Membranes Under Stress

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Membrane under stress

Introduction:

The cell membrane is responsible for regulating the movement of substances into and out of the cell. This regulation is determined partly by the composition of the membrane. cell membranes consist of a double layer (bilayer) of lipid molecules and contain scattered protein molecules of various sizes. Membranes also subdivided cells into compartments and regulate the movement of substances between these compartments. Different types of molecules pass across membranes in different ways:

Tiny molecules – certain very small molecules, such urea and water, can pass between the lipid molecules of the membrane.

Lipid soluble substances – substances of various sizes that can dissolve in lipids, such as chloroform and alcohol, are able to dissolve into the lipid bilayer and so pass through the membrane.

Water soluble substances – most water soluble substances cannot pass through the lipid bilayer. Those water soluble substances that can cross the membrane, such as amino acids and simple sugars, do so through special channels within protein molecules that span the membrane. Some proteins channels allow only particular molecules to pass through. In certain cases, energy is required to transport a molecule through a protein channel.

It is not possible to observe membranes directly, so this activity is an indirect study of the effects of different substances and treatments on living beetroot cells. Each beetroot cell has a large central vacuole bounded by a membrane and contains the red pigment anthocyanin. The whole cell is surrounded by celluar membrane. If both membranes remain intact, anthocyanin pigment cannot escape into the surrounding medium. But if the membranes are stressed or damaged, red pigment will leak out and be seen in the surrounding medium.

Aim:

To investigate the effect of different substances on beetroot cell membrane and to make some inferences about the structure of cell membrane  

Hypothesis:

The Ph's were going to react less because the beetroot wouldn’t have been as ruined from the chemicals and not as much colour would leak out

Materials:
o 11 petri dishes – approximately 7cm diameter

o Marking pen o Length of paper towel

o Fine forceps with clean tips

o Distilled water solutions of pH 2, 4, 6, 8 and 10 alcohol (ethanol) solutions – 1%, 25% and 50%

o Washed beetroot slices – at least 55 in 100mL beaker of water

Method:

1. In an area designated by your teacher, lay out enough toilet paper towel on which to set out 11 petri dishes.

2. Use a marking pen to mark the lid pf each petri dish with the details of the solution it will contain (see the list of stock solutions in the Materials section). Do not make the labels too big.

3. Arrange the dishes on the towel in the order in which they are listed in the Materials section. Labelling the paper towel as well may help you avoid mix-ups with the lids.

4. Using the class stock solutions, pour sufficient of each solution into the appropriate petri dish to a depth that convers the beetroot slices. Do not overfill the dishes, as spilt solution makes later observation difficult.

5. Use the forceps to collect at least 55 beetroot slices into a 100mL beaker of water. Drain the water from the slices before proceeding.

6. Using the forceps, put five slices into each of the dishes, and place the lid on the dish. Rinse forceps before going on to the next dish of solution.

7. After 30 minutes observe the dishes for evidence of pigment leakage

8. Repeat your observations on the same day at least 2 hours later

9. Repeat your observations 24 hours later

10. Dispose of the dishes as directed

Safety:

Hazards – glassware/ breakable, chemical, sharp objects

Management of hazards – safety glasses, closed in shoes, long hair tied back, lab coats, gloves

Results:

Before-

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After –

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Discussion:

Given the results, the lower the pH the higher the effect on the beetroot cell membranes, there was a very low colour change in the surrounding medium when a pH level was greater than 7. This may have occurred because pH 7 is neutral and a pH greater than 7 is basic or alkaline. At a pH level greater than or equal to 7, the solution was unable to breakdown the beetroot cell membrane because it is a strong base, which does not have the properties to breakdown a cell membrane. The solutions with a pH level of less than 7 had a higher amount of red pigment in the surrounding medium. This is because a pH of less than 7 is acidic and therefore has a greater effect on the beetroot cell membrane. The acidic pH solution broke down the beetroot cell membrane, and therefore the red pigment leaked into the surrounding medium.

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