A level Biology: Post your doubts here!

[Paradoxical]

one of disadvantage of GM crops is development of superweeds.......can somebody explain how gm crops cn lead to development of superweeds?

I found this website helpful:
http://www.sciencemuseum.org.uk/antenna/futurefoods/debate/debateGM_CIPenv.asp

 

[ppaayas]

Anybody got a textbook for download? Please!

 

[hassam]

Anybody got a textbook for download? Please!

http://ebooksfreedownload.org/2011/...ational-aas-level-biology-revision-guide.html

 

[hassam]

http://xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s11_qp_51.pdf
IN question 1 part a.........we have t0 make a range of solutions of different molarities.......i thought that we cud make 1M sucrose soln.....and then use it to prepare the rest using serial dilution technique.......BUT ER AND ms both are saying not to use serial dilution......nd i cnt understand whats wrong with this technique?

 

[rz123]

http://xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s11_qp_51.pdf
IN question 1 part a.........we have t0 make a range of solutions of different molarities.......i thought that we cud make 1M sucrose soln.....and then use it to prepare the rest using serial dilution technique.......BUT ER AND ms both are saying not to use serial dilution......nd i cnt understand whats wrong with this technique?

hmmm neither can i

 

[VelaneDeBeaute]

AoA!
So we were going through some technical practical papers at school and the practical itself is easy to perform with all the given instructions, the theoretical part of it is to me really confusing! I make guesses about what the points could be; but either i get vague ideas or i have so many distinct points that i'm confused up with which ones to write and which ones not to! I am currently using Salma Siddiqui's CIE suggested practical book but it ain't much of a help! How do you overcome such problems, and what kind of understanding do they look for in practical papers?
JZK in advance!

 

[Nibz]

W.S

I think, the theoretical part shouldn't be a problem if you know the facts well. You can probably do well in this part of the paper once you're done with the whole syllabus. With enough 'Bio knowledge' (which comes from books), you can provide good assumptions/suggestions. My opinion.

Good Luck

 

[Nibz]

This can be of some help:

 

[VelaneDeBeaute]

^Thankyou very much Nibz! I hope the problems end up as we wind up the syllabus!

 

[larina]

This can be of some help:

do u have any notes for A2?

 

[larina]

Assalamo Alaikum
Can someone please explain me the whole menstrual cycle including all the hormones?!

thanks.

 

[rz123]

hope it helps source is Revision Guide marry jones

 

[hassam]

LARINA - do chek out http://www.biologymad.com/ under AS level ....there ll be a subheading hormones

 

[hassam]

why tumour cells are used to form hybridoma?
(well MARY JOnes says that since plasma cells do not divide they can't be used alone for producing antibodies)

 

[aliya_zad]

Monoclonal antibodies are obtained from clones of single B cells. Unfortunately, B cells will not grow in culture and this problem is solved ONLY by fusing them with cancerous B cells..the hybridomas then grow in culture and secrete antibodies..

 

[rz123]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s07_qp_2.pdf
2 c part. kindly help!

 

[aliya_zad]

TESTUBE A- results are negative coz the starch has been digested by the enyme at a pH of 6.5( in this case starch absent so iodine test is -ve)
TESTUBE B- starch is not digested by the enzyme coz the pH is 2.00 which is acidic. starch is digested in alkaline conditions. hence starch is present and the iodine test is +ve.
TESTUBE C- enyme is boiled which means it has been denatured and starch can no longer be digested. starch is present.
TESTUBE D- no starch has been added to the testube in the first place. starch is absent and the result is therefore -ve.

 

[rz123]

Thanks aliya_zad !

 

[rz123]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_s07_qp_2.pdf
Q.4 b , can someone explain in a better way i mean a detail answer. thanku

 

[aliya_zad]

FROM SOURCE TO CELL C-
consider the companion cell first,where there is active loading of sucrose taking place.
H+ ions are pumped from the companion cells to mesophyll cells containing sucrose by active transport using ATP as an energy source.
As a result the H+ conc builds up in the mesophyll cells generating a potential difference across the membrane.
The H+ ions then move back into the companion cell down a conc. gradient through carrier proteins co-transporting sucrose molecules.
The sucrose molecules then move through the plasmodesmata into the sieve tube element(cell C)

FROM CELL C TO SINK-
When the sugar enters the cell C, due to low water potential being set up water enters by osmosis.
This builds up hydrostatic pressure.
At sink sugar is being used up( for respiration, conversion of sucrose into glucose and fructose)
This creates a pressure gradient between the source and the sink, causing mass flow of solution in phloem sieve tubes from source to sink.

Hope this is detailed enuf!!