A level Biology: Post your doubts here!

[♣♠ Magnanimous ♣♠]

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.

Well, relate this pic with that figure in paper and label it
Here you go -->

 

[MariamEltawil]

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.

 

[Saad Amjad.]

how was p42 guys??

 

[Saad Amjad.]

why is no one answering??..im expecting gt to be below 60..:/

 

[♣♠ Magnanimous ♣♠]

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.

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
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.

 

[Saad Amjad.]

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.

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

 

[ShreeyaBeatz]

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

Hi Amjad
yes I did yesterday
How much do you expect the threshold to be
The second last question was pretty hard :/

 

[Saad Amjad.]

im guessing it to be below 6o for sure..the suggest questions were tricky :/

 

[buddy097]

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.

 

[DarkEclipse]

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.

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]

 

[DarkEclipse]

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.

All of them, except antibody production.

 

[Saad Amjad.]

Hi Amjad
yes I did yesterday
How much do you expect the threshold to be
The second last question was pretty hard :/

im guessing it to be below 6o for sure..the suggest questions were tricky :/

 

[ShreeyaBeatz]

im guessing it to be below 6o for sure..the suggest questions were tricky :/

yeah!
what did you write for name A, B and C ?

 

[Saad Amjad.]

yeah!
what did you write for name A, B and C ?

lol left it just 3 marks..well im checking how's everyone's exam just to guess the gt..btw what did you give for A,B and C??

 

[ShreeyaBeatz]

lol only knew that A was RuBP hahha

 

[Wolfgangs]

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*?

 

[DarkEclipse]

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*?

It isn't really possible. How much did you score?

 

[Wolfgangs]

It isn't really possible. How much did you score?

I scored B in Paper 11, A/B in Paper 21 and C in Paper 31.

 

[DarkEclipse]

I scored B in Paper 11, A/B in Paper 21 and C in Paper 31.

I meant your percentage.

 

[ABC12348]

A= Rubp B=fatty acids C=glucose. what did you write?