Transport in plants Flashcards
Why does transpiration occur
As a consequence of the need for gas exchange
Potato meter
-Measure how far the air bubble moves across the ruler subject to different condition to measure the volume of water uptake
Why is the results of the potatometer only an estimate
-Water could be used in photosynthesis
-To maintain turgor pressure in plant cells
Translocation
The movement/ transport of assimiliates from source to sink in plants
Translocation steps
1) Phloem loading at the apoplast pathway
2) H+ pumped out of the cc through H+ pumps by active transport
3) H+ builds up outside the cc
4) H+ wants to diffuse back into the cc
-to get back in it is co-transported with sucrose through the co-transport proteins
5) Sucrose diffuses from cc into STE through the plasmodesmata
WP lowered in STE
6) H2O moves into STE by osmosis
-Generates turgor pressure for mass flow
Explain the benefit to plants of internal transport systems.
Small SA:V - diffusion from outer surface not sufficent. Transport ensure molecules reach all tissues allows high metabolic rate
What type of tissue makes up the cambium
Meristem
Sources of error in an investigation
Not all leaf surfaces covered; leaks in apparatus; shoot not cut under water
error in reading
Suggest how water is being lost from the cut stem when all the leaves have been treated with petroleum jelly.
Evaporation from upper leaf surfaces
Why does it not matter that a hydrophyte has a high leaf SA
High rate of transpiration does not matter as
plant lives in an aquatic habitat so water is lost easily
and easily replaced
Similarities in xylem/ phloem function
Solutes carried in both; both carry mineral/salts; both use
mass flow and hydrostatic pressur
Differences in phloem and xylem function
Transport in phloem can take place in
different directions and transport in xylem
only takes place up the plant
phloem carries carbohydrates and xylem
does not
phloem transport uses living cells and xylem
does not
xylem uses, capillary action / cohesion and
adhesion, and phloem does not
Explain how glucose produced in photosynthesis is translocated to parts of the plant where glucose is metabolised or stored.
Glucose is converted to an
assimilate / sucrose in
photosynthesising cells
* Apoplast route
* Active process
* Proton pump in companion cells
* H+ concentration gradient
* Co-transport of H+ and sucrose into
companion cell
* Structural adaptations of
companion cells, e.g. many
mitochondria, increase surface
area of cell surface membranes
* Passive loading via symplast route
* Role of plasmodesmata
* entry of sucrose / solutes
decreases water potential of
phloem / sieve elements
* water enters phloem from
surrounding cells / xylem
* results in higher hydrostatic
pressure
deduce a possible mechanism to account for the increased unloading and transport of sucrose in the modified plants
sucrose unloaded at sinks and invertase
converts sucrose into, glucose /
monosaccharide (1)
increases sucrose concentration gradient
between phloem and sink (1)
causes increased unloading of sucrose from
phloem (1)
two from
increases solute gradient between source
and sink (1)
removal of water from phloem increases
pressure gradient between source and sink
(1)
contributes to increased movement in
phloem (1)
