A level Biology: Post your doubts here!

[princeali97]

does anyobdy have a guess paper for this years biology exam?

Im not making a guess.But i just feel curious that they might give sth from COPD and related topics.

 

[VelaneDeBeaute]

Thanks alot can u tell me why is it difficult to develop an effective vaccine for malaria

1.they have many antigens
2.eukarayote have many different satges of life cylce
3.mutation changes antgens
4.Parasite only vulurnable at certain stage of life cycle

Also, whatever vaccine is developed can not generate a strong enough immune response to eradicate all the parasite in the body.

 

[kitkat <3 :P]

1.they have many antigens
2.eukarayote have many different satges of life cylce
3.mutation changes antgens
4.Parasite only vulurnable at certain stage of life cycle

Thank

 

[MiniSacBall]

Hey can anyone please check this answer?? Lemme knw if i need to add more and if you have a better answer plz gimme View attachment 41185View attachment 41185

Well you answer is correct but you don't need to add the last line, B-cells develop into plasma cells upon next attack, which is ok but doesn't needs to be there. Because they only want how antibodies are produced. I guess you need to include T-Lymphocyte Cells, not only plasma because B-lymphocytes are activated or stimulated by T-cells, by producing cytokines. So include T-lymphocytes in your answer. You might also want to include Role of macro phage (Antigen-Presenting Cell).
You wrote the right answer i guess instead of B-cells having immunoglobin write T-cells having immunoglobin/receptors to detect the antigen, which then... [clonal selection, expansion], produce cytokines to stimulate B-Cells which develop into plasma and memory cells. Plasma cells .....[functions]
T-Cells should be included in your answer.

 

[kitkat <3 :P]

Also, whatever vaccine is developed can not generate a strong enough immune response to eradicate all the parasite in the body.

Thank u )

 

[MiniSacBall]

Also, whatever vaccine is developed can not generate a strong enough immune response to eradicate all the parasite in the body.

A simple answer is a vaccine cannot be developed, even if it is developed malaria has thousands of anitgens which mutate/ are different during their life time. So even if the vaccine is developed it will very in-effective. Because malaria has thousands of antigens which change during their life cycle. And it uses antigen concealment [Lives in RBC and liver cells], which prevent anti-bodies or is away from effective immune response.
And is only venerable in a certain period of time.
Hope this helps

 

[princeali97]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_2.pdf
Q4 )a) Its easy But i need a Model ans!

Companion cells pump out H+ ions outside the cell by the process of active transport against the conc. gradient using energy from ATP molecules.This causes the concentration of H+ ions to increase outside the companion cell causing them to move down the conc. gradient.H+ ions and sucrose molecules move into companion cell through a cotransporter molecule.Sucrose moves into the companion cell against the conc. gradient and then they move into sieve tube thru plasmodesmata.

 

[MiniSacBall]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_23.pdf

I don't understand Q 4 b (ii)

Mark Scheme is shit i have to say in this case i got confused too.
Well we can't see symptoms because, the fetal hemoglobin is produced inside the body and has no signs. So like we can't know.
A type of similar answer i know it is not good but some thing like we don't know when is hemoglobin being produced, it is normal or fetal ..etc.

 

[Mohammed salik]

Companion cells pump out H+ ions outside the cell by the process of active transport against the conc. gradient using energy from ATP molecules.This causes the concentration of H+ ions to increase outside the companion cell causing them to move down the conc. gradient.H+ ions and sucrose molecules move into companion cell through a cotransporter molecule.Sucrose moves into the companion cell against the conc. gradient and then they move into sieve tube thru plasmodesmata.

Gd..
So sucrose moves Into companian by active transport or difusion?

 

[princeali97]

Gd..
So sucrose moves Into companian by active transport or difusion?

Active Transport !!

 

[Mohammed salik]

Active Transport !!

ok
Shukran bro

 

[princeali97]

Q5(b)...i need an explanation...http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w13_qp_21.pdf

 

[princeali97]

ok
Shukran bro

No probelem

 

[MEltag123]

Q4(b) please. I coudn't find the mark scheme.
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_qp_2.pdf

 

[princeali97]

Q4(b) please. I coudn't find the mark scheme.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_2.pdf

It increases the surface area of the membrane allowing greater amount of co-transporter molecule to help in moving sucrose into phloem sieve tubes.

 

[kitkat <3 :P]

Mark Scheme is shit i have to say in this case i got confused too.
Well we can't see symptoms because, the fetal hemoglobin is produced inside the body and has no signs. So like we can't know.
A type of similar answer i know it is not good but some thing like we don't know when is hemoglobin being produced, it is normal or fetal ..etc.

Can we say that whn the fetal Hb Increases the adult Hb decrease which binds more to the oxygen so symptoms can be observed as the oxygen concentration is not affected ._.?

 

[joanna omar]

Q5(b)...i need an explanation...http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w13_qp_21.pdf

A change in a DnA or amino acid sequence leads to mutations.....Expalin then base subtituation of sickle cell anemia where T changes to A
* take comprative fig of the amino acid from diagram
ANd this mutation it could lead to altering the functin of protein and whole polypeptide changes

 

[MEltag123]

It increases the surface area of the membrane allowing greater amount of co-transporter molecule to help in moving sucrose into phloem sieve tubes.

Thanks

 

[Mohammed salik]

Q5(b)...i need an explanation...http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w13_qp_21.pdf

I will try..
In Sickel Cell anaemia Glu is replaced with val. ( u shuld know this)
If u look at Previous Part Glu is CTC.. And Val is CAC.. i chose this because they asked for One base substitutions. No coming to the answer..
A change is DNA triplet is a mutation which is cause By Substituion of A in PLace of T in DNa Template.. This in turn Alters mRNA codon and as we know Diffrent tRNA are specific to each amino acid so these Would be changed too and tRNA brings an Incorrect amino acid Val instead of Glu... This alters Polypeptide chain and Produces an Incorrect Polypeptide!
If u want u could mention Codes on mRNA and tRNA!

 

[Mohammed salik]

A change in a DnA or amino acid sequence leads to mutations.....Expalin then base subtituation of sickle cell anemia where T changes to A
* take comprative fig of the amino acid from diagram
ANd this mutation it could lead to altering the functin of protein and whole polypeptide changes

Its Worth 5 Marks.. U cant Finish it this way..
Atleast i wont..!