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    Hey everyone, I am a medical student who doesn't really have time to do any proper, paid tutoring, however I am interested in teaching and helping people in general. I have tutored before, so if anyone is stuck on any GCSE/AS/A2 biology (or chemistry too for that matter) then feel free to ask and I'll help. Also if anyone has any questions about applying to medical school then I can help there too as I was in that position only last year, so it's fresh in my mind. I got 4 A's at AS and 3 A*s at A2 (bio, chem, maths, all above 95%)
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    This is probably the most easy question for you, but I always get confuse in which part of the body produce which enzyme for digesting food......please make it as simple as it can be cause I am just doing IGCSEs. Thanks.......Actually if there are interesting parts can you also tell me......just because my brain might just fall asleep by looking at tables again. Thanks!!
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    (Original post by Mosmps1)
    This is probably the most easy question for you, but I always get confuse in which part of the body produce which enzyme for digesting food......please make it as simple as it can be cause I am just doing IGCSEs. Thanks.......Actually if there are interesting parts can you also tell me......just because my brain might just fall asleep by looking at tables again. Thanks!!
    Okay, in its simplest form:
    Mouth = Salivary carbohydrases e.g. amylases
    Stomach = Proteases e.g. pepsin
    Pancreas = Pancreatic carbohydrases (amylases again), proteases (trypsin) and lipases
    Lining of small intestine = Carbohydrases (maltase, lactase, sucrase) and proteases

    The mouth and stomach also produce lipases, but don't worry much about that unless you have to, I didn't.

    I'm not sure how much detail you need to know, but when I did GCSE, I remember we only had to remember that amylases are made in the mouth and pancreas, and maltase, lactase and sucrase are made in the small intestine, everything else we simply had to remember as lipases, carbohydrases or proteases.
    If you're struggling to remember that list above, then just try and think of some ways of remembering them, in other words, think of something that stands out, a good way to remember that carbohydrases are in the mouth is to think that when you chew bread for a long time, it begins to taste sweet (because the enzymes are breaking the polysaccharides into sweet disaccharides), and I don't know about the stomach, but whatever helps you to remember what is made where.
    Not sure if that was helpful or not, if you're still stuck on something let me know
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    I also need to know about lipases. But I always confused myself with the functions between bile from gall bladder and lipases. Which one actually breaks fat molecules down to glycerol and fatty acids?
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    (Original post by Mosmps1)
    I also need to know about lipases. But I always confused myself with the functions between bile from gall bladder and lipases. Which one actually breaks fat molecules down to glycerol and fatty acids?
    Okay, so bile is made in the liver and stored in the gall bladder, lipases are made in the pancreas. The key thing to remember is that bile HELPS with the breakdown of fats but it does not break down fat. Let me explain, bile contains bile salts, which are emulsifiers, in other words they allow fat and water to mix. If you eat fat, it will clump together in the water in your bowel and will therefore have a smaller surface area. This small surface area slows down the rate at which fat is broken down by the lipases.
    If you want to know, the way bile salts work is by clustering around the fat particles, bile salts have "water-loving" hydrophilic heads and "water-hating" hydrophobic tails, the salts therefore cluster around the fat particle with their heads facing outward. This keeps the flat droplets small and therefore increases the rate at which the lipases break them down to fatty acids and glycerol.

    So to answer your question
    Lipases break down fat molecules
    Bile helps keep the surface area of these fat molecules large so that the lipases can break down the fat more quickly
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    How does the 3-5 thing on DNA and the action of DNA polymerase work?
    And for chemistry is there an easier way to remember ionisation energies, the factors affecting it and the trends?
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    which uni's did you apply for and why
    and which uni are you studying in?

    thanks
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    (Original post by thea_)
    How does the 3-5 thing on DNA and the action of DNA polymerase work?
    And for chemistry is there an easier way to remember ionisation energies, the factors affecting it and the trends?
    Right, so DNA is made up 2 strands, and each strand is made up of repeating units called nucleotides. A nucleotide has a phosphate group, a nitrogenous base and a pentose sugar called deoxyribose. Deoxyribose has 5 carbons, and those carbons are labelled 1' (1-prime) to 5' clockwise. So the 1' carbon is bonded to the base, the 3' carbon is bonded to the OH group and the 5' carbon is bonded to the phosphate. So each DNA strand has a 5' end and a 3' end, the 5' end is the end with the unbound phosphate group and the 3' end is the end with the unbound OH group. Now, as we know, the DNA sequence is a string of letters (ATCG), when reading the genome, you read it in the 5' to 3' direction. So if you had a sequence 5'-ATGGCTAC-3', that would be read ATGGCTAC rather than CATCGGTA.

    The key point in DNA replication is that DNA polymerase can only bind to the 3' end of a growing DNA daughter strand. So DNA binds to the 3' end of a primer (don't worry about what this is unless you're at A2 level) and bonds the nucleotides together, so polymerase moves in a 5' to 3' direction. It gets a bit more complicated than this, as you get okazaki fragments, and I won't go into what they are unless you want me to, or unless you need to know what they are, but I never did before uni.

    As for ionisation energies, it is very important to understand the subshell sequence, and that as you move a long a period, you get an increase in protons in the nucleus, so if we look at period 3, Mg is greater than Na because it has 1 more proton, but Al is LOWER than Mg because Al has electron config of [Ne]3s2 but Al has an electron config of [Ne]3s2 3p1, and that 3p1 electron is actually further from the nucleus. The other weird one is P being greater than S, and that's because phosphorus has half shell stability, one of sulfur's electrons is sharing a p orbital and therefore experiences repulsive forces. So yh, just know the subshells, it really helps
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    (Original post by Ishea16)
    which uni's did you apply for and why
    and which uni are you studying in?

    thanks
    Bristol, Birmingham, BSMS and Imperial, got offers from BSMS and imperial and I am currently at imperial. I applied to these ones because I messed up on the UKCAT, I got lucky and aced my BMAT so BSMS and imperial were good choices, the other 2 were a tad too competitive at the interview stage (because they required no entrance exams). Basically, I played to my strengths, which were my grades and my BMAT score (although I took a gamble with that because you do your BMAT after you apply). That's how you get into medical school, unless you're good at everything in which case you could probably get in anywhere
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    (Original post by AortaStudyMore)
    Bristol, Birmingham, BSMS and Imperial, got offers from BSMS and imperial and I am currently at imperial. I applied to these ones because I messed up on the UKCAT, I got lucky and aced my BMAT so BSMS and imperial were good choices, the other 2 were a tad too competitive at the interview stage (because they required no entrance exams). Basically, I played to my strengths, which were my grades and my BMAT score (although I took a gamble with that because you do your BMAT after you apply). That's how you get into medical school, unless you're good at everything in which case you could probably get in anywhere
    ahh thats a good strategy
    so you think its better to do BMAT and UKCAT in case you mess one of them up?
    thanks
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    (Original post by Ishea16)
    ahh thats a good strategy
    so you think its better to do BMAT and UKCAT in case you mess one of them up?
    thanks
    If you do badly in the UKCAT, then you kind of have no choice but to do the BMAT if you still want to get into medical school, because almost everywhere needs the UKCAT now apart from the "sciency medical schools" (oxbridge, UCL & imperial) and bristol I think. So this kind of suited me anyway, as science is my strong point, and BMAT is definitely a more science-focused exam compared to the UKCAT, and imperial's medicine course is also very science-orientated (I've done far more research and statistical analysis in my first 2 terms here than medical procedures). So yh UKCAT is very important, unless you're like me in which case the BMAT was a better alternative
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    Hello, I have a question about chemistry. How did you remember the reactions for alcohols?
    Also, chemistry's probably the hardest out of all my subjects and everyone I know is struggling so much, so how did you manage to get such good grades (congrats btw) and are there any tips you could give?

