VCE Biology Question Thread

[Evolio]

For gene regulation in 3/4 bio, you study the LAC operon which is found within certain bacteria that produce lactase to breakdown lactose.
An operon is a section of DNA composed of a section of related genes with an upstream operator all under the control of a promoter as shown simply in the below diagram
(Image removed from quote.)
You will notice that upstream of this operon is a corresponding regulatory gene. This will be expressed to produce a repressor protein which is complementary to the operator.
An inducer is a molecule that will bind to this regulatory protein to inactivate the repressor protein via a confirmation/shape change which prevents binding to the operator. For 3/4 biology at least, the inducer will always be the allolactose (or sometimes just lactose) because we study the LAC operon.

Thus, if this allolactose (inducer) is absent, the repressor protein will bind to its complimentary operator region and will block the action of RNA polymerase, thus preventing the expression of the genes within this operon. However, is allolactose is present, the allolactose (inducer) will bind to the repressor protein and cause a conformation change which prevents complementary binding to the operator region, thus enabling the binding of RNA polymerase thus the expression (induction) of the genes contained within that operon.

Hope this helps!

It does!
Thank you Erutepa!
 

[DBA-144]

How much depth is needed for 'sources and mode of transmission' of signalling molecules'? Apart from source and mode of transmission, do we need to memorise functions, time of effect, examples, etc.? How specific is VCAA with the 2 things they have required? eg. do I need to if lipid soluble molecules travel to target cell in a vesicle or a protein?

Thanks.

[Rom_Dog]

How much depth is needed for 'sources and mode of transmission' of signalling molecules'? Apart from source and mode of transmission, do we need to memorise functions, time of effect, examples, etc.? How specific is VCAA with the 2 things they have required? eg. do I need to if lipid soluble molecules travel to target cell in a vesicle or a protein?

Thanks.

VCAA doesn't require you to have extensive knowledge on signalling molecules. Apart from plant hormones (especially auxin), you won't need to memorise other specific signalling molecules. Exam questions for biology are mostly application based so they'll ask you to adapt familiar knowledge to an unfamiliar scenario where they'll provide you with background information. You are definitely required to know sources and modes of transmission however specific functions and times of effect don't need to be known. What you do need to know is the process of signal transduction, that is the process of reception -> transduction -> cellular response. You should know where receptors for hydrophilic and hydrophobic signalling molecules are found within the cell, how signal amplification works and how some signal molecule-receptor complexes directly act as transcription factors. It is also worth noting the intrinsic and extrinsic pathways for apoptosis (don't worry about pathway or receptor specifics) and other examples of cellular responses such as growth or movement.

I hope this helps!

[PhoenixxFire]

Apart from plant hormones (especially auxin), you won't need to memorise other specific signalling molecules.

You actually don't need to know about specific plant hormones anymore either - it was in the old study design, and some schools still teach it & assess it on SACs, but you definitely don't need to know their names or what they do for the exam.

[DBA-144]

How are effector proteins involved in signal transduction?

In trying to explain how signal transduction causes a response, how would I word this?

eg. ...secondary messengers are activated and a specific enzyme then moves into the nucleus eliciting a specific response from the cell.

This is just the last bit that I am unsure about.

Any help is appreciated

[Donut]

How do I know what I should exactly state in the answers to get full marks?

How are effector proteins involved in signal transduction?

The signal at the end of signal transduction activates a specific gene which in turn synthesises effector proteins to produce a response in accordance to the signal that was received

[PhoenixxFire]

How do I know what I should exactly state in the answers to get full marks?

It basically just comes down to practice. You can have a look at similar questions from past VCAA exams to get an idea of what to include, but you can't just memorise answers for bio so you really just have to practice answering them and then going back and correcting your answers to figure out what to write.

[DBA-144]

How do I know what I should exactly state in the answers to get full marks?
The signal at the end of signal transduction activates a specific gene which in turn synthesises effector proteins to produce a response in accordance to the signal that was received

What would the response be then? Is it a change in gene expression, or is it the response carried out by the effector protein?

[Donut]

What would the response be then? Is it a change in gene expression, or is it the response carried out by the effector protein?

The effector protein carries out the response.

An example is increasing blood glucose levels.
The receptor detects a drop in blood glucose levels and releases glucagon (effector).
Glucagon then carries out the response and binds to the receptors of a liver cell which activates enzymes that catalyse the conversion of glycogen to glucose.

[Evolio]

Hello guys!
So I have a SAC 5 coming up and you have to design your own experiment relating to unit 3 stuff.
My experiment was testing the effect of amylase on different types of fruits i.e watermelon, banana, apple, lemon and dates.
My hypothesis was that dates will have the highest rate of reaction.
I did my experiment and I got really unexpected results (my POV anyway) and it was that white furry fungi was growing on the apple and banana. So my experiment backfired.
I'm not sure if I can relate this to biology unit 3 concepts so does anyone know how I can relate?
 I was also wondering whether anyone had any other original experiments relating to enzymes that would be good to carry out and would give quantitative data?
I am really struggling now and feel utterly hopeless. Any help at all would be appreciated.
Thanks.

