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Biology - To determine the tensile strength of plant fibres.

What is the variable that cannot be readily controlled? And how would you minimise the impact.

I just don’t understand this question

This is the method I wrote:

1. The plant material should be left to soak in a bucket of water for about a week in order for the fibres to be easily extracted (retting).
2. Once the fibres have been removed, connect them between 2 clamp stands and gradually add mass in the middle until the fibre snaps. Note the mass required to snap the fibre.
3. Try this again but with individual fibres from different plants and different ways of combining fibres (e.g. twists). You can also compare the tensile strength of the stem to the individual fibres.

IV: The type of fibre used (from different plants)

DV: The amount of mass that can be added before the fibre snaps

CV: Length of fibre – each fibre should be roughly the same length for a fair comparison
Size of each individual mass – a set of the same weights can be used

Reply 1

username5778034

The question means to ask what is the factor that is hard to control. The main aim of the experiment is to know how difference in the plant fibre material contributes to their tensile strength.
There could arise variation within a single type of fibre due to its age difference so its best to use use a large sample of fibres of roughly the same age from the same location.