An Experimental Study on the Effect of Temperature on Membrane Permeability using Beta Vulgaris 


Aim/ Objective: To what extent does the temperature of water, ranging from 0℃ to 70℃ with 10℃ increments, impact the membrane permeability of Beta Vulgaris (beetroot) when measured by absorbance, when the sizes of the B. vulgaris tissues, 1㎤ and amount of water it is placed in, 22㎤, is kept constant?


Growing up, my father has had an increasing interest in creating, and making me consume vegetable juice. I would watch from afar as he made a concoction of many vegetables, with the main vegetable being beetroot.

Not only would the drink have a surprisingly dark red pigment despite there being many other vegetables in the drink, but I also noticed that my father’s hand would often become stained with a red pigment whilst the other vegetables left little residue.I became curious as to why that happened so I decided to do a little research. It turns out that betalain pigments are contained in the vacuole in the cells of the beetroot and the release of the colour had to do with its plasma membrane.

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I realized I had learned about similar topics in the SL Biology curriculum earlier in the year. Since this was something I was interested in learning more about, I decided to look at this for my IA. The aim of my IA is to investigate the relationship between temperature and membrane permeability.

Plant cells, alongside prokaryotic and eukaryotic animal cells, are surrounded by a plasma membrane. These membranes are “semi-permeable”, which means that they control the movement of substances that go in and out of the cell.

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However, only certain molecules would be allowed to pass through. Plasma membranes are mainly made of phospholipids,proteins and cholesterol. Phospholipids consist of two hydrophobic hydrocarbon tails and a hydrophilic phosphate head. This means the tails (each composed of a fatty acid chain) are not attracted to water but, the heads are. This makes the phospholipids amphipathic, as it has both hydrophobic and and hydrophilic parts.The membrane’s phospholipids naturally form bilayers in water due to the amphipathic properties of the phospholipid molecules.The phosphate heads face outwards towards the surrounding solution, while the fatty acid tails face inwards. The two main types of proteins in a plasma membrane are the integral and peripheral proteins. Integral proteins are mostly hydrophobic which allows them to extend to the hydrophobic core of the phospholipid bilayer. Proteins that extend all the way across the membrane are called transmembrane proteins. Peripheral proteins are hydrophilic so, they are found on the outside and inside surfaces of membranes attached either to integral proteins or to phospholipids.Cholesterol, like integral proteins are mostly integrated into Figure 1. Structure of the Plasma Membrane the membrane as it is hydrophobic. However, cholesterol is in animal cell membranes. It is not in plant cell membranes because unlike animal cells, they have a rigid cell wall(Allott,Mindorff, 2014).

Cell membranes are often represented as a fluid-mosaic model (Singer, Nicolson,1972). Having fluidity means its membrane components can move position and being mosaic means its phospholipid bilayer is embedded with protein. The mosaic’s movement makes it impossible to form a barrier which is completely impenetrable, thus it has the ability to be influenced by outside factors.The membrane’s permeability can be affected by organic solvents, temperature and pH.The focus of this IA is how temperature impacts membrane permeability. Different plant species have their own optimal temperature range for growth and reproduction. Consequently, extreme variations in temperature can influence intracellular macromolecules (nucleic acids and proteins) and membrane structure of plant cells (Ruelland, Zachowski, 2010). These properties suggest that as the water temperature increases, the absorbance level of a plant cell also increases until it reaches a point of denature( which destroys the characteristic properties of a macromolecule).

To test the impact of temperature on membrane permeability, Beta vulgaris (beetroot) was used. B.vulgaris are root vegetables that appear to have a dark red/purple colour because their cells contain a water soluble pigment called betalain. This pigment is a useful indicator of membrane fluidity. This is because the betalin is kept within the vacuole of intact B.vulgaris cells. An increase in membrane fluidity will cause betalin to leak out of the cell, indicating an increase in membrane fluidity. In order for the betalain to be released, the beetroot must be cut.The water used in the experiment is initially clear. When the betalin from the B.Vulgaris is released, the water will turn red. The amount and concentration of the pigment varies depending on the extent to which the temperature is manipulated. The concentration of betalain released is equivalent to the permeability and the amount of damage sustained to the plasma membrane of the B.Vulgaris cells. To look at how different temperatures impact membrane permeability, a colorimeter will be used to measure the absorbance.

A colorimeter is a device used for measuring the amount of light that is transmitted and absorbed passing through a pure solvent (a solvent that does not have any impurities), such as water. It compares the amount of light that gets through a solution with the amount which is getting through a sample of pure solvent. The device must be adjusted to verify that the wavelength of the beam of light passing through the solution is complementary to the wavelength of the colour of the solution. Pigments can absorb light at different wavelengths.For the B.Vulgaris, betalin is red with a wavelength of 680 nm. Its complementary colour is green with a wavelength of 495-570 nm.

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An Experimental Study on the Effect of Temperature on Membrane Permeability using Beta Vulgaris . (2022, Apr 16). Retrieved from

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