VCE Biology Question Thread

[anotherworld2b]

Then for this question
Outline an investigation:
Do you have to write up a whole investigation?)
So far I have this:
File a horizontal line on each thumbnail as well as toenail? (singular/plural?)
Measure the growth of each thumbnail and toenail every day and record measurement.

Also for this question:
Q3. Patients who have suffered severe blood loss or dehydration have to be given large volumes of fluid. A fluid that is often given is a 0.9% solution of sodium chloride, known as normal saline. Why is saline solution given rather than just plain water?
I've attempted to answer this question would this be right? I'm not exactly sure about the effect of saline solution on blood loss and dehydration

The fact that normal saline has 0.9% of sodium chloride means that its composition is comparatively similar to the amount of ‘salt’ in the blood stream. Whereas, if plain water is given to the patient the normal concentration of ‘salt’ in the blood will decrease causing the blood to become dilute. If this happens the body’s natural response would be to extract the excess water and expel it from the body through the anti diuretic hormone. Therefore, saline solution is given to prevent dehydration.

[doher109]

Hey just a quick note on your reply to the saline question.

The actual reason for giving 0.9% Saline as opposed to Water isn't that it would make the blood more dilute if water was given (even though it technically would).

The reason is that it would cause haemolysis of RBCs (water entering them as the extra-cellular environment would be hypo-osmolar).

By giving 0.9% saline you replenish the ECF volume without affecting the Osmolarity of the ECF/destroying RBCs.

[anotherworld2b]

Hmm so basically having saline solution instead of water prevents haemolysis of RBCs.
Why does water enter the RBCs? Just to clarify extracellular environment refers to the environment/surroundings around the RBCs?
Also what do you mean by hypo-osmolar?
In regards to  'By giving 0.9% saline you replenish the ECF volume without affecting the Osmolarity of the ECF/destroying RBCs.'
What does ECF stand for? Also if water causes haemolysis why doesn't saline solution do this? Is it due to the amount of sodium chloride in saline solution being similiar to the concentration of sodium chloride in blood?
I understand to an extent that saline solution can replenish the body but how can it be used for severe blood loss?
I am sorry for asking so many questions    I haven't learned about this concept before and I would like fully understand what happens and why it happens.

[doher109]

Hmm so basically having saline solution instead of water prevents haemolysis of RBCs.
Why does water enter the RBCs? Just to clarify extracellular environment refers to the environment/surroundings around the RBCs?
Also what do you mean by hypo-osmolar?
In regards to  'By giving 0.9% saline you replenish the ECF volume without affecting the Osmolarity of the ECF/destroying RBCs.'
What does ECF stand for? Also if water causes haemolysis why doesn't saline solution do this? Is it due to the amount of sodium chloride in saline solution being similiar to the concentration of sodium chloride in blood?
I understand to an extent that saline solution can replenish the body but how can it be used for severe blood loss?
I am sorry for asking so many questions    I haven't learned about this concept before and I would like fully understand what happens and why it happens.

Hey! Sorry about that i'm currently doing Medicine @ Monash and all the terms we use are quite different from Biology in VCE.

I'll start from the top.

-Water enters via passive diffusion (through the plasma membrane) & some channels.
- ECF = Extracellular environment = outside of cells
- Hypo-osmolar = Hypotonic = it is more dilute than inside of cells
- Exactly! The concentration of solutes inside of RBCs ~300mOsm (mOsm is a unit of measurement for concentration) 0.9% NaCl is also ~300mOsm. Due to this being equal haemolysis doesn't occur.
- Don't worry about this last point for exams but out of interest here is the explanation in the context of Emergency Medicine/Trauma.
- If someone has say a gun shot wound and loses 2L of blood. They now have 2/3 of their normal circulating volume of blood. This cause blood pressure to fall and hence blood doesn't go to where it should (for example there isn't enough blood to reach the brain). So if this patient comes in they will actually get some blood and run it into their veins in an attempt to fill the body back up with blood. However, in some cases (not enough blood on hand/haven't got time to get the blood) they will just use 0.9% saline solution in order to temporarily increase blood pressure and ensure at least some RBCs reach the brain etc. Eventually blood will be given and/or the bone marrow will make new RBCs!

[anotherworld2b]

Thank you for your help
I've tried to write a response using this new information and was wondering if its correct

Chapter 4 - Q4.
Patients who have suffered severe blood loss or dehydration have to be given large volumes of fluid. A fluid that is often given is a 0.9% solution of sodium chloride, known as normal saline. Why is saline solution given rather than just plain water?

