VCE Biology Question Thread

[PopcornTime]

It’s not really converted. An enzyme is just a protein with a specific structure. There are molecules (enzymes I think) that fold the polypeptide into its tertiary shape. I’m pretty sure that’s all you need to know. What specifically did it say on the examiners report?

Well it wasn't relevant to the above, but the multiple genes leading to multiple proteins questions, but wasn't sure if post-translational modifications could result in an enzyme:

2017 VCAA Q1. c):
• different post-transcriptional modification or modifications of the pre-mRNA
• different exons are joined or alternative splicing
• different nucleotide sequences/mRNA sequences, code for a different protein
• post-translational changes to the protein; for example, alternative folding

Since vcaa referred to post-translational modifications, would it be wise to go through it?

[Sine]

Well it wasn't relevant to the above, but the multiple genes leading to multiple proteins questions, but wasn't sure if post-translational modifications could result in an enzyme:

2017 VCAA Q1. c):
• different post-transcriptional modification or modifications of the pre-mRNA
• different exons are joined or alternative splicing
• different nucleotide sequences/mRNA sequences, code for a different protein
• post-translational changes to the protein; for example, alternative folding

Since vcaa referred to post-translational modifications, would it be wise to go through it?

nah you definitely don't need to know how protein folding occurs or any other post translation modification occurs.

[PhoenixxFire]

Well it wasn't relevant to the above, but the multiple genes leading to multiple proteins questions, but wasn't sure if post-translational modifications could result in an enzyme:

2017 VCAA Q1. c):
• different post-transcriptional modification or modifications of the pre-mRNA
• different exons are joined or alternative splicing
• different nucleotide sequences/mRNA sequences, code for a different protein
• post-translational changes to the protein; for example, alternative folding

Since vcaa referred to post-translational modifications, would it be wise to go through it?

Yeah definitely not examinable - it would not be the only possible answer to a question. I suspect for this question you would have just had to mention it not talk about it in detail.

[MAGGOT]

do we still need to know about the negative feedback model and stimulus response model in year 12 bio

[darkz]

do we still need to know about the negative feedback model and stimulus response model in year 12 bio

You don't need to know much about the negative feedback model, but the study design now puts a lot more emphasis on the stimulus response model

[PopcornTime]

Can anyone confirm how the following could be improved?

Accuracy
- minimise systematic errors
- correct use of material

Precision
- minimise random errors
- use of quantitative results, as it  provide a precise measurement of data

validity
- 1 independent variable
- many control variables

reliability
- compare primary to secondary data
- repeat the experiment
- if I couldn't repeat the experiment, then how can reliability be ensured

repeatability
- confused about how this could have been improved
- how could this have been ensured throughout an experiment?

reproducibility
- confused about this as well
- how could this have been ensured throughout an experiment?

Also, does using complex apparatus (like a sensor), improve accuracy or precision?

[PhoenixxFire]

Can anyone confirm how the following could be improved?

Accuracy
- minimise systematic errors
- correct use of material

Precision
- minimise random errors
- use of quantitative results, as it  provide a precise measurement of data

validity
- 1 independent variable
- many control variablesbetter to say ‘all other variables controlled’, there doesn’t need to be lots controlled, but all variables affecting it need to be.

reliability
- compare primary to secondary data
- repeat the experiment
- if I couldn't repeat the experiment, then how can reliability be ensuredYou can use a large sample initially (which you should do anyway)

repeatability
- confused about how this could have been improved
- how could this have been ensured throughout an experiment?
if your experiment is reliable it will be repeatable and reproducible. The only other thing to consider is making sure your method is clear.

reproducibility
- confused about this as well
- how could this have been ensured throughout an experiment?

Also, does using complex apparatus (like a sensor), improve accuracy or precision? Accuracy. If you are using bad equipment it will still give you the same results each time so it is precise. (Unless there are other errors going on)

[PopcornTime]

So, just to confirm, comparing primary to secondary data improves reliability?

[PhoenixxFire]

So, just to confirm, comparing primary to secondary data improves reliability?

Sorry I missed that bit. It doesn’t improve reliability but comparing your results to it can help you determine if your results are accurate. You can’t improve reliability of your experiment without changing your experiment.

[juntyhee]

Can someone confirm this explanation of how enzyme concentration affects reaction rate?

Initially, increasing catalase concentration led to a higher chance of effective collisions between the catalase and hydrogen peroxide molecules due to a greater quantity of enzyme active sites for substrate to bind to. This led to the formation of more enzyme substrate complexes, consequently increasing the reaction rate.
   
However, the quantity of available substrate molecules decreased as more began to saturate enzymes. With less free floating hydrogen peroxide molecules, there is a decreased chance of effective collisions between catalase and hydrogen peroxide. Hence, increasing catalase concentration had less of an effect on reaction rate beyond 0.01% catalase concentration.

