VCE Biology Question Thread

[jonwil]

Just starting VCE Unit 3 Biol
Just some tips for the year (in Yr 11)
Should I be worried if some practice exams look 50% impossible to do?
I feel like i can already stab at nearly half a Unit 4 exam after reading through the book
is it good or bad?

[vox nihili]

Well if the cells are placed in a salt solution, we assume that they are placed in a hypertonic solution. So, this means that the water inside the cells is at a higher concentration as compared to the extracellular fluids, hence the water diffuses out into the lining, which would relieve the congestion. Also, take note that the solution was only 10% salt solution, hence the osmotic gradient was not large enough to crenate the cells.

So we know that genes are switched on and off, relative to when the cell/tissue/organ/organism needs the product (protein) most. So, to improve lactose digestion, we will assume that the bacterial cells need an excess of lactase, the enzyme that catabolises lactose into its constituent monosaccharides. So a drug can promote the transcription of the lactase gene, by acting as an 'activator' protein, in VCE, no need to know more than that, simply that some proteins/drugs/molecules act as gene activators, and if this drug activates the gene transcription regardless of whether the cell does it manually or not, then the lactase gene will be transcribed and eventually translated into lactase.

Krebs cycle is the first step of cellular aerobic respiration. So the products of glycolysis, which is 2 pyruvate molecules, enter the mitochondrial matrix and here they are ready to undergo the Krebs cycle. So one pyruvate molecule reacts with CoA (coenzyme A, no need to know what this is exactly) to produce a molecule of CO2, NADH and Acetyl CoA. The Acetyl CoA undergoes further biochemical reactions to further produce 3NADH molecules, FADH2, ATP and another 2 CO2 molecules. So, in total, as there are 2 molecules of pyruvate per glucose molecule, the outputs of the Krebs cycle from 1 glucose are: 6CO2, 8NADH, 2FADH2, 2ATP.

Drawing an actual cycle or diagram really helped me memorise the steps and products, because in VCE knowledge, this step is best memorised as there are in reality thousands of reactions that are involved, so draw a diagram and put it up on your wall so that everytime you look up, you see it.

The opposite could also be true: the drug acts to remove a repressor


As an aside, cosine, the mechanism of control of the lac genes is going to become a verrrrry big feature of your uni life soon :p

[blacksanta62]

Hello, I'm doing a prac/SAC fairly soon about photosynthesis. Teacher hasn't given out any questions or anything but she suggested I go and think about certain things we read in the handout so I have some questions.

The prac is about Elodea in the test tube and the effect light intensity will have on photosynthesis. One of the key steps was to ensure total darkness for 2 minutes before exposing it to light for 30 seconds (or something around that) and counting the O2 bubbles then moving the lamp further away. Was this to simulate the night period plants experience in which photosynthesis cannot take place? And also 'restart' photosynthesis, so we could get a more accurate measure from the time the plant was exposed to light?

Would the IV be the amount of light given to the plant while the DV is the amount of O2 bubbles produced?

We're using tap water in this prac. Tap water contains ions and the thylakoid membranes are made of a phospholipid bilayer, Is there anything important about this? Or is this to simulate the natural pond surrounding the elodea

Thank you

Edit: Bump. Some more questions:
1) The prac setup included a thermometer in the solution, why is this necessary when measuring light intensity and it's affect on photosynthesis? Is the lamp strong enough to raise the temperature of the water?

2) When the lamp was close to the beaker O2(g) bubbles produced was high, does this mean that either CO2(g) conc or temperature are the limiting factors? Furthermore, when we moved the lamp further away the the O2(g) produced was lower, is light intensity now the limiting factor?

3) Can too much light intensity damage the enzymes at all?

