VCE Biology Question Thread

[Sine]

When should I start doing VCAA practice exams?

I have started doing some Unit 3 past papers from companies such as NEAP & STAV, what scores should you be getting on the private company papers for an A+?

[pi]

When should I start doing VCAA practice exams?

I have started doing some Unit 3 past papers from companies such as NEAP & STAV, what scores should you be getting on the private company papers for an A+?

I think towards mid/late August might be a good time to give a few a go, save the recent ones for later.

'How long should my piece of string be?' Aim for the highest you possibly can, that is, 100%. If you're not getting that, you have room to improve!

[cosine]

I think towards mid/late August might be a good time to give a few a go, save the recent ones for later.

'How long should my piece of string be?' Aim for the highest you possibly can, that is, 100%. If you're not getting that, you have room to improve!

Good advice Pi, but some commercial ones have things outside the study design, so should we ignore these questions?
Also areas of weaknesses for me are immune system and others such as plant defence system, would you recommend refining these errors before doing practice, or do some practices and gather up the weaknesses and then refine them?

Thanks man!

[vox nihili]

Few questions about Unit 3:

- Do we need to know the specifics about the protein molecules that protrude out of the phospholipid bilayer? For example, if a question asks what type of protein molecule assists glucose to diffuse from the high concentration outside the cell into the cell, the answer is protein carriers through facilitated diffusion, but would protein 'channels' be wrong, as they are two different type of functioning proteins?

- Does cholesterol in the membrane maintain fluidity in the sense that when it's too cold, it will not allow the membrane to solidify, and when it is too hot, it will not allow it to melt - essentially does cholesterol stabilise the membrane?

- Is cholesterol a lipid or a carbohydrate?

- What's the main difference between simple and complex carbohydrates? Are simple carbs basically monosaccharides and disaccharides, whereas polysaccharides are considered complex because of their complexity?

- Do we actually need to know the different between alpha glucose and beta glucose?

- Are the only polysaccharides we need to know: cellulose, glycogen, chitin and starch?

- I know glycogen and starch are energy storage carbohydrates, but is starch also found in animals/humans or only plants?

- If only plants, then is it true that plants contain structural cellulose and energy storage starch?

- Are plants the only organism that produce/synthesise glucose?

- How much do we need to know about the light dependent and independent stages of photosynthesis? Do we need to know further than just: Light dependent occurs in the thylakoid membranes and the electrons of the pigments (mainly chlorophyll) get excited and split water molecules into hydrogen ions and oxygen, where the oxygen binds with another molecule to form oxygen gas, and the hydrogen ions and electrons are occupied by 'unloaded' carrier molecules called NADP+, as well as ADP + Pi. Then these two loaded molecules NADPH and ATP leave the thylakoid membranes and undergo the calvin benson cycle in the stroma of the chloroplast, where carbon dioxide from the atmosphere is broken down into further products, essentially producing glucose.

- Do ALL plants photosynthesise? If not, can you give an example of plants that do not, and obtain their energy through other organisms?

Thanks for the help guys, any responses will be greatly appreciated, many thanks.

1. You do need to know the difference between a protein channel and a carrier protein. You should understand the various types of proteins embedded in the plasma membrane, though you would not be expected to give specific examples. For instance, you should know proteins involved with transport are there and the broad groups that these proteins fall into (i.e. channel and carrier); however, you would not be expected to give an example of a carrier protein or a channel protein. Likewise, you should also know that transmembrane receptors are embedded in the membrane, but would not have to elaborate particularly much on this.

2. I'm not entirely sure if that's how cholesterol works in the membrane, but it does seem to make sense. Counterintuitively, it does both stabilise the membrane and contribute to its fluidity. Knowing that it does this and not necessarily how it does it is well and truly sufficient.

3. A lipid.

4. Basically, although saying that polysaccharides are complex because of their complexity is probably something to avoid in an exam. Complex carbohydrates are carbohydrates with lots of monomers, as you've suggested.

5. Nope. It probably is worthwhile noting that cellulose contains beta glucose, whilst glycogen and starch contain alpha glucose. An easy way to draw a comparison between the two.

