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A level Biology: Post your doubts here!

A

asma tareen

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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...
agha saad 22
 
A

asma tareen

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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...
agha saad 22
 
bubbles1997

bubbles1997

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@yesha said:
Hmmm.. Thanks.. Bt still i'll appreciate if u can give me some more tips... :)
Click to expand...
your're welcome. Well, solve a full year papers theory like May/June - Oct/Nov 2013 with the help of marking scheme. underline those questions which you don't understand because there are few students who are great at theory but their question COMPREHENSION is weak. Try to understand what the examiner wants. When you've done with it, solve the rest of the papers.
I hope it will be helpful! Please pray for me as well.
 
S

sumeru

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10 is B because in amine acid which is H2N-C(R)H-COOH, when a peptide bonds form one amino acid looses the OH from carbo-oxyl group and other looses the H from its amine group...keeping this concept, if u look the options B is the correct one.
13 is B ...When triglyceride is hydrolysed, the product is fatty acid, which contains COOH, which is a acid and this decreases the pH.
25 is D...At night there is low rate of transpiration s0 there is less pressure which means the xylem will be broader....like pressure is inversely proportional to the diameter.
26 is D because when the sucrose is loaded into phloem, it's flow does not depends on each other, they can flow in either direction in two different phloems....but since they are loaded from the leaf, they occur at the same time.....
31 is B ...the question says "the tubes of the gas exchange system narrow and extramucus is produced."...so more mucus means, ciliated epithelium has to work fast to remove the mucus and the tubes narrow, smooth muscle expands and contracts faster, because with narrower gas exchange system...it will be difficult to breathe....
 
N

NinjaInPyjamas

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sumeru said:
10 is B because in amine acid which is H2N-C(R)H-COOH, when a peptide bonds form one amino acid looses the OH from carbo-oxyl group and other looses the H from its amine group...keeping this concept, if u look the options B is the correct one.
13 is B ...When triglyceride is hydrolysed, the product is fatty acid, which contains COOH, which is a acid and this decreases the pH.
25 is D...At night there is low rate of transpiration s0 there is less pressure which means the xylem will be broader....like pressure is inversely proportional to the diameter.
26 is D because when the sucrose is loaded into phloem, it's flow does not depends on each other, they can flow in either direction in two different phloems....but since they are loaded from the leaf, they occur at the same time.....
31 is B ...the question says "the tubes of the gas exchange system narrow and extramucus is produced."...so more mucus means, ciliated epithelium has to work fast to remove the mucus and the tubes narrow, smooth muscle expands and contracts faster, because with narrower gas exchange system...it will be difficult to breathe....
Click to expand...
thank you really helped! :)
 
S

sumeru

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joanna omar said:
Please anyone ....Help me in paper 1 Doubts ?
June 04 ---> Q7 - Q19
Nov 04 ---> Q25
June 05 ---> Q11 -
Nov 05 ---> Q20 - Q24 - Q33 - Q38

sumeru
Click to expand...
June 4
Q.7 is C....for this you have a formula which is N^r.....where N is the no of amino acids....and r is no of peptides you want to make...like in this question r is 2(dipeptide)...s0 12^2=144
Q.19 is B...this is pretty easy......reduction division means the chromosomes are haploid..i.e they turn into haploid from diploid....so, for the first diagram, it is S where haploid is formed from diploid and for the second one it is V where gametes are formed...and gametes are haploid...so the answer is B
 
S

sumeru

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joanna omar said:
Please anyone ....Help me in paper 1 Doubts ?
June 04 ---> Q7 - Q19
Nov 04 ---> Q25
June 05 ---> Q11 -
Nov 05 ---> Q20 - Q24 - Q33 - Q38

Alazne Diamond
Click to expand...
Nov 4
Q.25 is D...well i can't tell you specific reasons for D but i can tell you why A B C might be incorrect if you want.
June 5....
Q.11 is D...Because A is incorrect alpha helix is a secondary structure and at ph 2, it has secondary structure.....B is incorrect because it only has secondry structure so you don't need to concern on its tertiary structure....C is incorrect because it is now a random coil, so its primary structure is still intact but at ph 10 it has completly lost the alpha helix...so it's secondary structure is lost
Nov 5
Q.20...B...Because mitosis means cells are produced which are genetically identical...so 2n produces 2n...
Q.24...B...Because adenine pairs with thymine and when uracil is present then thymine is absent in question, now if you look at the question...the % are similar in B and C and when Uracil is present C is absent, which means in the presence of uracil, C (Thymine ) is not there and C had similar % with B ...then B must be adenine
Q.33...C ...because vital capacity is the minimum volume of air that can be breathed in and then breathed out by the lungs....so the differnce between the volume at full inspiration and full expiration should give you the answer...
 
Karim Nabil

Karim Nabil

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5.GIF


its answer is B, any explanations cause i just squeeze my mind trying to believe it is B
 
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