Hi, can we submit pracs for review?Hey,
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?You have basically answered WHAT is happening in this situation. The questions wants to know WHY it is important.
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.Oh okay. So would the root cells become too turgid if there was a steep concentration gradient of sodium ions?
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).
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).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!
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!
I think your answer should look at:Thank you so much for the sample response! I wasn’t thinking about osmosis, only diffusion, so I only mentioned movement of sodium ions.
- 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. :)
Hey guys, :D1) 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.
(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:[I received 1.5 marks]
- 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.
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! 8)
Question: Describe the process of allopatric speciation.Your answer covers the three main points you need to include, but doesn't focus on the right areas.
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
Due to this, there is reproductive isolation, where there is no exchange of genetic information between the two populations.Careful. Reproductive isolation is the name of a specific set of conditions - it's what's occurring when species are unable to interbreed and produce viable, fertile offspring when brought back together. I assume you're just using reproductive isolation to mean that they can't interbreed, but in this case the lack of exchange of genetic information is due to geogrpahic isolation and you could lose marks if examiners think you're referring to the conditions of reproductive isolation, rather than just using those words to mean they're not interbreeding.
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.
@rameen I'm having a crack at it here, working off your answer. I approached it by first outlining some key points of allopatric speciation, then explaining the process of speciation, and then outlining the result.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
Feel free to have a go at rewriting it if you want :)
Doing VCAA practise exams and question 3b. from VCAA 2014 is...I think you would still get the marks, especially since carrier proteins do facilitate the diffusion of glucose
When glycogenolysis occurs in a cell, the concentration of glucose in the cytosol increases. Glucose passes through the plasma membrane by facilitated diffusion.
Explain how the facilitated diffusion of glucose occurs? (2)
My answer is...
- There is a lower concentration of glucose inside the cell than outside the cell.
- Glucose binds to carrier proteins which facilitate the passage of glucose into the cell along its concentration gradient.
However the VCAA report says that "Glucose moves through protein channels and along the concentration gradient."
Would I still get a mark for saying carrier protein rather than protein channel?
Thanks everyone
Thank you so much for all your help!!You've probably written too much here - the answer is fine, but you'll waste time that could be used on other questions. This would be a 3 mark question in the exam, so you should be able to answer it with three sentences.
This is my updated response:
Allopatric speciation occurs when a population is separated by a geographical barrier,preventing gene flow due to their isolation.which prevents gene flow
The populations are exposed to different environmentsal conditions and are therefore, subject to different selection pressures.These selection pressures result in changes in allele frequencies as one allele of a particular gene may favour the reproduction and survival of one population, but not the other.
You need to mention that it's the subsequent accumulation of genetic differences that leads to speciation
Speciation occurs over time, which makes the two populations unable to produce fertile, viable offspring.
( I didn't realise how difficult it is to structure a good response :/ )At least it's something you only have to learn once. When you figure it out you'll be able to apply it to all your questions without having to learn how to structure each one individually.
Survivability and fitness aren't synonymous - e.g. fitness can also include number of viable offspring.
Remember also that speciation isn't always allopatric. You don't need to memorise sympatric speciation or anything, but if a question asks about speciation without implying a geographical barrier consider other possible causes of change in allele frequencies until eventually the two populations would not be able to produce viable offspring together.
I haven't read any context around that question, but to me there is nothing implying a geographic barrier
So in that case, what would be an example of a different approach to the question (if I'm not going to talk about geographic barriers)?
Hi everyone,You only got one mark because your first point is a use for dna profiling, but it's not an ethical issue.My answer:
- Question 1: Describe two ethical implications or issues associated with the use of DNA profiling [2 marks]
I got one mark.
- The man has the right to know if he is the father of the child in order to maintain a relationship with him.
- The child had no say in providing his DNA sample and if he actually wants to know who is his biological father - which is unethical.
Who's being screened here? I assume Carl?My answer:
- Question 2: Carl's partner has no history of Huntington's disease in her family, however, the chances of any of their children having the disease is 50%. Describe one social and one ethical issue or implication associated with the use of this technology. (Genetic screening) [2 marks]
I got 1 mark
- Ethical: Carl and his partner will constantly worry about having a child that will inherit Huntington's disease.
- Social: This may cause a division between those that can or can not afford genetic screening.
Hey,
I have a question, can someone please help me clarify this and improve my answer:
1. Sucrose cannot cross the plasma membranes of red blood cells, but glucose can. Red blood cells are immersed in the following solutions:
■ a hypertonic sucrose solution
■ a hypertonic glucose solution
■ a hypotonic sucrose solution
■ a hypotonic glucose solution.
a Which solution would be expected to cause the greatest water loss and shrinkage of the red blood cells? Explain.
b Which solution, if any, might cause the red blood cells to burst? Explain.
For a) I wrote: A hypertonic sucrose solution is described as where the solute concentration is greater outside the cell and since sucrose cannot enter Red Blood Cells, the solution will remain hypertonic and the water may flow out of the cell via osmosis causing the cell to shrink.
For b) I wrote: A hypotonic glucose solution is described as where the solute concentration is greater inside the cell and since glucose can enter Red Blood Cells, water may flow into the cell via osmosis causing the cell to burst.
Any help is appreciated
For both your answers, it may be best to clearly state which solution is expected to cause (...), such as "The hypersonic sucrose solution would likely cause the greatest water loss and shrinkage in the red blood cells as...".
I also think you went into a little too much detail in explaining WHAT the terms mean, rather than why they would cause these cells to shrink/swell/whatever. The question assumes you know what the terms hypo and hypertonic mean and dont ask you to define them, so doing so is pretty much a waste of time.
Hope this helps!