My sac is tomorrow, thanks

Bump: clicked 'modify' instead of 'quote'. Thank you

[anniebrejcha]

hi again!
i just got my second sac back today,  and i'm happy with my results but i'm also really disappointed in myself as i am still stuffing up the 'practical' questions (the hypothetical prac' questions if you know what i mean!).

most specifically writing hypotheses and presenting data obtained. i am fine with interpreting data and the details but i'm losing marks when explaining it in terms of the prac'.
ive always had a bit of trouble with these kinds of questions and i was wondering if anyone had any tips for me!    they really are just the distance between me and a perfect score and im feeling a bit frustrated about it now!

[blacksanta62]

]Hey modulus, yes we need to know the amounts of inputs and outputs for both. With photosynthesis it's a bit easier since it's just ADP+PI and NADP+ becoming APT and NADPH in their respective reactions. With cellular respiration it does get a little trickier but as cosine said, diagrams help when trying to remember this. I'll insert a quote underneath.

On a personal note, having a biology examiner for a teacher, he recommends you just know the amounts instead of the basic minimum, never know if a SAC question (most likely) will ask you to list the inputs and outputs and it's better to go in there safe then come out sorry. Hope I helped
 

Krebs cycle is the first step of cellular aerobic respiration. So the products of glycolysis, which is 2 pyruvate molecules, enter the mitochondrial matrix and here they are ready to undergo the Krebs cycle. So one pyruvate molecule reacts with CoA (coenzyme A, no need to know what this is exactly) to produce a molecule of CO2, NADH and Acetyl CoA. The Acetyl CoA undergoes further biochemical reactions to further produce 3NADH molecules, FADH2, ATP and another 2 CO2 molecules. So, in total, as there are 2 molecules of pyruvate per glucose molecule, the outputs of the Krebs cycle from 1 glucose are: 6CO2, 8NADH, 2FADH2, 2ATP.

Drawing an actual cycle or diagram really helped me memorise the steps and products, because in VCE knowledge, this step is best memorised as there are in reality thousands of reactions that are involved, so draw a diagram and put it up on your wall so that everytime you look up, you see it.

hi again!
i just got my second sac back today,  and i'm happy with my results but i'm also really disappointed in myself as i am still stuffing up the 'practical' questions (the hypothetical prac' questions if you know what i mean!).

most specifically writing hypotheses and presenting data obtained. i am fine with interpreting data and the details but i'm losing marks when explaining it in terms of the prac'.
ive always had a bit of trouble with these kinds of questions and i was wondering if anyone had any tips for me!    they really are just the distance between me and a perfect score and im feeling a bit frustrated about it now!

Can a mod or someone with more experience answer this question?? Cheers

[vox nihili]

hi again!
i just got my second sac back today,  and i'm happy with my results but i'm also really disappointed in myself as i am still stuffing up the 'practical' questions (the hypothetical prac' questions if you know what i mean!).

most specifically writing hypotheses and presenting data obtained. i am fine with interpreting data and the details but i'm losing marks when explaining it in terms of the prac'.
ive always had a bit of trouble with these kinds of questions and i was wondering if anyone had any tips for me!    they really are just the distance between me and a perfect score and im feeling a bit frustrated about it now!

If you do your pracs on separate days to answering the question, go home the night you do the prac and write a flow chart of the prac. THen try to present the prac to yourself, explaining why you do everything. It also is worthwhile googling your prac, you'll almost certainly find a write-up online or teacher notes etc.

More broadly, you should be looking to find examples of the biological concepts you've learned about in the real world. There's absolutely nothing you've learned that can't be related to the real world (I mean, it's science so obviously). This is a good skill generally for your learning but will also help you deal with pracs and deal with problems on exams.

[anniebrejcha]

If you do your pracs on separate days to answering the question, go home the night you do the prac and write a flow chart of the prac. THen try to present the prac to yourself, explaining why you do everything. It also is worthwhile googling your prac, you'll almost certainly find a write-up online or teacher notes etc.

