Investigating transport in plants

Question 1

What happens in the ringing experiment and what is the experiment trying to prove?

Answer 1

Phloem is taken out, it’s responsible for sugar transportation, not the xylem.

Question 2

How did the ringing experiment prove that phloem is responsible for sugar transportation?

Answer 2

When you remove the phloem, sugar cannot be transported so the top is swollen because sugar cannot move down as the phloem is removed so it proves that enable to let the sugar to be transported, phloem is needed for the process.

Question 3

During the ringing experiment, it shows that phloem is needed for sugar transportation, what happens to those photosynthetic cells and non-photosynthetic cells?

Answer 3

The non-photosynthetic cells die because they cannot produce glucose themselves through photosynthesis but the photosynthetic ones can.

Question 4

What happens in the tracer experiment and what is the experiment trying to prove?

Answer 4

Plants are grown under isotopic conditions and it shows that phloem is responsible for translocation because only sugar is present in the phloem.

Question 5

During the tracer experiment, how does the result prove that there’s only sugar present in the phloem?

Answer 5

• So a plant is grown under different conditions - CO2 and carbon 14 CO2 and when it’s in carbon 14 environment, it produces radioactive glucose.
• The stem is then x-rayed where glucose is present and it will show up as black sections on the x-ray but other tissues won’t, therefore, it proves that translocation happens in the phloem alone because sugar is not present elsewhere.

Question 6

What is the evidence which translocation of organic molecules occurs in the phloem?

Answer 6

• When phloem is cut, a solution of inorganic molecules flows out.
• Plants provided a radioactive carbon dioxide can be found to have radioactive carbon in their phloem after some time.
• Aphids are small insects with needle-like mouthpieces. The mouthpieces pierce the phloem so aphids can be used to observe the content of the sieve tube. These contents show daily variations in the sucrose content of leaves which also has the same change of sugar content in the phloem.
• The removal of a ring of phloem led to accumulation of sugars above and caused it to swell and below has died.