Expert: Florence M Rollwagen - 11/12/2008

Question
QUESTION: I want to know characteristic of phloem sieve tubes. Is it high or low solute potential of the cell content? Thanks you kindly

ANSWER: Hi Ling:  Thanks for your question.

Phloem is a type of tissue in plants that transports carbohydrates from the leaves (where photosynthesis manufactures sugars) to the fruits and roots of the plant.

I'm not sure what you're asking about the solute potential of the cells, but I think you want to know about diffusion and movement of sugars through the phloem.  

The movement of materials through the phloem is carried out by positive pressure (unlike xylem movement which is negative pressure).  What happens is that sugars are loaded into the phloem cells in the areas where they are produced (leaves) which increases the solute concentration.  Water then diffuses (osmosis is the diffusion of water across a membrane) into the cell (high concentration to low concentration) and materials are forced down the phloem tubes to the rest of the plant.

Here is some good websites for plant structures:
http://www.cartage.org.lb/en/themes/sciences/botanicalsciences/PlantsStructure/P

http://www.bio-medicine.org/biology-definition/Phloem/

Hope this helps!

FM Rollwagen, PhD

---------- FOLLOW-UP ----------

QUESTION: Thanks you..It helped me a lot..I am actually asking which of the following features is characteristic of phloem sieve tubes? A) solute potential of the cell content -high B) solute potential of the cell content-low


which is the right answer? Since i want to know more about this..I change the question shorter.. Thanks you kindly

ANSWER: Hi again, Ling:

The sugars are loaded into the phloem tubes by active transport.  Remember that active transport requires ATP and moves a substance against the concentration gradient.  That is, from an area of low concentration to an area of high concentration.  If by asking about solute potential do you mean solute concentration?  If so, then I've just answered that question.

Whenever you ask about solute concentration it has to be in relation to some other concentration.  For example, inside and outside a cell across the membrane.  Which do you mean?

I think you are trying to trick me into answering a homework problem.

FM Rollwagen, PhD

---------- FOLLOW-UP ----------

QUESTION: No, i didnt trick you. I'm doing revision on past questions. This question have been repeated after several years. It have marking scheme so that you wil know the correct answers but the answer for this question previously is high solute potential of the cell content but remember i said it have been repeated after several years. It have the answer low solute potential of the cell content. I'm not sure is the correct answers so i ask it here. I'm asking about solute potential. Much appreciated

Answer
Hi again:

You’ve gotten somewhat beyond what I ordinarily know, but I searched for [“solute potential” phloem] in Google.  The quotes are necessary because they keep the indicated words together.  If you didn’t use quotes you would get solute and potential separately.

So, having searched in that manner I found more information for you:

http://www.mnstate.edu/marryand/Plantphy347/6-Translocation%20in%20the%20Phloem.

http://books.google.com/books?id=UEGW-7C-bxYC&pg=PA253&lpg=PA253&dq=%22solute+po


Hope this helps!

FM Rollwagen, PhD