Mass Transport in Plants - Xylem Flashcards
angiosperm
flowering plant
xylem
transports water and mineral ion
phloem
transports sucrose and a.a. (PS products) in water as sap
fibre in vascular bundle
provides mechanical support
parenchyma cells
packing cells
which cells in the vascular bundle are living?
parenchyma cells
which cells are tapered in the vascular bundle?
tracheids
why are xylem vessels dead?
lignified walls are impermeable stopping exchange so cell dies and it loses its organelles
function of lignin rings
strengthens cell wall, prevnting xylem collapsing as water moves up
transpiration
the evaporation of water out the mesophyll cells to become water vapour in the air spaces, and the subsequent diffusion of the water vapour out the stomata
percentage of water taken up that is transpired
99%
what happens to the water that isn’t transpired?
it is used for photosynthesis and maintaining turgid pressure
by what process does water vapour pass out of the stomata?
diffusion
how does water move across the leaf?
evaporation of water decreases the WP so cells pull water from neibouring cells
why is so much water transpired?
- acts as a coolant
- mineral ions dissolve in water so more water brings more ions through roots
- need to keep stomata open for PS and RS
desribe the movement of water through the xykem by cohesion tension (5)
- water transpires out the leaves
- decreases water potential in leaves,
- creating tension on water column
- water pulled up in a single column due to cohesion between molecules as a result of hydrogen bonds
- water sticks to side of xylem because of adhesive properties
name the 6 parts of a stem
- epidermis
- cortex
- phloem
- cambium
- xylem
- pith
name the 8 parts of a root
- epidermis
- exodermis
- cortex
- endodermis
- pericycle
- phloem
- cambium
- xylem
describe and explain the location of the vascular bundle in a stem
- located on periphery of stem
- stem arial structure so subject to bending strains imposed by wind
- require support in peripheries to support from all directions
describe and explain the location of the vascular bundle in the root
- located in the centre
- root below ground so subject to pulling force of gravity
- support needed in central column to support pull in single direction
root pressure theory
- mineral ions actively transported into root
- decreases WP
- water drawn up by osmosis
- mire mineral ions therefore more water taken up increasing hydrostatic pressure in root, pushing wtaer up stem
capillary action theory
- ability of liquid to flow through a narrow spae, usually against gravity
- occurs bc of intermolecular attraction forces
cohesion (+ in wtaer movement)
attraction between the same molecules (water-water)
adhesion (+ in water movement)
attraction between different molecules (water-lignin)
3 features of a root hair cell to increase uptake
- Large SA so many mitochondria
- many carrier proteins
- thin cell walls so don’t interrupt water flow
type of uptake of mineral ions
- partly passsive - facilitated diffusion
- mostly active - AT
evidence of active trasnport of mineral ions
- ion concentration of root much greater than in soil - against gradient, needing energy - AT
- adding RS inhibitor decreases uptake - requires ATP therefore AT
4 steps of movement in a potometer
- wtaer transpires
- water taken up by shoot
- water moves along capillary tube
- air bubble moves
what is the reservoir used for in a potometer?
used to return bubble to start for repetitions
8 steps of setting up a potometer
- cut shoot underwater
- assemble potometer and insert shoot underwater
- remove from water, keeping end of tube in beaker
- ensure all joints airtight, e.g. used vaseline
- dry leaves
- remove end of tube to create air bubble
- record starting position of air bubble
- record distance and time moved of air bubble
rate of water uptake formula
speed of air bubble movement x cross-sectional area of tube
4 factors affecting transpiration rate
- light intensity
- temperature
- humidity
- air movement
explain how increased light intensity affects transpiration rate
- increases transpiration rate
- increased light intensity stimulates stomatal opening for gas exchange for PS
- increased number of stamata open increases SA for diffusion of water vapour
explain how increased temperature affecs transpiration rate
- increases transpiration rate
- increases evaporation out mesophyll cells
- air spaces in leaf become more saturated with water so increase diffusion gradient to outside leaf
explain how increased humidity affects transpiration rate
- decreases transpiration rate
- as water oves out, remains in air raound stomata so air saturated
- reduces diffusion gradient fom inside to outside leaf
explain how increased air movement affects trasnpiration rate
- increases
- saturated air moves away, increasing diffusion gradient
