Cell Membrane Permeability (Iqbal Thabet)

Title: The Effect of Temperature on Membrane Permeability

Principle(s) Investigated:

The cell membrane structure and how it relates to its functionality.

The damaging effect of temperature on the integrity of cell membrane and loss of selective permeability function.

Standards:

HS-LS1-2. Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multi cellular organisms.

HS-LS1-3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.

These performance expectations were developed using the following elements of the Disciplinary Core Ideas:

LS1.A: Structure and Function

§ Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1)

§ Multi cellular organisms have a hierarchical structural organization, in which any one system is made up of numerous parts and is itself a component of the next level. (HS-LS1-2)

Materials:

• Water baths – preset at required temperatures
  • A large beetroot
• Knife
  • Test tubes or (jars)
• Colorimeter, we are using the (smart phone app Galactica lux) instead to measure color intensity
  • Towels
  • Gloves
  • Google spreadsheet

Procedure:

1. Prepare 4 water baths preset to a range of temperatures: 0, 40, 60, 100 °C.

2. Place each tube (jar) into the corresponding temperature water bath for five minutes.

3. Cut 4 beetroot cylinders using a cork borer, Using a knife, trim them to the same length. Wash the cylinders thoroughly with distilled water and pat dry with paper towel.

4. Add one beetroot cylinder to each of the six tubes (jars) and leave for 15 minutes.

5. Now shake the tubes once, and then, using forceps, carefully remove the cylinders from each tube and discard.

6. Decant enough liquid from each test tube to exactly fill a colorimeter cuvette (4 cuvettes together). This step was skipped, and the liquid in the jars was directly examined for light intensity.

7. Since the colorimeter was not available in the lab, the smart phone Galactica Lux was used to measure light intensity of the liquid inside the jars.

8. Plot a graph of light intensity against temperature.

Data Collection Link

Student prior knowledge:

Students should have knowledge of the following facts:

- Basic structure of plasma membrane and the membranes surrounding cellular organelles which is a bi layer phospholipid with protein channels and carriers.

- Plasma membrane plays the essential role in cellular homeostasis by regulating transport into and out of the cell.

- For the cell membrane to maintain its function, it has to stay in its bi layer semi solid state. Many factors affect the membrane integrity and change its fluidity, and if they persist, they irreversibly damage the membrane, causing it to lose it selective transport function, leading to leakage of materials contained inside the membrane compartments.

Explanation:

The maintenance of the living cell depends upon the integrity of its membrane and on its high selectivity as a permeable barrier between the cell and its surroundings. Altering the nature of the membrane leads to altering its properties, and its permeability. Irreversible changes in the permeability of the membrane usually lead to the death of the cell.

Beetroot cells contain large amounts of a reddish pigment called betacyanin, contained almost entirely in the large central vacuoles of the cells. Betacyanin in living beetroot cells remains inside the vacuoles, surrounded by a vacuolar membrane that has the same composition as the plasma membrane. Environmental stresses can damage the

membranes, allowing betacyanin to leak through the vacuolar membrane and the plasma membrane. This

leakage of betacyanin will produce a red color in the water surrounding the stressed beet. Thus

the degree of membrane damage can be determined by monitoring the intensity of the color

leakage resulting from the environmental stressing factor used.

In this experiment, we will study the effect of changing the temperature on the permeability of living beetroot cells.

Questions & Answers:

1- What makes beets useful experimental models for studying cellular membranes?

Beetroot cells have a central large vacuole that contains the red pigment, Betacyanin. the vacuole is bounded by a membrane with the same structure as the plasma membrane. So, studying the cell membrane characteristics by observing vacuole's membrane can give the same information we are looking for. In this case, the pigment, betacyanin is used as an indicator of cell membrane damage. So, it provides a good model and has a good indicator. When the cell membrane is damaged, the pigment leaves the vacuole into the solution where we can measure color intensity.

2- What mechanisms do you suggest by which temperature changes the physical status of cell membranes and eventually damages them?

Temperature damages cell membranes by 2 mechanismes:

- Increasing the fluidity of the hospholipid bi layer, which means loss of selectivity of the membrane function

- Denaturing membrane proteins, which results in loss of protein-mediated selective transport system.

3- What makes the Galactica Lux app (that measures color intensity) an acceptable substitute to the colorimeter?

You can use it to directly for quick and rough measurement of the light intensity (color intensity).

It also does not require preparing corvettes that are needed if the colorimeter is to be used.

Besides, collecting data using Galactica Lux and plotting them against temperature, shows the same trend of the effect of temperature on cell membrane.

Applications to Everyday Life:

1- A major application of the effect of temperature on the structure and functionality of cell membranes is the process of Pasteurization. In this procedure, the temperature is raised to levels that are damaging to the cell membranes of the pathogenic organisms and so they are killed and the food products get sterilized.

2- A second application on the effect of temperature on cell membrane is cooking. Cooking disturbs cell membrane integrity and help releases the nutrients from inside the cell to the outside. This happens by liquefying the phospholipid bi layer and by denaturing membrane proteins.

3- The third application is refrigeration. The refrigerator is usually set at a temperature of 40 °F or less, while most bacteria grow and multiply within a range of (40 and 140 °F), known as the danger range. The temperature inside the refrigerator changes the physical properties of the bacterial cell membrane and so it impairs its permeability which interferes with the cells' functions and growth. This leads eventually to impeding bacterial replication and slows down the spoilage of food.

Photographs: Include photos and diagrams that illustrate the how the investigation is performed.

Anticipated curve:

3 phases:

- Loss of gel-like consistency

- Rapid increase in absorbance due to protein denaturation

- Plateau (concentration equilibrium with the solution)

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Videos: Include a video of your investigation

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