A level Biology: Post your doubts here!

[Mstudent]

in prophase chromosomes recoil and condense and the centriole divide to reach at the oppsite pole of the cell. hope this helps

So in that case B is correct? So why in the marking scheme did they chose seperation of centrioles not the formation of chromosomes (Condensation of chromosomes)?

 

[Brisingr]

So in that case B is correct? So why in the marking scheme did they chose seperation of centrioles not the formation of chromosomes (Condensation of chromosomes)?

chromosomes are seen or formed before nuclear division

 

[Mstudent]

chromosomes are seen or formed before nuclear division

Oh, ok, now I get it, thank you very much!

 

[SohaibButt]

Anyone?

 

[Mstudent]

Anyone?

For the first question,

first you have two DNA strands made of N15
Then you replicated them with N14 to make two MOLECULES , each with a new N14 strand and an old N15 strand
then you replicated one of them again with N14, so you will have, TWO MOLECULES, one with TWO N14 strands, the old one and a new N14 strand, and another MOLECULE with and old N15 strand and a new N14 strand,

so at the end you have 4 DNA strands, two OLD STANDS and two New strands, so 50%

 

[shahzaib ihsan]

View attachment 62446
Answer in ms is B.
But shouldn't the answer be A?
ER also says: T-lymphocytes can secrete cytokines. Cytotoxins are released by certain pathogens.
which means C is incorrect but A is correct, right? I never heard of T-lymphocytes leaving blood

i cant understand this too,
this looks the same like the question 36 october/november 2015 variant 12..

 

[shahzaib ihsan]

Anyone?

1. the question is about semiconservative replication.
the first offspring of n14 and n15 was all hybrid dna, i.e. 100% hybrid dna. when it was allowed to divide one more time, half of it was original and half was new, so that means 50% hybrid was left

2.
i) it says blood in human veins not the walls of human veins, so i don't think collagen will be present in blood.
ii) carbonic anhydrase is present in all red blood cells, and blood always contain red blood cells regardless of the vessel it is flowing through .
iii)the vessels which carries oxygenated blood from lungs to the heart are veins (pulmonary veins) which contain redblood cells containing oxyhaemoglobin.
so answer should be d

 

[SohaibButt]

1. the question is about semiconservative replication.
the first offspring of n14 and n15 was all hybrid dna, i.e. 100% hybrid dna. when it was allowed to divide one more time, half of it was original and half was new, so that means 50% hybrid was left

2.
i) it says blood in human veins not the walls of human veins, so i don't think collagen will be present in blood.
ii) carbonic anhydrase is present in all red blood cells, and blood always contain red blood cells regardless of the vessel it is flowing through .
iii)the vessels which carries oxygenated blood from lungs to the heart are veins (pulmonary veins) which contain redblood cells containing oxyhaemoglobin.
so answer should be d

For the first question,

first you have two DNA strands made of N15
Then you replicated them with N14 to make two MOLECULES , each with a new N14 strand and an old N15 strand
then you replicated one of them again with N14, so you will have, TWO MOLECULES, one with TWO N14 strands, the old one and a new N14 strand, and another MOLECULE with and old N15 strand and a new N14 strand,

so at the end you have 4 DNA strands, two OLD STANDS and two New strands, so 50%

Thank you!

 

[Mstudent]

Thank you!

You're welcome, anytime

 

[Metallic9896]

View attachment 62446
Answer in ms is B.
But shouldn't the answer be A?
ER also says: T-lymphocytes can secrete cytokines. Cytotoxins are released by certain pathogens.
which means C is incorrect but A is correct, right? I never heard of T-lymphocytes leaving blood

I think here you have to think from a different perspective. Yes we may not remember that T lymphcytes leave the blood or not. But we reject A because of the 'only found in blood' part. They AREN'T only found in blood because how can that be true when you know that they are produced in the bone marrow and mature in the thymus gland? Those parts aren't part of the blood so at any time when you scan a person for T lymphocytes you'll "find" them in 3 places at least: blood, bone marrow, and thymus gland. This is why I think A is rejected. The cytokines part is correct but your concern should be the 'only found in' part.

 

[darks]

View attachment 62446
Answer in ms is B.
But shouldn't the answer be A?
ER also says: T-lymphocytes can secrete cytokines. Cytotoxins are released by certain pathogens.
which means C is incorrect but A is correct, right? I never heard of T-lymphocytes leaving blood

I think B refers to killer T cells. The killer T cells DO leave the blood to reach infected cell (i mean how else can it reach an infected cell?) to attach to it and release toxins. A is definitely incorrect as it states the T-lymphocytes are only found in blood.

 

[darks]

I think here you have to think from a different perspective. Yes we may not remember that T lymphcytes leave the blood or not. But we reject A because of the 'only found in blood' part. They AREN'T only found in blood because how can that be true when you know that they are produced in the bone marrow and mature in the thymus gland? Those parts aren't part of the blood so at any time when you scan a person for T lymphocytes you'll "find" them in 3 places at least: blood, bone marrow, and thymus gland. This is why I think A is rejected. The cytokines part is correct but your concern should be the 'only found in' part.

