VCE Biology Question Thread

[PhoenixxFire]

So would you recommend also talking about how eventually as you increase the substrate concentration, the active sites become saturated with substrates and substrate no longer becomes a limiting factor? Or is that irrelevant to the question?

No I wouldn't talk about enzymes becoming saturated at all - you don't know that that is what would become the limiting factor, temperature could be the limiting factor after you increase substrate concentration.

You would need to say:
-Substrate becomes a limiting factor when it is present in low concentrations.
-When there is a low concentration of substrate in the cell, it is less likely that the substrate will bump into the enzymes and therefore reactions will occur less frequently.
-Increasing substrate concentration would increase the rate of reaction until it is no longer the limiting factor.

[Mr West]

hey,

would it be correct to say that temperature and pH level can be irreversible inhibitors of enzymes?

[PhoenixxFire]

hey,

would it be correct to say that temperature and pH level can be irreversible inhibitors of enzymes?

It sort of is, but it doesn't really fit with how you are taught about it in VCE so I would avoid it. Better to just say that they can denature enzymes.

[Mr West]

It sort of is, but it doesn't really fit with how you are taught about it in VCE so I would avoid it. Better to just say that they can denature enzymes.

Thankyou,

could you say that the denaturing of an enzyme is an irreversible inhibitor, or do we only talk about poisons being irreversible inhibitors

[Poet]

Thankyou,

could you say that the denaturing of an enzyme is an irreversible inhibitor, or do we only talk about poisons being irreversible inhibitors

Hey Mr. West,

The denaturation of an enzyme can be reversible (the tertiary structure can actually reform) if the damage isn't too serious, so I would just stick to talking about inhibitors in a substrate sense, and poisons such as cyanide acting as inhibitors. Especially because this is not a required knowledge, and in VCE we're not talking about enzymes being inhibited by factors such as temperature and pH, only denatured.

[PhoenixxFire]

Thankyou,

could you say that the denaturing of an enzyme is an irreversible inhibitor, or do we only talk about poisons being irreversible inhibitors

Irreversible = Cannot be undone
Inhibition = Stops something from working

So yes it is an irreversible inhibitor - but if you're given a question that says 'name an irreversible inhibitor' on your SAC, unless you have no other option (e.g. multiple choice or you forgot), don't write temperature or pH.

[darkz]

Thankyou,

could you say that the denaturing of an enzyme is an irreversible inhibitor, or do we only talk about poisons being irreversible inhibitors

I wouldn't really say that denaturing of the enzyme is an irreversible inhibitor, rather that temperature/pH resulted in the irreversible inhibition of an enzyme. However then again, as PhoenixxFire said, temperature and pH aren't really taught as inhibitors of enzymatic activity in VCE rather just as factors that affect the rate of enzymatic activities, while we're pretty much just taught about the two types of enzyme inhibitors - competitive and non-competitive. As for irreversible inhibitors, any molecule that makes a covalent bond with an enzyme changing its 3D structure, thus permanently damaging it would be considered irreversible - which does include poisons

[FabAsianZung]

PART A: GERMINATING SEEDS ALONE
​1.​Place sufficient germinating seed to cover the base of the wide-mouth flask to a depth of just over 0.5 cm.

​2.​Set up the 2-holed stopper with the pipette, glass tubing, rubber tubing and clamp as in figure 4.2A. Release the clamp so that the rubber tubing is open.

​3.​Use a pipette filler to draw some coloured fluid into the graduated pipette
(figure 4.2B). Cover the top of the pipette tightly with your finger.

​4.​Assemble the stopper into the flask keeping your finger tightly on the pipette.

​5.​Close the clamp on the rubber tubing and only then release your finger from the pipette.

​6.​Note the time when the set-up is completed, and at the same time record the level of the coloured solution in the graduated pipette.

​7.​Wait 10 to 15 minutes, note the exact time you have waited, and record the level of the coloured solution in the graduated pipette.

Part B involves potassium hydroxide in a container placed in the middle of the flask, before it is tightly enclosed again just like Part A.

Haha, I kinda failed in this experiment for my SAC (we're doing 2 different prac), since my group couldn't close the clamp on the tubing tightly enough, so the coloured solution dropped down to the bottom of the flask.

Can anyone please explain to me what was supposed to happen in Part A and Part B?

Thank you in advance once again!

