A level Biology: Post your doubts here!

[joanna omar]

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This is A.S portion they got in paper 4 ,where u had to remember from immunity chapter the structure of Antibody
1.It have 2 heavy polypeptides and 2 light polypeptides Joined by disulfide bonds in between
2.A variable region in which antigen fits
3.They are protein in nature
4.Hinge region

 

[joanna omar]

June 2012 (v2)

Q10) It must be Reducing sugar. ANS IS B. Sucrose is Non -reducing.

Q27) Ans is D.. All 4 of them are found In Blood plasma, so They r also present in Tissue fluid and lymph (because these r made from Leaked blood plasma)
Nov 2012 (v2)
Q1)Greastest number of cells mean Least Magnification which is with A (5*10=50)

Q17) The process which move subtances Down the conc. Gradient (i.e From High Conc to Low Conc) result in Equilibrium.
Those are 2 , 3 and 4. So ans is D.

Q15)A, B AND C are related With phoospho lipids. But Option D is Related to Glycolipids which act as receptor (these r not Phospholipids)

Q24) Ans is A.
Option 3 :- Apoplast way never involves cell surface membranes so it is wrong. Only Option without 3 is A .

Q34)(C) First Look at Oxygen Used up .. which is 19-12.5=6.5 cm^3 This is Per 100 cm^3
Wee need to find out in 5 dm^3 = 5000 cm^3
6.5 : 100
X : 5000
X= 325 cm^3.

Nov 2012 (v2)
Q38) (c) iF x decreased so the primary producer Increased causing the Empty Circle to Increase ( bcz they have more food) This inturn Increased B and C.
But B also increased A so No change it overall population of B. C is top Carnivore so they remained Most!

Q21)B it says Two strands... Gene is One strand Only! so its B rest of them are correct!

Q30) It says Mucus is increased which causes More exocytosis in Goblet cell So option 2 is wrong. Only Ans without 2 is B.

Q36) I m Confused Between A and C. I would rather go with C (firstly Mark scheme says So) and Secondly Parasite lives in liver and RBC so vaccine don't Reach there.
A says Many stages but doesnt Explain the change in Antigen In every stage .

Q39) It says energy used For Photosynthesis. so it would be total Energy ( Net + energy lost) Because Energy which was lost was made by photosynthesis.
So (27 000 + 3 000/1*10^6) * 100 = 3.00% ans is D


Hope i Helped

Thanks A bunch and of course no doubt this really helped me

 

[Mohammed salik]

Thanks A bunch and of course no doubt this really helped me

You Are welcome.. If any Doubt Feel Free to Ask

 

[Snow Angel]

please can someone explain question 22 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_11.pdf
and question 22 and 19 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_12.pdf

what is the difference between base pairs and nucleotides.

please answer as soon as possible. thanks in advance

 

[Snowysangel]

please can someone explain question 22 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_11.pdf
and question 22 and 19 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_12.pdf

what is the difference between base pairs and nucleotides.

please answer as soon as possible. thanks in advance

Bases are a part of nucleotides. Every nucleotide has a pentose sugar, a phosphate group and one of the four bases Adenine, thymine/uracil, guanine and cytosine.

 

[Snow Angel]

Bases are a part of nucleotides. Every nucleotide has a pentose sugar, a phosphate group and one of the four bases Adenine, thymine/uracil, guanine and cytosine.

thnx can u please explain the questions as well ?

 

[Karim Nabil]

please can someone explain question 22 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_11.pdf
and question 22 and 19 from: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_12.pdf

what is the difference between base pairs and nucleotides.

please answer as soon as possible. thanks in advance

p11
q22>
DNA have 700 base pairs as mentioned in qp
we know that A pairs with T by 2 hydrogen bonds and C pairs with G by 3 hydrogen bonds
he mentioned maximum number of hydrogen bonds, so assume that DNA have only C-G
so....
3*700=2100 hydrogen bonds ... answer is D

p12
q19>
telomers are located at the end of chromosome to protect the ends from being damaged by fusing with the next chromosome.
in the qp, substance X is same as telomers, so cells divide continually without any damage of chromosomes , but without it, chromosomes are damaged so
cell division eventually slows and stops, answer is A
q22> answered above...

