Edexcel 6BIO2 ~ 3rd June 2013 ~ AS Biology

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 :s-smilie:

Reply 684

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 :s-smilie:

I'm so confused with that aswell :frown:

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

can bobk explain?

Reply 685

Original post by CoolRunner

I'm so confused with that aswell :frown:

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 :frown:

Reply 686

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 :frown:

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 ;

Reply 687

mynameisntbobk

18

Original post by CoolRunner

I'm afraid it is (a really old paper)

http://intranet.wellingtoncollege.org.uk/resource.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?

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 :s-smilie:

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 :frown:

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

Reply 688

DanielDaniels

14

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.

Reply 689

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!

Reply 690

DanielDaniels

14

mynameisntbobk try this time hehe :

Reply 691

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 :smile:

Reply 692

diggy

19

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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Reply 693

Tha Realest

10

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.

Reply 694

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

- this says plant cell walls do have primary and secondary parts :/

Reply 695

Tha Realest

10

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.

Reply 696

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

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Brilliant! Thanks!

(edited 10 years ago)

Reply 697

mynameisntbobk

18

Original post by yarshad

- 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

Reply 698

mynameisntbobk

18

Original post by Daniel Atieh

mynameisntbobk try this time hehe :

okay that makes a bit more sense thanks

Reply 699