M3 - MOVEMENT OF WATER AND TRANSPIRATION Flashcards
(13 cards)
How does water enter the plant
Into the roots via osmosis bc there will always be a steel conc gradient due to plant always losing water
Travels through root correct and the endodermis before reaching the xylem
How does water travel through the symplast pathway
Water enters the cells cytoplasm and then moves from cell to cell through the plasmodesmata
How does water travel through the apoplast pathway
Water passes from cell to cell through the cell walls
Water can travel through cell walls easily bc they’re absorbent - this makes it the main pathway
What is the casparian strip
Bc water and substances in it can bypass the cell membrane, it can’t control entry of toxic substances
Therefore theres waxy strip within the cell walls which is impermeable to water
Water must pass through the cell membrane and into the cytoplasm - this allows membrane to control which substances enter the xylem
What two forces allow water to move up the xylem
Cohesion and tension
What is tension
‘Sucking force’ created when transpiration occurs, pulling more water into the leaf
Like a straw
What is cohesion
Water molecules are attracted to each other
Strong hydrogen bonds cause them to ‘stick together’ forming a column of water
So when tension pulls water up, the whole column of water moves up
What is adhesion
Attraction of water to non-water molecules
Attraction of water to xylem walls helps water move up through the vessel
stomata’s role in transpiration
Transpiration is the loss of water vapour through the stomata through evaporation
The stomata’s open during daytime for gas exchange where they take in co2 and get rid of oxygen
Plants will close stomata at night
What is transpiration
Cells surface are covered w thin layer of water which evaporates - high conc of water vapour
1. When stomata opens, water diffuses out bc it’s got lower concentration outside
2. Continuous evaporation means water potential of cells decrease and water moves via osmosis from adjacent cells
3. Those cells water potential decreases, causing water to move into them and so on
4. This reaches xylem so water is being pulled out of xylem - TENSION
Factors affecting transpiration rate
High Light intensity - more photosynthesis, more gas exchange, more evaporation out of stomata bc it’s open more
High temperature - more KE, faster diffusion, increases water potential gradient between inside and outside
High wind - water molecules will be blown away from plant, maintaining steep water potential gradient
Hugh Humidity - decreases transpiration bc the water potential gradient will be low
POTOMETER PRACTICAL
Based upon assumption that water uptake = water lost
1. Cut of plant shoots underwater to prevent air from entering
2. Potometer is filled w water and air bubbles removed
3. Cut plant is attached to potometer using rubber seals and petroleum jelly so it’s AIRTIGHT
4. Capillary tube lifted out of water beaker for 5 seconds and placed back into water
5, record the distance of air bubbles movement towards the plant
Potometer - calculate rate of transpiration
Volume of water evaporated DIVIDED by the time it took to lose that water
