Transcript 3D_tpt of subst in xylem and phloem modified

Using these materials…
•
•
•
•
Red ink
A plant (eg celery)
Microscope
Knife
Transverse
sectioning of stem
Examine the
section
under
microscope
Under the microscope……
Evidence
• Xylem stained red.
• Water is being transported in the xylem.
Translocation
• Transportation of manufactured food
products (sugars and amino acids) in the
phloem is known as translocation.
Leaves
•Source
•Location where
food is
manufactured
Fruits/roots
•Sink
•Location where
food is being
transported to.
Movement of sugars in the phloem
• Using aphids
• Using carbon-14 isotopes.
• Using the ’ringing experiment’
Using aphids
Feed on the stems
Carbon
dioxide
Sieve
tubes
Evidences
• Liquid the exude out of the cut end of the
proboscis contain sugar and amino acid.
• Viewed under microscope, proboscis found
embedded in the sieve tube.
Think about it!
• Why do plantations infested with aphids have
reduced fruit yield?
Using the ringing experiment
• Remove the bark of the
tree would remove the
phloem and the
cambium.
• Predict what would
happen at the cut region?
Using the ringing experiment
• The region above
the cut end
swells due to the
accumulation of
sugar.
Evidences from ‘ringing’ expt
• Removing of bark remove phloem.
• Swelling above the cut region shows that
sugar is being accumulated in that region as
phloem transport is being disrupted.
Use of radioactive Carbon-14 isotopes
Radioactive
12CO
2
14CO
2
Use of radioactive Carbon-14 isotopes
14CO
14C H 0 + C0 + H 0
+
H20

2
6 12 6
2
2
Sugar transported in the
phloem also show
radioactivity.
Put an x ray film on top
Cross section of stem
Evidences
• Plants exposed to radioactive 14CO2 would
contain radioactive sugar in the phloem.
• The presence of radioactive sugars is detected
by an x-ray film.
Think about it!
Young leaf
exposed to
carbon dioxide.
No radioactivity
detected . Why?