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A level Biology: Post your doubts here!

Soldier313

Soldier313

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Alice123 said:
For w08
From Fig 3.1, we have 2 categories of alleles of the gene
  1. membrane protein allele
  2. muscle protein allele
Now for membrane protein alleles, IA and Ia:(look at the fig)

  • IA and Ia have equal frequency (you can easily count them)
  • Ia is smaller and negatively charged. This is because, according to the technique of electrophoresis, the smaller fragments move faster towards they anode. (DNA is negatively charged phosphate backbone which are attracted towards the anode ie downwards) The smaller they are, they move faster and the more negatively charged they are.
For muscle protein allele:

  • Ima is the smallest
  • Imb is the largest among muscle protein allele
Overall notice that muscle protein alleles are smaller (more negatively charged) than muscle protein allele

hope i could help Soldier313
Click to expand...


JazakAllah khair for that :)
But erm my doubt is that how can we determine which of the alleles are more negative without being provided with the direction of movement of the fragments?
 
Alice123

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Soldier313 said:
For question 2 b ii of this paper, why does the ms state that the answer only has to be to 2 decimal places. And the er goes on to state that the answer should have been to 3 significant figures rather than 4. Isn't 0.66 2 sgf or am i confusing stuff here? :unsure:


And for the same year, qn 3 b iii, how can we know that I (ma) is the smallest allele or the most negatively charged one? I mean we aren't provided with the direction of movement of the fragments.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_ms_5.pdf

Thank you :)

Irfan1995 and anyone else taking p5
Click to expand...

and for 2bii
0.66 is 2sf...

dnt know about the significant figures, i think the results should have the same decimal places as the info given
@Irfaan1995 can answer better
 
Alice123

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Soldier313 said:
JazakAllah khair for that :)
But erm my doubt is that how can we determine which of the alleles are more negative without being provided with the direction of movement of the fragments?
Click to expand...

the smaller it is
  • the faster it move
  • it will be more towards the anode
  • the more negative it will be
 
Soldier313

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Alice123 said:
the smaller it is, the more negative
Click to expand...

um are you sure about that? coz it sounds kinda peculiar to me :p
I mean it's not always the case that the smaller the fragment the larger the charge right?

actually from what we've been taught, it is only when the direction of movement is provided, that we can determine the charge and size etc :( am so confused :unsure:
 
Alice123

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Soldier313 said:
um are you sure about that? coz it sounds kinda peculiar to me :p
actually from what we've been taught, it is only when the direction of movement is provided, that we can determine the charge and size etc
Click to expand...

you wont be penalised if you dont mention about the charge, only size will earn you full
Yea i am sure
 
I

Irfan1995

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Soldier313 said:
For question 2 b ii of this paper, why does the ms state that the answer only has to be to 2 decimal places. And the er goes on to state that the answer should have been to 3 significant figures rather than 4. Isn't 0.66 2 sgf or am i confusing stuff here? :unsure:


And for the same year, qn 3 b iii, how can we know that I (ma) is the smallest allele or the most negatively charged one? I mean we aren't provided with the direction of movement of the fragments.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_ms_5.pdf

Thank you :)

Irfan1995 and anyone else taking p5
Click to expand...

When dealing with standard errors, you don't work with significant figures. From what I know, the value and standard error should have the same number of decimal places.
Lets say that you want to measure things with a meter ruler (measures to the nearest mm). The length of a paper would be 29.7 cm (3 s.f), but the length of a finger could be about 5.2 cm (2 s.f). You wouldn't measure the finger as 5.20 cm (3 s.f) just for the sake that all measurements have to be to 3 s.f. In this case, the number of decimal places is a more appropriate measure of accuracy than significant figures.

Q3)b)iii)
If an electric field is applied, the force is the product of the charge and the electric field (F = qE). We also know that the force is the product of the mass and acceleration (F = ma)
Setting both of them equal:
qE = ma
a = (qE)/m
From the last equation, we can see that as mass decreases (smaller strands), the acceleration (hence speed) increases (and vice versa). In the typical gel electrophoresis, the charge density of every single strand is exactly the same.

