VCE Biology Question Thread

[cosine]

hey guys! So I had my prac for biology unit 3 and 4, on Osmosis, with the eggs , and I was just wondering has anyone done it already?
I could use a little help on what to write up for my discussion 
thanks!!

Why exactly does high temperature deform the shape of an enzyme? And is the enzyme in general losing it's shape or only the active site?

Also, how does substrate concentration affect the enzyme activity/rate? I don't understand how it could increase it?

Oh and in a hypothesis, do we need to be specific such as: It is hypothesised that high temperatures will reduce enzymatic activities. Or do we need to consider both aspects like: It is hypothesised that the temperature in which an enzyme acts will affect the activity.

Thanks

[cosine]

Can someone explain inhibition on enzymes to me, specifically how they affect the rate? Thank you

[vanessa14]

And another thing, can someone explain what this means?

Plant cells take in water by osmosis until the cell wall pushes back on the cell's contents with the same pressure

?

[cosine]

And another thing, can someone explain what this means?

Plant cells take in water by osmosis until the cell wall pushes back on the cell's contents with the same pressure

?

I don't think this makes sense. When a plant cell intakes excess water via osmosis, the vacuole which stores the water actually expands towards the plasma membrane and causes it to exert turgor pressure as it pushes against the cell wall. This state is called turgid.

[Mieow]

And another thing, can someone explain what this means?

Plant cells take in water by osmosis until the cell wall pushes back on the cell's contents with the same pressure

?

Pretty sure this just means that the cell wall exerts the same amount of pressure against the vacuole/cell to prevent it from bursting.

[vox nihili]

Pretty sure this just means that the cell wall exerts the same amount of pressure against the vacuole/cell to prevent it from bursting.

Yeah this is correct. It's not really the best way to put it. But it means that no more water can flow in because the pressure of the contents of the cell against the cell wall is equal to the osmotic pressure.

That said, the way I just put it was likely more confusing (though more correct).

[cosine]

My teacher said that I lost marks on my prac because in my conclusion I did not refer to my results and I didn't restate hypothesis. Can someone help me out, what is the best template to write up a biology conclusion? Thanks

[vox nihili]

My teacher said that I lost marks on my prac because in my conclusion I did not refer to my results and I didn't restate hypothesis. Can someone help me out, what is the best template to write up a biology conclusion? Thanks

A conclusion should establish whether your hypothesis was correct with regards to the results of your experiment. Use your results to demonstrate its correctness or its not correctness. The conclusion should also specifically give any key results as well.

[vanessa14]

Yeah this is correct. It's not really the best way to put it. But it means that no more water can flow in because the pressure of the contents of the cell against the cell wall is equal to the osmotic pressure.

That said, the way I just put it was likely more confusing (though more correct).

I understand that but what if I wasn't dealing with a plant cell and just an animal cell with only a cell membrane? Can the water diffuse back out and the amount of water in the cell decrease?

[grannysmith]

I understand that but what if I wasn't dealing with a plant cell and just an animal cell with only a cell membrane? Can the water diffuse back out and the amount of water in the cell decrease?

Water will always diffuse to the region of high solute concentration. However, water continuously moves back and forth regardless of osmotic pressure. That's why we always refer to the net movement of water molecules. Does this answer your question?

[vanessa14]

Water will always diffuse to the region of high solute concentration. However, water continuously moves back and forth regardless of osmotic pressure. That's why we always refer to the net movement of water molecules. Does this answer your question?

Kind of, yeah  I just dont know how to write an analysis question on that. One of the questions was something like why does the mass of a egg decrease after its been in water for so long? Prior to this, it always had water moving in, so I dont understand why the water would suddenly move out, after say 20 minutes...
And thats why I asked if the water moves back out somehow...
Sorry, Im not sure if my explanation makes any sense at all.

[cosine]

What is the site on an enzyme that a non-competitive inhibitor binds to?

