Evidence for and against translocation Flashcards
Describe aphids to investigate mass flow
-Aphids pierce the phloem, and there bodies are removed leaving mouthparts behind
-sap flows out quicker near the leaves than further down stem
-evidence of pressure gradient
How can the translocation of solutes be proven experimentaly?
-supply part of plant with an organic substance which has a radioactive label.
-e.g. CO2 containing radioactive isotope 14 C
-radioactive carbon is then incorporated into organic substances produced by leaf ( e.g. sugars produces by photosynthesis ) which will be moved around plant by transloaction
-movement of these substances tracked using autoradiography
-results demonstrate translocation of substance from source to sink over time
-so autoradriographs of plants killed at different times show overall movement of solutes ( e.g. products of photosynthesis ) from leaves towards roots.
What are the two objections to mass flow?
-Sugar travels to many different sinks, not just one with the highest water potential as mass flow would suggest.
-The sieve plates would create a barrier to mass flow, a lot of pressure would be needed for the solutes to get through at a reasonable rate.
Describe metabolic inhibitor to investigate mass flow
-metabolic inhibitor ( which stops ATP production ) is out in the phloem then translocation stops
-evidence that active transport is involved
Mass flow is a model to what process?
Translocation
Describe radioactive tracers to investigate mass flow
-A radioactive tracer ( e.g. 14 C ) can be used to track the movement of organic substances in plants
-Autoradiograph shows how radiation has spread
Describe ringing to investigate mass flow
-A ring of bark is removed from a woody stem
-A bulge forms above the ring
-Fluid from buldge has a higher conc of sugars than the fluid from below the ring
-This is evidence of downwards flow of sugar
