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A level Biology: Post your doubts here!

♣♠ Magnanimous ♣♠

♣♠ Magnanimous ♣♠

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Lola_sweet said:
In paper 3 when we have to plot a graph is it a must the x-axis starts with 0 like igcse bcuz this markscheme shows the axis starting with 5

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_ms_31.pdf

Qs 1)b)ii)

Also hw is the mean in Qs 1)b)i) 85
my answer is 77

Qs paper:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_31.pdf
Click to expand...
Well it can start with 5 but there should Z on x axis. Remember in Maths of IGCSE!
And yeah that 85 is wrong answer in mark scheme.
It is 77.2
Sometimes there are mistakes in the markschemes. :)
 
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♣♠ Magnanimous ♣♠

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Saad Amjad. said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_42.pdf can someone please help me with 4(b)..its labeling of the seminiferous tubule.
Click to expand...
Well, relate this pic with that figure in paper and label it :)
Here you go -->
clip_image00817.jpg
 
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MariamEltawil said:
Could someone answer this please?
What is the maximum and minimum numer of hydrogen bonds in a length of DNA containing 700 nucleotides and why?
I just don't get it :/ thanks in advance.
Click to expand...
Well I am unsure but I will try.

700 nucleotide.
Hydrogen bonds are present between the Nitrogenous Bases ( A T G C )
A (adenine) can only form hydrogen bonds with T (thymine) and C (cytosine) can only form bonds with G (guanine)
A form two hydrogen bonds with T i.e. A=T
and G form THREE hydrogen bonds with C.
One nucleotide has onebase pair i.e. A=T. This whole is one base pair :p
So now 700 nucleotide means 700 nitrogenous bases. But the number of hydrogen bond will be diff coz Aand T two H bond and in G and C three H bonds.
So 700/2 = 350 for all those nitrogenous bases who have 2 H bonds and another 350 who have 350 for for all those nitrogenous bases who have 3 H bonds.
Now, 350*2 ===> 700 (2 H bonds nitrogenous bases).
and 350*3 ==> 1050 (3 H bonds)
Sum is 700 + 1050 -> 1750 is answer.

I am 99% unsure though I thought of this thing.
I hope you check the answer in book.
 
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Saad Amjad.

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♣♠ Magnanimous ♣♠ said:
Well it can start with 5 but there should Z on x axis. Remember in Maths of IGCSE!
And yeah that 85 is wrong answer in mark scheme.
It is 77.2
Sometimes there are mistakes in the markschemes. :)
Click to expand...
did you sit for bio p42 today??..i really need to discuss the answers with someone..confused abt a few questions...or if you could tag someone who might..thanks in advance :)
 
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buddy097

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Which of the following occur due to mitosis? Cell repair,Cell replacement,the production of antibodies from B lymphocyte memory cells and the production of root hairs.
 
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DarkEclipse

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MariamEltawil said:
Could someone answer this please?
What is the maximum and minimum numer of hydrogen bonds in a length of DNA containing 700 nucleotides and why?
I just don't get it :/ thanks in advance.
Click to expand...

The hydrogen bonds between A-T is double, and between G-C, it's triple.
The maximum number would be if the entire length of DNA would contain G-C. This means 700 pairs of G-C.
Therefore:
700 (total nucleotides) * 3 (total hydrogen bonds) = 2100. [MAXIMUM]
2100 Hydrogen bonds is the maximum number.

Now, the minimum one is a little complicated. Traditionally, since A-T have double bonds, and if we assume that the entire length of DNA would contain A-T, this would give 700*2 = 1400 bonds. But the two hydrogen bonds between A-T and the three bonds between G-C form to achieve stability. Therefore, if we assume that the DNA molecule is unstable, and if we assume that the entire length of DNA would contain A-T, then we'd have to also assume that this is due to single bonds between A-T, which does not achieve stability. Therefore, 700 nucleotides with one bond per nucleotide:
700*1 = 700. [MINIMUM]
 
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Wolfgangs

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I have a question related to my grades. In AS Levels May/June 2014 session, I scored "a" in Mathematics and Physics, while I scored "c" in Biology (I know that my overall grade is bad). Is it still possible to score an overall A in Biology? By what percent is it possible? What about A*?
 
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Wolfgangs said:
I have a question related to my grades. In AS Levels May/June 2014 session, I scored "a" in Mathematics and Physics, while I scored "c" in Biology (I know that my overall grade is bad). Is it still possible to score an overall A in Biology? By what percent is it possible? What about A*?
Click to expand...
It isn't really possible. How much did you score?
 
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