Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Water is carried in the xylem while sugars and amino
acids in the phloem
...

Ringing experiments:
Woody stems have an outer protective layer of bark on
the inside of which is a layer of phloem that extends all
round the stem
...

At the start, a section of the outer layers is removed
around the complete circumference of a woody stem
while it is still attached to the rest of the plant
...
Samples of liquid that has accumulated in this region are
found to be rich in sugars and other dissolved organic
substances
...

These observations suggest that removing the phloem
around the stem has led to:

1
...


The interruption of flow of sugars to the region
below the ring and the death of tissues in this region
...
If xylem was the tissue responsible for this, you
would not have expected sugars to accumulate above
the ring nor tissues below it to die
...
Radioactive sugars
can be traced as they move within a plant using
autoradiography
...
The film becomes blackened
where it has been exposed to the radiation produced by the sugars
...
As the other tissues do not blacken the
film, it follows that they do not carry sugars and
that phloem alone is responsible for their translocation
...


when phloem is cut, a solution of organic molecules flow out
...


Plants provided with radioactive CO2 can be
shown to have radioactively labelled carbon in
phloem after a short time
...


Aphids penetrate the phloem using their mouthparts, they can therefore be used to extract the
contents of the sieve tubes
...


The removal of a ring of phloem from around the
whole circumference of a stem leads to the accumulation of sugars above the ring and their disappearance from below it

---