A level Biology: Post your doubts here!

[Aqsa Saleem]

Re: Stuck in Biology?? Post your doubts here!!

Assalamoalaikum!

Please, help me with this question:
Describe the function of vasa recta.

Mark scheme points:
-removing water;
-from/ reabsorbed by collecting ducts;
-ref. to maintain water potential gradient (in medulla)

Jazakumullah Khair..

Vasa recta functions to maintain the hyperosmolarity created by the Loop of Henle. Lies in countercurrent manner adjecent to the tubules. (U shaped) As blood flows down the descending limb of vasarecta, it takes up solutes from medullary interstitium (water moves out into interstitium) , and as blood flows in ascending limb, the concentration of solutes reaches very high, it gives off solutes to medullary interstitium and water moves in to the vasa recta. Thus, it maintains the hyperosmolarity by removal of water.

 

[A_K_D]

For this paper shouldn't the answer for question 10) be B because it forms a disulfide bond due to the S-H groups?

Thank you

 

[ZohaibAsad]

Cysteines are amino acids, they join together to form polypeptides. The only way to do this is by forming peptide bonds. Hence, D is the answer. Disulphide bonds can be formed but for their original function they don't need to be formed and hence are not formed.

 

[A_K_D]

no1 uses this forum... but here it goes!

does the separation of the sister chromatids by the duplication of the centromere happen in metaphase or anaphase? some textbooks so metaphase and anaphase but I dont know which stage is good for cambridge or which stage it occurs closest to. By looking at some of the multi choice questions there is clearly an answer to a definite stage.

So to summarise: does separation of sister chromatids occur in anaphase or metaphse?

Thanks,

 

[A_K_D]

also when cie talks about bronchioles do you take it as respiratory or terminal and respiratory contains goblet cells

 

[N.M]

no1 uses this forum... but here it goes!

does the separation of the sister chromatids by the duplication of the centromere happen in metaphase or anaphase? some textbooks so metaphase and anaphase but I dont know which stage is good for cambridge or which stage it occurs closest to. By looking at some of the multi choice questions there is clearly an answer to a definite stage.

So to summarise: does separation of sister chromatids occur in anaphase or metaphse?

Thanks,

firstly, centromere does not duplicate, it splits
2ndly the seperation n splitting happens in the anaphase not in metaphase...

 

[xtremeforums]

In may/june 06: http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_s06_qp_1.pdf

The answer to question 17 is A. I understand why A is correct, but D also makes sense doesnt it? The cylinders are now placed in a more dilute solution so water moves, by osmosis, into the cylinders making the water potential less negative...? Am i wrong?

 

[Irfan1995]

also when cie talks about bronchioles do you take it as respiratory or terminal and respiratory contains goblet cells

Both. For example, respiratory bronchioles don't have any smooth muscle, but terminal bronchioles do. That's why if they ask for the presence of smooth muscles in bronchioles, both answers are accepted.

 

[autumnsakura]

Can cell wall restrict entry of water? Referring to question 14. The answer says D

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w10_qp_11.pdf

 

[Ashiq Sookarry]

Cell wall is fully permeable. however pressure generates as a result of presence of cell wall. if there is no cell wall. no turgor pressure

 

[autumnsakura]

Cell wall is fully permeable. however pressure generates as a result of presence of cell wall. if there is no cell wall. no turgor pressure

thanks!


I have another question on NPP. So does NPP include respiration energy? Refering to question 39.
http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w11_qp_12.pdf

The answer is B so does it means 1200 + 5000 divided by 1 000 000 times 100% ? So we have to add the respiration as well? I m so confused with NPP and GPP...

 

[xtremeforums]

http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_w08_qp_1.pdf

Question 36.
Why does increasing resistance to antibiotics and other drugs increase the spreading of malaria? Malaria is caused by a protoctista not a bacterium... ?
Please answer...

 

[autumnsakura]

http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_w08_qp_1.pdf

Question 36.
Why does increasing resistance to antibiotics and other drugs increase the spreading of malaria? Malaria is caused by a protoctista not a bacterium... ?
Please answer...

maybe we should focus on 'including other drugs'?

 

[ZohaibAsad]

http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_w08_qp_1.pdf

Question 36.
Why does increasing resistance to antibiotics and other drugs increase the spreading of malaria? Malaria is caused by a protoctista not a bacterium... ?
Please answer...

You are assuming antibiotics cannot act against protozoa, which is a wrong assumption

 

[Rutzaba]

can some one help this guy---------------------------> Yaar can anyone help me with DCPIP please?

hunter.m48

 

[PhyZac]

Asslamu Alikum Wa Rahmatullah Wa Barakatoho....

Can someone please explain these for me.?


Why is the answer of question 27 "A"?

And for the below one ....that is question 5 the answer is "B" ??

 

[PhyZac]

Assalamu Alikum Wa Rahmatullah Wa Barakatoho.

Sir badrobot14 Can this be a sticky thread. I took time for me to find a place for biology doubts.

 

[badrobot14]

Assalamu Alikum Wa Rahmatullah Wa Barakatoho.

Sir badrobot14 Can this be a sticky thread. I took time for me to find a place for biology doubts.

WaAlaikum AsSalam WaRahmatullahi WaBarakatuhu,

hmm... sure.. I think I should... for now at least, I'm sticking it.. but once it becomes active, I might unstick it.. coz it looks bad if you enter a forum and half the page is taken up by sticky threads only....

 

[Amy Bloom]

Asslamu Alikum Wa Rahmatullah Wa Barakatoho....

Can someone please explain these for me.?
View attachment 21578

Why is the answer of question 27 "A"?

And for the below one ....that is question 5 the answer is "B" ??

View attachment 21579

Hi PhyZac
Well, cell 3 is a xylem vessel, whilst cell 2 is a "normal photosynthesising cell" and cell 1 a phloem cell. so you would expect that the water potential in cell 3 to be much less negative than the other cells because it contains water mainly. cell 2 will be less negative than cell 1 as cell 1 has a high conc. of sugars so has a less water potential. so the answer there must be A only.

for the second question according to me is the goblet cell because it releases a great deal of mucus, so it is bound to contain smooth endoplasmic reticulum (structure responsible for release of proteins.

Hope my answer helped u and good luck.

 

[nightmaressana]

Can i just know that In the disease chapter, there is a lot given about mental diseases and physical and how to readthe health charts(in bradfield and essential bio), is it a part of syllabus? Can i skip it?

And can someone please explain me the pressurechanges graph in the heart chapter in detail? Thank you!