practical 5 membrane permeability

outline the method

why do we wash the beet root

• Cutting the beetroot damages some cells, releasing pigment (betalain) immediately.

• If you don’t rinse them, that pigment would already be in the water before the experiment starts.

• That would make your results inaccurate, because it wouldn’t all be due to temperature — some pigment would have leaked out just from cutting.

• Rinsing removes any surface pigment released during cutting so that:

  Any pigment measured later comes only from temperature-induced membrane damage, not from the initial cutting process.

why do we use blue filter 

Why you use a blue filter (blue light) in the colorimeter:

• Beetroot cells contain the red/purple pigment betalain.

• This pigment absorbs green/yellow light most strongly and reflects red light (which is why beetroot looks red).

• In a colorimeter, you want to use the complementary color of the pigment — the color that the solution absorbs the most.

• Blue light (the complement of red) is used so that changes in pigment concentration produce maximum absorbance differences.

• In simple terms:

  Using blue light gives the most sensitive and accurate measurement of how much red pigment has leaked out.

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