A level Biology: Post your doubts here!

[Mohammed salik]

Plzz expain me thez questions

Q20) Distance between centromere and poles decrease as time goes on Because The get pulled towards the pole so i should be 1! Now asn could only be A or B.
Distance between centromere of SISTER CHROMATIDS increase because they become seprated and pulled towards the pole so it should be 2. So the Answer is A.!
DO YOU NEED Q21 ASWELL?

 

[mehria]

Plzz expain me thez questions

Q21 => first of all note that UAG is for RNA while we r given the strand of a DNA...
so for ths question if we put T at position A then it'll gve TTC i.e. AAG n that's nt the stop codon... then move to the option B.. when we put T in between A n C it'll gve ATC and when we cnvert it in RNA strand then it'll chnge to UAG.. n yahi stop codon hai to ths is the correct ans

 

[mehria]

Q20) Distance between centromere and poles decrease as time goes on Because The get pulled towards the pole so i should be 1! Now asn could only be A or B.
Distance between centromere of SISTER CHROMATIDS increase because they become seprated and pulled towards the pole so it should be 2. So the Answer is A.!
DO YOU NEED Q21 ASWELL?

i did that for her but if i've done any mistake then do correct it

 

[Mohammed salik]

Q21 => first of all note that UAG is for RNA while we r given the strand of a DNA...
so for ths question if we put T at position A then it'll gve TTC i.e. AAG n that's nt the stop codon... then move to the option B.. when we put T in between A n C it'll gve ATC and when we cnvert it in RNA strand then it'll chnge to UAG.. n yahi stop codon hai to ths is the correct ans

Perfect

 

[Karim Nabil]

Plzz expain me thez questions

q28 june 2008 > one complete cycle is atrial systole (AS) + ventricular systole (VS) + ventricular diastole, in the figure one heart beat takes 0.75s, cross multiply
1 beat=0.75s
x beat=60s
x=60/0.75=80 beats per minute ; answer is C
q29> in this graph 3 and 4 for atrio-ventricular valves(tricuspid or bicuspid valves) and 1 and 2 is for semi-lunar valves
at position 3 bicuspid valve closes and at position 4 it opens
at position 1 semi-lunar valves opens and at position 2 it closes

at q23>first, question says that they are bases in a DNA so no uracil
secondly, they are bonded by 3 hydrogen bonds so it is only cytosine and guanine
thirdly, guanine is a purine which is a 2 ring structure while cytosine is a pyrimidine which is a 1 ring structure, answer is C

q20>

• distance between centromeres and poles of spindle is same or little variations happens at metaphase as they are are arranged at equator then after some time anaphase happens where distance decrease, this is best descriped by curve 1
• as they are in anaphase distance between centromeres of sister chromatids increase as they are pulled to opposite poles, this is best descriped by curve 2
• distance between poles of spindle is relatively increasing as poles are moving to opposite poles, this is best descriped by curve 3

answer is A

q21> stop codon for transcription is UAG
we have to find the complementary DNA code which is ATC
in this question he gaves you some codes and ask for where to place the T, it should be b/w A and C ; answer is B

Q16>initial length/final length means the ratio of initial to final, same water potential means no change in length then ratio have to be 1 , extend line from 1 in y-axis to the curve and see corresponding value at x axis, answer is C

 

[mehria]

Plzz expain me thez questions

Q16=> Jani ths is the same question we did at scul..... at y-axis we r given with initial/final.. so when the water potential is same then no osmosis will occur n there will b no chnge in length... suppose that the actual length of the potato strip is 2cm ...as there is no osmosis the initial/final=2/2= 1 cm... so frm the graph on y-axis check where it is given the value of 1..then read the x-axis reading at that point n u'll get ur ans... n that is 0.45s ....

 

[Snowysangel]

Is meiosis in the As level syllabus?

 

[mehria]

Is meiosis in the As level syllabus?

no... but still u shud knw the basics of it that we've studied in igcse or olevels

 

[Karim Nabil]

Is meiosis in the As level syllabus?

yes...
all you have to know about meiosis is as follows:

1. definition
2. number of daughter cells produced
3. type of offspring produced
4. no. of chromosomes in each human cell
5. type of cells produced
6. use of this process

 

[mehria]

yes...
all you have to know about meiosis is as follows:

1. definition
2. number of daughter cells produced
3. type of offspring produced
4. no. of chromosomes in each human cell
5. type of cells produced
6. use of this process

so isn't it the same as it was in olevels?

 

[alevelnerd]

why does concentration of urea increase in distal collecting tubule and collecting duct????

 

[Karim Nabil]

so isn't it the same as it was in olevels?

i told her what i know......
it maybe in o-level but don't expect me to remember the syllubus i've finished 1 year ago !!

 

[Mashal zeb]

Thank u so muchhh nabil, mehria and salik dat realy helped! So nyc of u

 

[mehria]

Thank u so muchhh nabil, mehria and salik dat realy helped! So nyc of u

post ur other doubts in that thread... n stop sayng thanks to me.....

 

[Snowysangel]

yes...
all you have to know about meiosis is as follows:

1. definition
2. number of daughter cells produced
3. type of offspring produced
4. no. of chromosomes in each human cell
5. type of cells produced
6. use of this process

But the different phases/stages of meiosis aren't, am I right?

 

[joanna omar]

But the different phases/stages of meiosis aren't, am I right?

Yes, this is just in A.2 ,,,,,,,all u need to know is about mitosis stages only

 

[sumeru]

i am in doubt with potometer , i don't have for it enough info.... can it come in 4 marks question?
there is repeated question for diseases that can be cured by anibiotics in p1, i know that virus an and any eukaryotic organisms cannot be cured due to many stains they have, but it is sometimes tricky!

Potometer is not that difficult....just go through the book once, i think you will understand it....and i have seen a potometer related question in p2..so there's a chance

 

[alevelnerd]

why does concentration of urea increase in distal collecting tubule and collecting duct????

 

[Karim Nabil]

But the different phases/stages of meiosis aren't, am I right?

yes, they aren't required by AS-qualification as joanna omar says

 

[Igcse stuff]

does anyone have good summarized bio AS and A level notes, really need them