VCE Biology Question Thread

[nerdmmb]

in the potato osmosis sac i have been asked to explain 3 possible sources of error? What are these?

Don't know why my last post didn't show but anyways, my guess is:
-You may have read the mass of the potato or amount of solution (whilst measuring) inaccurately
-You may have dried the potato slices with paper towel excessively
-There may have been more or less salt in one or more of the solutions

[MM1]

As slothpumba pointed out, not part of the course.

But, because it's relatively basic, the answer is no. Water itself isn't actively transported. Although, active transport can be used to maintain water balance and that's by actively transport salts either in or out of the cell, thereby setting up a concentration gradient and receiving water via osmosis.

Thanks! Also, can it be said that a small-scale concentration gradient between two solutions means that osmosis would occur at a slower rate?

[Rishi97]

How does water get through the semi-permeable membrane when the main role of this phospholipid bi-layer is to keep water out?

[nerdmmb]

How does water get through the semi-permeable membrane when the main role of this phospholipid bi-layer is to keep water out?

The main role of the membrane isn't to keep water out; it's to manage the inputs and outputs of the cell. The membrane has tiny pores between the phospholipids which allow water molecules to diffuse through. Conversely, it is impermeable to charged and polar molecules which therefore require protein channels or specific protein carrier molecules.

[Rishi97]

ok. 
So if the water travels through the tiny pores, the hydrophobic tails wont stop it from entering the cell?

[Rishi97]

sorry for posting it twice. My computer stuffed up

Mod: don't worry, fixed it

[vox nihili]

Thanks! Also, can it be said that a small-scale concentration gradient between two solutions means that osmosis would occur at a slower rate?

Absolutely! This is a really important factor in diffusion and osmosis. The larger the conc. gradient, the faster the rate of diffusion/osmosis.

[slothpomba]

ok. 
So if the water travels through the tiny pores, the hydrophobic tails wont stop it from entering the cell?

It's not VCE level but the membrane has specific channels to allow water in called Aquaporins. It's been awhile since i've done biochem so i could be mistaken but i thought water was in the category of molecules that are so small that they can simply just slip through the membrane by diffusion without any specific need for channels, carriers, etc.

[vox nihili]

It's not VCE level but the membrane has specific channels to allow water in called Aquaporins. It's been awhile since i've done biochem so i could be mistaken but i thought water was in the category of molecules that are so small that they can simply just slip through the membrane by diffusion without any specific need for channels, carriers, etc.

All of that's right (as far as I know).


Water slips through the gaps, it's just a bit of a slower process than aquaporins obviously.

[nerdmmb]

All of that's right (as far as I know).


Water slips through the gaps, it's just a bit of a slower process than aquaporins obviously.

So, if we be a bit specific and mention aquaporins instead of pores, will that be okay?

[MM1]

How do peripheral proteins work? What do they do?

[slothpomba]

So, if we be a bit specific and mention aquaporins instead of pores, will that be okay?

Consult your teacher, it definitely wasn't taught in VCE when i did it and it's a relatively (for biology anyway) new discovery.

[vox nihili]

So, if we be a bit specific and mention aquaporins instead of pores, will that be okay?

No, don't talk about them at all, they're not in the course as slothpomba and I have both indicated. As far as you're concerned, water can filter through the tiny holes of the membrane itself and that's how it gets through. You will not receive any credit for talking about aquaporins no matter how correct it is.

[Rishi97]

In the potato sac for osmosis, Why do we have to calculate the percent change in mass instead of just using the change in
mass itself?

[alchemy]

In the potato sac for osmosis, Why do we have to calculate the percent change in mass instead of just using the change in
mass itself?

So you can graph it and refer to it when explaining your results.