However, in native gel electrophoresis/SDS-PAGE electrophoresis (I learnt about it last year in my school, but I don't think it's included in the A2 syllabus), the charge density varies. I'm not going to bother myself explaining how it works.
The important bit is that the acceleration is proportional to the charge density (see equation above), so pieces that have a greater charge will move faster (and vice versa)
 
I

Irfan1995

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externityxzx said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_51.pdf
answer: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_ms_51.pdf
can anyone please explain the answer for 1. (b)(i)? thanks!!
Click to expand...

Serial dilution:
Take 20 ml from the 4,000 mg/dm^3 solution and put it in a test tube.
Take 10 ml from that solution and put it in another test tube. Then add 10 ml of water. This is the 2,000 mg/dm^3 solution.
Take 10 ml from the 2,000 mg/dm^3 solution and put it in another test tube then add 10 ml of water. This is the 1,000 mg/dm^3 solution.
Keep on repeating the same procedure until you reach the 250 mg/dm^3 solution.
Take 10 ml from the 250 mg/dm^3 solution and throw it away. This is to keep the volume of all test tubes constant.

Good luck :)
 
Soldier313

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Irfan1995 said:
When dealing with standard errors, you don't work with significant figures. From what I know, the value and standard error should have the same number of decimal places.
Lets say that you want to measure things with a meter ruler (measures to the nearest mm). The length of a paper would be 29.7 cm (3 s.f), but the length of a finger could be about 5.2 cm (2 s.f). You wouldn't measure the finger as 5.20 cm (3 s.f) just for the sake that all measurements have to be to 3 s.f. In this case, the number of decimal places is a more appropriate measure of accuracy than significant figures.

Q3)b)iii)
If an electric field is applied, the force is the product of the charge and the electric field (F = qE). We also know that the force is the product of the mass and acceleration (F = ma)
Setting both of them equal:
qE = ma
a = (qE)/m
From the last equation, we can see that as mass decreases (smaller strands), the acceleration (hence speed) increases (and vice versa). In the typical gel electrophoresis, the charge density of every single strand is exactly the same.

However, in native gel electrophoresis/SDS-PAGE electrophoresis (I learnt about it last year in my school, but I don't think it's included in the A2 syllabus), the charge density varies. I'm not going to bother myself explaining how it works.
The important bit is that the acceleration is proportional to the charge density (see equation above), so pieces that have a greater charge will move faster (and vice versa)
Click to expand...



Wow, thanx a lot for the explanations......they really helped.....
 
Mairaxo

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Soldier313 said:
For question 2 b ii of this paper, why does the ms state that the answer only has to be to 2 decimal places. And the er goes on to state that the answer should have been to 3 significant figures rather than 4. Isn't 0.66 2 sgf or am i confusing stuff here? :unsure:


And for the same year, qn 3 b iii, how can we know that I (ma) is the smallest allele or the most negatively charged one? I mean we aren't provided with the direction of movement of the fragments.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_ms_5.pdf

Thank you :)

Irfan1995 and anyone else taking p5
Click to expand...
direction of movement is downwards so lighter ones moved most down. 0.66 is 2sf and 2dp.
 
Soldier313

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Mairaxo said:
direction of movement is downwards so lighter ones moved most down. 0.66 is 2sf and 2dp.
Click to expand...

Thank you, but the problem was that the qn paper hadn't specified the direction of movement, unless i missed seeing it somehow.
 
Soldier313

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Aoa wr wb
Can someone please upload the histogram for qn 1 of this paper, i mean usually histograms have intervals along the x-axis right?
I can't decide the width of the bars :(

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_ms_5.pdf
_____________

And for qn 2 a of this paper, i am getting 13 % as my value, but the ms says 12 % . I don't get where i may have done a mistake

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_5.pdf
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_ms_5.pdf
 
Mairaxo

Mairaxo

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Soldier313 said:
Aoa wr wb
Can someone please upload the histogram for qn 1 of this paper, i mean usually histograms have intervals along the x-axis right?
I can't decide the width of the bars :(

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_ms_5.pdf

_____________

And for qn 2 a of this paper, i am getting 13 % as my value, but the ms says 12 % . I don't get where i may have done a mistake

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_5.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_ms_5.pdf
Click to expand...
Q2- find the mean of both. before coffee=0.1725 after coffee=0.1525 subtracting them u get 0.02. then 0.02/0.1725*100 u get 11.59 thats almost 12% :)
 

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