ISA grade!

So Triple Science is worth three different qualifications, one for each of the three sciences.

Chemistry is split into 4 units and across all 4 units you would need a UMS score of 360/400 - which is equivalent to 90 out of 100 UMS on each unit. 43 marks, last year, would have been equal to 88 UMS. Therefore you would need 272/300 UMS across the three chemistry exams. However, 43 marks this year may be worth more or less UMS.

UMS itself changes your raw mark to a number out of 100 (with sciences). The way they change it is they look at how the year group did nationally and then create grade boundaries from the raw marks. These raw marks are then changed to UMS where the grade boundaries always stay the same (90 - A*, 80 - A, 70 - B etc). They then allocate each raw mark a UMS score depending on how far you where from each grade boundary.

Here is a UMS converter for AQA if you want to have a look at how raw marks are converted to UMS scores.
http://www.aqa.org.uk/exams-administration/results-days/grade-boundaries-and-ums/ums-converter

Will I have to get higher than minimum for an A* in the other units as a result of me getting 43/50?

Marginally, yes.

I mentioned that you will need 272 UMS out of 300 UMS available in the three exams.

90 UMS is normally the minimum for an A* and this would get you 270/300 UMS.

Therefore, you need to be 2 UMS above the bare minimum for an A* across 3 exams.

I got 41/50 which is an A but if you really want an A* then you would really need to get around 45/50 to get an A* in general.