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The investigation is to find the optimum conc of Mg2+ ions in the mineral ion solution used to grow plants
The Ms : https://qualifications.pearson.com/c...c_20130815.pdf
Q3c I think the last Mp answers the main "How to find optimum conc."
question, but I don't get it.
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The mark scheme is predominantly describing the process you need to go through in order to find the optimum concentration of Mg2+ ions for plant growth. The most accurate way to do this is by plotting known data points (x axis: ion conc., y axis: plant growth), drawing the curve of best fit, taking the peak of it (largest plant growth), and stating its associated ion concentration to be the optimum. In order to this, you need to design a reliable experiment from which you can obtain your data.

Hence, the large part of the marks will be awarded for stating your dependent and independent variables, other controlling factors, methodology, range of concentrations, etc. (marks 1-11 on the MS). You cannot accurately find the optimum concentration without conducting a viable experiment.
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Also check out:

Looking at the Question AND the Mark Scheme, I would think that the examiner wants you:
a) to say something about using a graph to predict something.
b) that something can be just reading off values off the y axis corresponding to certain values on the x axis, which is often an objective of an experiment.
c) to look at where the graph reaches a maximum i.e. the conc-n at which the plants grow fastest or have the largest leaves (whatever you described in Q3(a)) - you will know that magnesium is a part of the chlorophyll molecule, so is needed for healthy leaves/stem (green bits). You can predict (though NOT easily I agree!) this last bit (c) from the statement in the beginning of Q3 (copied below).

"Plan an investigation to find the optimum concentration of magnesium ions in the mineral ion solution used to grow the plants."

Please also go through my post below to get an idea as to how to answer Qs on graphs.


Last edited by macpatgh-Sheldon; 2 years ago

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