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Recent content by rexsun

  1. R

    a hard Biology question

    Hey guys, here is one question that I think is pretty hard and is not explained anywhere in the book. I will put it as follows: Which statements explain why injections of vaccine may not provide protection against Vibrio cholerae? 1, V.Cholerae bacteria infect the intestine 2. The toxin...
  2. R

    A question on Biology AS level

    Hello guys, It is suggested that diffusion across walls is different from diffusion across membranes. So if I say, oxygen diffuses into alveoli across squamous epithelium of capillary and across alveolar wall, am I right or wrong ?
  3. R

    AS Biology, a bit confused

    Hi guys. I'm doing chapter 8 at this moment and was confused by the sentence, on page 150, which states' If the protein concentration and rate of loss from plasma are not in balance with the concentration and rate of loss from tissue fluid, there can be a build-up of tissue fluid, called...
  4. R

    About the lock and key model of enzyme

    Hi everyone, I'm studying enzyme at this moment and I want to ask about the lock and key model. In the textbook, the enzyme is described as the lock and the substrates keys, yet I think this description is confusing. I think the logic could also go this way: the enzyme is the key and substrates...
  5. R

    Confused about prevention of Cholera taken by travellers

    Hello everybody. I'm currently learning Chapter 12 in the book written by Fosbery(the recommended Cambridge book), and I find it hard to understand. The book says, as in the last sentence of page 199, that travellers from areas free of cholera to those where cholera is endemic used to be advised...
  6. R

    Physics, Chemistry, Biology --------> Hardest Questions Compiled #A Level Version

    Thanks much!
  7. R

    A level Biology: Post your doubts here!

    Thanks Hanona! Great explanation. I now understand, thanks much. Merry Christmas.
  8. R

    Biology---- Please help!!!

    It depends. U are taking CIE A-level right? I'm using International AS and A-level Biology Coursebook, written by Jones, Fosbery, Gregory and Taylor. You'd better have a look at various textbooks to see which one fits your taste best.
  9. R

    Biology---- Please help!!!

    Hello everybody. I have been confused by the following question for a long time...Please help The answer for this question is D. But why can't C be right? I thought that stomata are open because of guard cells but not transpiration.
  10. R

    A level Biology: Post your doubts here!

    Hello everybody. I have been confused by the following question for a long time...Please help The answer for this question is D. But why can't C be right? I thought that stomata are open because of guard cells but not transpiration.
  11. R

    Chemistry: Post your doubts here!

    Thanks so much! Though I still don't quiet understand what's meant by SP^2 and why it's 120 degree. Anyway I will find out.Thanks
  12. R

    Please help! Chemistry sucks.

    Thanks so much. I have exam tomorrow, your reply is really helpful!!
  13. R

    Chemistry: Post your doubts here!

    First question The answer, as the mark scheme says, is B. I chose A and got it wrong..Can anybody kindly explain a bit about that please!!! The Second one Could anybody explain how to decide the bond angle in this case? D can be ruled out because N has lone pairs, but for the remaining...
  14. R

    Please help! Chemistry sucks.

    First question The answer, as the mark scheme says, is B. I chose A and got it wrong..Can anybody kindly explain a bit about that please!!! The Second one Could anybody explain how to decide the bond angle in this case? D can be ruled out because N has lone pairs, but for the remaining...
  15. R

    Further Mathematics: Post your doubts here!

    Find the area of the surface generated by rotating about the x-axis for curve y=e^(3x), from x=1 to x=4
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