mass trasnport of water in plants Flashcards
what are the adaptations of xylem
consists of lignin in the cell walls which adheres to the water this also provides strength and prevents the plant from collapsing
xylem has no organelles so that the water can flow
there are no end walls to form continuous system of tubes for water transport
the pits allow the water to travel to certain leaves and help
provide water for photosynthesis
the lignin is impermeable to keeps water in
what’s adhesion , cohesion , tension and transpiration
-adhesion forces between the water molecules and xylem walls (hydrophilic)
-cohesion forces between water molecules forming a continuous column of water (hydrogen bonding)
-tension is the pull generated by water evaporation. this is creates a negative pressure inside xylem than outside it
-transpiration is the evaporation of water which usually happens through stomata
describe the cohesion tension theory of water transport in the xylem
-water is lost from the lead through transpiration through stomata
-this lowers the water potential of the mesophyl leaf cells
-water is then pulled up the xylem creating tension
-water molecules cohere by hydrogen bonding forming a CONTINUOUS WATER COLUMN
- adhesion of water molecules of the xylem walls due to hydrophilic lignin
what are the factors effecting rate of transpiration
• Temperature: More kinetic energy, more evaporation from mesophyll cells, more diffusion of water vapour through stomata. A higher air temperature can hold more moisture so it has a lower water potential, so gradient is steeper
• Humidity: Air inside leaf is saturated, whereas external air has lower water potential. Increases in external humidity would lower the gradient
• Air movement: Wind removes the layer of saturated air just outside the stomata which reduces the water potential so water potential gradient steeper, transpiration increases.
• Light intensity: Increased light opens the stomata more to allow more carbon dioxide in for photosynthesis so transpiration increases
how does the decrease in pressure affects water flow in transpiration
Stomata open;
Allow converse
2. Transpiration highest around mid-day as middle of day warmer / lighter;
2. Allow ‘Sun is at its hottest’
3. (Increased) tension / water potential gradient;
Ignore ‘pull, suck’
3
(ii) (Inside xylem) lower than atmospheric pressure / (water is under) tension;
explain why the values for the pressure in the xylem are negative
due to increase in tension
explain why you have to cut the shoot in water when using it in potometer
ensured that air bubbles don’t enter the xylem so there’s a continuous water column
explain why not all water is used in transpiration
because the plant uses water for photosynthesis
plant uses water for turgidity
what does a potometer do
created a sealed environment with water that can be used to measure water uptake based on the distance an air bubble moves over time
what’s limitation of the potometer
it assumes water loss by transpiration is approximately the same as water uptake by roots
some water may be used in photosynthesis and taken up to make the cell more turgid
measurements may also be affected by water made in respiration
how do u set up a potometer
-set up under water and cut the shoot under water so that the air bubbles do not enter xylem and break continuous water column
-seal the joins with vaseline which prevents leaks and or air being drawn in
-dry off the leaves after removing with water , this would decrease the water potential gradient and affect rate of transpiration
-use a large number of leaves at a measurable rate
-draw an air bubble in
-leave to equilibrium then measure the distance the air bubbles moved in a given time
-move bubble back to the start using a reservoir of water and repeat to increase reliability
What’s a method used to find the rate of water loss per mm2 of surface area
Measure area of the leaf by drawing around each leaf and counting squares (both sides)
The divide the rate of water loss by the area and total surface area of the leaf