6. Yes

7. Starch is only found in plants. Animal cells lack the cellular machinery needed to synthesise starch. Likewise, plants lack the enzymes needed to synthesise glycogen. That animal cells contain glycogen and plant cells starch is the consequence of divergent evolution.

8. Yes, this is the key difference between the two on a functional level. Naturally, on a molecular level, there are differences as well. Indeed, I've already mentioned those above.

9. Not at all. Nearly all cells can produce glucose. Recall that humans store glucose as glycogen. When glycogen is broken down, glucose is produced as a consequence of its break-down. You may not think that this constitutes production of glucose, and indeed you may be right, as technically you're breaking bigger parts into smaller parts and that could make it everything a bit confusing; however, glycogenolysis (the break-down of glycogen) is not the only process that results in the production of glucose. Indeed, animal cells are actually able to produce glucose from pyruvate in a process called gluconeogenesis.
So if you were asked a question "can animal cells produce glucose?" then the answer is undoubtedly yes. However, I think your question is asking whether plant cells are the only cells that can produce glucose from carbon dioxide. No, they're not. Many bacteria are also capable of photosynthesis. Indeed, chloroplats are actually bacteria that have existed endosymbiotically inside of plant cells for millions of years.

10. That's almost sufficient. You need to know the inputs and outputs of each stage and where they occur. You should also understand the different factors that can modulate photosynthesis. E.g. availability of light/CO₂, heat etc.

11. My understanding is that there are plants that don't, but I can't provide any further information about that.

[pi]

Good advice Pi, but some commercial ones have things outside the study design, so should we ignore these questions?
Also areas of weaknesses for me are immune system and others such as plant defence system, would you recommend refining these errors before doing practice, or do some practices and gather up the weaknesses and then refine them?

Thanks man!

Yeah ignore questions outside of the study design, if you're not sure you can always post the question here and someone here will know if it's in the SD or not.

I think refine weaknesses by going over content you get wrong is good tact. I wouldn't suggest "compiling" them by not acting on them until later, that sounds risky to me.

[grannysmith]

Yeah ignore questions outside of the study design, if you're not sure you can always post the question here and someone here will know if it's in the SD or not.

I think refine weaknesses by going over content you get wrong is good tact. I wouldn't suggest "compiling" them by not acting on them until later, that sounds risky to me.

Yeah, one thing I realised (perhaps a little too late) is that you should just do as many practice questions as early as possible. This applies to any topic. I can assure you that it's highly improbably for one to exhaust all resources at their disposal. And if you do, well, that's even better.

[cosine]

Yeah ignore questions outside of the study design, if you're not sure you can always post the question here and someone here will know if it's in the SD or not.

I think refine weaknesses by going over content you get wrong is good tact. I wouldn't suggest "compiling" them by not acting on them until later, that sounds risky to me.

Many thanks, guys!

[Sine]

Yeah ignore questions outside of the study design, if you're not sure you can always post the question here and someone here will know if it's in the SD or not.

I think refine weaknesses by going over content you get wrong is good tact. I wouldn't suggest "compiling" them by not acting on them until later, that sounds risky to me.

Yeah, one thing I realised (perhaps a little too late) is that you should just do as many practice questions as early as possible. This applies to any topic. I can assure you that it's highly improbably for one to exhaust all resources at their disposal. And if you do, well, that's even better.

Thanks for the advice 

Would making a list of definitions be good revision for Unit 3 and to look over through the year till the end of year exam? Or printing out assessors reports?

[HighTide]

1. You do need to know the difference between a protein channel and a carrier protein. You should understand the various types of proteins embedded in the plasma membrane, though you would not be expected to give specific examples. For instance, you should know proteins involved with transport are there and the broad groups that these proteins fall into (i.e. channel and carrier); however, you would not be expected to give an example of a carrier protein or a channel protein. Likewise, you should also know that transmembrane receptors are embedded in the membrane, but would not have to elaborate particularly much on this.