Water enters via passive diffusion through the plasma membrane and some channels (fluid mosaic model) into Red blood cells . The extracellular environment (outside of cells) is hypo-osmolar (hypotonic) is more dilute than inside of cells. As a result if plain water is given the concentration gradient between the extracellular environment and the inside of the red blood cells will bring about diffusion. Diffusion is the net movement of particles from a high concentration to a low concentration until at equilibrium. In this case water will diffuse from the extracellular environment into the red blood cells however the red blood cells cannot contain this excess fluid causing haemolysis. What would happen to the body when haemolysis occurs?

The fact that normal saline has 0.9% of sodium chloride means that its composition and concentration is comparatively similar to the amount of ‘salt’ in the blood stream.  The concentration of solutes inside of Red blood cells ~300mOsm (unit of measurement for concentration) is equal to 0.9% if NaCl. As a result of this similar concentration haemolysis does not occur when a patient who has suffered severe blood loss or dehydration is given saline solution. Saline solution will replenish the extracellular fluid without affecting the osmolarity of a patient suffering from dehydration. If a patient has suffered severe blood loss, saline solution will temporarily increase blood pressure to enable red blood cells to continue to circulate the body until blood is given or the bone marrow makes new Red blood cells.

[instax101]

Do we need to cover DNA fingerprinting? I find the study design a bit vague and in relation to it.

[Butterflygirl]

If there was a question asking "What is gene expression?" for 1 mark. Would this definition suffice:

Gene expression is when genes are re-written into proteins.

If it was for 2 marks, I would need to mention transcription and translation right?

Thanks >.<

[plsbegentle]

If there was a question asking "What is gene expression?" for 1 mark. Would this definition suffice:

Gene expression is when genes are re-written into proteins.

If it was for 2 marks, I would need to mention transcription and translation right?

Thanks >.<

Gene expression is the process whereby DNA is transcripted and translated which synthesises a new protein. 1mark
OR
Gene expression is the process which information on a gene is coded to assemble/produce a new protein molecule. 1mark

If the question was 2 marks, i would actually just briefly describe how gene expression occurs.
For example, Gene expression is the process whereby DNA is being copied into mRNA by the enzyme polymerase, it then will be read by a ribosome to produce an amino acid chain so a new protein molecule is made.

[Butterflygirl]

Gene expression is the process whereby DNA is transcripted and translated which synthesises a new protein. 1mark
OR
Gene expression is the process which information on a gene is coded to assemble/produce a new protein molecule. 1mark

If the question was 2 marks, i would actually just briefly describe how gene expression occurs.
For example, Gene expression is the process whereby DNA is being copied into mRNA by the enzyme polymerase, it then will be read by a ribosome to produce an amino acid chain so a new protein molecule is made.

Thanks

[geminii]

Hi

I was reading the bio notes and it says:

"The pre-mRNA is modified in three ways:

• -Segments of the pre-mRNA are spliced and removed from the pre-mRNA and the remaining pieces joined together. The spliced and removed pieces are called introns and the pieces that remain and are joined together are called exons.
• -A methyl cap is added to the 5' end of the RNA strand.
• -A poly-A tail is added to the 3' end of the RNA strand."

I'm just a bit confused as to why the pre-mRNA needs to be modified in the first place, aka why segments of the pre-mRNA are spliced and removed etc. (from the first bullet point). I also don't quite understand the other two bullet points either. Would someone be able to explain this in more depth?

Thanks so much

[mtse]

"The pre-mRNA is modified in three ways:

• -Segments of the pre-mRNA are spliced and removed from the pre-mRNA and the remaining pieces joined together. The spliced and removed pieces are called introns and the pieces that remain and are joined together are called exons.
• -A methyl cap is added to the 5' end of the RNA strand.
• -A poly-A tail is added to the 3' end of the RNA strand."

I'm just a bit confused as to why the pre-mRNA needs to be modified in the first place, aka why segments of the pre-mRNA are spliced and removed etc. (from the first bullet point). I also don't quite understand the other two bullet points either. Would someone be able to explain this in more depth?

