mass transport in plants Flashcards
what is the xylem tissues role
transports water and mineral ions through stem up to leaves
how is xylem tissue adapted for its function
cells joined with no end walls forming continuous tube —> water can flow as continuous column
cells contain no cytoplasm —> easier water flow no obstruction
thick cell walls with lignin —> support to withstand tension and prevent water loss
pits in side walls —> allows lateral water movement
what is cohesion theory
how water moves up xylem against gravity via transportation system
what is transpiration
loss of water vapour from plant leaves by evaporation through stomata
describe the process of transpiration
leaf
1. water lost by transpiration water evaporated from mesophyll cells into air spaced and water vapour diffuses through stomata
2. reducing water potential of mesophyll
3. water drawn out of xylem down water potential gradient
xylem
4. creating tension in xylem
5. hydrogen bonds result in cohesion
6. water pulled as continuous column
7. water also adheres to walls
root
8. water lost entered the roots via osmosis
what is the phloem tissue
transports organic substances eg. sucrose in plants
what 2 cells are in the phloem and their adaptations
sieve tube elements
- no nucleus —> easier flow
- end walls between cells perforated
companion cells
- many mitochondria- ATP for active transport
what is translocation
movement of absolutes from sources to sinks by mass flow
describe the process of translocation
at the source
- active transport loads solutes from companion cells
- lowering water potential in sieve prices
- so water entered by osmosis from xylem
- increasing hydrostatic pressure
at the sink
- solutes removed to used or stored
- increasing water potential in sieve plates
- water leaves by osmosis
- lowing hydrostatic pressure
mass flow
- pressure gradient form source to sink pushed solutes
how would you use tracer experiments to investigate transport in plants
leaf supplied with radioactive tracer
radioactive carbon incorporated into organic substances during photosynthesis
these move around by translocation
movement tracked using Geiger counter
how would you use ringing experiments to investigate transport in plants
remove and kill phloem eg. remove ring of bark
bulge formed in source side of ring
fluid from bulge has higher conc. of sugars than below
tissues bellow ring due as cannot get organic substances
how to interpret evidence form tracer and ring experiments and to evaluate evidence for and against mass flow hypothesis
is there evidence to suggest phloem is involved
is there evidence to suggest respiration/ active transport involved
is there evidence to show movement from source to sink - what are these
is there evidence to suggest movement from high to low hydrostatic pressure
could movement be due to another factor
how would you investigate transpiration
potometers
how to set up a potometer
- cut a shoot underwater at a slant to prevent air entering
- assemble potometer with capillary tube end submerged in beaker of water
- insert shoot underwater
- ensure apparatus is watertight
- dry leaves and allow time for shoot to acclimatise
- shut tap to reservoir
- form an air bubble - quickly remove end of capillary tube from water
how to use a potometer to investigate the effect of a named environment variable on rate of transpiration
- record position of air bubble
- use stop watch to record time
- record distance moved in time
- calculate volume of water uptake
- use radius of capillary tube to calculate cross sectional area (pie x radius squared)
- multiply by distance moved - calculate rate of water uptake
- divide volume by time - change one variable (wind, humidity, light, temperature )
- keeps all other variables constant