Haha what a co incidence that we decided to ans. the same Q

 

[Metallic9896]

Haha what a co incidence that we decided to ans. the same Q

Hahah coincidence indeed. BTW I think they don't refer to killer T cells although what you said about killer T cells is correct they DO get at the site and release cytotoxins, I just checked. But that would make option C the most correct option as it says 'They can leave the blood and excrete cytotoxins when exposed to bacteria'. But answer is B cause they are asking about the T lymphocytes which haven't specialized into killer T cells nor formed themselves into helper T cells. They are plain ol' T lympoctyes which leave blood and accumulate at the site of infection, THEN divide to form killer T cells that release cytotoxines OR form helper T cells that release cytokines. So let's summarize the story as:

T lymphocytes are formed in the bone marrow, mature in the thymus gland, patrol in the blood, and can leave the blood to accumulate at the site of infection.
At the site of infection, they can differentiate to form killer T cells that release cytotoxins.
At the site of infection, they can differentiate to form helper T cells that release cytokines.

 

[darks]

Hahah coincidence indeed. BTW I think they don't refer to killer T cells although what you said about killer T cells is correct they DO get at the site and release cytotoxins, I just checked. But that would make option C the most correct option as it says 'They can leave the blood and excrete cytotoxins when exposed to bacteria'. But answer is B cause they are asking about the T lymphocytes which haven't specialized into killer T cells nor formed themselves into helper T cells. They are plain ol' T lympoctyes which leave blood and accumulate at the site of infection, THEN divide to form killer T cells that release cytotoxines OR form helper T cells that release cytokines. So let's summarize the story as:

T lymphocytes are formed in the bone marrow, mature in the thymus gland, patrol in the blood, and can leave the blood to accumulate at the site of infection.
At the site of infection, they can differentiate to form killer T cells that release cytotoxins.
At the site of infection, they can differentiate to form helper T cells that release cytokines.

That's a perfect answer Some information that i did not know.

 

[darks]

So in our book, There is section from page 168 to 171 (Mary Jones 4th edition, Haemoglobin, Bohr shift, CO2 Transport), no matter how much i learn and try to understand this, I basically always end up doing the 1-3 questions asked from this topic, wrong. I have attached example Qs.. If anyone can help me with this topic, Please do.

 

[shahzaib ihsan]

So in our book, There is section from page 168 to 171 (Mary Jones 4th edition, Haemoglobin, Bohr shift, CO2 Transport), no matter how much i learn and try to understand this, I basically always end up doing the 1-3 questions asked from this topic, wrong. I have attached example Qs.. If anyone can help me with this topic, Please do.
View attachment 62452 View attachment 62453

same case here, in almost every paper i pick the wrong answer to this topic's question.. i guess this topic in book is not good

 

[Anas Abbal]

how to solve this i am unable to get the answer

 

[Xaverian]

Please anyone who could assist me with the question no 2 of this link????? Please
Link: http://papers.gceguide.com/A Levels/Biology (9700)/9700_s16_qp_11.pdf

 

[shahzaib ihsan]

Please anyone who could assist me with the question no 2 of this link????? Please
Link: http://papers.gceguide.com/A Levels/Biology (9700)/9700_s16_qp_11.pdf

i have done this recently... you have to use the formula m=I/a (magnification= image size/actual size)

m=1500, image size of x-y = 3 cm acutal size: A=I/M = 3/1500= 0.002cm
so 1 cell is actually 0.002 cm long, how many cells will be 1 cm long? 1/0.002 (unitary method) = 500

 

[janedoe]

Question 4
The majority of candidates answered this incorrectly. A build-up of lipids in cells means that the excess lipids
are not being broken down. Excess lipids are normally broken down by hydrolytic enzymes found in the
lysosomes.

This is what the examiner report says. This is one of the reasons I really dislike Biology paper 1s. Some questions are simply too vague with overlapping correct options. Their emphasis is the 'build up' part and not the enzyme not being produced part. My first instinct was that Golgi apparatus is not part of 'producing' the enzyme, as we read and are expected to learn that it is involved in 'packing' the enzyme or adding non-protein elements to it, but that's something too trivial to be reason enough. More importantly, I guess what they mean to say is that in the production process, anything could be at fault, from the gene sequence of the enzyme to the ribosomes to the endoplasmic reticulum and the Golgi apparatus - all of these could be or one of these could be faulty. However, something that for CERTAIN won't function is the lysozomes because they are what the enzymes eventually should end up and if the enzymes aren't produced then for certain they won't end up there. These 2 arguments are what I could think of in favor of option A, but I do understand why anyone would have an issue with this question, including myself. They should have written something like, 'Which cell structure MUST not function correctly.." writing must in bold etc.

Ok, thank you.