[darkz]

PART A: GERMINATING SEEDS ALONE
​1.​Place sufficient germinating seed to cover the base of the wide-mouth flask to a depth of just over 0.5 cm.

​2.​Set up the 2-holed stopper with the pipette, glass tubing, rubber tubing and clamp as in figure 4.2A. Release the clamp so that the rubber tubing is open.

​3.​Use a pipette filler to draw some coloured fluid into the graduated pipette
(figure 4.2B). Cover the top of the pipette tightly with your finger.

​4.​Assemble the stopper into the flask keeping your finger tightly on the pipette.

​5.​Close the clamp on the rubber tubing and only then release your finger from the pipette.

​6.​Note the time when the set-up is completed, and at the same time record the level of the coloured solution in the graduated pipette.

​7.​Wait 10 to 15 minutes, note the exact time you have waited, and record the level of the coloured solution in the graduated pipette.

Part B involves potassium hydroxide in a container placed in the middle of the flask, before it is tightly enclosed again just like Part A.

Haha, I kinda failed in this experiment for my SAC (we're doing 2 different prac), since my group couldn't close the clamp on the tubing tightly enough, so the coloured solution dropped down to the bottom of the flask.

Can anyone please explain to me what was supposed to happen in Part A and Part B?

Thank you in advance once again!

Hey, so not sure if this is 100% right, so someone else will need to confirm what I'm saying, but it should be on the right track.

The aim of your experiment seems to just be mainly to explore respiration in plants. So in part A, the seeds are allowed to respire and thus any change in the level of liquid in the pipette is directly attributed from that. As O2 gas is used up in respiration, the liquid level will fall, but then since CO2 is then produced the liquid level should increase slightly in the pipette.

For part B, the addition of potassium hydroxide simply reacts with the carbon dioxide to produce potassium carbonate and water. However the products don't really have a measurable increase in the volume inside the flask so the liquid level should fall as the oxygen is being used up by respiration.

[PopcornTime]

Explain why yeast fermentation cannot go indefinitely?

I know that lactic acid fermentation will result in muscle fatigue (which is why it doesn't go indefinitely), but not sure about yeast fermentation.

[HighSchoolerRS]

Explain why yeast fermentation cannot go indefinitely?

I know that lactic acid fermentation will result in muscle fatigue (which is why it doesn't go indefinitely), but not sure about yeast fermentation.

Fermentation produces ethanol and carbon dioxide. If there is sufficient glucose, the yeast will continue to undergo fermentation until the accumulation of ethanol kills it because ethanol is toxic.

[PopcornTime]

Can anyone help me with the following question from the Biozone 3/4 book?

60: investigating aerobic respiration in yeast

3. Why did absorbance of control tube change?

[PopcornTime]

Accuracy is how close a measured value is to the true value, but how do we know what the true value is?

Lets say for a cell respiration experiment.

[persistent_insomniac]

Hey can someone plz help me with these questions it would be much appreatied (to do with cellular respiration):
- In glycolysis why is it that only the 6 carbons part of the glucose are broken down and not the 12 hydrogens or 6 oxygens.
- What do you call NADH, ATP, CO2, FADH2 etc?  (can you just refer to all of them as coenzymes or molecules?)

Does anyone know where I can buy the biozone 3&4 workbook like what bookshops around the south-eastern suburbs have them??

Thanks!

Mod edit: Please refrain from double posting. Next time, click the 'modify' button on your first post -- Calebark

[HighSchoolerRS]

Hey can someone plz help me with these questions it would be much appreatied (to do with cellular respiration):
- In glycolysis why is it that only the 6 carbons part of the glucose are broken down and not the 12 hydrogens or 6 oxygens.
- What do you call NADH, ATP, CO2, FADH2 etc?  (can you just refer to all of them as coenzymes or molecules?)

Does anyone know where I can buy the biozone 3&4 workbook like what bookshops around the south-eastern suburbs have them??

Thanks!

Mod edit: Please refrain from double posting. Next time, click the 'modify' button on your first post -- Calebark

The entire glucose molecule is broken down in glycolysis. Glucose is broken down into two pyruvates and 2 ATP and 2 NADH molecules are produced.
NADH, ATP and FADH2 are coenzymes.
CO2 is just carbon dioxide and therefore a gas molecule.
Not sure about the last question sorry.
Hope this helped