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A level Biology: Post your doubts here!

Karim Nabil

Karim Nabil

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Mashal zeb said:
Somebody explain ths question plz
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At the first the egg cell was haploid cell (1n) , then after fertilization occurs, it became a diploid cell (2n), after that cell is in interphase where growth and DNA replication occurs(almost 90% of the cell cycle time),in interphase cell became 4n, the cell enters mitosis with the same quantity of DNA (4n), and then at telophase(X)
the number of DNA(4n) is halved to (2n) for the two Daughter cells to have the same identical number of DNA as the body cells
so the answer is D, hope that helped you!
 
Mashal zeb

Mashal zeb

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Karim Nabil said:
At the first the egg cell was haploid cell (1n) , then after fertilization occurs, it became a diploid cell (2n), after that cell is in interphase where growth and DNA replication occurs(almost 90% of the cell cycle time),in interphase cell became 4n, the cell enters mitosis with the same quantity of DNA (4n), and then at telophase(X)
the number of DNA(4n) is halved to (2n) for the two Daughter cells to have the same identical number of DNA as the body cells
so the answer is D, hope that helped you!
Click to expand...
It did thank u so muchh :)
 
ZaqZainab

ZaqZainab

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NinjaInPyjamas said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_1.pdf

q37 q26 please!
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37. When an antigen enters for the first time primary response takes place. to make antibodies cells undergo clonal selection to produce a colony of cells that are specific for the antigen. Most of these clones differentiate into the plasma cells, also called effector B cells (which produce the antibodies) , and the rest are memory cells. which survive for longer. so there are memory cells made and still present till 20 days
26 the attachment
 

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NinjaInPyjamas

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ZaqZainab said:
37. When an antigen enters for the first time primary response takes place. to make antibodies cells undergo clonal selection to produce a colony of cells that are specific for the antigen. Most of these clones differentiate into the plasma cells, also called effector B cells (which produce the antibodies) , and the rest are memory cells. which survive for longer. so there are memory cells made and still present till 20 days
26 the attachment
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Jazakh'Allah khair sister! :D
 
Mashal zeb

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Can somebody help me wd da last question :-/ i realy did nt get it
 

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Karim Nabil

Karim Nabil

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Mashal zeb said:
Can somebody help me wd da last question :-/ i realy did nt get it
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amino acid=3 nucleotides
in DNA we have double strand, one sense strand carrying all info. and other anti-sense strand that is only complementary strand used to stabilize DNA molecule
so we divide 6000 by 2 as only one strand is carrying info.=3000
1 amino acid= 3 nucleotides
x amino acid= 3000 nucleotides
x=3000/3= 1000 amino acids
so the answer is B :)
 
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Mohammed salik

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joanna omar said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_11.pdf

Can Anyone help me out in paper 1 doubts !!

june 2011 v1 ----> Q6 -Q11 -Q14 -Q25 -Q35 -38
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Q6 :- (A)The question asks for greatest mass of Non- Reducing sugar, which means the difference between Before and after Hydrolysis must be greatest, which is in A!
Q11:-(A) Triglycrides dont have Hydrogen bonds, So Not D.Cellulose has Hydrogen bonds so Not B either. Collagen is helical in nature (not branched) so not C. Ans is A
Q14:-(C) If the inhibitor binds to E-S complex then active site doesnt change shape. so 1 is wrong. and With inhibitor V(max) never increases, so Ans is C!
Q25:-(B)5 is wrong because they are in Dry conditions, So only ans is B or C. Fewer Stomata would reduce gas exchange so the ans is B.
Q35:-(D) Emphysema has no Link with Atheroma(cant be C). Tar causes more Mucus (if he stopped smoking, so A is wrong).Stopped smoking reduces inflamation to lung tissues so Macrophage decrease. Only other option is D.
Q38:-(A) Vaccine dont only work against viruses, bcz there r vaccines for TB as well,, so only option without 4 is A.
Hope i Helped :). if u need detailed explanation do let me Know!
 
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Mohammed salik

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roxylara said:
It's may/June 2007 Q4. Yes the answer is A. How'd you do it?
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First find Out What One unit on Graticule represents.
It says the Slide has division of 0.1 mm, which are equivalent to 50 on Graticule. So 1 division on Graticule is 0.1/50 =0.02 mm.
Now look at Diagram One, Take the pollen which grows Straight (parallel to scale), Then place a ruler and see the increase in its size after 4 hours, which turns out to be from 25-35 which is 10 Graticule units. the actual Increase is 10 * 0.02=0.2 mm , But this is in 4 Hours. the question asks for One Hour , then divide this value by 4 which gives 0.05 mm = 5 Micrometer Per Hour.
Hope i Helped :)!
 
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