Effect of temperature on cell membranes

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Activity 2.7 Why does the colour leak out of cooked red cabbage?

Planning

The aim of this experiment is to find out how temperature affects cell membranes and at what temperature the cell membrane breaks down and the pigment leaks out. When cell membranes are heated, the bonds between the fatty acids in the phospholipid bilayer break and the membrane breaks down to release the cell’s contents, in this case, cell pigment particularly. But the pigment in isn’t contained in the cytoplasm, it is contained within the vacuole. For the pigment to be released, both the cell membrane and the vacuole membrane need to be broken down. The theory behind the cell membrane deteriorating is quite simple. The cell requires a partially permeable membrane which can move fluidly; this is achieved because of the phospholipids structure. The fatty acids in the phospholipid aren’t all straight; there is one straight and one kinked. This fact means that the separate phospholipids can’t pack together very tight, thus lowering the intermolecular forces between the phospholipids. Upon heating, the intermolecular forces between the phospholipids break and the membrane breaks. So, from my scientific understanding, I hypothesis that at greater temperatures there will be more pigment released, but more precisely there will be a small percentage of pigment at low temperatures and then a large percentage at greater temperatures.

To test how temperature affects the cell membranes of the red cabbage we will treat the red cabbage (described in more detail in the procedure section) at different temperatures, ranging from 30°C to 80°C. I believe that in this range of temperatures the cell membrane will break down and pigment will leak out of the red cabbage. I won’t take any readings below 30°C because if the pigment was able to leak out at temperatures below 30°C then pigment would leak out at room temperature, and that isn’t the case. I will also expect a graph to look like the below diagram:

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This would be the perfect graph of results, I believe, because the temperature where the cell membrane breaks all the pigment should leak out, leading to the sharp, possibly vertical, line on the graph. I would also expect there to be 0% pigment leakage at temperatures below the temperature at which the cell membrane breaks down; this is because I believe the membrane will still be fully intact and operational at the temperatures below the temperature where the cell membrane breaks, ergo no pigment leakage. A more realistic graph would be an S-shape, similar to that found in cumulative ...

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