OCR exam board PAG 7.2

Have this prac lined up, never done it before and it looks hideous. Not sure where to start.
Still waiting for the Bacillius subtillis to come in.
Found a lot of things out of stock.
 
I remember doing that one, there is a lot of prep and sterilising involved. It does say in the notes that an alternative could be used instead of using E. coli. I think I gave up with the idea of LB broth and just used the nutrient broth that I usually culture the bacteria in.
 
I agree. Technically its not difficult, it just seems to be an exercise in providing bulk loads of equipment. 10 agar plates per student, 8 sterile bijou bottles. Its definitely one of those ones that whoever wrote it wasn't thinking it through properly.

From bitter experience I try and sway the teachers to do 7.1 first as it at least covers the antiseptic technique part of the practical so the students can work faster when they have to plate up their 10 plates for 7.2
 
I remember doing that one, there is a lot of prep and sterilising involved. It does say in the notes that an alternative could be used instead of using E. coli. I think I gave up with the idea of LB broth and just used the nutrient broth that I usually culture the bacteria in.
We just use nutrient broth and have switched to E.coli as it seems to grow more reliably.
 
When setting this up I had two main issues. Firstly the shear amount of plates and equipment needed, as they ask for 10 plates per pair, so potentially 100 per class (at the time we have five biology classes), plus large numbers of bijou bottles. In the end I agreed with the teachers that two pairs would form a group for results sharing, i.e. one pair would use the 24hr culture and the other the 48hr culture then share results, cutting the amount of plates and bottles needed by 50%.

The other thing is that because you need to make up 24hr and 48hr cultures you can't set it up on Friday because of the weekend, so the practical can only be done from Wednesday onwards (i.e. starting the 48 hour culture Monday morning then the 24hr culture Tuesday morning). As the group are meant to look at the plate after 24 hours it is actually only really suitable to carry out on Wednesday and Thursday, although I suppose if you do it on Friday you could stick the plates in the fridge to slow growth to look at on Monday at a push.
 
When setting this up I had two main issues. Firstly the shear amount of plates and equipment needed, as they ask for 10 plates per pair, so potentially 100 per class (at the time we have five biology classes), plus large numbers of bijou bottles. In the end I agreed with the teachers that two pairs would form a group for results sharing, i.e. one pair would use the 24hr culture and the other the 48hr culture then share results, cutting the amount of plates and bottles needed by 50%.

The other thing is that because you need to make up 24hr and 48hr cultures you can't set it up on Friday because of the weekend, so the practical can only be done from Wednesday onwards (i.e. starting the 48 hour culture Monday morning then the 24hr culture Tuesday morning). As the group are meant to look at the plate after 24 hours it is actually only really suitable to carry out on Wednesday and Thursday, although I suppose if you do it on Friday you could stick the plates in the fridge to slow growth to look at on Monday at a push.
Totally agree on both issues. Whoever planned this practical wasn't thinking of how much equipment would be needed for a class, or about the timings to fit around school.
I've been asked for it first period on a Monday before now. The teacher seemed surprised when I pointed out that I don't work weekends!
 
When setting this up I had two main issues. Firstly the shear amount of plates and equipment needed, as they ask for 10 plates per pair, so potentially 100 per class (at the time we have five biology classes), plus large numbers of bijou bottles. In the end I agreed with the teachers that two pairs would form a group for results sharing, i.e. one pair would use the 24hr culture and the other the 48hr culture then share results, cutting the amount of plates and bottles needed by 50%.

The other thing is that because you need to make up 24hr and 48hr cultures you can't set it up on Friday because of the weekend, so the practical can only be done from Wednesday onwards (i.e. starting the 48 hour culture Monday morning then the 24hr culture Tuesday morning). As the group are meant to look at the plate after 24 hours it is actually only really suitable to carry out on Wednesday and Thursday, although I suppose if you do it on Friday you could stick the plates in the fridge to slow growth to look at on Monday at a push.
I do cheat a bit now and make 48hr cultures (or thereabouts) and then on the morning of the practical dilute down to half strength the 48hr cultures to make "24hr" cultures. Its not perfect, but I figure that as long as one is half the strength of the other you're on the right lines. Not had any complaints so far. By the time the students have botched the serial dilutions its all pretty academic I find.
 
Totally agree on both issues. Whoever planned this practical wasn't thinking of how much equipment would be needed for a class, or about the timings to fit around school.
I've been asked for it first period on a Monday before now. The teacher seemed surprised when I pointed out that I don't work weekends!
Yep, ditto. I'm not totally unreasonable though - I told the teacher that *they* were very welcome to come in on the Sunday and prepare the 24hr broths. For some reason they decided to change the practical to a Wednesday...
 
We just do 7.1. There aren't enough hours in the day to prep for all three and as the students only need to carry out one we don't do the other 2
 
We usually do 7.1 so i don't know why this particular teacher is doing this, guess she is "trying it out". Same teacher wanted algae balls until told we have none of the equipment, turns out she watched a video clip and didn't actually know what was involved!
Love the diluting of culture, will be doing that. I think this prac is going to take them a long time. Have been struggling to find enough equipment.
Might try the half do 24 and half do 48 angle.
 
Teachers like this practical from the point of view that it ticks off a lot of practical skills in one go. The serial dilution part at the beginning should be a whole dedicated practical in its own right though - the amount of time it takes the kids to do and the number of times they muck it up. I do now check with the teacher asking for it whether the kids have done serial dilution before, and if not I suggest they spend some time going through the concept beforehand.
 
We do both 7.1 and 7.2. Like previous post the teachers like to do 7.2 because it ticks off a lot of the practical skills. Our teachers always make sure that a previous lesson is spent doing serial dilutions so most of the students have an idea what to do. It is a lot of prep but we do get some good results and the students regard it as 'proper science'!!!
Saying that we only did 7.1 this year do to covid.
 
Fortunately, most of the equipment for 7.2 can be prepared a pretty long time in advance, so given plenty of notice, as long as you have the volume of bottles etc, you can gradually work through making up the litres of broth and sterilising all the bijou bottles etc. I actually mothballed most of the glassware and sterile nutrient broth which i had prepared just prior to March 2020 lockdown so the practical never went ahead. It was finally done in May this year and all I had to do was make up the bacterial cultures and pour the plates, so it wasn't half as much work!
 
Top