help! some questions - (Jul/17/2006 )

Hello all,

I have some questions in plant nutrition and nutrient uptake mechanisms.

1. what are the advantages/ disadvantages of nutrient levels which are expressed in concentration and content?

2. concentration can be expressed in dry weight basis and fresh weight basis. Why dry weight basis is preferred and when we may use fresh weight basis?

3. what are the driving forces for passive uptake and where the energy comes from?

I did basic answer; however, my answers were not satisfied. Please help, thank you!!

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Hi

It helps if you give your answers as well, so that we can point you in the right direction.

for no.1 think about what concentration tells us and what content tells us (presuming relative content or percentage)

2.think about relative water content between tissues or species.

3. one word: osmosis. You must have heard of it if you are being asked these types of questions.

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Hi, bob1,

thank you for the reply.

for the #1, my answer is concentration is the relative/percentage amounts of the substance which is mixed with another sunstance. And content can be looked as the "real value" of substance in the mix. Therefore, high concentration does not mean high content. Using concentration may be a misleading that plants do uptake that much nutrient.

However, sometimes people use content (g of nutrient per plant or per leaf), I have no idea about this one .... (I mean the difference between content and concentration). What I wrote was "content" gives you a real number which told you how much plant really uptake.

Please help me put about the advantages/disadvantages of using these two expression.

for # 2, I put down the answer as you said. But my teacher said .. he is looking for when and why we use fresh weight basis and when and why we use dry weight basis.

for #3. except the concentration gradient, what are the other two driving forces?? for passive uptake and how are they function?

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Wasn't there something with water transpiration from leaves > negative pressure > suction of water ? There is a continous connection between leave-vessels - big xylem vessels - root, if I remember right.

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I think I got your point.....

as I know transport in plant can be active and passive. Are these two uptake system all shared the same driving force? (and the only difference is energy consumed?)

if so, I think I got the point....
Thank you for the answer

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