VCE Biology Question Thread

[Rishi97]

OMG!!! Thank you sooo much. This is so helpful
It's actually really hard to believe that u r in yr 11. Do u do yr 12 biology?

[nerdmmb]

OMG!!! Thank you sooo much. This is so helpful
It's actually really hard to believe that u r in yr 11. Do u do yr 12 biology?

No worries. Thank-you too- it helped me revise

Haha yeah I do nothing big though. Glad it helped!

[MM1]

Hey
I have a sac coming up on osmosis and here are the key concepts we need to know:

•   Draw and label fluid mosaic model of the plasma membrane

This is a really great representation of the bilayer.

Spoiler

The pores between the phospholipids allow small uncharged and lipophilic substances such as alcohol and water to diffuse through.


For example, imagine a frog in a pond; if the pond has a lot of salt dissolved in it- it is hypertonic to the frog and water will therefore diffuse into the frog possibly making it burst.

Water is polar(not lipophilic) and therefore hydrophilic. However it is able to diffuse through the bilayer.

Water will diffuse out of the organism because the pond is more concentrated; it's hypertonic to the frog so water moves from an area of low solute con. to high solute con. 

[Chang Feng]

Is there a difference when mentioning just high concentration and high solute concentration for diffusion.

[nerdmmb]

Is there a difference when mentioning just high concentration and high solute concentration for diffusion.

Yes, you need to mention what concentration you are referring to. Concentration of water, solute, etc. otherwise the examiner can misinterpret it and it may cost you marks.

[Chang Feng]

But then if its saying diffusing Is the passive net movement of solute it ignores water molecules, and despite it being a special case of diffusion being osmosis, isn't it still diffusion to. And water molecules aren't solute. Just wondering, I maybe wrong??  It seems like just having to write as much info for definitions as possible, as we don't know which points the examiners want for definition. This seems really time consumer- there is no other way is there?

[alchemy]

But then if its saying diffusing Is the passive net movement of solute it ignores water molecules, and despite it being a special case of diffusion being osmosis, isn't it still diffusion to. And water molecules aren't solute. Just wondering, I maybe wrong?? 

Osmosis is the term used to refer to movement of water molecules. When speaking about 'diffusion', it's a tendency to mention solute. Actually, referring to either solute or water concentration in your definition is fine but, don't just leave your response "vague" by saying "high concentration". You need to mention high concentration of (what?).

[nerdmmb]

But then if its saying diffusing Is the passive net movement of solute it ignores water molecules, and despite it being a special case of diffusion being osmosis, isn't it still diffusion to. And water molecules aren't solute. Just wondering, I maybe wrong??  It seems like just having to write as much info for definitions as possible, as we don't know which points the examiners want for definition. This seems really time consumer- there is no other way is there?

Unfortunately there isn't. Osmosis refers to the net movement of water molecules not solutes. Osmosis is an example of diffusion.
Another reason why you need to mention what you are referring to is because you need to state what is being diffused at a higher rate between the two mediums.
Simply stating that diffusion is a net movement from a higher solution is too vague
Having said that, it's good to be concise but also specific.

[alchemy]

Water is polar(not lipophilic) and therefore hydrophilic. However it is able to diffuse through the bilayer.
Water will diffuse out of the organism because the pond is more concentrated; it's hypertonic to the frog so water moves from an area of low solute con. to high solute con. 

Good pick up MM1.

Great answers by nerdmmb as well. I tried making my own answers for those questions and they ended up being much worse

[nerdmmb]

Good pick up MM1.

Great answers by nerdmmb as well. I tried making my own answers for those questions and they ended up being much worse

Thanks! Haha I actually didn't notice that! Biological terms confuse the crap out of me!

I'm pretty sure yours are better! I guess practice just makes perfect

[Chang Feng]

  Okay then thanks. Helps. Also another question when referring to hypotonic or hypertonic is it always with relation to the cell. As in if I was to say hypertonic is the net movement of water molecules from outside the cell to inside the cell, along the concentration gradient, across a semi-permeable membrane until equilibrium is reached. Is it implied that the water is going inside cell. Or do we have to say its the movement of water molecules ... to the concentration in question. Also hypertonic, hypertonic is always across a semi-permeable membrane right??

[nerdmmb]

  Okay then thanks. Helps. Also another question when referring to hypotonic or hypertonic is it always with relation to the cell. As in if I was to say hypertonic is the net movement of water molecules from outside the cell to inside the cell, along the concentration gradient, across a semi-permeable membrane until equilibrium is reached. Is it implied that the water is going inside cell. Or do we have to say its the movement of water molecules ... to the concentration in question. Also hypertonic, hypertonic is always across a semi-permeable membrane right??

Yupp! You only mention hypertonic or hypotonic when you're making a comparison between two solutions

Hypertonic and hypotonic is not necessarily always in relation to a semi permeable membrane

[alchemy]

  Okay then thanks. Helps. Also another question when referring to hypotonic or hypertonic is it always with relation to the cell. As in if I was to say hypertonic is the net movement of water molecules from outside the cell to inside the cell, along the concentration gradient, across a semi-permeable membrane until equilibrium is reached. Is it implied that the water is going inside cell. Or do we have to say its the movement of water molecules ... to the concentration in question. Also hypertonic, hypertonic is always across a semi-permeable membrane right??

The terms hypertonic and hypotonic are in relation to solute concentration. You might want to recheck over what you wrote. There seems to be a few errors in your expression such as, "hypertonic is the net movement of water molecules..."

[RazzMeTazz]

In the secondary structure, the polypeptide chain undergoes coiling (alpha helices) and folding (beta sheets) due to hydrogen bonding between the different amino acids.

Is this hydrogen bonding between the R groups of the amino acids?

Thanks!

[MM1]

Good pick up MM1.

Great answers by nerdmmb as well. I tried making my own answers for those questions and they ended up being much worse

You should've posted your answers as well regardless; it's a way to improve by practice I'd recommend perhaps memorising some good definitions for the types of movements and picking up on key words. It's pretty hard to formulate a good response at first but with practice, it'll surely improve.