2. I'm not entirely sure if that's how cholesterol works in the membrane, but it does seem to make sense. Counterintuitively, it does both stabilise the membrane and contribute to its fluidity. Knowing that it does this and not necessarily how it does it is well and truly sufficient.

3. A lipid.

4. Basically, although saying that polysaccharides are complex because of their complexity is probably something to avoid in an exam. Complex carbohydrates are carbohydrates with lots of monomers, as you've suggested.

5. Nope. It probably is worthwhile noting that cellulose contains beta glucose, whilst glycogen and starch contain alpha glucose. An easy way to draw a comparison between the two.

6. Yes

7. Starch is only found in plants. Animal cells lack the cellular machinery needed to synthesise starch. Likewise, plants lack the enzymes needed to synthesise glycogen. That animal cells contain glycogen and plant cells starch is the consequence of divergent evolution.

8. Yes, this is the key difference between the two on a functional level. Naturally, on a molecular level, there are differences as well. Indeed, I've already mentioned those above.

9. Not at all. Nearly all cells can produce glucose. Recall that humans store glucose as glycogen. When glycogen is broken down, glucose is produced as a consequence of its break-down. You may not think that this constitutes production of glucose, and indeed you may be right, as technically you're breaking bigger parts into smaller parts and that could make it everything a bit confusing; however, glycogenolysis (the break-down of glycogen) is not the only process that results in the production of glucose. Indeed, animal cells are actually able to produce glucose from pyruvate in a process called gluconeogenesis.
So if you were asked a question "can animal cells produce glucose?" then the answer is undoubtedly yes. However, I think your question is asking whether plant cells are the only cells that can produce glucose from carbon dioxide. No, they're not. Many bacteria are also capable of photosynthesis. Indeed, chloroplats are actually bacteria that have existed endosymbiotically inside of plant cells for millions of years.

10. That's almost sufficient. You need to know the inputs and outputs of each stage and where they occur. You should also understand the different factors that can modulate photosynthesis. E.g. availability of light/CO₂, heat etc.

11. My understanding is that there are plants that don't, but I can't provide any further information about that.

Hi Cosine and Mr.T-Rav,
For question 2, cholesterol acts as a buffer against changes in the fluidity. When the temperature changes, the membrane fluidity changes. Cholesterol acts to prevent these changes in the membrane fluidity by preventing the movement of phospholipid molecules in the membrane. If VCAA were to test this in an exam, they would definitely provide adequate background information as it is outside the scope of VCE Bio.
Q11. These are called holoparasitic (don't photosynthesize) or hemiparasitic plant (partially but can photosynthesize). There aren't many well known examples of holoparasitic plants, but there are heaps of hemiparasitic plants such as the mistletoe. This is also outside VCE scope.

Thanks for the advice 

Would making a list of definitions be good revision for Unit 3 and to look over through the year till the end of year exam? Or printing out assessors reports?

Hi Sine,
Each individual has a different way of learning. If a glossary suits you, you should probably follow it. Another way would be to revise and understand processes so you know the role something plays in an overall system. I.e. If you were looking at the immune system, perhaps revise first line, second line and third line of immunity and thereby understand where all the pieces fit in.
Hope this helps 

[Sine]

 Hi Sine,
Each individual has a different way of learning. If a glossary suits you, you should probably follow it. Another way would be to revise and understand processes so you know the role something plays in an overall system. I.e. If you were looking at the immune system, perhaps revise first line, second line and third line of immunity and thereby understand where all the pieces fit in.
Hope this helps 

Thanks HighTide,  honestly I don't like the idea of actively memorising definitions but would rather understand what is going on so that at any time I would be able to define something. Rather than only knowing what I have memorised. 

[StupidProdigy]

How do I do question 1c and 3? I'm having a hard time understanding punnet squares and all this genotype stuff, is there any really clear explanations anyone would recommend? Thankyou!!
and question 10 if anyone is keen, not to worried about it though, more after the theory behind it thanks

[heids]

How do I do question 1c and 3? I'm having a hard time understanding punnet squares and all this genotype stuff, is there any really clear explanations anyone would recommend? Thankyou!!
and question 10 if anyone is keen, not to worried about it though, more after the theory behind it thanks

Firstly, you didn't do question 1a quite right.  Where there are two alleles at one gene locus, one recessive and one dominant, the dominant is a capital letter (e.g. B) and the recessive is lower-case of the same letter (e.g. b).  It doesn't matter what letter you choose, but they MUST be the same.

