Investigating the effect of temperature on the movement of pigment through cell membranes.

Investigating the effect of temperature on the movement of pigment through cell membranes

Results

Group 2 are the results that we obtained.

Analysing evidence and drawing conclusions

Transmission in this case means, when we used the colorimeter it is the percentage of light that was able to go through the solution of water and beetroot pigment.

I have spilt the graph of my results up into three sections so that it is easy to explain what is going on inside the cells. Also because there are three distinct sections on the line of best fit of my results.

There is one major trend in the results that were obtained and it was that there was a large dip in the transmission results mid way through the results. The dip was started from 52% and with in temperature increasing by 10°C every time in 30°C the transmission dropped from 52% to 6% which on the graph is the largest drop for my results.

Another trend in the results is that the transmission starts to drop slowly from 25°C then decreases rapidly from 35°C and then trails off at 65°C.

Here are the gradients that I have done on the graph to help show how steep the line of best fit is in each of the three sections:

Section 1 - 25°C to 35°C

Section 2 - 35°C to 65°C

Section 3 - 65°C to 85°C

The higher the gradient the steeper the line is. These three gradients show that the steepest part is section 2 and the flattest is section 3 which backs up what I have said.

Section 1 - 25°C to 35°C

Seeing as there wasn’t that much pigment coming out of the cell, only a transmission of 56%, this indicates that the cell membrane is still intact. The reason why there was some pigment left in the water in the early stages is because some of it had diffused out of the beetroot cells. There wasn’t much pigment diffusing out of the beetroot cells because the particles haven’t been given a lot of kinetic energy because the temperature is low so they aren’t moving about that much as they would be if the temperature was higher. Only some of the pigment would have diffused out of the cell because the transport protein will only allow certain sized particles through it. The transport protein provides a channel for hydrophilic ions and polar molecules to pass through the membrane. The pigment in the cell has been actively transported out of the cell, which means it goes with the concentration gradient.

Some of the pigment might have actually come from the cells that had been cut to get the equal pieces. Even though, after the pieces had been cut they were washed, all of the pigment was probably not washed out and could have come out in the heated water.

Here is a diagram showing how some of the beetroot pigment has diffused out of the cell by facilitated diffusion and the rest has stayed inside the cell:

Inside beetroot Outside of cell

Section 2 – 35°C to 65°C

In ...

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Here is a diagram showing how some of the beetroot pigment has diffused out of the cell by facilitated diffusion and the rest has stayed inside the cell:

Inside beetroot Outside of cell

Section 2 – 35°C to 65°C

In this section there has been the largest rate of the pigment leaving the cell. This is due to many reasons:

The temperature has been increased therefore the particles have a larger amount of kinetic energy meaning they move a lot quicker. As well as moving quickly they will collide more frequently and the collisions will also be more intense.

With the large particles of pigment having a lot more kinetic energy than before, this means that the cell membrane wasn’t able to with stand the force of which the pigment particles collided into it. Therefore the cell membrane wasn’t intact and large holes have occurred.

Seeing as there is still a greater concentration of pigment inside the cells the pigment diffuses out of the cell into the water. Therefore the pigment has diffused with the concentration gradient going from high concentration to low concentration. There is now no restriction to the size of the pigment particle, which means that all the pigment particles no matter the size are able to diffuse out of the cell.

Another reason for the pigment getting out of the cell was the fact that the temperature had got so high that the globular proteins in the cell membrane denatured. This meant that there were the holes that pigments made in the cell walls and there were holes that the proteins left after being denatured, this meant that pigments could freely leave the cell.

The rise in the temperature also caused the hydrogen bonds in the secondary structure, which hold the protein together, to break. This means that the structure goes down to a primary structure from a secondary structure, the reason being is because the hydrogen bonds that were keeping chains of amino acids together to form a α (alpha) helix have been broken. With the hydrogen bonds broken the chains of amino acids unravel, leaving lots of chains of amino acids. This means that there are now gaps in the cell membrane allowing the pigments to leave the cell.

Section 3 - 65°C to 85°C

In this section the graph trails off due to a number of reasons:

The temperature has got so high that the membrane has been completely destroyed. The pigment particles inside the cell have got so much kinetic energy now that the phospholipid bilayer can no longer with stand the impacts of the pigment particles.

The concentration gradients are virtually equal now because the concentration of the pigment outside of the cell is the roughly the same as that inside the cell. The concentration inside the cell is still slightly higher so therefore the pigment moves with the concentration gradient so it leaves the cell.

Evaluation

With my set of results I believe there is only one anomaly, which is the 55°C result. The reason why I believe this result to be an anomaly is due to the fact that looking on the line of best fit it seems to be a greater distance away from the line than any other results. The 55°C results from the line of best fit looks to be too low, the result obtained is 5% transmission lower than the line of best fit. The furthest away that any other result is only 1% transmission.

For the group averages that were obtained I believe these to be very inaccurate, the reason being is because there were 9 groups obtaining evidence and for each of the methods to be the same is very unlikely. This fact lowers the reliability of the group average, I can back this statement up by using the results. If all the groups used the same method then the results would have been very close to each other but this isn’t the case:

For the first temperature (25°C) tested the transmission results range from 34% to 72%. Like wise the results for the temperature 65°C range from 32% to 0% in transmission. This shows that the methods of all the groups weren’t the same meaning the group averages aren’t that reliable.

There are a few limitations in the procedure of the experiments that lower the accuracy of the results:

When it came to the shaking the test tube which contained 5cm3 (cubed) of distilled water and a piece of beetroot. The shaking wasn’t very accurately done because you can’t guarantee that with each shake the same amount of force was being applied. The different temperatures might have been shaken at different forces and frequencies meaning that the more force used the more pigment would have come out of the cell than one shaken with less force.

Another limitation to the procedure was the maintaining of a constant temperature of the water baths used. We used a water baths that we made by heating up a beaker full of water with a Bunsen burner the problem was the tripod that was used. Once we had reached the temperature that we wanted the Bunsen burner was turned off. The tripod being metal was still conducting the heat it had gained into the water bath meaning that the temperature of the water bath would rise after the Bunsen burner had been turned off.

With the temperature rising above the wanted temperature this could have been why the 55°C result was an anomaly. The temperature of the water bath for this result could have increased more than in the other results. Meaning that the pigment particles had more kinetic energy than they should have had, therefore more of the pigment particles might have made a hole in the membrane allowing more pigment out than it should have done.

The way that the method of the experiment could have been improved to improve the accuracy of the results would have been to use an electrical water bath. The reason why is because these water baths are able to maintain the set temperature unlike the water bath that we used that increased the temperature after the Bunsen burner had been turned off.

Another way of improving the method to improve the accuracy of the results would be to use a device that would be able to shake the test tubes with the same amount of force and frequency for a required period of time. This would mean that each of the experiments would be on a level par with each other and would increase accuracy.