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A2 OCR Exam: 24th May 2005 - Biology Practical watch

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    (Original post by endeavour)
    I asked for model results, even at the expense of losing some marks, but I was denied!
    i would be ok losing marks for messing at the experimen, but the questions made no sense to me due to the fact my experiment for C worked too well or something. I have no idea what it was going on about
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    wow thats quite bad (in response to bilalhassam)
    i unfortunately didnt get those results i got the 2nd and 4th but i got the first being my fastest and 3rd being my slowest. I really hope they lower the grade boundaries -would make me a happy chappy
    unfortunately we couldnt have specimin results so the points i would of lost for having them i lost anyway for wrong results.
    im not sure how they could say no marks for that Q - would they make us do another one?
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    My experiment didn't work at all so my teacher gave my the specimen results that only C contained starch. But my school is complaining about the first part of the exam as the results were so difficult to obtain.
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    yes, endeavor, u are right... it is about equilibrium... so i spose u'll get marks for talking about optimum pH ... but... according my college's specimin results... the optimum was 7 (which was C)... the ethanoic acid and NaOH changed the pH and became less optimum...
    Willb1986... i dunno bout your specimin results....?!!?!
    My college is comlaiing as well....
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    i asked for model results too and was given them cause i only got starch shown in A.
    The results showed D was fastest then I cant remeer if it was a or c and then no starch in B.
    I still didn;t understand the expereiment though
    I've failed - looks like i'm not goign to uni!
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    (Original post by endeavour)
    Well unfortunately I didn't work it out until after the exam! I basically made some results up, but couldn't work out why starch seemed to appear (I had thought that it was being hydrolysed)

    Argghhhhh I really needed a solid A on this, to at least compensate for the synoptic!
    Oh well, at least there was plenty to write (or complain..) about in the evaluation!!
    D SHOULD NOT HAVE PRODUCED STARCH!!! Its impossible
    the enzyme converts starch and phosphate into glucose phosphate... this is when phosphate is in excess... if the glucose phosphate is in excess the reaction is reversed! D had been prepared with boiled extract and so the enzyme will have denatured. i thought my D produced starch but realised that this was due to D being a lot darker than the other samples...

    AND Please everyone... dont worry bout performing badly... at the very least the boundries would be dropped and the results scaled up. The practical is worth 10% and the marks for the actual results would only work out to be a coulple %... just concentrate on your other exams now... whats done is done.........
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    (Original post by Chopsta)
    Hi guys, thanx for all the advice and tips people have posted on here - were much appreciated!! The practical. God these guys call themselves examiners??? I think they need bloody english rather than biology. They cant even write in sentences! Ne one else think so??? I mean come on, the last part on section a " using iodine, spotting tiles and a clean pipette remove samples from the tubes at regular timed intervals and test for starch in the tubes ", I cannot remember how it went, but it kinda implys to test for starch in the tubes, doesnt it? Luckily i didnt do that but my other friends who were in another lab, loads of them did that, and there were tears and evrything, and the teachers didnt have specimen results, becoz the solutions had been only prepared that mornin so... The microscope question was fine i thought, got 6.6% i think 4 vasc. and 3% for phloem, but the other bit i really didnt like. Another thing was the question that confused me, wen it sed somthing like, explain ur results u got from the tubes, well i didnt get ne results from the tubes, got them from the spotting tiles!!! Neva mind ova nd done with now, got chem to think about on thurs!!!

    The method was very confusing, and i wasted too much time re-reading it!!! I didnt have any knowledge about what to expect, so i couldnt prepare myself for what i had to endure this morning :mad:

    I did very badly overall, and i'm starting to see the seriousness in how much revesion is needed to pass biology at A2
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    WHAT THE FRIKIN HELL HAPPENED THIS MORNING, I FEEL ABUSED AND MENTALLY RAPED.

    everyone just laughed after the experiment,

    ok number 1. They say put all the stuff on the spotting tiles and start adding the solutions etc. Oh but wait a minute as when i looked to the top of the next page they are like yeah make a frikking table, start the stopwatch and record your results. OI OCR U muppets why dont u tell us this before adding the samples to the iodine and then we will be ready to start timing.

