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    hey guys, in class we did a lot about cancer, like oncogenes, proto-oncogenes and tumor suppressor genes etc. How well do we need to know that stuff cos it doesnt seem to be a very popular topic in past papers?
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    (Original post by mynameisntbobk)
    I've got to say I actually didn't understand that question, so I wouldn't be able to explain it.. I got it wrong when I did it


    it's not in the spec but I can see them putting it in.. maybe the simple specs such as multi/single cellular etc
    i thought of it like this...what u thnk?Name:  cross.jpg
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    (Original post by mynameisntbobk)
    you're not alone don't worry though, there's still time to get the essential stuff down
    thanks for answering my questions Bobk been great help.

    that's not an edexcel paper is it?
    pit's don't contain plasmodesmata do they? if anything, plasmodesma contain pits..

    I would have said areas of reduced cell walls, which are arranged in pairs between adjacent cells..
    yh I would have also said that, regions of the cell wall where it is thin, only a single layer of cellulose is deposited, the secondary cell wall is absent. they aid in movement and transport of substances between cells.


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    OK, so i'm slightly confused about this primary and secondary cell wall shiz.

    is this present in cellulose plant cell walls too as well as plant fibres?

    If so what exactly is it
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    (Original post by yarshad)
    OK, so i'm slightly confused about this primary and secondary cell wall shiz.

    is this present in cellulose plant cell walls too as well as plant fibres?

    If so what exactly is it
    I'm so confused with that aswell

    I;m not sure which one has lignin or cellulose and which one is thicker?

    can bobk explain?
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    (Original post by CoolRunner)
    I'm so confused with that aswell

    I;m not sure which one has lignin or cellulose and which one is thicker?

    can bobk explain?
    Well, in my revision guide is says that PLANT CELL WALLS have primary and secondary cellulose cell walls.

    In the primary cell wall. Microfibrils are laid down in a criss cross manner, embedded in a glue of hemicellusoes and pectin. There is no lignin

    Secondary plant cell wall - microfibrils laid down in sheets and cellylose microfibrils are unidirectional. they are embedded in a glue of hemicelluloses and pectins but have lignin :/


    But what about plant fibres? do they have primary and secondary cell walls
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    (Original post by yarshad)
    Well, in my revision guide is says that PLANT CELL WALLS have primary and secondary cellulose cell walls.

    In the primary cell wall. Microfibrils are laid down in a criss cross manner, embedded in a glue of hemicellusoes and pectin. There is no lignin

    Secondary plant cell wall - microfibrils laid down in sheets and cellylose microfibrils are unidirectional. they are embedded in a glue of hemicelluloses and pectins but have lignin :/


    But what about plant fibres? do they have primary and secondary cell walls
    Thank you! I understand!

    Plant fibres

    • cellulose microfibrils (in cell wall) ;
    • reference to net-like arrangement (of microfibrils) ;
    • secondary cell wall ;
    • reference to secondary cell wall being thicker ;
    • idea that these features make them the plant fibres strong ;
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    (Original post by CoolRunner)
    I'm afraid it is (a really old paper)

    http://intranet.wellingtoncollege.or....aspx?id=68553

    Go to question 3.
    oh right, well that was before the spec change, I'm sure what we have now would be fine if it came up
    (Original post by Daniel Atieh)
    i thought of it like this...what u thnk?Name:  cross.jpg
Views: 591
Size:  41.6 KB
    I've got to say its still confusing, I would have thought both allels on either side of the point of crossing over would have been changed

    (Original post by Rubyturner94)
    yh I would have also said that, regions of the cell wall where it is thin, only a single layer of cellulose is deposited, the secondary cell wall is absent. they aid in movement and transport of substances between cells.


    Posted from TSR Mobile
    I forgot about the funtion, but yeah, I'd probably also mention diffusion just in case
    (Original post by yarshad)
    OK, so i'm slightly confused about this primary and secondary cell wall shiz.

    is this present in cellulose plant cell walls too as well as plant fibres?

