VCE Biology Upgrade My Answer

[Bri MT]

VCE BIOLOGY
UPGRADE MY ANSWER

What is this thread for?
If you want feedback on your answers so you can get more marks for your knowledge, this is the place!

Step 1. Share a question you didn't get full marks on, including your answer and how many marks the question was worth
Step 2. Wait for another user (maybe even multiple!) to provide feedback on how they might've approached the question and how you could improve your answer
Step 3. Apply the feedback you've learnt to aim for higher marks more confidently


Who can/will provide feedback?
Everyone is welcome to contribute; even if you're unsure of yourself, providing different perspectives is incredibly valuable.

Please don't be dissuaded if you haven't finished Year 12, or didn't score as highly as others, or your advice contradicts something else you've seen on this thread, or whatever; none of this disqualifies you from helping others. And if you're worried you do have some sort of misconception, put it out there and someone else can clarify and modify your understanding! 

There'll be a whole bunch of other high-scoring students with their own wealths of wisdom to share with you, including TuteSmart tutors! So you may even get multiple answers from different people offering their insights - very cool.


To ask a question or make a post, you will first need an ATAR Notes account. You probably already have one, but if you don't, it takes about four seconds to sign up - and completely free!

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[SmartWorker]

Hi, can we submit pracs for review?

[PhoenixxFire]

Hi, can we submit pracs for review?

Hey,
It depends what the prac is for - if it's work that you're going to be submitting for a SAC (e.g. U4 AOS3) then we can't help you with it as that's against VCAA rules. If it's not something that you're going to be submitting then we can give you feedback on it

[interessant]

Hi! This is my first post and I had my first sac in term 1. This is one question I didn’t get full marks on - could someone please give some feedback?
Question: Two species of plants are found, and both live in highly saline soils. Sodium is transported via facilitated diffusion in root cells. Suggest why this is vital for the survival of these Antarctic plants. (3 marks)
My answer: The root cells need sodium ions to survive in the harsh saline environment, and so there is a net passive movement of sodium ions from an area of high concentration of sodium ions in the highly saline soils to an area of low concentration of sodium ions in the root cells across a semipermeable membrane via channel proteins until equilibrium is reached.
Thanks again.

[Sine]

Hi! This is my first post and I had my first sac in term 1. This is one question I didn’t get full marks on - could someone please give some feedback?
Question: Two species of plants are found, and both live in highly saline soils. Sodium is transported via facilitated diffusion in root cells. Suggest why this is vital for the survival of these Antarctic plants. (3 marks)
My answer: The root cells need sodium ions to survive in the harsh saline environment, and so there is a net passive movement of sodium ions from an area of high concentration of sodium ions in the highly saline soils to an area of low concentration of sodium ions in the root cells across a semipermeable membrane via channel proteins until equilibrium is reached.
Thanks again.

You have basically answered WHAT is happening in this situation. The questions wants to know WHY it is important.

[interessant]

You have basically answered WHAT is happening in this situation. The questions wants to know WHY it is important.

Oh okay. So would the root cells become too turgid if there was a steep concentration gradient of sodium ions?

[Erutepa]

Oh okay. So would the root cells become too turgid if there was a steep concentration gradient of sodium ions?

If the soil was highly saline and had a high concentration of sodium relative to the roots, then water would move from the root cells into the soil (water moves towards the solute).
Given this, maybe it will be a bit more obvious why it is important for the root cells to transport sodium into the cell, remembering that plants do need water to survive.

[interessant]

If the soil was highly saline and had a high concentration of sodium relative to the roots, then water would move from the root cells into the soil (water moves towards the solute).
Given this, maybe it will be a bit more obvious why it is important for the root cells to transport sodium into the cell, remembering that plants do need water to survive.

Ohhh! So the root cells would become plasmolysed or flaccid due to the movement of free water molecules from the cells to the soil. Thank you!

[enociz]

Ohhh! So the root cells would become plasmolysed or flaccid due to the movement of free water molecules from the cells to the soil. Thank you!

I think your answer should look at:
- The problem (there is a lot of sodium in the soil as opposed to the root cells, leading to a strong concentration gradient by which water is able to have a net movement out of the cells and into the lower water potential in the highly saline soil)
- The solution given (when the passive diffusion of salt into the root cells occurs, it balances the concentration gradient by equalising the salt concentration inside the cell with that in the soil)
- The impact this has (this prevents the net movement of water out of the cell by removing the concentration gradient needed for the osmosis of water molecules to occur, allowing the plant to retain the water needed to survive)

That might be too much detail for each part, but it should cover the 3 marks.

[interessant]

I think your answer should look at:
- The problem (there is a lot of sodium in the soil as opposed to the root cells, leading to a strong concentration gradient by which water is able to have a net movement out of the cells and into the lower water potential in the highly saline soil)
- The solution given (when the passive diffusion of salt into the root cells occurs, it balances the concentration gradient by equalising the salt concentration inside the cell with that in the soil)
- The impact this has (this prevents the net movement of water out of the cell by removing the concentration gradient needed for the osmosis of water molecules to occur, allowing the plant to retain the water needed to survive)

That might be too much detail for each part, but it should cover the 3 marks.