    2. All our results were wrong , nearly everyone said D produced starch, and i thought i had a good explanation for C except i later found my results r wrong so basicallly ive defied the laws of biology aand enzymes etc. i spent a whole page justifying *******s results.

    3. This third point is the funniest. OCR want a theme running through the plans and practical so IF U R GONNA DO THIS MAKE IT GOOD. Dont come up with something as lame as naming ranuladsafdsgdhg bulbousvdvkg (buttercup) all the time just to link it to the plan. And they also think that getting us to estimate the % cover of bundles and phloem is really a good way of linking it to quadrats, OCR SUCK, BIOLOGY SUCKS.

    ok, i feel better now.
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    what did everyone draw for the last question? I didn't understand, so i just drew what i remembered from last year -- what a sieve tube and a companion cell looked like!
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    Indeed the exam sucked. Everyone ion my year got a reaction for D.. I didnt relaise till after the exam we really werent meant to get that.. i did wonder about the heat and the enzyme within it. Most of it, just padded it out. ah well.
    (Original post by emilie1313)
    I've failed - looks like i'm not goign to uni!
    In the overall sceme over two years results its worth like 5% dont fret.

    and
    "ok number 1. They say put all the stuff on the spotting tiles and start adding the solutions etc. Oh but wait a minute as when i looked to the top of the next page they are like yeah make a frikking table, start the stopwatch and record your results. OI OCR U muppets why dont u tell us this before adding the samples to the iodine and then we will be ready to start timing."
    Going to sound stupid, But didnt you teacher ever tell you to sit and read it all through, entire practical, before you start...? Makes it alot easier.
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    OMG i know!!!! I sat there completely confused thinkin y the hell am i looking for iodine to go blue-black when the sodding enzyme is supposed to be breaking starch down????

    I found that tube A (with ethanoic acid) was the first to show blue-black - i put it down to the acid altering the pH - this changes the charges on the R groups + hence affects the temporary bonds between the active site + substrate

    Test tube B (with sodium carbonate) came next - again I put it down to pH - but it effected it to a lesser extent as the pH only changed to 8.

    Test tube C was the slowest (with the exception of D) as the pH was at its optimum

    Test tube D i got no starch since the enzyme had been denatured :s bit of an iffy one that - wasn't sure what was happenin lol

    Anyway that's my take on things - but rest assured I was as completely confused as everyone else!!!!

    Ellie xxx
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    i jus thought it was crap!

    grrrr... better do way better in the papers or im screwed!
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    (Original post by trachea)
    WHAT THE FRIKIN HELL HAPPENED THIS MORNING, I FEEL ABUSED AND MENTALLY RAPED.

    everyone just laughed after the experiment,

    ok number 1. They say put all the stuff on the spotting tiles and start adding the solutions etc. Oh but wait a minute as when i looked to the top of the next page they are like yeah make a frikking table, start the stopwatch and record your results. OI OCR U muppets why dont u tell us this before adding the samples to the iodine and then we will be ready to start timing.

    2. All our results were wrong , nearly everyone said D produced starch, and i thought i had a good explanation for C except i later found my results r wrong so basicallly ive defied the laws of biology aand enzymes etc. i spent a whole page justifying *******s results.

