A level Biology: Post your doubts here!

[A*****]

Bio View attachment 63761 View attachment 63762 Bombs Away!!!View attachment 63760 I understand that the objective lens should be x10 but why must the eyepiece lens be x5?

After dividing once, all DNA will be 14+15 so all will be at L and after 2 divisions, there will be half 14+14 and half 15+14

 

[Kanekii]

After dividing once, all DNA will be 14+15 so all will be at L and after 2 divisions, there will be half 14+14 and half 15+14

im still a bit confused in this i dont understand the 2nd division part sorry for my dumbness

 

[A*****]

im still a bit confused in this i dont understand the 2nd division part sorry for my dumbness

I hope this is understandable...the red ones are those from the original strand and the green ones are the newly synthesised strands....because it is cultured in a medium containing N-14 only, so all the new strands will be N-14

 

[innovative_1]

Hisham Khan

 

[A*****]

Hisham Khan

Oh did a great effort that u found this!
I was even not satisfied with it

 

[A*****]

Hisham Khan

It's an open challenge Hisham Khan plz clarify us

 

[innovative_1]

It's an open challenge Hisham Khan plz clarify us

Oh yes pls hisham be right here we r waiting for u actually we got really impressed from ur last performance so it would be good to hear from u again

 

[Kanekii]

I hope this is understandable...the red ones are those from the original strand and the green ones are the newly synthesised strands....because it is cultured in a medium containing N-14 only, so all the new strands will be N-14

This is just perfect thanks

 

[A*****]

This is just perfect thanks

Glad that it helped

 

[innovative_1]

One thing more pls hisham this time control ur angry birds don't let them to escape it's my humble request

 

[kirzzz]

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]

2100 is not the maximum number of hydrogen bonds. since there are two strands of DNA, we divide 700 by 2, which is equal to 350 base pairs.
G-C pairs have three hydrogen bonds as opposed to two hydrogen bonds between A-T pairs. we assume that all the nucleotides are G-C to maximize the number of hydrogen bonds (as the question states).
therefore, if 1 base pair equals three hydrogen bonds, how many hydrogen bonds exist between 350 base pairs? cross multiply and youll get the answer as 1050, which is the option C

 

[Hisham Khan]

 

[SohaibButt]

Need help

 

[kirzzz]

Need helpView attachment 63774 View attachment 63775 View attachment 63776

is the answer to question 14 A?

 

[Hisham Khan]

Need helpView attachment 63774 View attachment 63775 View attachment 63776

14:A
13:C I guess
17:B?

 

[kirzzz]

wait

14:A
13:C I guess
17:B?

wait so the answer is A?

 

[Hisham Khan]

is the answer to question 14 A?

yes

 

[SohaibButt]

Y

wait

wait so the answer is A?

Yup it's A

 

[kirzzz]

Need helpView attachment 63774 View attachment 63775 View attachment 63776

the answer for question 13 is B (i guess) because look;
A - is partially true, the cell surface membrane and the membranes of the organelles allow intracellular transport but they also allow extracellular transport. because the term "extracellular transport" is not stated, im guessing that A is only partially true.
B - seems the correct option because the carbohydrate chains that are present on glycoproteins form hydrogen bonds with water molecules and help to stabilise the membrane structure.
C - not really sure but why would enzymes attach to the membranes of organelles?
D - lyzomes themselves have a membrane to prevent their contents from coming into contact with other organelles so why would the membranes protect the organelles?

 

[SohaibButt]

wait

wait so the answer is A?

In q17 why 2 is wrong? The rate of active transport doesn't increased if higher conc inside the vacuole?