Experiments that show the movement of substances in xylem and phloem

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

12CO2

14CO2Radioactive

14CO2 + H20 14C6H1206 + C02 + H20

Use of radioactive Carbon-14 isotopes

Sugar transported in the phloem also show radioactivity.

Cross section of stem

Put an x ray film on top

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?