A level Biology: Post your doubts here!

[Rizwan Javed]

thank you both of you! I feel a lot better now!
Rizwan Javed
and wow 40/40 is a lot! yeah that's what I am aiming for as well! you took AS already or will you take in May/June?

This May/June.

 

[Eugene99]

It's C. How?

 

[Akshajistari]

View attachment 59507
It's C. How?

If you use the stage micrometer scale, 1 div = 0.1mm. Therefore, one division on the eyepiece graticule is 0.0025 mm , as 0.1/40= 0.0025mm.

Then, the radius using the eyepiece graticule scale is 0.0025mm x 50 div = 0.125mm

0.125mm= 125 micrometers

SO area = pi x r x r = pi x 125 x 125


=4.9x10^4 micrometer^2

 

[Eugene99]

D

 

[Akshajistari]

View attachment 59510
D

Y is alpha glucose, while X is beta glucose.
So, A and B are immediately eliminated because amylose and amylopectin are both polymers of alpha glucose.
C is eliminated because cellulose contains beta glucose, not alpha.

The only option left is D which is correct if you cross reference with your theory since glycogen's monomer is alpha glucose.

 

[Eugene99]

question 19...how to solve this?

 

[Rizwan Javed]

View attachment 59523
question 19...how to solve this?

Just use the concept that Adenine (A) base-pairs with thyamine (T) and Cytosine (C) pairs with Guanine (G).

There are 5 T in strand 2 so there'll be 5 A in strand (Since A-T complementary base pairing)
Similarly, there're 7 C in strand 2, so there'll be 7 G in strand 1 (C-G complementary base pairing)

Now for strand 1, you've got these figures:

A: 5
C: ??
G: 7
T: 4

There are 19 nucleotides in one strand.
So you can find C by :
19 - (7+4+5) = 3

So the answer is B.

 

[Eugene99]

Just use the concept that Adenine (A) base-pairs with thyamine (T) and Cytosine (C) pairs with Guanine (G).

There are 5 T in strand 2 so there'll be 5 A in strand (Since A-T complementary base pairing)
Similarly, there're 7 C in strand 2, so there'll be 7 G in strand 1 (C-G complementary base pairing)

Now for strand 1, you've got these figures:

A: 5
C: ??
G: 7
T: 4

There are 19 nucleotides in one strand.
So you can find C by :
19 - (7+4+5) = 3

So the answer is B.

YESSS I get that. thank you!
I thought T from strand 1 was going to pair with A from strand 1! silly me! how can it pair with itself? that caused all the problem!

 

[iSean97]

If this question was 10 marks.

Anyone can help me form sentences?

translation ;

A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein I protein / polypeptide, synthesis
moves towards / combines with, ribosome ;
ref to small and/or large sub-units ; I small / large ribosome
codon(s) ; only accept in correct context
transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
anticodon(s) ; only accept in correct context
(complementary) base pairing ;
any e.g. of codon:anticodon base pairing ; need six bases
ref to polyribosome(s) / used by many ribosomes ;
(mRNA short-lived) ref to production of protein for short period of time ;

 

[Eugene99]

Why is the answer B?
0.2 mm is 200 nm, why wouldn't it be visible under 220 resolution? and how are A, C and D incorrect?

 

[Rizwan Javed]

View attachment 59530
Why is the answer B?
0.2 mm is 200 nm, why wouldn't it be visible under 220 resolution? and how are A, C and D incorrect?

Resolution is the ability to distinguish between two objects close together.

A is incorrect because it says that at smallest distance in a particular situation, it easy to differentiate between two points. That means that resolution must be high. So resolution does not decrease.

C is incorrect because membranes are about 7nm in diameter. Resolution is half the wavelength. Since, the wavelength is 600nm that means that anything smaller than 300nm can't be seen. So membranes which are much smaller than 300nm are impossible to be seen.

D is incorrect, because as the wavelength increases, the resolution decreases.

So B is the answer. The diameter of bacterium is 200nm. This is less than the resolution that means that they can't be seen. And this what the statement states. So this option is correct.

 

[Eugene99]

If this question was 10 marks.

Anyone can help me form sentences?

translation ;

A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein I protein / polypeptide, synthesis
moves towards / combines with, ribosome ;
ref to small and/or large sub-units ; I small / large ribosome
codon(s) ; only accept in correct context
transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
anticodon(s) ; only accept in correct context
(complementary) base pairing ;
any e.g. of codon:anticodon base pairing ; need six bases
ref to polyribosome(s) / used by many ribosomes ;
(mRNA short-lived) ref to production of protein for short period of time ;

How is this? It covers the first 8 points though.