    3. This third point is the funniest. OCR want a theme running through the plans and practical so IF U R GONNA DO THIS MAKE IT GOOD. Dont come up with something as lame as naming ranuladsafdsgdhg bulbousvdvkg (buttercup) all the time just to link it to the plan. And they also think that getting us to estimate the % cover of bundles and phloem is really a good way of linking it to quadrats, OCR SUCK, BIOLOGY SUCKS.

    ok, i feel better now.
    trachea, u said it! This is the worst paper i have ever done. bar none. i feel so depressed. i can not believe the questions they set. the wording was contradictory and the layout was terrible. i honestly STILL do not know what the practical was trying to achieve... hydrolysing starch or making it. must have panicked when i saw it.

    all i could truthfully answer was the ; evaluation / all the slide bit / one of the questions about ph

    how many marks do u guys think i will get?

    i feel like iv failed biology today because of this one paper.
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    I thought it was ok generally. We were given specimen results becoz the iodine didnt change colour at all for any of the A B C D solutions. It was that only C changed to black.
    I am really confused about the % thing now on section 2. Does anyone know for definite if we were supposed to do 1/4 pi r squared. I dodnt, i just worked out a basic % based on the number of squares?
    Hu else did it like me?? :confused:
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    [QUOTE=Nixta]I thought it was ok generally. We were given specimen results becoz the iodine didnt change colour at all for any of the A B C D solutions. It was that only C changed to black.
    QUOTE]
    i hate my school cos i asked for the results but they said we werent allowed. i think the system is really unfair. :albertein
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    To everyone who positive starch test for D
    did you by any chance wipe your tile with a cloth before performing your test because if so you will have contaminated it with starch from the paper, at least that what happened at our school. I ended up testing the freaking tissue paper in the end, and at the end when i asked the invigilator, he told me I was right and there was starch in the cloths provided. Great thinking!
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    I said that D HAVE starch (since I am saying what I am seeing)

    My theory is:
    A/B - no enzymes, denatured by pH extremity, no starch made

    C - enzyme working, glucose phosphate turned into starch, iodine turns blue-black

    D - enzyme denatured already, starch present in the first place - therefore test is postive

    for me, C/D is postive and A/B is negative!!

    PS the % coverage thing, I just estimated the squares - how many marks will I lose!!
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    As the practical was poorly planned with a clear lack of common sense on the behalf of OCR, is there the slightest chance that a mass complaint could render the exam results that they have accumulated from the practical void. Surely if enough centres complained then OCR would have to act upon such mass histeria. I feel that it is unapropraite for them to accumulate results based in a floored practical.

    Does anyone have any ideas of how a boycott would be bought about??
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    (Original post by ecolier)
    I said that D HAVE starch (since I am saying what I am seeing)

    My theory is:
    A/B - no enzymes, denatured by pH extremity, no starch made

    C - enzyme working, glucose phosphate turned into starch, iodine turns blue-black

    D - enzyme denatured already, starch present in the first place - therefore test is postive

    for me, C/D is postive and A/B is negative!!

    PS the % coverage thing, I just estimated the squares - how many marks will I lose!!
    That's exactly what i said!!! Looks like we're wrong about D though. Bloody OCR...honestly, of all the god damn things they could have chosen they pick some obscure twisted experiment and an AS one...well done them!!! (well said trachea by the way!!)
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    What a laughable practical that was. My A, B and C solutons didn't turn blue-black like you normally see with the starch complex, and they stayed a very similar colour to the original solutions. In the end I just made my results up:

    A - 8 mins
    B - 8 mins
    C - 5 mins
    D - no starch

    The pH testing was awful as well. A gave me a pH of 5.5 and B a pH of 6.0. Bloody Universal Indicator and pH colour charts.

    The write up was mind boggling, though I did mention how pH may have had an effect on A and B, optimum conditions, denaturing of enzymes and all that hokery pokery. What I didn't understand was what was catalysing the reverse reaction. I just guessed that it was the same enzyme which catalysed the hydrolysis of starch into glucose phosphate, and blabbered on about changing the position of equilibrium and blah blah.

    I know that the method for the experiment is designed to be complete trout so that you have a lot to write for the evaluation, but this was mostly incomprehensible.

    The microscopy was fine, though counting the squares was annoying and I've probably fecked up a bit by forgetting that it was a 1/4 of a circle and not a square. :banghead:
    I may have lost another mark or so on the high power diagram of the sieve tubes, seeing as I stupidly forgot to include the cell walls and just drew outlines.

    Revision here I come!
 
 
 
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