A level Biology: Post your doubts here!

[periyasamy]

Hai, can anyone help me with some biology mcq from may june 2013 .Thanks a lot.
Answer for 1st question is b.

 

[periyasamy]

Guys a few other questions too.If u have some time,can u help me by explaining it a bit .Thank u...Really appreciate it................
in this question why option d is not accepted.Answer is option b.

 

[periyasamy]

why option d is rejected?Thank u again........

 

[ahmed abdulla]

CAN some one help me with this
two questions ?>

 

[periyasamy]

CAN some one help me with this
two questions ?>

For the 1st question,simple concept primary consumer n the producer must always be closely associated or related so must be either c or d.Ans should be d as primary consumer must be in lesser number than producer.

 

[periyasamy]

Hello !
I need help in q 24

Buddy,I think answer should be a as first of all option c and d should be directly cancelled as the two strands of dna must be antiparallel in direction one 3-5 n another 5-3.Then option a is choosen not b as dna no uracil,instead thymine.

 

[periyasamy]

The following events occur during transcription.
1 Bonds break between complementary bases.
2 Bonds form between complementary bases.
3 Sugar-phosphate bonds form.
4 Free nucleotides pair with complementary nucleotides.
Before the mRNA leaves the nucleus, which events will have occurred twice?
A 1 and 2 only
B 1, 3 and 4 only
C 2, 3 and 4 only
D 1, 2, 3 and 4

Answer is A, anyone can explain pls

Buddy ,got this from somebody's post b4.
Bonds are broken once when DNA unzips, and the next time when the mRNA has been formed and is separated from the DNA strand.
Bonds form the first time when free nucleotides join the strand to form mRNA, and the second time when mRNA is formed and DNA strands zip-up to coil.
Sugar phosphate bone forms only once for mRNA. Pairing of *free nucleotides* occurs once too

 

[Gehad Mohamed]

Ans 2 is C, because resolution is half the wavelength of the given wave, hence when wavelength increases resolution decreases, however increasing or decreasing resolutions doesn't affect magnification
Ans 8 is A, read the text book for that, it's a theory type question.
Ans 9 is C, because all the electrons are already bonded in that molecule, it has no capacity to bind further.
Ans 17 is B, mitosis only involves nucleus division, it's not responsible for cell growth.

Hope this helps,

thanks alotttttt it really helps

 

[periyasamy]

Can someone explain me q no 19 of mayjune 2013 p1 please, urgently. http://olevel.sourceforge.net/papers/9700/9700_s13_qp_12.pdf

what is the answer?

 

[Gehad Mohamed]

Ans 2 is C, because resolution is half the wavelength of the given wave, hence when wavelength increases resolution decreases, however increasing or decreasing resolutions doesn't affect magnification
Ans 8 is A, read the text book for that, it's a theory type question.
Ans 9 is C, because all the electrons are already bonded in that molecule, it has no capacity to bind further.
Ans 17 is B, mitosis only involves nucleus division, it's not responsible for cell growth.

Hope this helps,

thanks alotttttt it really helps

 

[Gehad Mohamed]

Buddy,I think answer should be a as first of all option c and d should be directly cancelled as the two strands of dna must be antiparallel in direction one 3-5 n another 5-3.Then option a is choosen not b as dna no uracil,instead thymine.

Thanks

 

[periyasamy]

thanks alotttttt it really helps

Just think that question 9 why option c cannot is because r group suppose to be a carbon chain group but the option c is another amino acid itself.
Instruction above said structure of one amino acid ,,,option c will make it to have two amino acid.

 

[periyasamy]

q

HIV-1 protease is an enzyme produced by the HIV virus.
Two identical chains of 99 amino acids form the enzyme. In each chain, amino acids 25, 26 and
27 in the sequence form part of the active site.
Which orders of protein structure control the shape of the active site?
A primary, secondary, tertiary and quaternary
B primary, secondary and tertiary only
C primary and quaternary only
D quaternary only

Answer is A, why isnt it B? :O

quartenary must be since two identical chain of 99 amino acids mean two polypeptide chains......>>>>>>than one polypeptide chain is resembling quarteary level.

 

[Gehad Mohamed]

Just think that question 9 why option c cannot is because r group suppose to be a carbon chain group but the option c is another amino acid itself.
Instruction above said structure of one amino acid ,,,option c will make it to have two amino acid.

