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A-Level Biology Question

I'm just in the middle of revising and answering questions. I'm less than happy with my answers for the following question and would appreciate feedback:

The effect of temperature on the permeability of cell membranges can be investigated by using fresh carrot. When discs of carrot are placed in water there is a slow release of chloride ions from the vacuoles of the carrot cells (are these diffusing through the membrane or across gated channel proteins). A number of sets of equal sized discs were cut and placed into water at different temperatures, from 35 to 70 degrees celcius. The graph shows the rate of release of chloride ions over this temperature range [Graph showing shallow increase from 35-50 and steep increase from 50-60 then leveling out at 60+].

a) Suggest why it is necessary to wash the discs before placing them into water at different temperatures.
[I rambled on about ensuring water potential is equal in each of the samples but am not really sure].

b) Explain the increase in rate of release of chloride ions between the temperatures of (i)35-45 degrees celcius (ii) 50-60 degrees celcius.
[I rambled on about increase KE = faster diffusion. But why is there a significantly higher gradient for (ii) than for (i)? Do they cross via gated channel proteins which have denatured or something?

c) What assumption is made about the cell wall of the carrot cells is made in this investigation?
[Umm, the cell walls are of equal thickness and permeability?]

Thanks for any help.
Reply 1
it would help if you actually scanned the graphs / questions and posted it. ifs that possible. Kind of hard interpreting 'shallow increase'
Reply 2
Reptile
it would help if you actually scanned the graphs / questions and posted it. ifs that possible. Kind of hard interpreting 'shallow increase'


I've copied the question out. Regarding the graph, there's no numerical interpretation needed. I just need to explain why the rate suddenly becomes so much faster when going from 50 to 60 degrees celcius.
Do the ion channels still function when the cells are dead?
Reply 3
Gaz031
I've copied the question out. Regarding the graph, there's no numerical interpretation needed. I just need to explain why the rate suddenly becomes so much faster when going from 50 to 60 degrees celcius.
Do the ion channels still function when the cells are dead?

Eeh if the channels are made of proteins, wont they denature?
Reply 4
hihihihi
Eeh if the channels are made of proteins, wont they denature?

I would think so, but there are admittedly many contradictions in biology.
The gradient of the line very suddenly changes though. Perhaps the question isn't a good one.
Reply 5
Gaz031
I'm just in the middle of revising and answering questions. I'm less than happy with my answers for the following question and would appreciate feedback:

The effect of temperature on the permeability of cell membranges can be investigated by using fresh carrot. When discs of carrot are placed in water there is a slow release of chloride ions from the vacuoles of the carrot cells (are these diffusing through the membrane or across gated channel proteins). A number of sets of equal sized discs were cut and placed into water at different temperatures, from 35 to 70 degrees celcius. The graph shows the rate of release of chloride ions over this temperature range [Graph showing shallow increase from 35-50 and steep increase from 50-60 then leveling out at 60+].

a) Suggest why it is necessary to wash the discs before placing them into water at different temperatures.
[I rambled on about ensuring water potential is equal in each of the samples but am not really sure].

b) Explain the increase in rate of release of chloride ions between the temperatures of (i)35-45 degrees celcius (ii) 50-60 degrees celcius.
[I rambled on about increase KE = faster diffusion. But why is there a significantly higher gradient for (ii) than for (i)? Do they cross via gated channel proteins which have denatured or something?

c) What assumption is made about the cell wall of the carrot cells is made in this investigation?
[Umm, the cell walls are of equal thickness and permeability?]

Thanks for any help.


I would say for a.) that they need to be washed to remove contaminants such as any pesticides or fertiliser compounds that contain chloride ions as they would give a misrepresentation of the ion concentration released by the carrot.
for b.) i would have thought that it is because cell membranes and ion channels have denatured and the export of the chloride ions from the cell is no longer controlled but is simply released. The reason why the gradient is larger at 50 - 60 is because most proteins denature completely at 45 degrees so below this temp. there will be incomplete denaturation of membranes and protein (ion) channels - therefore less chloride released.
for c.) - probably sumthing like that.
Reply 6
ryan750
I would say for a.) that they need to be washed to remove contaminants such as any pesticides or fertiliser compounds that contain chloride ions as they would give a misrepresentation of the ion concentration released by the carrot.
for b.) i would have thought that it is because cell membranes and ion channels have denatured and the export of the chloride ions from the cell is no longer controlled but is simply released. The reason why the gradient is larger at 50 - 60 is because most proteins denature completely at 45 degrees so below this temp. there will be incomplete denaturation of membranes and protein (ion) channels - therefore less chloride released.
for c.) - probably sumthing like that.

A) Not really: If you cut the carrot, what happens? There will be cut cells, thus introducing Cl- already spilt from the burst vacoules. So its to wash off these really.

B) Plant proteins tend to denature at temepratures far less than 45 degrees, a good reasonable explaination would be that yes there would be some protein denaturation, and thus releasing some Cl- ions that way. However tis important to realise that the membrane will be increasingly fluidised, and thus Cl- will be able to just diffuse across from the patches of membrane that would suddenly "break up"

C) Cell walls are very permeable already, no question about that.
Reply 7
Thanks for the help to the above.
I thought cell walls were relatively thick as they maintain plant turgor pressure, especially when strengthened by cellulose?
Reply 8
Gaz031
Thanks for the help to the above.
I thought cell walls were relatively thick as they maintain plant turgor pressure, especially when strengthened by cellulose?

They are fairly thick I think, but they are also very permeable. Strength and permeability are not mutually exclusive :smile: The structure of the wall just means it allows anything to pass through (pretty much); if it didn't, the membrane would be fairly redundant!