A level Biology: Post your doubts here!

[Awesome12]

http://theallpapers.com/papers/CIE/AS_and_ALevel/Biology (9700)/9700_s11_qp_11.pdf
q.14
why cant the answer be A ?

They have aforementioned that the inhibitors bind to the enzyme substrate complex. Such complexes are found only at the active site. Thus the inhibitor is a competitive inhibitor, and you can negate 2.

 

[Jeezan]

They have aforementioned that the inhibitors bind to the enzyme substrate complex. Such complexes are found only at the active site. Thus the inhibitor is a competitive inhibitor, and you can negate 2.

the answer is C

 

[Awesome12]

the answer is C

Ah well, the examiner report says this:

If the inhibitor binds to the enzyme/substrate complex, it will not alter the shape of the active site. Also, by binding to the enzyme/substrate complex, the maximum rate of reaction will not be increased.

 

[Jeezan]

Ah well, the examiner report says this:

If the inhibitor binds to the enzyme/substrate complex, it will not alter the shape of the active site. Also, by binding to the enzyme/substrate complex, the maximum rate of reaction will not be increased.

alright thank you :')

 

[Laila39]

O

Let's consider DNA made of only N14 to have mass of 14 units and those made of N15 completely to have a mass of 15 units.

If DNA made of N14 atoms is placed in a solution containing N15 atoms only:

At first mass of all DNA molecules is 14 units.

After first division, mass of all DNA molecules is 14.5 units.

After second division, 50% of DNA molecules have a mass of 14.5 units, the other 50% have a mass of 15 units.

After third division, 25% of DNA molecules have a mass of 14.5 units., the other 75% have a mass of 15 units.

After fourth division, 12.5% of DNA molecules have a mass of 14.5 units., the other 87.5% have a mass of 15 units.

I could go on but I think you see a pattern. I love math so there:

After nth division, [ 200/(2^n) ]% of DNA molecules have a mass of 14.5 units, the other [ 100 - 200/(2^n) ]% have a mass of 15 units.

mg

Let's consider DNA made of only N14 to have mass of 14 units and those made of N15 completely to have a mass of 15 units.

If DNA made of N14 atoms is placed in a solution containing N15 atoms only:

At first mass of all DNA molecules is 14 units.

After first division, mass of all DNA molecules is 14.5 units.

After second division, 50% of DNA molecules have a mass of 14.5 units, the other 50% have a mass of 15 units.

After third division, 25% of DNA molecules have a mass of 14.5 units., the other 75% have a mass of 15 units.

After fourth division, 12.5% of DNA molecules have a mass of 14.5 units., the other 87.5% have a mass of 15 units.

I could go on but I think you see a pattern. I love math so there:

After nth division, [ 200/(2^n) ]% of DNA molecules have a mass of 14.5 units, the other [ 100 - 200/(2^n) ]% have a mass of 15 units.

Wow I actually do finally get it! I made my teacher explain this to me a million times but I finally got it today, thankss!

 

[Lola_sweet]

I believe this has to do with definition of net primary productivity as well as gross primary productivity.
Since these are not in our syllabus, I wouldn't worry too much about it.

Productivity aient in the syllabus

 

[qwertypoiu]

Productivity aient in the syllabus

Efficiency yes.
Like loss of energy and bla bla..
But net primary productivity and gross primary productivity are not in the syllabus.

 

[Laila39]

How does the female Anopheles carry Plasmodium from an infected person to an uninfected person?
Secondly when the questions asks how an immune response is generated do we just mention the B and T lymphocytes and clonal expansion etc or phagocytosis? I always get confused about the requirements in the immunity questions

 

[qwertypoiu]

How does the female Anopheles carry Plasmodium from an infected person to an uninfected person?
Secondly when the questions asks how an immune response is generated do we just mention the B and T lymphocytes and clonal expansion etc or phagocytosis? I always get confused about the requirements in the immunity questions

Immune response is to do with action of lymphocytes, not phagocytes

 

[Laila39]

Immune response is to do with action of lymphocytes, not phagocytes

Lol I feel dumb but thanks and so basically we write the whole procedure with T-helper cells and B-lymphocytes and after the antibodies bind with the antigens, phagocytosis occurs and thats when the macrophages are mentioned?

