Topic 9.2 Flashcards
(18 cards)
What is the phloem?
a vascular tissue that transports sugar from the source to the sink.
What does the phloem consist of?
living cells called sieve tubes, each cell in the sieve tube is called a sieve tube element
What do sieve tube elements lack?
cytoplasm, mitochondria and other organelles.
We can tell that sieve tube elements need ‘life support’ from …
companion cells
Where can the companion cells be found?
next to each sieve tube element
what connects the sieve elements and companion cells?
plasmodesmata
What are the sieve tube elements filled with?
phloem sap
what is a sieve plate?
walls that have pores, which help connect sieve elements.
Generally, describe the structure and the function of the phloem.
reduced organelles in sieve elements, companion cells, plasmodesmata, sieve plate, cell membrane.
What is a source?
a part of the of the plant that exports sugar to other parts of the plant (sinks).
What are sinks?
part of the plant that cannot produce sugars, thus the source transports it to the sink
What is translocation?
the process of transporting sugars from the source to the sink.
Discuss the process of translocation.
1) Sugar is made by the source (in photosynthesis or released from storage organs)
2) Sucrose is actively transported into the companion cells.
3) Sucrose diffuses through the plasmodesmata and into the sieve tube elements.
4) Solute concentration increases in the sieve tube.
5) water (from the xylem) will go into the sieve tube via osmosis.
6) There will be high hydrostatic pressure at the source.
7) which will cause water and dissolved sugar to be pushed towards source.
8) when the dissolved water and sugar reaches the sink, the sugar will be unloaded at the companion cells (actively or passively).
9) the solute concentration will decrease at the sink.
10) causing the water to go back to the xylem (via osmosis).
What are aphids?
small sap sucking insects.
How do aphids get to the phloem sap?
they use their long stylets (mouth parts that are sharp) to pierce the phloem tube without triggering defensive responses in the plant.
if I were to cut the aphids stylet while it was feeding on the phloem sap, what would happen?
the aphid will die, and the phloem sap will continue to flow out (because of high hydrostatic pressure in the sieve tubes)
Discuss the aphid stylets and radioactive CO2 experiment.
1) plants that have 1 leaf are trapped with radioactive CO2.
2) Leaves will use the radioactive CO2 to perform photosynthesis, thus also producing radioactive sucrose.
3) sucrose will be transported to different parts of the plant.
4) The aphides will feed on the phloem sap at different locations along the stem.
5) Stylet is cut off in order to collect plant sap, to see if there is radioactive sucrose.
What is the equation for the rate of translocation
Distance travelled / time