 

[emogurl_gl]

Somebody explain ths question plz

Hope this helps

 

[emogurl_gl]

I have question regarding S12 42 question 3. (b)

Please helppppp!

 

[NinjaInPyjamas]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_12.pdf

someone please explain q18!

 

[goodluckayesha]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s04_qp_4.pdf Q7b
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w05_qp_4.pdf Q6b
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_qp_42.pdf Q9a
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s10_qp_41.pdf Q10b
these r section B questions for some my book dsnt contain required information and for some i dont get how to link up ms points it woul be really helpful if some could post the required aanswers as per the pattern we r required to write

 

[Snow Angel]

p11
q22>
DNA have 700 base pairs as mentioned in qp
we know that A pairs with T by 2 hydrogen bonds and C pairs with G by 3 hydrogen bonds
he mentioned maximum number of hydrogen bonds, so assume that DNA have only C-G
so....
3*700=2100 hydrogen bonds ... answer is D

p12
q19>
telomers are located at the end of chromosome to protect the ends from being damaged by fusing with the next chromosome.
in the qp, substance X is same as telomers, so cells divide continually without any damage of chromosomes , but without it, chromosomes are damaged so
cell division eventually slows and stops, answer is A
q22> answered above...

thnx but the question 22 in p12 is not regarding nucleotides not base pairs. can u explain the diference?

 

[Karim Nabil]

thnx but the question 22 in p12 is not regarding nucleotides not base pairs. can u explain the diference?

my pleasure
q22> DNA double strand structure consists of sense strand that carries all info. in a DNA and anti-sense strand that is complementary only to the sense strand to stabilise the DNA molecule
so 700/2=350 as only one strand is carrying info.
350*3=1050 as we assume that DNA molecule contains only C-G base pairs because maximum number of hydrogen bonds is needed
answer is C

 

[sidbloom1995]

can anyone show me how to draw the graph for this question?
i did draw one but im not sure that my answer is correct
it's from mj 06 p2

 

[Mohammed salik]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w12_qp_12.pdf

someone please explain q18!

Q18) (A)
First Column says "difference in cells at X in solution Y compared to the same cells in solution W" If u look at both cells in Diagram 2 the cells are More Turgid i.e More Water in them which means Water potential nearer To Zero (Less Negative).
And Second Column says Diffrence in solution.. The solution in Diagram 2 (Solution Y) Must Be High Water potential so that water moves in and Make cells Turgid.( Which means The solution should be Less Negative (Nearer to Zero).
Hope This Helped !!

 

[Fahm Deen]

May/June 2013 P-13 Q-14,15,32.
Can anyone tell me the procedure?

 

[Mashal zeb]

Professor karim plzz explain

 

[Karim Nabil]

Professor karim plzz explain

p> atrial systole> when both atria contracts
q-s> ventricular systole> when both ventricles contract
t> ventricular diastole> when both ventricles relax to be filled with blood
in the qp he asks flow of current through atria and recovery of ventricular walls
flow of current through atria means waves of excitation send by the pacemaker SAN to both atria for contraction; atrial systole , so it is P
recovery of ventricular walls means ventricular diastole so it is T
answer is P and T which is B

 

[Snow Angel]

my pleasure
q22> DNA double strand structure consists of sense strand that carries all info. in a DNA and anti-sense strand that is complementary only to the sense strand to stabilise the DNA molecule
so 700/2=350 as only one strand is carrying info.
350*3=1050 as we assume that DNA molecule contains only C-G base pairs because maximum number of hydrogen bonds is needed
answer is C

thnx

 

[Snow Angel]

in paper: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_1.pdf question 1

and in paper: papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w13_qp_12.pdf question 1

when C is the correct answer for q 1 from the first link why can't B be the correct answer for question 1 from the second link? please explain. thanks in advance