beetroot permeability experiment

Why beetroot is used

Beetroot contains a dark red pigment called betacyanin in its vacuole. The pigments are retained in the vacuole by a selectively permeable membrane called the tonoplast. It has a similar fluid mosaic structure to the plasma membrane with proteins embedded in the phospholipid bilayer. If these two membranes are damaged, betacyanin can leak out of the cells.

Serial dilutions

1 fold- add 1cm³ to each following 4 test tubes containing 9cm³ distilled water. Concentration starts at 1/10

2 fold- add 5cm³ to each following 4 test tubes containing 2cm³ distilled water. Concentration starts at 1/2.

Using a colorimeter

  • place supernatant (solution) in a cuvette

  • Add green filter. The more red the solution is, the more it will absorb the green light so light transmission is lower, absorbance is higher.

  • In between readings, calibrate with a sample of water

The effect of detergent on beetroot permeability

  • cut beetroot disks using a cork borer then trim them all down to the same length. Rinse and pat dry to remove excess pigment.

  • Make a serial dilution of detergent concentrations, one control of distilled water

  • Add a piece of beetroot to each concentration of detergent solution and heat in a water bath

  • Leave to cool for 10 mins

  • Transfer liquid from each test tube to cuvette

  • Place cuvette in colorimeter to measure the absorbance of the pigment. The higher the absorbance, the higher the concentration of the pigment.

  • Plot graph of absorbance against the independent

Can also use to investigate effects of temperature- heat in equal volumes of water at different temps

Explanation for findings

Detergent- permeability increases as detergent concentration increases. Detergent is a surfactant, so it has a hydrophilic polar head and hydrophobic non polar tail, like phospholipids. The hydrophobic tail inserts into the membrane’s phospholipid bilayer which disrupts it, making it leaky and allowing the pigment to escape.

Temperature- permeability increases as the temperature increases. This is because phospholipids in the phospholipid bilayer of the membrane are constantly moving, and as kinetic energy increases, they move faster. This disrupts the membrane, making it more fluid and at high temperatures completely break down, releasing the pigment.