Also, some enzymes are not primarily composed of proteins, right? For example, an enzyme could be inactive until a cofactor binds to it, so the enzyme is essentially composed of a protein part, and a non-organic non-protein part. So could you call the protein part the enzyme, or is the 'whole' structure (by this I mean including the cofactor) called the enzyme?

Oh and when a non-competitive inhibitor binds to the enzyme, it will deform the shape of the enzyme and consequently break the R-group/variable interractions. What is the proper term instead of 'break' the interractions?

Last question, promise. When the temperature is decreased in an enzyme-catalysed reaction, does it reduce the molecular kinetic movement of the substrate and enzyme, henceforth reducing the opportunity for the subtrate to bind to the cleft of the enzyme? If so, what about enzyme's whose optimum temperature is really low, does this mean that the molecular movements are still slow, but does this mean that the enzymatic activity is generally slow or is this beyond the scope of VCE biology?

Also, when an enzyme is exposed to it's optimum conditions/environments, does it perform at it's optimal ability? Is that the correct term?

Apologies for the inrush of questions

[grannysmith]

Kind of, yeah  I just dont know how to write an analysis question on that. One of the questions was something like why does the mass of a egg decrease after its been in water for so long? Prior to this, it always had water moving in, so I dont understand why the water would suddenly move out, after say 20 minutes...
And thats why I asked if the water moves back out somehow...
Sorry, Im not sure if my explanation makes any sense at all.

Alright then.. haha. I've never done this prac before so I hope you don't mind if I ask for some clarification. Did you place a de-shelled egg into (distilled) water? If it's placed in water, then obviously water would move into the egg due to the water being hypotonic relative to the egg.

So essentially, water moves into the region of high (solute) concentration; that is, into the egg cells. Now, this continues until equilibrium is reached i.e. when the solute concentration outside the egg cells is the same as inside. However, animal cells do NOT have a cell wall, unlike plant cells. Therefore you can imagine that equilibrium may not be reached before the boundaries of the cell (i.e. the cell membrane) cannot expand anymore such that the cell undergoes lysis (it bursts). If this occurs to one cell, then it's safe to say that many other cells will experience the same fate. Over time, you're losing egg which explains the decrease in mass.

Hope this helps!

[vox nihili]

I understand that but what if I wasn't dealing with a plant cell and just an animal cell with only a cell membrane? Can the water diffuse back out and the amount of water in the cell decrease?

The water concentration on both sides will equalise.

[vceva]

Hellloooo, going to try my best to answer your questions hahah

What is the site on an enzyme that a non-competitive inhibitor binds to?
any site other than the active site

Also, some enzymes are not primarily composed of proteins, right? For example, an enzyme could be inactive until a cofactor binds to it, so the enzyme is essentially composed of a protein part, and a non-organic non-protein part. So could you call the protein part the enzyme, or is the 'whole' structure (by this I mean including the cofactor) called the enzyme?
apoenzyme = protein portion.  you probably don't need to know this but apoenzyme + coenzyme = holoenzyme
Oh and when a non-competitive inhibitor binds to the enzyme, it will deform the shape of the enzyme and consequently break the R-group/variable interractions. What is the proper term instead of 'break' the interractions?
I'm not sure, but I think you only need to know that it changes the active site.

Last question, promise. When the temperature is decreased in an enzyme-catalysed reaction, does it reduce the molecular kinetic movement of the substrate and enzyme, henceforth reducing the opportunity for the subtrate to bind to the cleft of the enzyme? If so, what about enzyme's whose optimum temperature is really low, does this mean that the molecular movements are still slow, but does this mean that the enzymatic activity is generally slow or is this beyond the scope of VCE biology?
yes, hmm i don't know an enzyme which has a very low optimum temperature... but ALL molecules move slower at lower temperatures
Also, when an enzyme is exposed to it's optimum conditions/environments, does it perform at it's optimal ability? Is that the correct term?
I believe so.

you sound a little stressed, i don't think you need to worry about such technicalities and terms