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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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Reply 660

liviaaa

Does anyone want to do a Q and A to help revise?

Reply 661

angel1992

basically am stuck on genetics part. If a gene codes for a specific polypeptide chain how can you have different alleles which are the same gene because different alelles have different polypeptide chains( they usually have one amino acid thats different) and that would therefore make them different genes

Is it that the differences are so small, i.e. one amino acid difference still makes it the same polypeptide chain?

very confused
any ideas or explanation would be helpful?

Reply 662

ScienceGeek3

Original post by liviaaa

Does anyone want to do a Q and A to help revise?

Go for it

Reply 663

EffKayy

Original post by ScienceGeek3

Yeah or you could use the immunological comparisons of proteins which is the precipitate one.. I think :/

Yeah the serum thing.
Antigen etc...
more precipitate = more closely related.

Reply 664

ScienceGeek3

Original post by angel1992

Alleles are alternative forms of the same gene.. I don't know if that helps but I don't really understand what you're asking :/

Reply 665

EffKayy

Original post by liviaaa

Does anyone want to do a Q and A to help revise?

Yes (btw i think you had PSYA1 today? hope it went well :biggrin:

xx)

Reply 666

emmaf

ah ok, but do we need to know the method (injecting animals etc)?

Reply 667

angel1992

Original post by ScienceGeek3

Alleles are alternative forms of the same gene.. I don't know if that helps but I don't really understand what you're asking :/

im basically asking if different alleles give different polypeptide chains, and if they do how can they be for the same gene because one gene codes for one polypeptide chain doesnt it?

Reply 668

liviaaa

Original post by EffKayy

Yes (btw i think you had PSYA1 today? hope it went well :biggrin:

xx)

Yes I did, think it went quite well, but didn't like the essay Q that much! Thanks :biggrin:

--

Okay..

2 factors affecting transpiration rates, and how they affect the rate? (4 marks)

Reply 669

LifeIsGood

Original post by emmaf

ah ok, but do we need to know the method (injecting animals etc)?

You need to know the concept behind it which is that antigen binds to the antibody...

Reply 670

Master S P

How do trees pass on alleles? Meiosis or Mitosis? and how?

Reply 671

liviaaa

Original post by ScienceGeek3

Go for it

Function of the cell wall and chloroplasts?

Reply 672

ksimmi25

PLEASE SOMEBODY help me! :frown:

Show the results of density gradient centrifugation for 3 replications of E.coli beginning with 14N and then transferred to 15N and the opposite way round.

Can someone explain how to do this - i really don't understand 14N and 15N :/ apart from the fact that 14N is lighter.

Reply 673

ScienceGeek3

Original post by angel1992

im basically asking if different alleles give different polypeptide chains, and if they do how can they be for the same gene because one gene codes for one polypeptide chain doesnt it?

Oh I see, erm well yeah a gene contains the coded information for making polypeptides, so yes, I would assume different forms of a gene go on to make different of polypeptide chains :confused:

Reply 674

liviaaa

Original post by Master S P

How do trees pass on alleles? Meiosis or Mitosis? and how?

Depends on the type of tree. Some will need male/female seeds (meiosis), others can reproduce themselves (mitosis.)

Reply 675

liviaaa

Original post by ksimmi25

PLEASE SOMEBODY help me! :frown:

Isn't this unit one? :confused:

Reply 676

SmithytheDrummer

Original post by emmaf

Can someone simply explain immunological response as a way of comparing the relationship between species please? :]

Basically:

Animal A's blood (serum) is injected into animal B who produces antibodies at a quick rate.

The antibodies made by animal B will be specific to the antigens on animal A's somatic (body) cells.

These are then extracted and mixed with animals C, D, E etc. If the antigen of animal C's cells are similar to that of animal A's , antibodies will bind to them and form a precipitate.

The more precipitate formed, the more similar the animal's antigens are to animal A's and so the more similar the species are.

This is my understanding, although don't hold me to it :')

Reply 677

ScienceGeek3

Original post by liviaaa

Function of the cell wall and chloroplasts?

Cell wall provides mechanical strength to the plant and prevent the bursting of the cell due to osmotic pressure..

Chloroplasts are used in the process of photosynthesis as they contain thylakoids which contain the green photosynthetic pigment cholorophyll. They are also used for maximum light absorption!

How does the strutcture of starch differ from that of cellulose?

Reply 678

EffKayy

Original post by liviaaa

Yes I did, think it went quite well, but didn't like the essay Q that much! Thanks :biggrin:

--

Okay..

2 factors affecting transpiration rates, and how they affect the rate? (4 marks)

Temperature - increase in kinetic energy increases rate, water pulled up faster? Im not sure how to word this . cohesion tension theory?

Air movement - the more air movement there is, the more dispersed the humid layer gets so it lowers the water potential in the air. High water potential near stomata? mesophyl layer? Concentration gradient? ?