Pre-mRNA needs to be modified:
1. to remove segments of mRNA that are "non-coding" - in a region of DNA, not all of it is necessary for that particular protein to be made and thus areas of it (called introns) are removed. This is called splicing. Splicing basically allows one sequence of DNA/RNA to code for various proteins depending on how it has been cut up.
e.g. if pre-mRNA has the sequence ABCDEFG
splicing may result in:
ABDFG creating protein type 1
ABCEG creating protein type 2
ACDEF creating protein type 3
This can be really helpful considering that we needs heaps and heaps of different kinds of proteins for all the different cells in the body but we only have so much DNA (about 2 metres in length apparently)

2. the mRNA has a poly-A (i.e. lots of Adenines) added to its tail end (3' end) and has a methyl (technically 7-methylguanosine - but not needed for vce) cap added to the "head" end of the strand (5' end). This capping and tailing allows the mRNA to be more stable (i.e. prevents enzymes from degrading the RNA strand) and thus assists it during its "transportation" from the nucleus to the cytosol. (imagine if enzymes were able to degrade the RNA as it moves to the cytosol, no protein would ever be successfully made) The cap and tail also allows translation to be more efficient (how... i'm not too sure sorry  )
Hope that helps

[Gogo14]

1. What is the difference between cytotoxic T cells and natural killer cells? They both lyse infected cells, but natural killer cells cannot read MHC 1 markers so how does it recognise infected cells?

2. In a virally infected cell, Tc cells signal it to undergo apoptosis right? But if there are already viruses inside the infected cell when it receives the signal, then wouldn't the T cell be helping the spread of the virus by allowing it to exit the cell and infect other cells?

3. In the ATAR notes bio book on P77-78, is there a diagram missing under 3.7 pedigrees?

Thnx

[Sine]

1. What is the difference between cytotoxic T cells and natural killer cells? They both lyse infected cells, but natural killer cells cannot read MHC 1 markers so how does it recognise infected cells?

2. In a virally infected cell, Tc cells signal it to undergo apoptosis right? But if there are already viruses inside the infected cell when it receives the signal, then wouldn't the T cell be helping the spread of the virus by allowing it to exit the cell and infect other cells?

3. In the ATAR notes bio book on P77-78, is there a diagram missing under 3.7 pedigrees?

Thnx

1. Cytotoxic T cells are a part of the adaptive immune system and require activation via interleukins from T helper cells. NK killer cells are a part of the innate immune system (2nd line).

2. Perforin will initiate apoptosis which will destroy cellular dna and degrade viral dna

3.sold my book 

[geminii]

3. In the ATAR notes bio book on P77-78, is there a diagram missing under 3.7 pedigrees?

Thnx

Yes, I just looked and it seems there is! If you need an example, however, here is a link: https://s-media-cache-ak0.pinimg.com/originals/6d/e7/68/6de768c243bb1b3cba048ca0d1886214.gif

Hope this helps!

[geminii]

Pre-mRNA needs to be modified:
1. to remove segments of mRNA that are "non-coding" - in a region of DNA, not all of it is necessary for that particular protein to be made and thus areas of it (called introns) are removed. This is called splicing. Splicing basically allows one sequence of DNA/RNA to code for various proteins depending on how it has been cut up.
e.g. if pre-mRNA has the sequence ABCDEFG
splicing may result in:
ABDFG creating protein type 1
ABCEG creating protein type 2
ACDEF creating protein type 3
This can be really helpful considering that we needs heaps and heaps of different kinds of proteins for all the different cells in the body but we only have so much DNA (about 2 metres in length apparently)

2. the mRNA has a poly-A (i.e. lots of Adenines) added to its tail end (3' end) and has a methyl (technically 7-methylguanosine - but not needed for vce) cap added to the "head" end of the strand (5' end). This capping and tailing allows the mRNA to be more stable (i.e. prevents enzymes from degrading the RNA strand) and thus assists it during its "transportation" from the nucleus to the cytosol. (imagine if enzymes were able to degrade the RNA as it moves to the cytosol, no protein would ever be successfully made) The cap and tail also allows translation to be more efficient (how... i'm not too sure sorry  )
Hope that helps

Thank you so much!! 

Another question - I know that in a karyotype, the X and Y chromosomes are obviously not homologous, since they are of different lengths and have different banding patterns. But what if the karyotype was of a female, and there were XX chromosomes? Would they be considered homologous, since they are both X chromosomes? Or are they non-homologous since they may have different banding patterns? (leading on to my next question - in a female karyotype, does the X and the other X have different banding patterns at all? Or do they have the same banding patterns?)

Thank you!!