Question 5 on Midterm 1

Go down

Question 5 on Midterm 1

Post  katleu on Thu Jan 31, 2008 9:03 pm

Can someone please explain why E) is the correct answer to this problem?

The questions is as follows:

5. To collect maple sugar, one inserts a tube into the trunk until the end reaches the phloem. If instead a tube were inserted with the end reaching the xylem, the result would be:

A) Water and minerals flowing steadily out only if it had rained recently.
B) Water and minerals flowing steadily out only if the sun were shining.
C) Water and minerals flowing steadily out unless the air was extremely humid.
D) Water and minerals flowing out only until xylem pressure was relieved.
E) No water flow or minerals.

I wrongly presumed that the answer was C: due to transpiration.

katleu

Posts : 11
Join date : 2008-01-24

View user profile

Back to top Go down

Question 5

Post  laurenbettencourt on Fri Feb 01, 2008 3:55 am

I think that water doesn't flow out because movement of water/nutrients in the xylem doesn't depend on pressure, but rather on the cohesive abilities of water (one molecule pulls the next up as it transpires through the stomata). So if there is a hole in the xylem, I don't think the water molecules will be able to move at all. If you think of it like a drinking straw, you see that no water is able to move when there is a puncture in the capillary. But...yeah, I'm not a TA so please correct me if I'm wrong.

laurenbettencourt

Posts : 1
Join date : 2008-02-01

View user profile

Back to top Go down

Re: Question 5 on Midterm 1

Post  TA Brian on Fri Feb 01, 2008 4:34 am

Yeah, I think Lauren is right. It seems very counterintuitive that water wouldn't flow out of the tube, but water wouldn't flow b/c the xylem flow isn't dependent on pressure flow but instead more of hydrogen-bonding. And yes, that straw analogy is really good; cohesion with the tube is probably also a contributor to the fact that water doesn't flow.

TA Brian

Posts : 19
Join date : 2008-01-19

View user profile

Back to top Go down

Re: Question 5 on Midterm 1

Post  katleu on Sat Feb 02, 2008 10:07 pm

oh, that makes a lot of sense. thank you!

katleu

Posts : 11
Join date : 2008-01-24

View user profile

Back to top Go down

Re: Question 5 on Midterm 1

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum