Bile + Lipase + Milk Coursework

[jason01]

Coursework title: Investigating the effect of a chosen factor on the activity of lipase.

I have decided to change bile concetrations and see how this effects the activity of lipase, but I do not have the faintest clue how to do the write up.

What should I mention and talk about?

Any help will be greatly appreciated.

[Happydadtoo]

Bile does two things (as well as being an excretory product)
1) raises pH to one near to the lipase optimum (remember the fatty acids produced will tend to lower pH, and chyme is pH 2)
2) increases the surface area of the fat droplets, and since the lipase is a hydrolysis enzyme, the water can only be available/present at the surface of each oil droplet
IF you are using a solution of bile SALTS (probable), then the pH effect will NOT be present (I assume you'll use a pH probe to measure the RoR)
You just need to ensure that the STARTING pH is somewhere JUST above optimum
HD2

[jason01]

Should I mention that milk that has not been pasteurised, already contains lipase?

[Happydadtoo]

yes, but it's not possible to BUY such milk in the uk.
only UHT milk could be guaranteed to have no lipase activity
hd2

[jason01]

Are these many improvements that can be made, in order to make the experiment more accurate?

[Happydadtoo]

go through each and everypiece of apparatus you use and see if it could be replaced with aomething more accurate (syringes with pipettes, for example)
Then look at anything which relies on your judgement (end-points) and suggest that theycould be replaced with instruments (like a colorimeter)
See if you could use a data-logger, to allow for more results over a longer time at more acurate time intervals
Do more repeats to allow for more RELIABLE results

You'll also do yourself a favour if you calculate the % error at each step and then add them together to give max poss error in the expt (totals of 50-100% are normal)

HD2

[jason01]

Would Chi-squared test be necessary here?

[Happydadtoo]

chi-squared requires you to have (sensible) 'expected results'
That means categorical data AND the ability to predict results.
In this case, you have neither.
Chi-suared is for behavioural and genetic expts ONLY
HD2

[jason01]

To get high grade what would you be expected to talk about, except for the experiment that you are doing?

[Happydadtoo]

there are basically two areas:
1a) go through your methodology and examine the whole thing to see if you could improve the individual pieces of apparatus you use (syringes > pipettes, for example), use of dataloggers etc
1b) Go through the OVERALL method and see if you could get the same answers, but by an entirely different method - such as measuring turbity in a colorimeter, rather than pH with a pH meter or making milk+ agar jelly blocks and seeing how quickly they break down/go clear in lipase
Part of this is to ensure more and better controls!

2a) Extension work:
suggest more repeats and over a wider range of variables - such as using different temps; a wider range of concs of both lipid and enzyme; different lipids (sat, mono-unsat, poly-unsat); lipase from different species; diff concs of bile salts; diff pH's etc etc

2b) Extension work:
Suggest use of much more advanced apparatus - such as 14C isotopes or G/L chromatography or mass specs or e/m imagery etc. These only need to be mentioned VERY briefly - such as the use of G/L chromatograms to identify the individual fatty acids produced to determine WHERE the lipids are being hydrolysed and into WHAT

The whole of this section needs to constantly refer back to the basic science involved - so ^repeats = more reliability, but 1000 repeats is not much reliable than 30, but takes 30x as long; lipase concs from 0.1-2% are probably MORE useful than concs from 0.00001 to 100% lipase (as those are the range of concs found in the gut); running the expt over longer time periods MIGHT be better - but at what time cost, given that you can calculate Vmax and the Merckalis-Menton equation from the data you have (PLEASE DON'T DO THEM!) etc etc etc

Basically, 'I would like to this xxxxxx , because I will then get better results because of yyyyyyyy .... and so on.
HD2

[jason01]

In "Conclusion" section would you advise having as much science as possible to account for possible anomalous results?

[Happydadtoo]

in general, yes (though 'as much as possible' sounds a bit OTT!)

[jason01]

I know this is a stupid question, but I know that some people last year at my school achieved 28/30. What would you say they would have to do to get full marks this time round?

[Happydadtoo]

Go to the AQA website and download the coursework mark-scheme; then 'tick the boxes'. It ereally isa s simple as that.
Sadly, there is a second hurdle to overcome - namely, that of your teacher. Nowhere in the mark-scheme does it say ANY section has to be 'perfect' or even 'nearly perfect'. Yet many teacher s refuse to award full marks because they think it (ie one small section) could have been better.
Rubbish!
My students rarely, if ever, got BELOW 26/30, with roughly 20% getting 30, 30% getting 29, 30% getting 28 and 15% getting 26/27.
Only those who refused to listen got below that.

I also obeyed the rules STRICTLY - students handed in work and I wrote comments on 'post-it stickers or a header sheet; they would then go away and correct/improve the work before handing it in to be marked.
The rules state 'teachers may not mark the work and then allow students to make improvements'.
I didn't break the rules; nothing was written ON THE STUDENTS' WORK - just on a cover-sheet
The student did not ask me to MARK it until the final submission.

Two other points I found helpful - have a looka t a top quality script from previous year/s so taht you can se what gets marks and wher marks are lost
Get a fellow-student to look CLOSELY through the script and correct/indicate any places where what you have written is not ABSOLUTELY clear.
Finally, check and recheck that you have ONLY used SI units
(no mins + secs - secs ONLY;
not ml - always cm3;
'g' not 'gms'
Table column headings have units, individual rows/numbers do not

Hope that helps a little - it's a pity that some teachers seem top believe in a 'macho' approach rather than to get the highest possible mark for their students. The ideal Moderator's report says 'the marks were generally rather generous, but within tolerances, so were passed.
Tolerances, incidentally, means +/- 3, so if the examiner thought you were worth 30/30, but your teacher gave you 27, 28 or 29/30, then NO CORRECTION WILL BE MADE.
And 3/30 is one heck of a lot of UMS points.
My own feeling is that the tolrance should be +/= 2 marks, with a blanket correction applied if a whole sample is generally more than 1 mark away from the moderator's standards (ie they are ALL a bit too high or low, as opposed to a single script).

The final point is whether your school/college takes internal moderation seriously - we did not, so one colleague's students were invariably punished because of her marking, whilst another had favourites who gained higher marks compared to others in teh same set.
Grossly unfair? Yes, and I hope not replicated elsewhere.
HD2

[Pesk]

Wow. Why didn't I notice this forum before?!
I'm doing almost the exact same coursework (effect of bile conc on pH of hydrolysed milk... or something like that...haven't done the title yet!), but now that I'm analysing the results, I seem to have no idea why I predicted (and gained) results that show the lower the concentration of bile, the more the pH of the milk drops. Why is this happening and is it expected?