Beetroot Evaluation AS Biology

I'm doing my Biology Evaluative coursework on thursday, and I just want to make sure all the stuff I say is correct and if not, whats wrong with it, and if I've left anything out please say!
So if I'm investigating how temperature affects the amount of pigment released from the cell surface membrane of the beetroot slices, and measuring this by putting a sample of the water with pigment in it in a calorimeter (assuming there is every limitation and control possible) the:

Independent variable would be: Temperature (degrees Celsius) [edit]
Dependant Variable: (mean) transmission of light (%) [edit]

Control Variables:
Size and shape of beetroot slices/discs
Volume of water in the test tubes
The type of beetroot (all discs must come from the same source of beetroot)
Number of discs in each tubes
Time each of the beetroot discs are heated for
Discs held separately so all are equally exposed to thermal treatment (on a mounted needle)

Limitations:
Inconsistant stirring of slices while submerged in water. Beetroot slices were not stirred in the same way for each, meaning inconsistent rate of pigment leakage. Modification: Standardise timing and method of stirring for each slices.
Insufficient number of values of independent variables e.g.. only at 40,50,60,70,80 degrees Celcius, so lack of results between intervals, meaning you could miss changes so making conclusions about trends are less valid. Modification: Include intermediate temperatures within the range e.g. 45,55,65,75 degrees Celcius.
Insufficient range of independent variables (40-80 degrees) lack of results beyond the range investigated could make it difficult to identify a trend or pattern. Modification: extend the range e.g. 20-80
Discs were handout, so discs will have a different surface area to volume ratio of the slices, so pigment release will differ. Modification: use a mechanical cutter slicer to prepare beetroots
Species of beetroot differ, so the concentration of pigment may differ/vary with age/ species. Modification: take samples all from the same source (same beetroot)
Repeats, if below 4 they are unable to detect anomalous results thus decreasing reliability. Modification: perform at least 4 replicates
If not calorimeter was used, then judging by eye can show lack of consistency in judgement, may lead to less precise, less accurate and less reliable results. Modification: use a calorimeter.

How to improve reliability:
Compare your results with other peoples results, or take a lot of replicates and take the mean of them.

Analysis:
20-45 degrees Celcius, The phospholipids can move around and aren't packed together as tightly- the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy- this increases the permeability of the membrane as pigment molecules are able to pass through the membrane. The higher temperature is the more kinetic energy the phospholipids have. This increases movement can disrupt the relatively weak forces holding the different parts of the polypeptide chains together, (like hydrogen bonds etc) and can make holes in the cell membrane inducing leakages, this allows substances that wouldn't normally enter of leave the cell, do so.
Above 45 degrees Celcius: The phospholipid bilayer starts to melt (break down) and the membrane becomes more permeable. Channel proteins and carries proteins denature as their tertiary structure unravels and their binding site changes shape and the membrane is no longer selectively permeable. They can't control what enters or leaves the cell - this increases the permeability of the membrane.
So as the temperature increases the % transmission of light decreases (as higher temperatures have higher pigment leakage therefore lower % transmission)

Okay I know no one is going to read all of this, but I like to get my thoughts down in a structure that makes sense to me, and this might help people who are doing the evaluative as well. If by any chance anyone reads this, it would be SO helpful if you could comment what you think, like if theres anything I should know for my evaluative. If any one has done the paper, is this all I roughly need to know, or have I missed anything out?

EDIT: Also what would be a couple of examples of sources of errors in this experiment?
Thank you!