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Effect of temperature on cell membranes

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Introduction

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. ...read more.

Middle

When it is boiled, pour a 250cm3 roughly half full with the boiling water. Next, with your thermometer, take the temperature of the boiled water: if it is colder than 80�C then boil another batch of water until it is warmer than 80�C; if it is hotter than 80�C then slowly add cold tap water until it is closer to 80�C. NB: take care with the boiling water as it could possibly scold or burn. * You are now ready to cook your first red cabbage sample. Take the piece from the boiling tube marked '80�C' and using a pair of tweezers, pick up the cabbage sample from that boiling tube and place it in the beaker full of 80�C water. Leave it to cook for a minute then put it back into its boiling tube, remembering to measure out 10ml of cold tap water to put in the boiling tube with the cabbage sample. Record the time for when the cabbage sample was placed in the boiling tube and leave for 30 minutes to let the pigment leak out, if any does. * Now repeat the previous step for the remaining temperatures: 70�C to 30�C. If the temperature in the 'cooking' beaker isn't right either add more boiling water to make it warmer or add more cold water to cool it down. ...read more.

Conclusion

Firstly, instead of using a beaker full of heated water, I could have used several water baths, set to the required temperatures. This would be better than using a beaker full of heated water because the water bath's temperature remains almost constant; whilst the beaker full of heated water's temperature changed whilst the cabbage was being cooked, the biggest change being at greater temperatures. Although, the beaker was plastic and prevented heat loss through the sides of the beaker, but the most heat loss was where the water was in contact with the air. Next, my method of cutting out the pieces of cabbage could be altered by using a cork borer. Although in my method I have made efforts to keep the pieces roughly to the same dimensions, the cork borer would have made all pieces to the same dimensions. Also, by using pieces all from the same leaf does it make a fair test? I found that not all the pieces from the same leaf were the same volume or had the same amount of pigment in it/colour to it. To eliminate any problems from this, I could have cut many pieces from several sections of the cabbage and chose the ones I would use by a method of random sampling. In conclusion, my results back up my hypothesis that as temperature increases the percentage of light absorbed increases (or the amount of pigment to leak out will increase), and the graph produced would be S-shaped. The temperature that the cell membrane breaks down is between 60�C and 70�C. ...read more.

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