More broadly, you should be looking to find examples of the biological concepts you've learned about in the real world. There's absolutely nothing you've learned that can't be related to the real world (I mean, it's science so obviously). This is a good skill generally for your learning but will also help you deal with pracs and deal with problems on exams.

thanks for your response!!!! i really appreciate it and im sure it will help me in future prac's.
i wasnt very clear in my explanation and my sac was actually just a test; not a practical. i was referring to the questions which suggest an experiment which you have to further interpret ; like where you have to come up with a hypothesis for it for example.
i hope this makes sense!
any tips on these kinds of questions would be lovely!

[vox nihili]

thanks for your response!!!! i really appreciate it and im sure it will help me in future prac's.
i wasnt very clear in my explanation and my sac was actually just a test; not a practical. i was referring to the questions which suggest an experiment which you have to further interpret ; like where you have to come up with a hypothesis for it for example.
i hope this makes sense!
any tips on these kinds of questions would be lovely!

Same thing applies. If you get into the habit of trying to frame the things you learn in Biology in how they apply in the real world, you'll find that you deal a lot better with those questions.

[blacksanta62]

 question that came up on my SAC about light intensity and it's affect on photosynthesis was: Why does a max rate of photosynthesis occur? And why does it not continue further? This isn't the exact question but it was something like that. This most likely wasn't my exact response but: the max rate of photosynthesis occurred because light intensity stops being the limiting factor. Regardless of how close we move the lamp photosynthesis will not continue at the rate it was before because the limiting factor is now either [CO2] or temperature.

Was this a safe answer to go with?
Thank you

[vox nihili]

question that came up on my SAC about light intensity and it's affect on photosynthesis was: Why does a max rate of photosynthesis occur? And why does it not continue further? This isn't the exact question but it was something like that. This most likely wasn't my exact response but: the max rate of photosynthesis occurred because light intensity stops being the limiting factor. Regardless of how close we move the lamp photosynthesis will not continue at the rate it was before because the limiting factor is now either [CO2] or temperature.

Was this a safe answer to go with?
Thank you

Yeah, it's a reasonable answer. I wouldn't limit, however, the examples of an alternate limiting factor to CO₂ or temperature. The most compelling option for me, to be honest, is that the presence of the enzymes themselves, which is probably what limits the rate of photosynthesis where light-intensity does not.

[blacksanta62]

Would it be correct to say that the enzymes present in chlorophyll are an input for light dep. and the enzymes present in the stroma are an input for light indep.?

Thank you

[cosine]

Would it be correct to say that the enzymes present in chlorophyll are an input for light dep. and the enzymes present in the stroma are an input for light indep.?

Thank you

Firstly, chlorophyll is a pigment, there are no enzymes 'in' chlorophyll. I think you mean enzymes in the chloroplast, in that case, no they are not inputs. The reason is because if anything is reused/recycled during a reaction, it is not presented in neither the products/reactants. That is also why people omit the NADPH and NADP+ from the reactions because they get reused in the same reactions.

[johnhalo]

Hello, I just want to clarify a confusion with the study design that I have. The 2013-2016 Study Design eliminates the need for us to cover homeostasis, but we still have to be comfortable with stimulus-response models. So my question is to what extent do stimulus-response models need to be covered?

Thanks

[Gogo14]

How would you answer questions where they ask you to design an experiment to test a hypothesis? The ones I have seen are only 3 marks, yet I spend ages writing a page to answer the question when there is only 5 blank lines for the answer. How would I answer the q to be concise and detailed, but still get full marks. And what are the key points marks are allocated to?

[TheAspiringDoc]

How would you answer questions where they ask you to design an experiment to test a hypothesis? The ones I have seen are only 3 marks, yet I spend ages writing a page to answer the question when there is only 5 blank lines for the answer. How would I answer the q to be concise and detailed, but still get full marks. And what are the key points marks are allocated to?

according to my teacher, it's not so much about how you measure your variables, but more to do with idenitifying what your variables would be, how they would support/contradict the hypothesis, and making sure there are controls and controlled variables.