    If so what exactly is it
    I think they're only in plant fibres, I haven't learnt about them in other plant cells.. anybody able to confirm/deny

    (Original post by CoolRunner)
    I'm so confused with that aswell



    I;m not sure which one has lignin or cellulose and which one is thicker?

    can bobk explain?
    Lignin is only present in secondary cell wall, and secondary cell wall is thicker

    (Original post by louisecharlotte)
    hey guys, in class we did a lot about cancer, like oncogenes, proto-oncogenes and tumor suppressor genes etc. How well do we need to know that stuff cos it doesnt seem to be a very popular topic in past papers?
    you don't need all of that, mainly oncogenes and supressor genes are the important part
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    (Original post by CoolRunner)
    Thank you! I understand!

    Plant fibres

    • cellulose microfibrils (in cell wall) ;
    • reference to net-like arrangement (of microfibrils) ;
    • secondary cell wall ;
    • reference to secondary cell wall being thicker ;
    • idea that these features make them the plant fibres strong ;
    I found this :
    Primary Cell Wall:
    1. Primary cell wall is the first formed cell wall and inner to middle lamella.
    2. It is thin and present in all types of cells.
    3. It is homogeneous in thickness and elastic in nature.
    4. It grows by intussusceptions.
    5. It is mainly composed of cellulose.
    Secondary Cell Wall:
    1. It is the later formed cell wall and inner to primary cell wall.
    2. It is thick and not present in meristematic and parenchyma cells.
    3. It is irregular in thickness and non-elastic.
    4. It grows by accretion.
    5. It is composed of hemicelluloses, lignin and pectin.
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    Final thing that I need help is:

    1) What is the difference between Xylem and Sclerenchyma?
    2) Do we need to know about Collenchyma, if so what is it?
    3) What is the function of sclernchyma and where is it located?
    4) What is the difference between pits and plasmodesma?
    5) Do we also need to know info about Pholem? if so please explain!

    Thanks!
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    mynameisntbobk try this time hehe : Name:  cross1.jpg
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    Hey, can some one describe differential gene expression? In the Jan 2009 paper
    ''Explain how differential gene expression can enable cells which have the same genetic material to have very different structures and functions''
    I have the answer from the mark scheme but i just want to know ow to answer it in other questions
    Thanks in advance
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    (Original post by CoolRunner)
    Final thing that I need help is:

    1) What is the difference between Xylem and Sclerenchyma?
    2) Do we need to know about Collenchyma, if so what is it?
    3) What is the function of sclernchyma and where is it located?
    4) What is the difference between pits and plasmodesma?
    5) Do we also need to know info about Pholem? if so please explain!

    Thanks!
    S and x.is for structural support due to being lignified
    X transports water and mineral ions

    Schlerenchyma is just above the vascular bundle look at the stem cross section diagram

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    (Original post by CoolRunner)
    Final thing that I need help is:

    1) What is the difference between Xylem and Sclerenchyma?
    2) Do we need to know about Collenchyma, if so what is it?
    3) What is the function of sclernchyma and where is it located?
    4) What is the difference between pits and plasmodesma?
    5) Do we also need to know info about Pholem? if so please explain!

    Thanks!
    1)
    Sclerenchyma fibres : ends closed vs ends open ( Xylem)

    Sclerenchyma have a short structure with tapered ends vs long cylinders (Xylem)

    Xylem vessel functions are water + Mineral transport and secondly support ( tough lignin ). While Sclerenchyma fibre function is just support.
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    (Original post by CoolRunner)
    Thank you! I understand!

