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A level Biology: Post your doubts here!

Alice123

Alice123

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Noor Ahmad said:
Do not panick,it isn't difficult.
Well,the ornithine cycle is nothing but the urea cycle.
Excess amino acids breakdown forming ammonia and ketoacids.
Amonnia enters the ornithine cycle where it combibines with carbon dioxide.
Here's the cycle.
Tried making as simple as possible.
Im sure you'll understand it.
Click to expand...
Thankyou soooo much :)
 
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dornam

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Can anyone explain me how the pregnancy testing kits? I can't understand from the CIE book. Basically, it says that a pink colour builds up even if hCG is present or not
 
knowitall10

knowitall10

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dornam said:
Can anyone explain me how the pregnancy testing kits? I can't understand from the CIE book. Basically, it says that a pink colour builds up even if hCG is present or not
Click to expand...
Here's my summary:
  • Pregnant women have hCG in their urine
  • antibody-gold complexes are attached to one end of the stick
  • the result strip (which has another immobilized antibody) is at the top of the strip.
  • when the antibody-gold complex is dipped into urine, if hCG is present, it'll bind to it- forming hCG antibody-gold complex
  • depending on hCG levels, the new complex formed will rise (level rises on the strip as the urine seeps up)
  • When the new complex binds with the immobilized monoclonal antibodies, a colour change occurs to show a positive result.
The book says that the procedural control region turns pink even if antibodies aren't there. That's the control basically. So if the pink colour is darker or lighter (depending on what the supplier of the strip wrote on the cover) than that of the control region, the test is positive.
 
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dornam

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Can you help me with this one? If I have 6.25 cm^3 of 10% solution, and I mix it with 3.75 cm^3 of water, what will be the concentration of the solution?
 
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dornam

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Yes, paper 3. But I need to understand this problem, it isn't necessarily related to the paper itself.
 
knowitall10

knowitall10

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dornam said:
Yes, paper 3. But I need to understand this problem, it isn't necessarily related to the paper itself.
Click to expand...
Use serial dilution my friend. Is the question requiring u to add that much water or are you doing it yourself?
 
knowitall10

knowitall10

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Noor Ahmad said:
Can some one tell me how do we measure the actual size of the specimen using a ruler? I dont really understand how are we supposed to do that. question 2a(ii)
And i'd be grateful if you guys could explain me what's meant by "A revised or new prediction' Q1 (f)
Thanks a ton!
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_y07_sp_31.pdf
Click to expand...
The ruler measurment is converted into micrometers or whatever the unit the question measures it in. and then apply the magnification formula:
Whatever you measured/ the actual = magnification. you know the magnification because you're using a microscope right? So if ur using x10 then put that in the formula and if ur using x40,then put that.
I hope i'm clear.
 
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