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Membrane Permeability CPAC 3
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- PEARSON (PEARSON)
Full CPAC 3 write up which achieved passing grade and fulfilled all necessary criteria for Biology Edexcel
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Hiba Majid 12EQUESTION TO BE INVESTIGATED: How does alcohol concentration affect the membrane structure of beetroot?
SCIENTIFIC RESEARCH:
● Beetroot is the taproot portion of a beet plant. The cells have membranes reflecting the fluid mosaic
model: a bilayer of phospholipids and within the layer, there is cholesterol proteins and
carbohydrates (Khan Academy, 2021)
● Effect of alcohol on structure of membrane: Ethanol is a nonpolar solvent which can sit between the
hydrophobic tails of the bilayer. This breaks the hydrogen bonds between the lipids, disrupting the
bilayer which increases permeability and makes the membrane more fluid. (Biophys J. 2006)
● Betalains: is the most common pigment in beetroots, responsible for their strong red colour. The red
colour compound betanin is not broken down in the body. Betalains are stored in the vacuole of the
cell. In order for the betalains to leave the cell, they must first leave the vacuole membrane and then
through the cell membrane. Betalains leave the cell via diffusion (Molecules, 2021)
● A colorimeter measures the absorbance of particular wavelengths of light by a specific solution. It
compares the amount of light getting through a solution with the amount that can get through a
sample of pure solvent. It is used for identification and determination of concentrations of substances
that absorb light (Britannica, 2014)
HYPOTHESIS: As the concentration of alcohol increases there is more disruption to the lipid bilayer, making
it more fluid, causing what is inside the cell to leak out and so more red colour will be present.
METHOD
1. Carry out instructions given (or those you have produced and researched) to complete the practical
(CPAC1)
2. List apparatus below and describe techniques used when measuring quantities with a particular piece
of apparatus:
Piece of apparatus Purpose of piece of apparatus Comment on how piece of equipment was used Appendix
accurately/appropriately/safely 5c
technique
Raw beetroot To observe the effect alcohol Low risk
has on the cell membrane Although beetroot juice is harmless, It will stain
skin and clothes badly
Size 4 core borer To cut volumes of beetroot Medium risk
pieces No harm should occur so long as the core borer
is used responsibly
Ruler To measure cylinders of Low risk
beetroot In order to ensure accuracy, the ruler must be
used properly, ensuring that it starts from 0cm
and that the ruler is kept along the piece of the
beetroot instead of at an angle to it
Distilled water To act as a control and as a Low risk
baseline for comparison Keep away from edge to avoid spillage so that
purposes no one will slip and hurt themselves
Filter paper/tissue To dry off excess dye that No risk
might have leaked out of the To ensure measurements that are taken later
beetroot cells while it was are accurate, you should not press down too
being cut due to damage to hard on the beetroot with the tissue to avoid
the cell membrane damage to the beetroot cells, which will lead to
more betalain being released.
Scalpel Cut the beetroot Medium risk
Cut away from fingers
Beaker Contain distilled water to Low risk
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