A level Biology: Post your doubts here!

[Mohammed salik]

Can someone please explain why ans should be B ?!

which year is this ?

It says NOT.
Ans is B
So 1 Occurs in alveoli where it picks up oxygen, in tissues it should be other way around.
and 3: The Hydrogen carbonate ion and H+ also combine in alveoli to form H2CO3. In tissues CO2 dissolves in H20 to give H2CO3 which must disassociate to form Hydrogen carbonate ion for transport within the Plasma.
Hope I helped!

 

[sumeru]

Can someone please explain how to do this?

Here is the calculation,from 1st diagram
50 eyepiece divisions=0.1 stage
1 EP=0.1/50 stage
Convert it to micrometer,
1EP=0.1/50 multiplied by 1000, which is 2 micrometer.
Now from 2nd diagram,
The increment in 4 hours is 10 division
So 1 division of EP=2
10 division of EP=2 into 10
=20
so in 4 hours, there is increment of 20 micrometer
In 1 hour=20/4
=5
So the answer is A.

 

[sumeru]

Can someone please explain why ans should be B ?!

Ok, 1 can't be correct, because in an active tissue, high amount of co2 are produced, so in the presence of co2, you can't expect HB to react with O2.
2 can be correct, because, you know that, co2 diffuses into the RBC and it forms H2CO3, catalysed by carbonic anydrase...the H2C03 dissociates into H+ AND HCO3-,Now the HB reacts with this H+ to form HHB.
3 can't be correct because as i mentioned H2CO3 DISSOCIATES to H+ and CO3-.......the reaction shown in 3 actually occurs in the alveoli.......
4 is correct which i explained above.....
Now the question asks you, which are not likely to accur....so your answer should be 1 and 3, which is B...

 

[sumeru]

So, guys exams are almost here...so if any of us has any confusions in any topic....let us discuss here and try to get clear of all the doubts we have.....

 

[Karim Nabil]

So, guys exams are almost here...so if any of us has any confusions in any topic....let us discuss here and try to get clear of all the doubts we have.....

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!

 

[alevelnerd]

How do mitosis facilitate gamatogenesis??

 

[midha.ch]

http://www.mediafire.com/download/smfz60x62dw4by5/Cambridge_International_Biology.pdf

I need the coursebook not the revision guide :/

 

[Karim Nabil]

I need the coursebook not the revision guide :/

well, this is the only book i was able to come up with.....
i don't think the coursebook is for free,and revision is better cause you got no enough time to start learning...it's only a week to start the exams !

 

[joanna omar]

How do mitosis facilitate gamatogenesis??

Okay so its is just mitosis then no need to talk about meiosis at all :
In males:
1)The process beings at the outer edge of germinal epithelium and new cells that are produced form towards the inner edge.
2)SPERMATOGONIA are cells attached to the epithelial layer of smeiniferous tubule,These cells are diploid and they divide by mitosis to form more spermatogonia
3) these cells they mature and increase in size to form primary spermatocytes.

In females:
1)after fertilistaion,germinal epithial cells they start to divide by mitosis to form diploid oogonia five weeks after formation of female embryo

Hope this helped

 

[joanna omar]

So, guys exams are almost here...so if any of us has any confusions in any topic....let us discuss here and try to get clear of all the doubts we have.....

That would be great,even we could decide to do topical revision until exams.

 

[Mashal zeb]

PlZz help me out

 

[Mashal zeb]

Plzz expain me thez questions

 

[joanna omar]

PlZz help me out

okay they said not involved
AUC its tRNA is UAG so not C
GUA(val) its tRNa is CAU so not A
GAA(glu) its tRNA is CUU so not B either
C,A and B are involved
so left out with answer is D where its is not involved

 

[Gehad Mohamed]

It says NOT.
Ans is B
So 1 Occurs in alveoli where it picks up oxygen, in tissues it should be other way around.
and 3: The Hydrogen carbonate ion and H+ also combine in alveoli to form H2CO3. In tissues CO2 dissolves in H20 to give H2CO3 which must disassociate to form Hydrogen carbonate ion for transport within the Plasma.
Hope I helped!

O/N 2013 p 13
Thnx alot

 

[Gehad Mohamed]

Ok, 1 can't be correct, because in an active tissue, high amount of co2 are produced, so in the presence of co2, you can't expect HB to react with O2.
2 can be correct, because, you know that, co2 diffuses into the RBC and it forms H2CO3, catalysed by carbonic anydrase...the H2C03 dissociates into H+ AND HCO3-,Now the HB reacts with this H+ to form HHB.
3 can't be correct because as i mentioned H2CO3 DISSOCIATES to H+ and CO3-.......the reaction shown in 3 actually occurs in the alveoli.......
4 is correct which i explained above.....
Now the question asks you, which are not likely to accur....so your answer should be 1 and 3, which is B...

Thank u soooo much

 

[Gehad Mohamed]

which year is this ?

O/N 2013 p 13

 

[mehria]

Plzz expain me thez questions

Hey post the year n variant aswell

 

[Karim Nabil]

PlZz help me out

in such questions related to genetics
first we have to make these >> DNA>mRNA>tRNA>amino acid
sickle cell haemoglobin > thr-pro-val-glu
mRNA codons are supplied for these amini acids by the question so first find complementary anticodons for each codon
complementary anticodons are>glutamine (glu) CUU or CUC ; proline (pro) GGA or GGG ; threonine (thr) UGA or UGG , valine (val) CAU or CAC
in the question there are only 4 options see the anticodon that is not written as above which is D

 

[Mohammed salik]

Plzz expain me thez questions

Q28) First Finf the time taken from One As to the Diastole (This is equivalent to One heart beat). the time is 0.75s.
so 1 heartbeat =0.75
x in 60sec
X=60/0.75=80 ans IS C.
Q29) plz learn this http://classconnection.s3.amazonaws...ressure_during_cardiac_cycle1320119803186.jpg
Q23) There are three Hydrogen bonds So it could only be Cytosine and Guanine bcz Adenine and thymine have two Hydrogen bonds ans is C

HOPE I HELPED

 

[Mohammed salik]

Plzz expain me thez questions

Q16) C just look at Graph where it givves No change in (Initial/Final lenght) (Between 0.98 and 1.00) it gives 0.45 ans is C