Vernier Software and Technology
Vernier Software & Technology

Chemistry of Membranes

Figure from experiment 4 from Investigating Biology through Inquiry


In this investigation, you will determine the stress that various factors cause on biological membranes. Membranes within cells are composed mainly of lipids and proteins, and often serve to help maintain order within a cell by containing cellular materials. Different membranes have a variety of specific functions.

One type of vacuole in the cells of plants, the tonoplast, is quite large and usually contains water. In beet plants, this membrane-bound vacuole also contains a water soluble red pigment, betacyanin that gives the beet its characteristic color. Since the pigment is water soluble and not lipid soluble, it is contained in the vacuole when the cells are healthy. If the integrity of a membrane is disrupted, however, the contents of the vacuole will spill out into the surrounding environment and color it red. This usually means the cell is dead. The intensity of color in the environment should be proportional to the amount of cellular damage.

During this Investigation, you will be using a spectrophotometer. In a spectrophotometer, light from the light source will pass through the solution and strike a detector. The solutions used in this experiment are colorless. If the beet pigment leaks into the solution, it will color the solution red. A higher concentration of colored solution absorbs more light and transmits less light than a solution of lower concentration. The spectrophotometer monitors the light received by the detector as either an absorbance or a percent transmittance value. The absorbance of light will be used to monitor the extent of cellular membrane damage.


In the Preliminary Activity, you will use a spectrophotometer to measure color changes due to the release of betacyanin caused by the damage to beet cell membranes by a 30% 2‑propanol solution. Isopropyl alcohol is another name for 2‑propanol.

After completing the Preliminary Activity, you will first use reference sources to find out more about biological membranes before you choose and investigate a researchable question. Some topics to consider in your reference search are:

  • biological membranes
  • vacuole
  • tonoplast
  • betacyanin
  • lipids
  • lipid solubility
  • 2‑propanol
  • alcohols

Sensors and Equipment

This investigation features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Investigating Biology through Inquiry

See other experiments from the lab book.

1Buffer Investigations
3Investigating Osmosis
4Chemistry of Membranes
5Investigating Protein
6ATesting Catalase Activity (O2 Gas Sensor)
6BTesting Catalase Activity (Gas Pressure)
6CTesting Enzyme Activity (Spectrometer)
7Introduction to Biofuels: Enzyme Action
8Analysis of Enzymes using Tyrosinase
9Cellular Respiration
10ASugar Metabolism with Yeast (Carbon Dioxide Gas)
10BSugar Metabolism with Yeast (Ethanol)
11Fermentation with Yeast
12Photosynthesis by Chloroplasts
13Transpiration of Plants
14Plant Pigments
15Heart Rate
16Investigating Dissolved Oxygen
17Investigating Primary Productivity
18Modeling Population Dynamics
19Water Monitoring
20Evolution of Cellobiase in Fungi
21Introduction to Molecular Evolution
22Evolution of Yeast

Investigation 4 from Investigating Biology through Inquiry Lab Book

<i>Investigating Biology through Inquiry</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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