    Thank youu x
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    (Original post by AortaStudyMore)
    If you do badly in the UKCAT, then you kind of have no choice but to do the BMAT if you still want to get into medical school, because almost everywhere needs the UKCAT now apart from the "sciency medical schools" (oxbridge, UCL & imperial) and bristol I think. So this kind of suited me anyway, as science is my strong point, and BMAT is definitely a more science-focused exam compared to the UKCAT, and imperial's medicine course is also very science-orientated (I've done far more research and statistical analysis in my first 2 terms here than medical procedures). So yh UKCAT is very important, unless you're like me in which case the BMAT was a better alternative
    oh I see,
    Thank you very much
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    (Original post by AortaStudyMore)
    Right, so DNA is made up 2 strands, and each strand is made up of repeating units called nucleotides. A nucleotide has a phosphate group, a nitrogenous base and a pentose sugar called deoxyribose. Deoxyribose has 5 carbons, and those carbons are labelled 1' (1-prime) to 5' clockwise. So the 1' carbon is bonded to the base, the 3' carbon is bonded to the OH group and the 5' carbon is bonded to the phosphate. So each DNA strand has a 5' end and a 3' end, the 5' end is the end with the unbound phosphate group and the 3' end is the end with the unbound OH group. Now, as we know, the DNA sequence is a string of letters (ATCG), when reading the genome, you read it in the 5' to 3' direction. So if you had a sequence 5'-ATGGCTAC-3', that would be read ATGGCTAC rather than CATCGGTA.

    The key point in DNA replication is that DNA polymerase can only bind to the 3' end of a growing DNA daughter strand. So DNA binds to the 3' end of a primer (don't worry about what this is unless you're at A2 level) and bonds the nucleotides together, so polymerase moves in a 5' to 3' direction. It gets a bit more complicated than this, as you get okazaki fragments, and I won't go into what they are unless you want me to, or unless you need to know what they are, but I never did before uni.

    As for ionisation energies, it is very important to understand the subshell sequence, and that as you move a long a period, you get an increase in protons in the nucleus, so if we look at period 3, Mg is greater than Na because it has 1 more proton, but Al is LOWER than Mg because Al has electron config of [Ne]3s2 but Al has an electron config of [Ne]3s2 3p1, and that 3p1 electron is actually further from the nucleus. The other weird one is P being greater than S, and that's because phosphorus has half shell stability, one of sulfur's electrons is sharing a p orbital and therefore experiences repulsive forces. So yh, just know the subshells, it really helps
    I don't know if this is going to sound stupid, but where does the OH group come from?
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    (Original post by rbvfer)
    Hello, I have a question about chemistry. How did you remember the reactions for alcohols?
    Also, chemistry's probably the hardest out of all my subjects and everyone I know is struggling so much, so how did you manage to get such good grades (congrats btw) and are there any tips you could give?

    Thank youu x
    Unfortunately mechanisms an equations in general just have to be memorised.
    The best thing to do (and this is what I did) is to write down all the key equations and mechanisms on one piece of paper and then try and commit those to memory. It's really worth it, as they're worth a lot in the exam. It takes time, but once you know them then it makes the exams so much easier. Chemistry is sadly mostly just a memory game, there isn't much understanding involved, and that's why people tend to find it so hard while others don't. But yh, what I would recommend in general is to make notes and just try and memorise them in whichever way is best for you, for me it would just be write them all out and recite them until I knew them, in other people's case it might making mnemonics. Also, 100% do past papers, they always repeat questions in the exams! So do them and learn the mark scheme answers.
    Tips in general would be to work hard throughout the year, and try and understand everything as you go, and make notes, also, what I do for everything is explain something in my head as if I was trying to explain it to someone who doesn't understand, because you don't truly understand something unless you can explain it simply to someome else (I'm sure einstein said that once)
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    (Original post by thea_)
    I don't know if this is going to sound stupid, but where does the OH group come from?
    The OH group is part of the structure of deoxyribose, google it and see, I would post a picture myself but I'm in a rush to get ready for lectures this morning!
    But yh, the OH group bonds to the OH on the phosphate of an adjacent nucleotide to form what's called a phosphodiester bond. This is a dehydration/condensation reaction (as a H and an OH are eliminated to form H2O) and it forms the sugar-phosphate backbone in DNA
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    (Original post by AortaStudyMore)
    The OH group is part of the structure of deoxyribose, google it and see, I would post a picture myself but I'm in a rush to get ready for lectures this morning!
    But yh, the OH group bonds to the OH on the phosphate of an adjacent nucleotide to form what's called a phosphodiester bond. This is a dehydration/condensation reaction (as a H and an OH are eliminated to form H2O) and it forms the sugar-phosphate backbone in DNA
    Ah okay, thank you!
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    hi! i was just wondering whether anyone can help me, I have a Biology ISA soon and i was wondering if anyone can help me with statistical tests and their calculations. ive had a look at previous ISA's on the Biology aqa site and they ask for calculating using formulas they give you. can anyone help with using the chi and spearmans formulas please? any help would be appreciated (doing some practice/revision for ISA).

