A level Biology: Post your doubts here!

[joanna omar]

View attachment 39470View attachment 39470 what is the answer and explanation please..

Is it C ? Cuz when C--N bond break by adding water it forms COOH PLUS NH2

Take care from the C it have double bond O which is Carobxylic group

 

[mehria]

nope..
i thought it is A but the answer is C how it can be.. i m really confused..

oh sry i read the question incorrectly.. i thought it is askng abt glycosidic bond
it is C bcuz peptide bond is made always between amine n carboxylic group... where as in A n D Nitrogen is bonded with other C atom that is nt a part of carboxyl group

 

[♣♠ Magnanimous ♣♠]

Is it C ? Cuz when C--N bond break by adding water it forms COOH PLUS NH2

yup it is C.. thanks.

 

[♣♠ Magnanimous ♣♠]

thank you so much....
u cleared my confusion otherwise i would have been lose one mark.. thanks again.

oh sry i read the question incorrectly.. i thought it is askng abt glycosidic bond
it is C bcuz peptide bond is made always between amine n carboxylic group... where as in A n D Nitrogen is bonded with other C atom that is nt a part of carboxyl group

 

[sumeru]

nope..
i thought it is A but the answer is C how it can be.. i m really confused..

Just remember that when a peptide bond is formed one amino acid looses a carbo-oxyl group and the other looses a hydrogen atom from amine group so.........if there is RCOOH+H2NR.....then after loosing OH and H it will be...RC-O-N-H

 

[mehria]

thank you so much....
u cleared my confusion otherwise i would have been lose one mark.. thanks again.

np

 

[♣♠ Magnanimous ♣♠]

thanks a lot.. really appreciate..

Just remember that when a peptide bond is formed one amino acid looses a carbo-oxyl group and the other looses a hydrogen atom from amine group so.........if there is RCOOH+H2NR.....then after loosing OH and H it will be...RC-O-N-H

 

[roxylara]

nope..
i thought it is A but the answer is C how it can be.. i m really confused..

It's because an Amino acid is -CONH. ALWAYS REMEMBER THIS. Since to form a peptide bond condensation reaction takes place which makes -CONH. It can't be A because that dosent represent -CONH. Can't be B Because it dosent show that Aswell. If can only be C because that Shows CONH. C double O N-H

 

[♣♠ Magnanimous ♣♠]

It's because an Amino acid is -CONH. ALWAYS REMEMBER THIS. Since to form a peptide bond condensation reaction takes place which makes -CONH. It can't be A because that dosent represent -CONH. Can't be B Because it dosent show that Aswell. If can only be C because that Shows CONH. C double O N-H

thanks a lot.

 

[roxylara]

Guys I need help How easy is it to score an A in the practical. I've heard you can't get an A altogether if you don't get it in the practical. How do I score In the practicals. I suck at them. I've practised but my schools lab is closing now to prepare for Cambridge. I have a practical booklet with a lot of unsolved papers In It but I still need help on the seriel dilutions etc. any tips?

 

[joanna omar]

Guys I need help How easy is it to score an A in the practical. I've heard you can't get an A altogether if you don't get it in the practical. How do I score In the practicals. I suck at them. I've practised but my schools lab is closing now to prepare for Cambridge. I have a practical booklet with a lot of unsolved papers In It but I still need help on the seriel dilutions etc. any tips?

June read the experiments and try to score full in written parts ...practical booklet you mean Past paper 3 ?

 

[roxylara]

June read the experiments and try to score full in written parts ...practical booklet you mean Past paper 3 ?

Yep. I find a lot of the information they give when they're telling you about the experiment I've heard the written parts actually carry more marks then the experiment itself :S and thankyou

 

[joanna omar]

Anyone Please... In paper 1, I have doubts In

June 08--->Q27
Nov 08 --->Q4 - Q31
june 09--->Q14 - Q12 -Q34
Nov 09--->Q15- Q21

mehria sumeru roxylara Alazne Diamond

 

[joanna omar]

Yep. I find a lot of the information they give when they're telling you about the experiment I've heard the written parts actually carry more marks then the experiment itself :S and thankyou

Thats why its all depends on ur explaining so dont worry and do know like mainly exp are either on food test or something relates to enxymes or diffusion osmosis so make sure u know thier concepts well to explain wht comes and gain marks and In drawing open M.s and just write all the points that the exmainers need to see with no broken lines and stuff

 

[midha.ch]

Anyone has the link to colourful version of bio Mary Jones book?? It's not available where I stay so can't buy it

 

[roxylara]

Thats why its all depends on ur explaining so dont worry and do know like mainly exp are either on food test or something relates to enxymes or diffusion osmosis so make sure u know thier concepts well to explain wht comes and gain marks and In drawing open M.s and just write all the points that the exmainers need to see with no broken lines and stuff

Thankyou

 

[joanna omar]

Thankyou

np....I wish that helped but if u need anything specifically feel free to ask

 

[sumeru]

Anyone Please... In paper 1, I have doubts In

June 08--->Q27
Nov 08 --->Q4 - Q31
june 09--->Q14 - Q12 -Q34
Nov 09--->Q15- Q21

mehria sumeru

june 8
q.27...C....First of all remove those options which contain PRESENT in lignification of cell wall....now low solute potential means very negative water potential, that's why the water flows into the cells, during loading of sucrose.
Nov 8
Q.4 B.....the magnification is given, so calculate the distance from the air space to rbc...use the formula of magnification, you'll get the answer
Q.31 D...i don't have any explaination for these....just remember that tidal volume is 500 cm3, the vital capacity is 3750 cm3.
june 9
Q.12 D...when lactose is hydrolysed, u get glucose....which can then be used for respiration......
q.14 ..Draw a tangent from 0 to calculate the initial rate of the reaction...
Q 34..A...T cell recognises the graft cells as abnormal cells, and they will destroy them....if you read other options carefully, they don't seem to be orrect...
And there are 2 variants in Nov 09....which one do u want?

 

[mehria]

Anyone Please... In paper 1, I have doubts In

June 08--->Q27
Nov 08 --->Q4 - Q31
june 09--->Q14 - Q12 -Q34
Nov 09--->Q15- Q21

mehria sumeru roxylara Alazne Diamond

June 08 Q 27:_ Phloem tubes are not lignified and solute potential of companion cells are more than sieve tube cells.
Nov 08 Q4:_ check the attachement

 

[Karim Nabil]

1 micrometer=1000 nm
s0, 0.2 micrometer=2oonm
But the resolution is only 220nm, so a object of size 200nm will not be visible because the microscope can't resolve it....

ahhhh...got that, thanks!