R-groups are hydrocarbons so why not CH3 ??!

 

[periyasamy]

ano anyone?

I can help u some question.
Question 14,when doing mean value,avoid anamalous readings
question 20-------that is a stage before prophase as chromosome not yet even form
questio 22------700*3,why multiply 3 is because highest pssibility when cytosine guanine form 3 hydrogen bond

 

[periyasamy]

http://olevel.sourceforge.net/papers/9700/9700_s13_qp_11.pdf Question 4 anyone??

For Question 4A
Note that the question is asking for the features that enable you to IDENTIFY that it is a prokaryote.
It is true that prokaryotes have cell wall, nucleus, ribosomes and DNA. However, eukaryotes also have those features. The only difference that tells you that it is a eukaryote or prokaryote is the DNA. Prokaryotes have a circular DNA and eukaryotes have linear molecules (chromosomes).

# The question is just trying to confuse you

Question 16D
For factors that increses the fluidity of the membrane are:
1) Unsatured phospolipid tail - Fatty acid tails are bent
2) Increse in temperature
3) Cholestrol

For 1 single bonds between carbon atoms in fatty acid chains means that it is saturated. Thus it decreases the fluidity of the membrane
2 Longer chains of fatty acid does not affect any fluidity of the membrane

Question 3 and 40 somewhat still confuses me

Correct me when I'm wrong! Thank you very much!

For Question 4A
Note that the question is asking for the features that enable you to IDENTIFY that it is a prokaryote.
It is true that prokaryotes have cell wall, nucleus, ribosomes and DNA. However, eukaryotes also have those features. The only difference that tells you that it is a eukaryote or prokaryote is the DNA. Prokaryotes have a circular DNA and eukaryotes have linear molecules (chromosomes).

# The question is just trying to confuse you

Question 16D
For factors that increses the fluidity of the membrane are:
1) Unsatured phospolipid tail - Fatty acid tails are bent
2) Increse in temperature
3) Cholestrol

For 1 single bonds between carbon atoms in fatty acid chains means that it is saturated. Thus it decreases the fluidity of the membrane
2 Longer chains of fatty acid does not affect any fluidity of the membrane

Question 3 and 40 somewhat still confuses me

Correct me when I'm wrong! Thank you very much!

question 40 ----option 2 wrong as it is harmfull(eutrophication)
--------option 4 is true as it is a fact.
Answer is a

 

[Gehad Mohamed]

Hello!
Plzz help me in Q 4/6 /
14 why D is wrong ?

18 why a?

 

[Ayyan :D]

why option d is rejected?Thank u again........

The question is about a ''Coronary By-pass''.
As the name of the surgical operation suggests, it is performed on the Coronary arteries that supply blood to the heart.
Option D says that ''diseased parts of Aorta'' are removed. Aorta is a completely different main artery that supplies blood to the body.
This surgical procedure is performed on Coronary arteries where fat deposits resulting in Atherosclerosis.
An alternate path is provided for the blood to be supplied to the heart to maintain the supply of oxygen and dissolved glucose.
What's the answer? I think it should be A?

 

[periyasamy]

Hello!
Plzz help me in Q 4/6 /
14 why D is wrong ?

18 why a?

what year?

 

[periyasamy]

The question is about a ''Coronary By-pass''.
As the name of the surgical operation suggests, it is performed on the Coronary arteries that supply blood to the heart.
Option D says that ''diseased parts of Aorta'' are removed. Aorta is a completely different main artery that supplies blood to the body.
This surgical procedure is performed on Coronary arteries where fat deposits resulting in Atherosclerosis.
An alternate path is provided for the blood to be supplied to the heart to maintain the supply of oxygen and dissolved glucose.
What's the answer? I think it should be A?

Thanks boss.

 

[periyasamy]

Y

The question is about a ''Coronary By-pass''.
As the name of the surgical operation suggests, it is performed on the Coronary arteries that supply blood to the heart.
Option D says that ''diseased parts of Aorta'' are removed. Aorta is a completely different main artery that supplies blood to the body.
This surgical procedure is performed on Coronary arteries where fat deposits resulting in Atherosclerosis.
An alternate path is provided for the blood to be supplied to the heart to maintain the supply of oxygen and dissolved glucose.
What's the answer? I think it should be A?

Yeah ,its A .Thanks agn.