Translation takes place, making use of nucleotides to make amino acid chains. The mRNA moves towards the ribosome and binds itself with the small subunit of ribosome. A tRNA molecule, which has a specific amino acid, with three exposed bases, (codons), form pairs with the complementary anticodons of the mRNA. Six bases at a time are exposed to the large subunit.

 

[Rizwan Javed]

How is this? It covers the first 8 points though.

Translation takes place, making use of nucleotides to make amino acid chains. The mRNA moves towards the ribosome and binds itself with the small subunit of ribosome. A tRNA molecule, which has a specific amino acid, with three exposed bases, (codons), form pairs with the complementary anticodons of the mRNA. Six bases at a time are exposed to the large subunit.

You made a few mistakes.

mRNA actually binds the smaller subunit, and its codons are exposed into the larger sub-unit. Also the codons are located on the mRNA not on tRNA. tRNA has anticodonds.

 

[Eugene99]

You made a few mistakes.

mRNA actually binds the larger small unit, and its codons are exposed into the smaller sub-unit. Also the codons are located on the mRNA not on tRNA. tRNA has anticodonds.

Yes thanks for pointing out. You are right about the codons thing but about the large subunit, my book says 'the mRNA binds to the small subunit' ain't it so?

 

[Rizwan Javed]

Yes thanks for pointing out. You are right about the codons thing but about the large subunit, my book says 'the mRNA binds to the small subunit' ain't it so?

Sorry Now I made a mistake.

 

[Eugene99]

Sorry Now I made a mistake.

It's okay! we all make mistakes, we are all humans...but those CIE guys who make Paper 1 never seem to realize that! When each option shouts at me 'i'm correct', then my human characteristics fail to justify

 

[Rizwan Javed]

If this question was 10 marks.

Anyone can help me form sentences?

translation ;

A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein I protein / polypeptide, synthesis
moves towards / combines with, ribosome ;
ref to small and/or large sub-units ; I small / large ribosome
codon(s) ; only accept in correct context
transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
anticodon(s) ; only accept in correct context
(complementary) base pairing ;
any e.g. of codon:anticodon base pairing ; need six bases
ref to polyribosome(s) / used by many ribosomes ;
(mRNA short-lived) ref to production of protein for short period of time ;

mRNA after leaving nucleus takes part in the process of translation. mRNA binds with the smaller sub-unit, with 6 bases exposed into the larger sub-unit at a time. A triplet of bases on the mRNA is known as codon. tRNA present in the cytoplasm carry a specific aminoacid towards the ribosomes. A tRNA having a complementary anti-codon to that of the codon on the mRNA binds with the first three exposed bases. A second tRNA carrying another aminoacid, binds with the next triplet of bases. The two amino acids are held in place till a peptide bond is formed between them. Many ribosomes can attach to a single mRNA forming polysomes. The mRNA after it has been decoded to form the required polypeptide chain is broken down in the cytoplasm; this means that the mRNA is short-lived.

 

[My Name]

If this question was 10 marks.

Anyone can help me form sentences?

translation ;

A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein I protein / polypeptide, synthesis
moves towards / combines with, ribosome ;
ref to small and/or large sub-units ; I small / large ribosome
codon(s) ; only accept in correct context
transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
anticodon(s) ; only accept in correct context
(complementary) base pairing ;
any e.g. of codon:anticodon base pairing ; need six bases
ref to polyribosome(s) / used by many ribosomes ;
(mRNA short-lived) ref to production of protein for short period of time ;

 

[My Name]

If this question was 10 marks.

Anyone can help me form sentences?

translation ;

A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein I protein / polypeptide, synthesis
moves towards / combines with, ribosome ;
ref to small and/or large sub-units ; I small / large ribosome
codon(s) ; only accept in correct context
transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
anticodon(s) ; only accept in correct context
(complementary) base pairing ;
any e.g. of codon:anticodon base pairing ; need six bases
ref to polyribosome(s) / used by many ribosomes ;
(mRNA short-lived) ref to production of protein for short period of time ;

View attachment 59531

Oh sorry I just scrolled up here and saw that you said 10 marks.
Obviously mine is no where near 10 marks.
Btw there almost no chance of it being for TEN marks.
Mostly max is 6 marks for a question.
Anyway,my answer will be good for 4.

 

[kareem22010]

Hey guys, can anybody help me with this question? i wrote my answer but i am not sure if it should fulfil the markscheme or not,so here is the question:

My answer:
a-glucose molecules are bonder together as monomers from carbon 1 to carbon 4 to form unbranched chain known as amylose. a-glucose molecules are bonded together by both c1 to c4 and c1 to c6 to from a polysacharride with a branched chain known as amylopectin.

so, how many points should i earn for my answer?

thanks in advance.