Thank you so much for the sample response! I wasn’t thinking about osmosis, only diffusion, so I only mentioned movement of sodium ions.

[FrankieDens]

Hey guys, 

(Please note that my school gives half-marks only for SACs to provide a more accurate ranking)

Q.How does the technique of DNA hybridisation enable scientists to determine the evolutionary relationships between species? [2 marks]
My answer:

• The higher the temperature to separate hybrid DNA strands, the more stronger the hydrogen bonds
• This means there are a lot of complimentary bases and the DNA between the two organisms are similar
• Therefore, it can be determined if two organisms shared a more recent common ancestor and how related they are.

[I received 1.5 marks]

So the teacher who marked my SAC circled 'the more stronger the hydrogen bonds' and wrote a question mark. They also said that instead of 'more recent common ancestor' I should have used 'more closely related' and that I should use terminology more carefully.
My question is, which one did I lose the half mark for and how would you improve my answer?

Thanks everyone! 

[PhoenixxFire]

Hey guys, 

(Please note that my school gives half-marks only for SACs to provide a more accurate ranking)

Q.How does the technique of DNA hybridisation enable scientists to determine the evolutionary relationships between species? [2 marks]
My answer:

• The higher the temperature to separate hybrid DNA strands, the more stronger the hydrogen bonds
• This means there are a lot of complimentary bases and the DNA between the two organisms are similar
• Therefore, it can be determined if two organisms shared a more recent common ancestor and how related they are.

[I received 1.5 marks]

So the teacher who marked my SAC circled 'the more stronger the hydrogen bonds' and wrote a question mark. They also said that instead of 'more recent common ancestor' I should have used 'more closely related' and that I should use terminology more carefully.
My question is, which one did I lose the half mark for and how would you improve my answer?

Thanks everyone! 

1) Hydrogen bonds don't differ in strength. If species share more dna bases, thy will have more hydrogen bonds holding the strands together. The more hydrogen bonds that need to be broken, the more energy that is required.

2) More closely related is better for this because you don't know if they shared a more common ancestor, that's the most likely reason that they'd have more bases in common, but it's also possible that after speciation they faced similar selection pressures and due to those selection pressures any individuals with mutations died, which kept their dna similar for longer (although if you're hybridising between non coding regions then this becomes irrelevant).

- The higher the temperature required to separate hybrid DNA strands, the more hydrogen bonds there are holding the strands together.
- More hydrogen bonds means that the strands of DNA have more complimentary bases, which means they are more closely related.
- Therefore, DNA strands of species that are more closely related will seperate at a higher temperature than DNA strands of species less closely related.

I'd say losing half a mark was probably due to the first problem, the second one isn't that big of a deal.

[Rameen]

Question: Describe the process of allopatric speciation.

My answer: The process of forming a new species due to a geographical barrier that separates a population. These isolated populations are subject to different selection pressures so when they meet again, they are no longer able to interbreed.

This question was 3 marks. How could I improve it?
Thank you in advance

[Evolio]

Hi!
You could also say that no gene flow occurs between the two populations due to the geographical barrier allowing no exchange of genetic information. Following on from the different selection pressures point, you could also say that there would be changes in allele frequencies as one allele may be favourable in one group but not favourable in the other group (due to the different selection pressures).
You could also say that mutations occur which affect mating.
When you mentioned that they are no longer able to interbreed, you could also add additional info about how the two members of the separate groups will not be able to produce fertile, viable offspring.

[PhoenixxFire]

Question: Describe the process of allopatric speciation.

My answer: The process of forming a new species due to a geographical barrier that separates a population. These isolated populations are subject to different selection pressures so when they meet again, they are no longer able to interbreed.

This question was 3 marks. How could I improve it?
Thank you in advance

Your answer covers the three main points you need to include, but doesn't focus on the right areas.
I'd get rid of the first half of the first sentence - you're describing the process not defining or explaining what it is.

The three point that you have to include are:
G - geographical isolation
S - selection pressures are different
D - differences accumulate to the point where they're unable to interbreed successfully.

You've got:
G - The process of forming a new species due to a geographical barrier that separates a population.
S - These isolated populations are subject to different selection pressures
D - so when they meet again, they are no longer able to interbreed.

Suggestions:
G - get rid of the first half. Say something more like "allopatric speciation occurs when a population is separated by a geographical barrier" instead.
S - This part is fine, I'd change it slightly though to get rid of "isolated" and instead put at the end of that sentence something about no gene flow occurring due to their isolation from each other/barrier.
D - you need to also mention accumulation of mutations/differences, and change your phrasing to be more specific "unable to produce fertile, viable offspring". You could also put the bit about no gene flow at the start of this sentence instead of the end of the previous one if that's easier.

Feel free to have a go at rewriting it if you want