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  1. I

    A level Biology: Post your doubts here!

    X = passes through the phospholipid bilayer Y = passes through the carrier protein (normally through active transport) Z = passes through a transport protein/channel (normally a passive process)
  2. I

    can i still get an A* in biology ?

    Just add up all the grades. You'll get 202/270 which is definitely an A*
  3. I

    A level Biology: Post your doubts here!

    20) The answer is C. Normally, we make RNA out of DNA (using the enzyme DNA Polymerase). Viruses have a way of making DNA from RNA (the opposite) using an enzyme called reverse transcriptase. This piece of information is required at the A2 level only, not AS. 22) Remember that the pressure in...
  4. I

    A level Biology: Post your doubts here!

    You got the 2000th post :P
  5. I

    can i still get an A* in biology ?

    Taking the curve/grade thresholds of the Oct/Nov '12 session (that's the most recent one): Getting a D in P1 means getting at least a 19/40, The minimum mark for an A in P2,3,4,5 are 39/60, 27/40, 67/100, and 20/30 respectively. Adding up all your grades would give you a 166/270. That would...
  6. I

    A level Biology: Post your doubts here!

    A primary structure of a protein is held by peptide bonds only. So there are no hydrostatic forces of attraction at all. This makes option A wrong. There are no ionic bonds in a secondary structure, only hydrogen bonds (responsible for the alpha-helix and beta-plated sheet). This makes option B...
  7. I

    A level Biology: Post your doubts here!

    The answer is A. How is it D? Diffusion evens out the concentrations; it tries to attain equilibrium. For example, if solution A is 1M sucrose, and solution B is 3M sucrose, when the particles diffuse, both solutions would be of 2M sucrose. Active transport does the opposite: it tries to widen...
  8. I

    A level Biology: Post your doubts here!

    I'll try to explain this as simply as possible. At (1), the AV valves close. At (2), the semilunar valves open. Before point (2), the semilunar valves are still closed. So between (1) and (2), both valves are closed. At (3), the semilunar valves close, and at (4), the AV valve starts to open...
  9. I

    A level Biology: Post your doubts here!

    Q13: Active transports pumps ions against a concentration gradient (from a region of low concentration to a region of high concentration). So the cell has a high concentration of potassium, but rather than going from high to low, it will go from low to high. So the low concentration of potassium...
  10. I

    A level Biology: Post your doubts here!

    Oct/Nov '09: 14: The initial rate of reaction is equivalent to the initial slope. Take up to 30 seconds (as the slope is nearly constant). The slope would be 3/30 = 0.1 20: They tell you that the code for valine is CAT. The mRNA codon would be the complement of CAT which is GUA (remember that...
  11. I

    physics unit 5 help !!!

    That's just how it is. This is a value they've given you in the question. You can't just question a given statement.
  12. I

    A level Biology: Post your doubts here!

    Things you have to know first: The atrio-ventricular (AV) valves open when the pressure of the blood in the atria is greater than that in the ventricles. We all know that blood flows from high pressure to low pressure. So when the pressure in the atria is high, blood will flow to the...
  13. I

    *Biology Paper 5 tips*

    When can we discuss?
  14. I

    *Biology Paper 5 tips*

    Most answers are quoted to 2 decimal places.
  15. I

    *Biology Paper 5 tips*

    My exam starts in 5 hours
  16. I

    *Biology Paper 5 tips*

    Everyone seems to be confused between the error bars based on the standard deviation, and those based on the standard error. Error bars whose range is +/- 2x standard deviation: This shows that 95% of the data in one set can be found within two standard deviations from the mean. Error bars...
  17. I

    *Biology Paper 5 tips*

    According to the mark scheme, both answers are correct. That is, it would be correct if you take the error bars +/- 2x standard deviation. It's also correct to take the error bars +/- standard error.
  18. I

    I'm always known to be the baby of my class :P

    I'm always known to be the baby of my class :P
  19. I

    *Biology Paper 5 tips*

    You've calculated the sample standard deviation. You're supposed to calculate the population standard deviation. The formula for the population standard deviation is exactly the same, but the denominator is "n" instead of "n-1" Personally, I don't think it's fair to provide you with the sample...
  20. I

    *Biology Paper 5 tips*

    Good luck :)
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