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  1. I

    A level Biology: Post your doubts here!

    I'm not sure if you took Chemistry before, but if you did, then this should be pretty simple. We know that the number of moles = mass/molar mass We want to prepare a 25 mmol/dm^3 solution. Simply add 25 mmol of sodium nitrate to 1 dm^3 of distilled water. 25 mmol = 25 x 10^-3 moles So now we...
  2. I

    A level Biology: Post your doubts here!

    They tell you that there is a cross between two cats without a tail. Since we know that the 'no tail' allele is dominant, and that there are some offspring that have tails, then both parents are heterozygous for that gene (Aa). If one of the parents were homozygous (AA), then none of the...
  3. I

    A level Biology: Post your doubts here!

    4 = 4 x 100% = 400% Or you could have just done (56/14) x 100% = 400%
  4. I

    A level Biology: Post your doubts here!

    The percentage increase would be 300%, but that's not what they're asking for. They wanted the RELATIVE increase. If you have a 40% sodium chloride solution, that would be eight times as concentrated as a 5% solution, but only a 700% increase. The relative increase would be considered 8 (which...
  5. I

    I don't really think that information is necessary. The mark scheme doesn't even mention it...

    I don't really think that information is necessary. The mark scheme doesn't even mention it. Anyways, the t-test just tells you that there is a significant difference between the two values. It does not tell you WHY they are different. So you can't prove the assumption just by saying "well, the...
    • Irfan1995
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  6. I

    A level Biology: Post your doubts here!

    Serial dilution: Take 20 ml from the 4,000 mg/dm^3 solution and put it in a test tube. Take 10 ml from that solution and put it in another test tube. Then add 10 ml of water. This is the 2,000 mg/dm^3 solution. Take 10 ml from the 2,000 mg/dm^3 solution and put it in another test tube then add...
  7. I

    A level Biology: Post your doubts here!

    When dealing with standard errors, you don't work with significant figures. From what I know, the value and standard error should have the same number of decimal places. Lets say that you want to measure things with a meter ruler (measures to the nearest mm). The length of a paper would be 29.7...
  8. I

    A level Biology: Post your doubts here!

    Hmm, maybe my previous explanation was a too simplistic one. With a chi-squared test, you have expected values and observed values. The value of chi-squared just tells you how much the observed values deviate from the expected ones. You don't actually have two sets of data. You have one set of...
  9. I

    A level Biology: Post your doubts here!

    Using the Oct/Nov 2012 curve, to get an A*, you have to get 194/260 If you already got an 84 in AS, then you will need to get a total of 110/130 in your A2. If you get an 85/100 in P4, then you must get 25/30 in P5 to score an A* Good luck!
  10. I

    A level Biology: Post your doubts here!

    When you are dealing with only one set of date: use chi-squared test When you're comparing between two sets of data: use the t-test Also, according to what I know, the chi-squared test is used for discontinuous data while the t-test is used for continuous data.
  11. I

    A level Biology: Post your doubts here!

    I'm actually a bit confused here. A normal histogram is supposed to have an interval rather than specific values. So I'm guessing here that they are asking for a bar graph (but the bars touch each other) with the number of beans plotted on the x-axis and the frequency on the y-axis.
  12. I

    A level Biology: Post your doubts here!

    1) When you're carrying out a t-test, you will have two different sets of readings. The degrees of freedom is: (number of readings in the 1st set - 1) + (number of readings in the 2nd set - 1) OR: (total number of readings - 2) In the question above, they say that "The cultures were sampled at...
  13. I

    A level Biology: Post your doubts here!

    Lets say you want to make lactose-free milk. Milk naturally contains lactase, so if you want lactose-free milk, you have to add an enzyme (lactase) to break lactose down to its constituent products (glucose and galactose). But if you take a glass of milk and add some enzyme solution, you'll...
  14. I

    A level Biology: Post your doubts here!

    Question 24: You're completely right about the glucose transport proteins being found on the cell membrane, but remember that hormone receptors are found there too. So the number of hormone receptors is limited to the cell's surface area rather than its volume. This makes the second column...
  15. I

    A level Biology: Post your doubts here!

    I just explained this in the post above! If anything needs further clarification, just say so!
  16. I

    A level Biology: Post your doubts here!

    1) Every single protein is held together by peptide bonds. It's not something unique found in collagen only. Plus, some proteins have a very low tensile strength, so they're not even used as structural proteins. 2) Lets say you have one of those inflatable beach boards and it's curled up. When...
  17. I

    Solved physics Paper 5??

    I'd love to help, but I take Physics with the Edexcel board. Our school also offered some advanced courses, so I may be able to help. But for now, I don't even know what a diagram is supposed to be!
  18. I

    A level Biology: Post your doubts here!

    1) Water enters by osmosis, a passive process. There is no need for mitochondria to uptake water. 2) The tidal volume (distance between a maximum and minimum) is 500 ml (equivalent to two vertical squares). The vital capacity (distance between the maximum and minimun in the large peak) is 3.75...
  19. I

    Bio p41 how was it

    Hello everyone, our exam was two days ago, so I'll try to remember my answers and post them here. 1) A: palisade mesophyll cells; B: guard cell; C: air space How does carbon dioxide enter: it enters through the stomata by diffusion where it will travel through the air spaces until it is absorbed...
  20. I

    A level Biology: Post your doubts here!

    1) Didn't I already answer this question before? Anyways, the first column shows how much reducing sugar is present. After hydrolysis, all the non-reducing sugar is broken down to reducing sugar. So the second column represents reducing sugar + non-reducing sugar So if you want the amount of...
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