    Plant fibres

    • cellulose microfibrils (in cell wall) ;
    • reference to net-like arrangement (of microfibrils) ;
    • secondary cell wall ;
    • reference to secondary cell wall being thicker ;
    • idea that these features make them the plant fibres strong ;
    Thanks

    (Original post by mynameisntbobk)
    x
    Name:  20130530_125931.jpg
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    Name:  20130530_125921.jpg
Views: 422
Size:  494.3 KB- this says plant cell walls do have primary and secondary parts :/
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    (Original post by CoolRunner)
    Final thing that I need help is:

    1) What is the difference between Xylem and Sclerenchyma?
    2) Do we need to know about Collenchyma, if so what is it?
    3) What is the function of sclernchyma and where is it located?
    4) What is the difference between pits and plasmodesma?
    5) Do we also need to know info about Pholem? if so please explain!

    Thanks!
    2) Collenchyma : found under epidermis in young stems in large veins of the leaves. Has thick cellulose walls , which are thick around the corners.

    Functions are : support and strengthen tissue + collenchyma with chloroplast is where photosynthesis takes place.

    ^ Don't need to know this - as it is not in the specification.
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    (Original post by Tha Realest)
    1)
    Sclerenchyma fibres : ends closed vs ends open ( Xylem)

    Sclerenchyma have a short structure with tapered ends vs long cylinders (Xylem)

    Xylem vessel functions are water + Mineral transport and secondly support ( tough lignin ). While Sclerenchyma fibre function is just support.

    2) Collenchyma : found under epidermis in young stems in large veins of leaves. Has thick cellulose walls , which are thick around the corners.

    Functions are : support and strengthen tissue + collenchyma with chloroplast is where photosynthesis takes place.

    ^ Don't need to know as it is not in the specification.

    (Original post by diggy)
    S and x.is for structural support due to being lignified
    X transports water and mineral ions

    Schlerenchyma is just above the vascular bundle look at the stem cross section diagram

    Posted from TSR Mobile
    Brilliant! Thanks!
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    (Original post by yarshad)

    Name:  20130530_125931.jpg
Views: 311
Size:  517.4 KB
    Name:  20130530_125921.jpg
Views: 422
Size:  494.3 KB- this says plant cell walls do have primary and secondary parts :/
    oh right, I guess its true then. My textbook doesn't mention it at all so I can't disagree
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    (Original post by Daniel Atieh)
    mynameisntbobk try this time hehe : Name:  cross1.jpg
Views: 207
Size:  98.2 KB
    okay that makes a bit more sense thanks
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    (Original post by CoolRunner)
    Final thing that I need help is:

    1) What is the difference between Xylem and Sclerenchyma?
    2) Do we need to know about Collenchyma, if so what is it?
    3) What is the function of sclernchyma and where is it located?
    4) What is the difference between pits and plasmodesma?
    5) Do we also need to know info about Pholem? if so please explain!

    Thanks!
    1) xylem is used for transport of water and ions and support wheras sclerenchyma is just for support. they both have lignin. xylem have open ends so they are continuous long tubes basically and sclerenchyma are short structures with ends closed
    2) i've heard it so many times but dont know what it actually so I hope we dont need to know it
    3) sort of answered the first part - its only used for support it is located on the outer edges of the stem wheras xylem are located much further in
    4) pits are thinning of the cell wall whereas plasmodesmata is where both cell walls are absent, lined with membrane and filled with cytoplasm - is what I'm reading
    5) nope. don't need to know about phloem

    (Original post by Whostolemycookie)
    Hey, can some one describe differential gene expression? In the Jan 2009 paper
    ''Explain how differential gene expression can enable cells which have the same genetic material to have very different structures and functions''
    I have the answer from the mark scheme but i just want to know ow to answer it in other questions
    Thanks in advance
    OK, so the correct stimulus needs to be supplied, e.g a chemical one.
    this turns some genes on and other off
    mRNA is synthesized from the active genes only, so the new protein is then made. The protein determines the function of the cell basically.

    Even if they have the same genetic material, there is likely to be different genes that are switched on or off if you understand what I mean, so different protiens would be made in the cells
 
 
 
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