NOTE: my experiment didn't hit the plateau so i don't mention that ALL substrate molecules are occupying an enzyme

[PhoenixxFire]

Can someone confirm this explanation of how enzyme concentration affects reaction rate?

Initially, increasing catalase concentration led to a higher chance of effective collisions between the catalase and hydrogen peroxide molecules due to a greater quantity of enzyme active sites for substrate to bind to. This led to the formation of more enzyme substrate complexes, consequently increasing the reaction rate. Yep this is right
   
However, the quantity of available substrate molecules decreased as more began to saturate enzymes.This is worded weirdly. The available amount of substrate decreases because it has been broken down With less free floating hydrogen peroxide molecules, there is a decreased chance of effective collisions between catalase and hydrogen peroxide.Yep but both of these sentences talk about substrate concentration not enzyme concentration Hence, increasing catalase concentration had less of an effect on reaction rate beyond 0.01% catalase concentration. Now your talking about enzyme concentration which is different to the above. Given you want to talk about the effect of enzyme concentration you should mention that given it didn't plateau, your enzyme concentration was not the limiting factor at this point and so further increases to enzyme concentration would not increase reaction rate.

NOTE: my experiment didn't hit the plateau so i don't mention that ALL substrate molecules are occupying an enzyme So this means that you haven't hit saturation point. So substrate is your limiting factor.

[juntyhee]

What do you mean that I should be talking about enzyme concentration only?

The reason why increasing enzyme concentration has a diminishing impact on reaction rate is because substrate concentration is decreasing as more is broken down... isn't that correct?

[PhoenixxFire]

The reason I said you should be only talking about enzyme concentration is because that's what you said at the top of your post.

If you have a constant substrate amount - somehow the reaction occurs but it replenishes itself. Say there is 100 substrate molecules. If you put in enough enzymes so that 100 reactions are always occurring at any given moment, then increasing the amount of enzymes beyond that will not increase reaction rate. It doesn't matter if you double the amount of enzymes, there are no more substrates for them to react with at any given time. So at this point substrate is the limiting factor - increasing enzyme concentration will not increase reaction rate because it is no longer limiting it (this will look like a plateau on a graph. X axis time, Y axis reaction rate.)

If you have a set number of enzymes and you increase the amount of substrate to the point where at any given time there are no enzymes available to catalyse a reaction then the enzyme concentration is the limiting factor. When this happens the enzymes are 'saturated' increasing the amount of enzymes will increase the rate of reaction until something else becomes the limiting factor.

increasing enzyme concentration has a diminishing impact on reaction rate is because substrate concentration is decreasing.

This is not entirely correct. It relates to what I said above. As the amount of substrate decreases, the amount of enzymes needed also decreases. Increasing enzymes above what is needed will always not increase reaction rate, the amount of substrate just changes the amount of enzymes that are needed.

[juntyhee]

The reason I said you should be only talking about enzyme concentration is because that's what you said at the top of your post.

If you have a constant substrate amount - somehow the reaction occurs but it replenishes itself. Say there is 100 substrate molecules. If you put in enough enzymes so that 100 reactions are always occurring at any given moment, then increasing the amount of enzymes beyond that will not increase reaction rate. It doesn't matter if you double the amount of enzymes, there are no more substrates for them to react with at any given time. So at this point substrate is the limiting factor - increasing enzyme concentration will not increase reaction rate because it is no longer limiting it (this will look like a plateau on a graph. X axis time, Y axis reaction rate.)

If you have a set number of enzymes and you increase the amount of substrate to the point where at any given time there are no enzymes available to catalyse a reaction then the enzyme concentration is the limiting factor. When this happens the enzymes are 'saturated' increasing the amount of enzymes will increase the rate of reaction until something else becomes the limiting factor.

This is not entirely correct. It relates to what I said above. As the amount of substrate decreases, the amount of enzymes needed also decreases. Increasing enzymes above what is needed will always not increase reaction rate, the amount of substrate just changes the amount of enzymes that are needed.

Hmm alright, does this statement make more sense?

At 0.01% catalase concentration, most H2O2 molecules have occupied a catalase enzyme. As such, increasing catalase concentration beyond this point has little effect on reaction rate as there are less available H2O2 molecules for catalase to bind to, reducing the chance of effective collisions - substrate concentration becomes a limiting factor.

[PhoenixxFire]

Hmm alright, does this statement make more sense?

At 0.01% catalase concentration, most H2O2 molecules have occupied a catalase enzyme The rest of this makes sense but this bit doesn't. You should say that the H2O2 molecules have been broken down or that they've had their reaction catalysed.. As such, increasing catalase concentration beyond this point has little effect on reaction rate as there are less available H2O2 molecules for catalase to bind to, reducing the chance of effective collisions - substrate concentration becomes a limiting factor.