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    Hey!

    I have my AS Bio exam next week (edexcel) and I am having problems with the following. Please can you help:

    What are Parenchyma?
    What is Stele?
    Could you please explain the sodium-potassium pump
    What's the definition of Tropic Levels?
    What do Companion cells do?- do they provide nutrients?
    What's the Chloride shift for- jus to transport CO2?
    Why is the Phloem alive and the Xlyem dead?
    On a picture, how can you tell the difference between the Phloem and Sclerenchyma?
    Is it Iron or Ion present in guard cells during gaseous exchange?
    Does flaccid mean all the water is drawn out?
    What's the electrochemical gradient?

    Will the Additonal Material in the Edexcel book be in the exam?
    Could you predict what may come up?

    Thank you very much, I really appreciate it.
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    (Original post by the_wizzz)
    Hey!

    I have my AS Bio exam next week (edexcel) and I am having problems with the following. Please can you help:

    What are Parenchyma?
    What is Stele?
    Could you please explain the sodium-potassium pump
    What's the definition of Tropic Levels?
    What do Companion cells do?- do they provide nutrients?
    What's the Chloride shift for- jus to transport CO2?
    Why is the Phloem alive and the Xlyem dead?
    On a picture, how can you tell the difference between the Phloem and Sclerenchyma?
    Is it Iron or Ion present in guard cells during gaseous exchange?
    Does flaccid mean all the water is drawn out?
    What's the electrochemical gradient?

    Will the Additonal Material in the Edexcel book be in the exam?
    Could you predict what may come up?

    Thank you very much, I really appreciate it.
    i ll answer as much as possible since i finished my biology examinations i forgot everything

    1)parenchym [ reffered to those found in the Xylem tissue ] are "normal" plant cell with all cell contents except chloroplast .. which is abscent due to the indirect contact of light to these cells .. so they dont photosynthesis so its useless to have chloroplasts, they have a iso-semetric shape.
    2)Stele is another name of the Vascular bundle, the one found in the roots .. so its a circular tube containing Phloem/ Xylem tissues and Cambium[Pericycle or whatever the spelling is ].
    3)i dunno whats the sodium pottasium pump :confused: .. but from the word pump i assume its talking about the co-transporter molecules found in the plasma membrane which load sodium-pottasium Actively.. Dont take the answer from me cuz thats ONLY what i think
    4)Trophic levels = Feeding levels found in a Food chain . Such as primary/secondary/teirtary consumers/producers etc.. each trophic level has its own energy

    Hey i g2g now i ll answer when i return .. Byez
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    Thank you very much for your answers!

    So, is the Cambium and pericycle the same thing?

    Why are there different type of parenchyma, like pith of parenchyma?
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    (Original post by the_wizzz)
    Thank you very much for your answers!

    So, is the Cambium and pericycle the same thing?

    Why are there different type of parenchyma, like pith of parenchyma?
    Pop these into google - it's amazing how much info is on the net

    EDIT - sorry that was a bit cruel: a tip for searching out specific terms in google:

    type in 'define:' and then what you are after. i.e

    definearenchyma

    the smiley bloody face, is ofcourse : p without the space in between! :P
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    I'll give that a try!
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    heya.....
    Companion cells work at the sources (where sucrose is loadad into the phloem). it pumps H+ out of the cell. it goes back in down its conc. gradient through a transport protein which takes sucrose with it at the same time. then the sucrose travels through the plasmodesmata ( the gaps in the cell walls that connect the companion cells to the vessel elements <phloem vessel>) into the phloem vessel to be transported.
    Voila.........
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    (Original post by spali)
    heya.....
    Companion cells work at the sources (where sucrose is loadad into the phloem). it pumps H+ out of the cell. it goes back in down its conc. gradient through a transport protein which takes sucrose with it at the same time. then the sucrose travels through the plasmodesmata ( the gaps in the cell walls that connect the companion cells to the vessel elements <phloem vessel>) into the phloem vessel to be transported.
    Voila.........

    You may be confusing companion cells with transfer cells.
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    (Original post by the_wizzz)
    Hey!

    I have my AS Bio exam next week (edexcel) and I am having problems with the following. Please can you help:

    1)What do Companion cells do?- do they provide nutrients?
    2)What's the Chloride shift for- jus to transport CO2?
    3)Why is the Phloem alive and the Xlyem dead?
    4)On a picture, how can you tell the difference between the Phloem and Sclerenchyma?
    6)Is it Iron or Ion present in guard cells during gaseous exchange?
    7)Does flaccid mean all the water is drawn out?
    8)What's the electrochemical gradient?

    Will the Additonal Material in the Edexcel book be in the exam?
    Could you predict what may come up?

    Thank you very much, I really appreciate it.
    Hey Me BAcK :cool:
    Companion cells function is to actively Load Organic Compounds [Mainly sucrose]. it does this by pumping out H ions which is an active method which requires ATP .. which when break down it releases energy ;
    ATP ----> ADP + P
    pumping the H ions out side of the phloem tissue into the surrounding cells makes a concentration gradient, where there is a high H ions concentration outside of the phloem tube , this will causes the movement of H ions [ by facilitated diffusion i suppose ].. to re-enter the companion cell withdrawining with it sucrose through a Co-transporter molecule.Same action found during re-hydration of a chloera Victim , where the person is given Glucose+salts +water. As the glucose get absorbed by the epithelium cells in the linning of the guts it picks up with it the Salts. Here the H ions picks up with it Sucrose.when the sucrose enters the companion cell it moves by diffusion to the Sieve Tube through the inter-connecting plasmodesmata.so the Overall function is to withdraw sucrose from photosynthetic cells [ Mesophyll ] so that it provide it to the seive tube so that it can be translocated
    2)Have no idea whats a chloride Shift :confused:
    3)Remember the xylem vessel is made up of vessel elements which started their ''life" as normal plant cells ,, however their walls where lignified which Blocks any exchange of substances between the cell and its environment, becuz the lignin is impearmable.so the cell just die leaving free empty space called lumen inside.. However the phloem tube are made up of sieve elements which are just like a normal cell .. however nucleous ,ribosomes and mitochondria are abscent+ chloroplast.And their walls are not lignified.
    4)no idea whats Scelernchyma :confused:
    5)No idea
    6) sAme
    7)yea ... basically turgid is when a plant cell is Full of water it becomes rigid the opposite is flaccide.. the protoplast would usually shrink away from the cell wall during plasmolysis
    8) no idiea .. BUT MAYBE .. its the deffrence between ions in 2 diffrent regions.. i just made this up so dont rely on Me on this ques

    Hey sorry i couldnt answer most cuz ur cirriculum seems to be diffrent than mine
    i Hope i helped ..
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    Cambium is the same as the Pericycle..hmmm
    hold on a second .. i think the cambium is found in the stem .. and the pericycle is found in the roots .. but yea their function is the same.
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    Thank you very much for your extesnive help FidoDiDo
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    (Original post by the_wizzz)
    Thank you very much for your extesnive help FidoDiDo
    Hey AnytimeZ :cool:
 
 
 
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