 

[qwertypoiu]

Lol I feel dumb but thanks and so basically we write the whole procedure with T-helper cells and B-lymphocytes and after the antibodies bind with the antigens, phagocytosis occurs and thats when the macrophages are mentioned?

T-cells cannot be activated by direct contact with pathogens, rather an antigen presenting cell has to display it for the T-cells.
This could be from an infected cell, or a macrophage, so you could mention macrophage first. Just saying.
But yeah, you need to mention response by B-cells, secreting antibodies, and T-helper cells secreting cytokines and T-killer cell destroying our own cells using lethal weapons like hydrogen peroxide.

PS. weapon part was joke getting bored from studies these days...

 

[Sadi66]

why population of top consumer is smaller

 

[qwertypoiu]

why population of top consumer is smaller

Because very few energy on top carnivore trophic level.
Tell me if you have a pizza party with only 3 pizzas can you invite 100 people? No!
You can only invite around 6 I'd say what do you think.

 

[Sadi66]

Because very few energy on top carnivore trophic level.
Tell me if you have a pizza party with only 3 pizzas can you invite 100 people? No!
You can only invite around 6 I'd say what do you think.

so not enough energy to support a large population will be accepted as an answer?

 

[Farhad221]

you

so not enough energy to support a large population will be accepted as an answer?

You will have to explain why like, only 10 percent energy is available from one trophic level to another plus top carnivores are usually at 4 trophic level hence only 0.01 percentage of energy supplied to the ecosystem reaches them.Also as top carnivore are big in size their energy requirements are high too so only a small number of them are found

 

[princess Anu]

http://maxpapers.com/wp-content/uploads/2012/11/9700_w13_qp_2.pdf
Somebody please explain me Q6 b what do we have to write here
I just don't understand Marking scheme this time, but here it is
http://maxpapers.com/wp-content/uploads/2012/11/9700_w13_ms_2.pdf

 

[princess Anu]

I don't get why are organisms getting bigger even though they do not have sufficient energy

you
You will have to explain why like, only 10 percent energy is available from one trophic level to another plus top carnivores are usually at 4 trophic level hence only 0.01 percentage of energy supplied to the ecosystem reaches them.Also as top carnivore are big in size their energy requirements are high too so only a small number of them are found

 

[Farhad221]

http://maxpapers.com/wp-content/uploads/2012/11/9700_w13_qp_2.pdf
Somebody please explain me Q6 b what do we have to write here
I just don't understand Marking scheme this time, but here it is
http://maxpapers.com/wp-content/uploads/2012/11/9700_w13_ms_2.pdf

In the Dna gene code the the base sequence is changed from CTT TO CAT adenine replaces thymine hence during transcription a different mRna is coded for when this mRna attaches to the subunit of ribosome die to the change I codon a different trna attaches due to specifity therefore different amino acid cones in the protein pri.ary sequence. As R groups are changed folding occurs differently. Due to chqngedionic and hydrogen bonding

 

[princess Anu]

In the Dna gene code the the base sequence is changed from CTT TO CAT adenine replaces thymine hence during transcription a different mRna is coded for when this mRna attaches to the subunit of ribosome die to the change I codon a different trna attaches due to specifity therefore different amino acid cones in the protein pri.ary sequence. As R groups are changed folding occurs differently. Due to chqngedionic and hydrogen bonding

I guess you read the wrong Que
It is the last question part b

 

[My Name]

In the Dna gene code the the base sequence is changed from CTT TO CAT adenine replaces thymine hence during transcription a different mRna is coded for when this mRna attaches to the subunit of ribosome die to the change I codon a different trna attaches due to specifity therefore different amino acid cones in the protein pri.ary sequence. As R groups are changed folding occurs differently. Due to chqngedionic and hydrogen bonding

That's question 5 b the member wants 6 part b.
Btw what is chqngedionic.