In the egg osmosis experiment we used a chicken egg as a model of an animal cell to demonstrate the movement of water across a semi-permeable membrane. We have learned about the different components of the plasma membrane, including the phospholipid bilayer, integral and peripheral proteins, glycoproteins and glycolipids. We know that it is sometimes referred to as a “fluid mosaic” referring to it’s flexible structure of different parts.
Today we are going to test the effect of temperature and solvents on the cell membrane, using cores of raw beetroot. Beetroot is brightly coloured due to the presence of betalain and this coloured pigment can assist us to determine the effect of different temperatures and concentrations of solvents on the cell membrane. When the cell membrane is damaged, the pigment leaks out, so the more damage that occurs, the darker the colour of the medium into which the pigment leaks.
Your task is to design and complete an experiment with an aim, hypothesis, list of materials and equipment, method, results, discussion and conclusion. Your variable can be temperature OR concentration of a solvent (ethanol, for example) or detergent.
Test Tube D (added later than others), Test tube C, test tube B and test tube A
The prac was aimed to show us the effect of different environmental temperatures on a plant plasma membranes.
Test tube A contains a beetroot core placed in 70 degree celcius water,
Test tube B contains a beetroot core placed in a 50 degree celcius water,
Test tube C contains a beetroot core placed in room temperature water,
and test tube D contains a beetroot core, frozen overnight and then placed in water.
We found that treatments to Test tube A and D had the most effect on the beetroot core. This is because the temperatures ruptured membranes allowing the red pigments inside the beetroot core to escape! The hotter or colder the temperatures were, the more membranes burst and more colour was released. The colour is contianed in plastids within the cell membranes of the beetroot.
Brilliantly written by Year 11 VCE biology students,
Chloe Wood the fantastic and Emily Huglin the awesome!
What’s beetroot got to do with cell biology? Well, today we did a practical experiment to investigate the effect of temperature on the plasma membrane of beetroot tissue. Why beetroot? Because it is relatively easy to identify the amount of damage to cell membranes by observing the pigment leakage from the tissue. We used four 5mm x 15mm cylinders of beetroot and four different treatments – room temperature (control), freezing overnight, 50 degrees Celcius and 70 degrees Celcius for 2 minutes each. Then each sample was placed in a test tube with 5 ml of water. What did our results show?
One of the questions in this practical asks why some people put hessian bags over their garden plants in winter and how some plants can survive freezing temperatures. Hessian bags can help to insulate plants against the effects of freezing – some wineries use large fans to keep air circulating over their crops for the same reason. Some plants are genetically more tolerant of frost. This article, from the CSIRO, describes how some plants can empty water out of the cell into the extracellular spaces, where the water can form ice without damaging the cell membrane. Another method is increasing solute concentration, for example by storing monosacharides in place of disacharides, which effectively lowers the freezing point of the cell contents. This is a bit like using anti-freeze in the car radiator during winter.
Revision questions (with answers!) for cell membranes at Biology-Questions-and-Answers.