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A level Biology: Post your doubts here!

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phanttasy

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My Name said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_12.pdf
Questions
19-Answer is A.Please briefly explain the function of telomeres.
22-Answer is C.How?
30-I find it hard to relate what happens when in these diagrams.Any help?
32-Answer is D.
37-Answer is D.I marked A.
Click to expand...

19: Telomere does not have any genetics material. It protect the ends of the chromosomes. It will "degenerate" in each nuclear division. So the cell will stop dividing if there is no telomere. If there is no telomere, the nitrogenous base in the end of chromosome will be "degenerate", so the genetic material cannot be pass down to the daughter cells.
22: DNA molecules are made up of 2 strands of DNA polynucleotides. So each strands can have 350 nucleotides. The maximum hydrogen bond between 2 nitrogenous bases is 3, so the maximum hydrogen bond in the DNA molecules is 3x350=1050
30: Y is always the vessel that carry the blood out from the heart eg, pulmonary artery and aorta. X has a similar pressure to Y, X has to be the ventricle as ventricle pumps blood into Y. Z is atrium as it has a lower pressure than X.
32:the valves is narrowed means the blood will be back flowed into the ventricle again. So the oxygenated blood transported to the rest of the body is less. So the wall of the ventricle become thicker to pump blood at higher pressure and the heart beat rate will actually become faster.
37: B cells is only stimulated later .. I think.. because B cells will only divide and differentiate when its receptor bind to the foreign antigen on the APC or stimulated bu the cytokine which is secreted by the T cells.

i had tried my best to explain your question based what i understood and learned from my lectures hope you can understand... and sorry for my broken English
you can check the function about the Telomere in the new CIE Biology coursebook
 
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phanttasy said:
19: Telomere does not have any genetics material. It protect the ends of the chromosomes. It will "degenerate" in each nuclear division. So the cell will stop dividing if there is no telomere. If there is no telomere, the nitrogenous base in the end of chromosome will be "degenerate", so the genetic material cannot be pass down to the daughter cells.
22: DNA molecules are made up of 2 strands of DNA polynucleotides. So each strands can have 350 nucleotides. The maximum hydrogen bond between 2 nitrogenous bases is 3, so the maximum hydrogen bond in the DNA molecules is 3x350=1050
30: Y is always the vessel that carry the blood out from the heart eg, pulmonary artery and aorta. X has a similar pressure to Y, X has to be the ventricle as ventricle pumps blood into Y. Z is atrium as it has a lower pressure than X.
32:the valves is narrowed means the blood will be back flowed into the ventricle again. So the oxygenated blood transported to the rest of the body is less. So the wall of the ventricle become thicker to pump blood at higher pressure and the heart beat rate will actually become faster.
37: B cells is only stimulated later .. I think.. because B cells will only divide and differentiate when its receptor bind to the foreign antigen on the APC or stimulated bu the cytokine which is secreted by the T cells.

i had tried my best to explain your question based what i understood and learned from my lectures hope you can understand... and sorry for my broken English
you can check the function about the Telomere in the new CIE Biology coursebook
Click to expand...
In question 22 why don't we multiply the number 700 by 3?

Actually the question 30 of this year is easy,but when in other papers they ask for when the valves are open..thats where I find it hard. So any thing for that,please?

Thank you for your help!
Btw I do not have the new coursebook.
 
phanttasy

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My Name said:
In question 22 why don't we multiply the number 700 by 3?

Actually the question 30 of this year is easy,but when in other papers they ask for when the valves are open..thats where I find it hard. So any thing for that,please?

Thank you for your help!
Btw I do not have the new coursebook.
Click to expand...

Because the hydrogen bond is between 2 nitrogenous bases on each strand..
If we multiply 700 by 3, it means that there are 700 nucleotides on each strand of DNA molecules. Since a DNA molecules has 2 strands of polynucleotides, there will be a total of 1400 nucleotides in the DNA molecules.

The question says that " in the length of DNA containing 700 nucleotides", it means that the total number of nucleotides of both strands is 700, which makes one strand having 350 nucleotides
 
phanttasy

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ashcull14 said:
View attachment 57523
Click to expand...
see the picture for the working.
the question ask the total time when both atrio-ventricular(AV valve) and semi-lunar valve(SL valve) closed at same time
so the time is basically the time between closing of (AV valve / SL valve) and the time just before the opening of (SL valve / AV valve)
the time between closing of AV valve and opening of SL valve is 0.03s, and the time between the closing of SL valve and opening of AV valve is 0.04s

hope you can understand my explanation ><
 

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    bio mcq j11 p12.PNG
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ashcull14

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phanttasy said:
see the picture for the working.
the question ask the total time when both atrio-ventricular(AV valve) and semi-lunar valve(SL valve) closed at same time
so the time is basically the time between closing of (AV valve / SL valve) and the time just before the opening of (SL valve / AV valve)
the time between closing of AV valve and opening of SL valve is 0.03s, and the time between the closing of SL valve and opening of AV valve is 0.04s

hope you can understand my explanation ><
Click to expand...
omg thank u so muchh its very well explained MA...got it :)
 
phanttasy

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My Name said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_11.pdf
question
18 Answer is C.
27 Answer is A.What are the parts labelled?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_12.pdf
question
15
17
Click to expand...

upload_2015-11-8_23-3-12.png
Not very sure about the plant part but I think is like this...

upload_2015-11-8_23-3-37.png
Blue represent hyrdrophilic region and yellow represent hydrophobic region
upload_2015-11-8_23-3-44.png

Please correct me if i am wrong! Let learn from the mistake ：D I just a student who will be completing his AS soon haha ! hope you can understand my explanation
 
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phanttasy said:
View attachment 57527
Not very sure about the plant part but I think is like this...

View attachment 57528
Blue represent hyrdrophilic region and yellow represent hydrophobic region
View attachment 57529

Please correct me if i am wrong! Let learn from the mistake ：D I just a student who will be completing his AS soon haha ! hope you can understand my explanation
Click to expand...
Thank you so much for your help!
For hyrdrophilic region and hydrophobic region...I did not learn in detail.:/
 
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