mass transport in plants Flashcards
xylem definition
water and mineral ions are transported to the leaves
phloem definition
transports sugars and organic substances from leaves to where they are needed
transpiration definition
water leaves the plant through stomatal pores
what are root adaptations
-hair like extensions to increase surface area
-thin cell wall so they have a shorter diffusion pathway
how does transport in roots occur
-root hair cells actively transport ions via carrier proteins
-lowers the water potential of the cytoplasm
osmosis definition
the nest movement of water molecules from an area of high water potential to low water potential across a partially permeable membrane through aquaporins
what are xylem adaptations
-dead hollow tubes with less organelles SO easier water flow
-end walls break down to form a continuous tube with no end walls SO water can form a continuous column
-lignin SO xylem can provide strength to withstand high pressure and tension
-xylem pits SO water can move laterally between xylem vessels and get around blocked vessels
Cohesion tension theory full process
-the stomata will open to allow co2 for photosynthesis which causes water to diffuse through osmosis from the air spaces in the leaf to the outside of the leaf
-loss of water in the air spaces causes water to move down the WPG from mesophyll cells to air spaces
-lowers the WP in the mesophyll cells so water moves via osmosis from the adjacent mesophyll cells
-sets up a water potential gradient across the leaf to the xylem
-water diffuse from the xylem enters the leaf causes water to be pulled up via TENSION through the xylem from the roots
-water forms a continuous column
-hydrogen bonds between water molecules cause them to stick together SO they have COHESION
-water is also attracted to the walls of the xylem so there are forces of ADHESION between the xylem and water
Negative pressure means??
pressure in the leaf is less of that in the outside of the leaf
Water potential in a tree
WP decreases (becomes more negative) as you go up the plant from the soil to the leaf to the outside ai
factors affecting rate of transpiration
-light
-temperature
-humidity
-air movement
Factors affecting transpiration:
Light
-Increase in light causes the stomata to open allowing water to leave and closes at night
-Rate of transpiration increases as light intensity increases
-However it plateaus due to another limiting factor
Factors affecting transpiration
Temperature
-An increase in temperature causes the rate of water diffusion (osmosis) to increase
-Water molecules move more rapidly with increasing temp due to increase Kinetic energy
-Rate of transpiration increases as temperature increases
-However ROT can decrease when temperature reaches an optimum temp so proteins denature and change in tertiary structure eg. aquaporins
Factors affecting transpiration
Humidity
-The air spaces in the leaf are saturated with water vapour
-The air outside contains much less water vapour
-so there is a greater WPG outside than inside when humidity increases
-water molecules transpire via osmosis from high to low WPG
-Rate of transpiration decreases as humidity increases
Factors affecting transpiration
Air movement
-Air movement moves water vapour away from the stomatal pores
-Increases the water potential gradient between inside and outside of the leaf
-so water vapour moves faster
-Rate of transpiration increases as air movement increases
potometer precautions
-seal joints to ensure watertight
-cut shoot under water to maintain a continuous column of water
-cut shoot at a slant to prevent the xylem closing and allows the continuous column of water to form
-dry off leaves so no water is in the stomata pores to disturb the water potential gradient
-insert into apparatus under water to maintain a continuous column of water
The phloem structure
-solutes are dissolved substances
-phloem tissue transports organic solutes
-phloem tissue is formed from cells arranged in tubes
sieve tubes function
-sieve tubes have no nucleus and few organelles
-there is a companion cell for each sieve tube
-sieve tubes are connected to each other through sieve plates
companion cell function
-carry out the living functions for sieve cells
-they have many mitochondria to synthesise the ATP through aerobic respiration for active transport of solutes
Translocation definition
-the movement of solutes to where they are needed in a plant
-requires energy from ATP
assimilates
solutes which are incorporated into the plant tissues
translocation process
-solutes from sources > sinks
-this requires energy
the companion cell actively transports solutes to the sieve tube
-this lowers the water potential in the sieve tub
-water enters the sieve tube via osmosis
-this increases the pressure in the sieve tube
-creates a pressure gradient to push the solutes towards the sinks
Ringing experiments
-ring of bark is removed from a woody stem
-a bulge forms above the ring
-conc in the bulge > conc below the ring
Evidence against ringing experiments
-sugar travels to many different sinks not just to one with the highest water potential
-the sieve plates create a barrier to mass flow
- a lot of pressure would be needed for the solutes to get through a reasonable rate
Evidence from radioactive tracers
-leaves are supplied with radioactive C(CO2) which is converted to glucose then sucrose
-this allows the radioactive C to be tracked through the plant as it is transported throughout the plant
-the movement of these substances are called autoradiography
-to reveal where the tracer has spread to in a plant
