VCE Biology Question Thread

[Sine]

I did an experiment with a chelate complex( faded yellow) in a dialysis tube and an alkaline solution (sodium hydroxide solution) within a beaker

When the dialysis tube was placed in the beaker the chelate complex turned light purple then purple.

I am told that an alkaline environment causes the chelate complex to turn purple./ Short polypeptides are light pink and long polypeptides are violet/purple.

Can someone explain how this has happened?

[vox nihili]

I did an experiment with a chelate complex( faded yellow) in a dialysis tube and an alkaline solution (sodium hydroxide solution) within a beaker

When the dialysis tube was placed in the beaker the chelate complex turned light purple then purple.

I am told that an alkaline environment causes the chelate complex to turn purple./ Short polypeptides are light pink and long polypeptides are violet/purple.

Can someone explain how this has happened?

It's very, very much outside of the Biology course.

[Sine]

It's very, very much outside of the Biology course.

Was given this as a SAC and the main question I am asking is a Sodium Hydroxide solution able to pass through dialysis tubing because if so that can be an explanation for the change of colour.

[vox nihili]

Was given this as a SAC and the main question I am asking is a Sodium Hydroxide solution able to pass through dialysis tubing because if so that can be an explanation for the change of colour.

Yep, absolutely. Sorry, I thought you were asking for the chemistry behind it. If the NaOH didn't move into the dialysis tubing, there'd be no alkaline environment and thus no colour change.

[kimmytaaa]

can someone help me with this question?
state the role of inhibitors in regulating enzyme activity?

[Reus]

can someone help me with this question?
state the role of inhibitors in regulating enzyme activity?

Firstly enzyme inhibitors are molecules that bind to an enzyme in which they subsequently block the active site in a competitive way leading to a decreased enzymatic activity. The binding of an inhibitor stops substrate from entering the active site, thus hindering the enzyme's activity/rate from catalysing the given reaction. In doing so, the enzyme's activity is regulated in correspondence to the concentration of inhibitors present.

[cosine]

osmosis is the 'net movement'

What exactly is meant by net movement ?

[Sine]

osmosis is the 'net movement'

What exactly is meant by net movement ?

The overall movement of water molecules, ex. more molecules are moving in to the cell than out, therefore net movement is into the cell.

[cosine]

The overall movement of water molecules, ex. more molecules are moving in to the cell than out, therefore net movement is into the cell.

If it's the overall, then does that mean 'some' water molecules are going in the opposite osmotic direction?

[Cogglesnatch Cuttlefish]

If it's the overall, then does that mean 'some' water molecules are going in the opposite osmotic direction?

yeah you cant ever have a 100% of the water going in one direction

[Jay.C]

Hey guys! Has any one done the sac where you grind up a liver and incubate it at diffrent temperatures? Then once that is done you add hydrogen peroxide and examin how much gas is produced. If so could you give me an idea of some of the questions I am likley to incounter in the theorie part. Also just to clarify the amount of O2 produced is the amount of enzyme activity, yes? Thanks! Also any other information you have about this prac would be much appreciated! 

[aaziz17]

Hey guys! Has any one done the sac where you grind up a liver and incubate it at diffrent temperatures? Then once that is done you add hydrogen peroxide and examin how much gas is produced. If so could you give me an idea of some of the questions I am likley to incounter in the theorie part. Also just to clarify the amount of O2 produced is the amount of enzyme activity, yes? Thanks! Also any other information you have about this prac would be much appreciated!

I done the SAC yesterday, you should know the reason for each step in the experiment, youll be asked to sketch the graph (temperature vs reaction rating out of 100), what happens when i enzyme is exposed to extremely high or low temperatures and experimental controls.
 Yes, the more oxygen the faster the enzyme is working because remember Hydrogen Peroxide (H202) gets broken into H20 and O2. And you should know the more oxygen present the bigger the flame will light up.

Overall , I found it helpful just to understand all things affecting enzyme reaction rate. The rest should be a breeze from there.
Anyways good luck!

[paper-back]

In biology are we allowed to use math symbols?
i.e. When writing something like Enzyme concentration is less than Substrate concentration can instead write it as
Enzyme concentration < Substrate concentration?

Also,
On a "How increasing enzyme concentration effects reaction rate" graph
Why is a there a continuous line instead of a a rapid drop as soon as enzyme concentration=substrate concentration?

[KingDrogba]

I know this may seem silly but is the control in the experiment, ALL six of those test tubes used in the first half of the prac, or is it just the test tube which has H2O2 and liver (step  2)?

Also, we had a problem of the stoppers popping off from the test tube due to the build up of gas from Hydrogen Peroxide being broken down in H20 and O2. What is a way of preventing this source of error?

Finally, the changes in pH, does that cause denature? Or simply just a decrease in function?

Sorry for the all the Q's, thanks for the help!

[nickjparkinson]

in response to Paperback

1) I would be wary about using mathematical symbols in the exam. There is a chance (albeit minute) that your examiner will misread the '<' symbol as a greater than symbol. It's far better to write out "less than" to avoid any confusion. It's not wasted time when you're ensuring that you get the marks.

2) In the graph you're talking about, when enzyme concentration equals substrate concentration, the system is in what is called "chemical equilibrium". This is pretty much just a fancy way of saying that the rate of reaction is constant. Consequently, the rate graph will plateau but not drop (as the reaction hasn't completely stopped, rather it is just occurring at a constant rate). I'm happy to elaborate on this further if you would like.

in response to PKingDrogba
I have to admit, I initially shared your confusion about the control of the experiment - it is not very well designed. I would argue that the control is the test tube to which nothing has been added but H202 as, essentially, this test tube (in which (fundamentally) no chemical reactions have taken place) allows comparison to the other test tubes.

The error due to the stoppers popping off is more of an instrument error. Although it's crude, I think the best way of minimising this error is to keep a finger on the stopper.

Your last question is vital. Dramatic changes in pH do cause denaturation!. When pH changes, ionic interactions in the tertiary structure of proteins may be disrupted. Consequently, the protein may unravel (denature). This is irreversible and changes the shape of the active site of enzymes. Consequently, function is impaired as the enzyme no longer has an optimal fit for its specific substrate.

Good luck for the year ahead and feel free to ask any more questions!