[DBA-144]

Hello guys!
So I have a SAC 5 coming up and you have to design your own experiment relating to unit 3 stuff.
My experiment was testing the effect of amylase on different types of fruits i.e watermelon, banana, apple, lemon and dates.
My hypothesis was that dates will have the highest rate of reaction.
I did my experiment and I got really unexpected results (my POV anyway) and it was that white furry fungi was growing on the apple and banana. So my experiment backfired.
I'm not sure if I can relate this to biology unit 3 concepts so does anyone know how I can relate?
 I was also wondering whether anyone had any other original experiments relating to enzymes that would be good to carry out and would give quantitative data?
I am really struggling now and feel utterly hopeless. Any help at all would be appreciated.
Thanks.

Hey,
So for your experiment, it seems like you had an error due to contamination since fungi began to grow. Can you please explain what your method was in order to help others help you a little bit more? How did you measure 'rate of reaction'? And how did you add the amylase into the fruits? Did you cut up the pieces of fruit, or just leave them whole? If you did cut them up, I suspect that the fungi would have attached onto the infected fruits and would have obtained nutrients/energy from them, hence that is why you saw such a huge (guessing here) amount of fungi on the fruits (they had a pretty favourable environment).

From here, you could potentially find out why you got this error. Generally speaking, contamination is said to be a random error, but this is because we assume that experimenters are competent and very experienced (not attacking you here, this is what we assume in general, such errors occur a lot in real science, I believe).

You could then say that the fungi grew on x and y fruits but not a or b because (x and y have higher energy contents and hence are more favourable conditions for fungi to grow on). THis is what sometimes happens; we look for a specific result, only to find out that the results say that x is not related to y, but z is related to y. From here, we tailor our methodology to find out more about the results obtained. From my knowledge, this actually occurs more often than you might think. I would give an example, but don't want to ramble even more haha. If you don't want to do what I describe below, you might be able to use the bit about how fungi grow in favourable conditions, in sunlight, with lots of energy and oxygen for them to undergo aerobic respiration. This makes it really easy to link to AOS 1.

Your second option is to repeat the experiment, or to do another experiment, if time allows. There are heaps of easy experiments you can find online by googling, for example.

Like I said, giving details about the method would help a bit more I guess.

Sorry for rambling so much. Hope this helps and good luck with your sac.

[Evolio]

Thank you so much for responding DBA-144!
Yeah, I was researching and I think the fungi grew because of the wet conditions since they thrive well and grow really fast in moist conditions.
The fruits were in pieces. I had two pieces of each fruit in each of the 5 petri dishes, cut roughly in rectangular pieces and I dropped amylase solution onto the fruit pieces until their entire surface was covered. Then I covered the petri dishes up and observed over a bit more than 1 week. It was a 5% amylase solution. The amylase was supposed to act on the starch on the fruits.
But the overarching problem is that I don't think I can get quantitative data from this experiment.
My teacher said to repeat it with controls where I have one fruit piece in amylase solution and another fruit piece not exposed to amylase solution. But I don't think I can get quantitative data, that's the real problem since it's a part of our rubric.

[DBA-144]

Thank you so much for responding DBA-144!
Yeah, I was researching and I think the fungi grew because of the wet conditions since they thrive well and grow really fast in moist conditions.
The fruits were in pieces. I had two pieces of each fruit in each of the 5 petri dishes, cut roughly in rectangular pieces and I dropped amylase solution onto the fruit pieces until their entire surface was covered. Then I covered the petri dishes up and observed over a bit more than 1 week. It was a 5% amylase solution. The amylase was supposed to act on the starch on the fruits.
But the overarching problem is that I don't think I can get quantitative data from this experiment.
My teacher said to repeat it with controls where I have one fruit piece in amylase solution and another fruit piece not exposed to amylase solution. But I don't think I can get quantitative data, that's the real problem since it's a part of our rubric.

What are you measuring? HOw do you know that amylase acted more on fruit a than fruit b? This is how you get quantitative data. THere are a few errors in your method.
These include but are not limited to:
-THe fact that you have not measured how much amylase was added to each solution
-THe conditions in which you will be holding the fruit pieces, i.e if they are in closed petri dishes, you must ensure that the petri dishes have been washed/sterilised to remove the growth of fungi for example.
-The pieces of fruit in each dish must be the same and the size of each fruit needs to be in the same measurements.
-You needed to ensure that the fruit were ripe i.e if they were too ripe/not ripe enough then there would have been fewer/more carbohydrates for the amylase to act on. This is hard to control but needs to be considered.
What is your IV and DV? 
Seems like it is rate of reaction and fruit used but how are you measuring rate of reaction? You don't have any way to measure that, you won't get any quantitative data.

Hope this helps.

[Donut]

Could anyone help with this question with an explanation?

Question 17
A typical animal hormone has different actions on different tissues because
A.   the various target cells have different genes.
B.   hormones are directed to specific targets by the circulatory system.
C.   the receptors on different target cells are linked to different cell mechanisms.
D.   each different response is connected to a different receptor for the same hormone.

[Owlbird83]

Could anyone help with this question with an explanation?

Question 17
A typical animal hormone has different actions on different tissues because
A.   the various target cells have different genes.
B.   hormones are directed to specific targets by the circulatory system.
C.   the receptors on different target cells are linked to different cell mechanisms.
D.   each different response is connected to a different receptor for the same hormone.

It would be C
A-All cells contain the same DNA so same genes
B-The hormones aren't directed to specific target cells, they travel through the blood, and will bind to only cells with a specific complementary receptor (the target cell).
C-Yes, the hormone binds to the receptors on different cells and the process that will happen inside the cell can be different depending on the cell and have a different response.
D- the receptors on cells for that particular hormone should be the same because it must have a complementary shape so that it can bind.

Hope this helps!