    it states on the statistic sheet for spearmans rank "where n is the number of pairs of items in the sample and D is the difference between each pairof ranked measurements" does this mean we have to rank our data from highest to lowest and use THAT to work out d and then d2?

    and general help for chi...
    MANY THANKS :-)
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    (Original post by randoms132)
    hi! i was just wondering whether anyone can help me, I have a Biology ISA soon and i was wondering if anyone can help me with statistical tests and their calculations. ive had a look at previous ISA's on the Biology aqa site and they ask for calculating using formulas they give you. can anyone help with using the chi and spearmans formulas please? any help would be appreciated (doing some practice/revision for ISA).

    it states on the statistic sheet for spearmans rank "where n is the number of pairs of items in the sample and D is the difference between each pairof ranked measurements" does this mean we have to rank our data from highest to lowest and use THAT to work out d and then d2?

    and general help for chi...
    MANY THANKS :-)
    Hey, I am writing this with a sickening hangover so I apologise if bits of what I write are rubbish, but I'll try my best! You've also unfortunately asked me about the 1 statistical test that I've never had to do, so my knowledge on chi squared is a bit limited, but from what I remember, it is used to determine if the values you obtain from experiments agree with what you predict the results would be. It'd help if you gave me a proper example question to take me through, but just to give you an idea of what I mean, imagine you have a maze with 2 paths in it, the end of 1 path has damp cotton wool and the end of the other path is dry. If you were to then place 100 maggots in your maze one at a time, if the dampness has no affect on where they go, then you would EXPECT that 50 go down each pathway, however if you record how many go down each, you might actually OBSERVE that 70 go down towards the damp wool and 30 go down towards the dry pathway. The value for chi squared is then something like sigma( (O-E)^2 / E ). (sigma just means sum). So in my quick example, O-E would be 20 and -20 for the 2 samples. Squaring the values just makes them positive (or else you sum would be 0), the squared values would be 400 each, dividing these by E gets 8, and adding them together get 16. So your chi-squared value = 16. You then have to refer to this value to one in a table to determine your P-value (the probability that the difference in results is due to chance). So first you need to determine the degrees of freedom, which is the number of options minus 1, in this case the number of options is 2 (the maggots could go down 1 of 2 routes), you then refer this to the table of critical values
    http://filestore.aqa.org.uk/subjects...-TRB-OGSSS.PDF ). For a df of 1, the critical value is 3.84, IF YOUR CHI-SQUARED VALUE IS GREATER THAN THE CRITICAL VALUE THEN p<0.05 = a statistically significant difference (I hope this is right, someone correct me if I'm wrong it's been a while since I've done this). I think a similar example to the one I just used has been done before, so have a look through past papers, and if you have any more questions about this then ask me.

    As for spearman's rank, yes you do rank all the values in the 2 samples, the key thing is to rank them all in the same way for both samples, i.e. don't rank one sample from highest to lowest and the other sample from lowest to highest. And then you go about working out your spearman's rank from those ranks. So find the difference in ranks, square them, add them up, multiply by 6, divide by n(n-1) and then take that away from 1. If your value is less than the critical value, then p<0.05

    Hope that helps, and I also hope it's all right, I could have done with my notes on it from last year, anyway I need to go and do something productive with my life.
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    Hey I am currebtly doing the new spec OCR A as level biology and I understand the work it's just I cant apply it very well and I was wondering if you could give me some tips for the exam? Every oast paper I've done I only get C's and once I did get a B but the thing is I know all of the details it's just when it comes to applying the knowledge in exams I can't do it very well
 
 
 
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