So, let's call this the b gene.  Which is dominant? Since we have a white and a brown, which produce ALL brown offspring, the brown must be dominant, because the white allele never shows through in the offspring.
--> brown = B, white = b.

What are the genotypes of the mice that were crossed?  This means, what are the genotypes of the parents, the white parent and the brown parent.  You know that each mouse has two copies of the gene (one on each of their chromosomes in the pair), one from their mum and one from their dad.

Now the white mouse MUST have both 'white' (b) alleles, because we already said that the 'brown' (B) allele is dominant; if the white mouse had the B allele, that would 'overcome' the b allele so the mouse would actually be brown.  So the white mouse has the genotype bb.

The brown mouse must have at least one B allele (because it's brown).  BUT.  If the other allele was 'white' (b), then 1/2 of its gametes would get the b allele, so 1/2 of its offspring would end up bb (one b from the brown parent, and one from the white parent), so 1/2 the offspring would be white.  But since we have ALL offspring brown, the other allele must also be B, because every single offspring must have a B allele.  ==> brown mouse genotype: BB.

1c: So, each of their kids (F1 generation) have the genotype Bb, because they get one B from the brown and one b from the white.  So now you're crossing a Bb x Bb.  Each parent has two possible gametes they pass down, so the punnett square shows the possible options of the next generation depending on which gametes they're 'made of'.

            B           b

B       BB          Bb

b       Bb          bb

From this we see that 3/4 of the 2nd generation have the B allele, so 75% of that generation will be brown.
 

Question 3
Let's go with: far-sighted = F, normal = f.
A normal man must have both f, because if he had the dominant F, then that would 'overcome' the f and he'd be far-sighted. ==> ff.
The far-sighted women must have one F (because she's far-sighted), and her father was normal so he must have been ff, so she must get an f from him. ==> Ff

            f           f

F       Ff          Ff

f       ff          ff

1/2 of those (50%) are ff, and thus normal.

Q10
The mother's genotype must be bb, because she's white and thus can't have a B allele.  The father must have at least one B, because otherwise he wouldn't be black.
7 black, 6 white suggests about 50/50 in the offspring.  Now if the father had BOTH B alleles, then every one of the offspring would get a B allele, so every one of them would be black.  This isn't the case, so the father must be [/b]Bb[/b].


Well that was a long explanation.  Let me know if anything doesn't make sense.

[StupidProdigy]

Thankyou so much bangalilok for the big clear explanation!

Unrelated, but what is the difference between a test cross and a dihybrid cross or punnet square?

[BakedDwarf]

Unrelated, but what is the difference between a test cross and a dihybrid cross or punnet square?

A test cross is crossing an individual showing the dominant phenotype with a homozygous recessive individual in order to determine its genotype; that is, whether the individual with dominant phenotype is homozygous or heterozygous for the particular allele:

- If any offspring with the recessive allele appear, the parent with the dominant phenotype is
 heterozygous

- If all the offsprings have the dominant phenotype, the parent with the dominant phenotype is
 homozygous

Whereas a dihybrid cross is a type of cross in which alleles of two different genes are involved; for example, dihybrid cross of a purebred tall pea plant with purple flowers and a short pea plant with white flowers

A Punnet square just shows the chance of each possible outcome when analysing monohybrid and dihybrid crosses

[Floatzel98]

I just had a question regarding genes and such. What exactly determines why a gene (or is it an allele?) is dominant over another? I have tried looking it up but my bio knowledge is only around a year 10 level and I can't really comprehend a lot of the answers. If i remember correctly, alleles are just pairs of genes that code for a specific phenotype. How does one of them overpower the other.

Sorry if its off-topic, just curious