apoplast pathway
What is the symplast pathway
Water moves through the symplast which is the continuous cytoplasm of the living plant cells connected through the plasmodesmata
How does water move through the symplast pathway
The root hair cell has a high water potential compared to the next cell along so water moves through each cell by osmosis until it reaches the xylem
What is the apoplast pathway
Water moves through the apoplast - which are the cell walls and intercellular spaces
How does water move through the apoplast
Water fills the intercellular spaces and as water moves into the xylem more water molecules are pulled through the apoplast due to waters cohesive properties
This pull abs cohesion creates a continuous flow of water through the open structure of the cellulose walls
Where does water end up reaching after travelling through the apoplast and symplast pathways
The endodermis which is a layer of cells surrounding the xylem
What is the casparain strip
A band of waxy material that runs around each endodermal cell forming a waterproof layer
What happens when water reaches the casparian strip
It is forced into the cytoplasm of the cell and joins the water in the symplast pathway
It then passes through a selectively permeable membrane leaving any toxic solutes from soil behind
Why is the rate of water moving from endodermal cells to xylem high
Xylem has a much lower water potential than endodermal cells
What gives water a push up the xylem
Root pressure
The active pumping of minerals into the xylem to produce movement of water
What is transpiration in plants
The movement of water out of plants via opened stomata - letting water vapour move out of plants with o2
What is the transpiration stream
The movement of water up from the roots to the highest leaves
What happens at the start of the transpiration stream
There is a transpiration pull which results in tension in the xylem and this helps water to move across roots from the soil
What happens to water molecules at the start of the transpiration stream
Adhesion occurs
They form hydrogen bonds with the carbs in the walls of the narrow xylem vessels
They also form hydrogen bonds with eachother through cohesion
This results in water exhibiting capillary action
What is capillary action in transpiration stream
When water rises up narrow tubes against the force of gravity
What happens to water after it travels up the xylem in the transpiration stream
Move out of xylem into leaves by osmosis
The water molecules then evaporate from the surface of the mesophyll cells into the air spaces of the leaf and then move out the stomata
What is the cohesion tension theory that
Water moves from soil in a continuous stream up xylem and across the leaf
What do scientists use To measure transpiration
A potometer
How do you measure the rate of water uptake in a transpiration stream
Distance moved by air bubble divided by time taken for air bubble to move that distance
What factors affect transpiration
Light intensity Humidity Temperature Air movement Soil - water availability
