VCE Biology Question Thread

[vox nihili]

Sorry I don't completely agree with Mr T-Rav's  answers.
At 0.7% saline solution - the injected solution would be of lower solute concentration than inside the cell - therefore the cell is hypertonic to the fluid outside the cell and due to osmosis, water would enter the cell.
This may not cause haemolysis (as it is very close to 0.9% saline solution) but the cell will definitely swell.

At 0.11% saline solution - the injected solution would be of higher solute concentration than inside the cell - therefore the cell is hypotonic to the fluid outside the cell and water would leave the cell - i.e. the cell will shrivel.

In the case of the first one, you're absolutely right. 0.7% saline is a hypotonic solution. My suspicion is that haemolysis would only occur in solutions with very little solvent or none at all. So, you correctly identify that the cell would swell without lysing.

I think you're mistaken to identify my answer as incorrect. A concentration of 0.11% is less than a concentration of 0.7%...so it's even more hypotonic than the 0.7% solution. The cell would not shrivel at all, but rather, it would swell (more so than the cells placed in the 0.7%).
Happy to continue discussing if you're unsure of why this is the case, but to anyone reading I would encourage you to take this as the correct answer.

[mtse]

I think you're mistaken to identify my answer as incorrect. A concentration of 0.11% is less than a concentration of 0.7%...so it's even more hypotonic than the 0.7% solution. The cell would not shrivel at all, but rather, it would swell (more so than the cells placed in the 0.7%).
Happy to continue discussing if you're unsure of why this is the case, but to anyone reading I would encourage you to take this as the correct answer.

Oh god my 2am state of mind kept insisting to me that 0.11%>0.7%, which is obviously wrong. 
Yep the cell will swell in a 0.11% solution

[anotherworld2b]

Yes if a pure water solution (saline solution without the 0.9% NaCl) was injected into a person, it would cause haemolysis (bursting of the red blood cells), which has many adverse effects

This can be explained by the phenomenon osmosis:
The concentration of solute inside the cell is equivalent to the concentration of solute in 0.9% saline solution. (This concentration is written as 300 milli-osmoles per litre). If pure water was injected into the blood stream then the water outside the red blood cell would be of a MUCHHHH lower concentration than inside the cell. Therefore to balance out the concentrations (reach equilibrium), water from outside the cell will diffuse INTO the cell. (Osmosis is the movement of water from an area of low concentration of solute to an area of high concentration of solute through a semi-permeable membrane) Depending on the amount of pure water injected, the amount of water that enters the cell may end up causing the cell membrane to burst and thus the cell will die. If this occurs systemically (all around the body), this means that the person will have no red blood cells = no transport of oxygen to organs = death
Sorry I don't completely agree with Mr T-Rav's  answers.
At 0.7% saline solution - the injected solution would be of lower solute concentration than inside the cell - therefore the cell is hypertonic to the fluid outside the cell and due to osmosis, water would enter the cell.
This may not cause haemolysis (as it is very close to 0.9% saline solution) but the cell will definitely swell.

At 0.11% saline solution - the injected solution would be of higher solute concentration than inside the cell - therefore the cell is hypotonic to the fluid outside the cell and water would leave the cell - i.e. the cell will shrivel. <-- just me being an idiot and thinking that 0.11>0.7 *facepalms*

This is extremely helpful thank you
I was wondering will the red blood cells continue to function properly despite the swelling from one scenario and shrivelling from the other?

I have another question I have to respond to but I'm not sure what else to explain and write about.

Q2. At one time. It was believed that disease was caused by ‘bad blood’. Taking large amounts of blood from a patient by bleeding (blood-letting) was widely practised as a cure for disease. Louis XII of France had blood taken 47 times in six months; Louis XV was bled 38 times, and Charles XII of England had blood taken numerous times, even just before his death. Describe some of the effects that the removal of large quantities of blood would have on a patient.

Blood-letting was a common practise in medical history which involved the removal of some of a patient's blood for therapeutic purposes to heal ailments. Some effects of the removal of large quantities of blood on a patient include: weariness and dizziness due to anaemia, fall in blood pressure, people may be tired, short of breath, and pale. Anemia results from a lack of red blood cells or dysfunctional red blood cells in the body. This leads to reduced oxygen flow to the body's organs.These effects occur because due to the removal of large quantities of blood, blood pressure falls because the amount of fluid left in the blood vessels is insufficient. The body’s oxygen supply is drastically reduced because the number of oxygen-carrying red blood cells has decreased so quickly.

[HighTide]

This is extremely helpful thank you
I was wondering will the red blood cells continue to function properly despite the swelling from one scenario and shrivelling from the other?

I have another question I have to respond to but I'm not sure what else to explain and write about.

Q2. At one time. It was believed that disease was caused by ‘bad blood’. Taking large amounts of blood from a patient by bleeding (blood-letting) was widely practised as a cure for disease. Louis XII of France had blood taken 47 times in six months; Louis XV was bled 38 times, and Charles XII of England had blood taken numerous times, even just before his death. Describe some of the effects that the removal of large quantities of blood would have on a patient.

Blood-letting was a common practise in medical history which involved the removal of some of a patient's blood for therapeutic purposes to heal ailments. Some effects of the removal of large quantities of blood on a patient include: weariness and dizziness due to anaemia, fall in blood pressure, people may be tired, short of breath, and pale. Anemia results from a lack of red blood cells or dysfunctional red blood cells in the body. This leads to reduced oxygen flow to the body's organs.These effects occur because due to the removal of large quantities of blood, blood pressure falls because the amount of fluid left in the blood vessels is insufficient. The body’s oxygen supply is drastically reduced because the number of oxygen-carrying red blood cells has decreased so quickly.

I haven't actually read the previous posts, but:
1) They won't function properly. Red blood cell structure is essential for its function. A swollen red blood cell may burst (hemolysis) if it takes in too much water, and if it bursts, it loses its structure. Crenation also changes the structure of the blood cell, and so it also affects the function. The reasoning behind this is that the red blood cells carry oxygen, and they can change their shape to move into certain areas.
2) The impact is dependent on how much blood is lost. If you lose blood, you lose red blood cells. If you lose red blood cells, you lose oxygen going around the body. At the time, there would be a drop in blood pressure, resulting in less blood going to some muscles, and fatigue. Since this is gradual, the result would most likely lead to anemia, as less oxygenated blood would be flowing to the organs. This would also result in fatigue, and pale skin. Obviously too much blood loss can also lead to death.
The fourth para "Blood letting..." is right, if that was your answer. That accurately lists all the possible outcomes.
But if you're uncertain, you should consider:
The need for blood--> What is blood composed of? ---> What's the function of whatever is in blood? --> What happens if you don't have it? Consider short term and long term.

[vox nihili]

Oh god my 2am state of mind kept insisting to me that 0.11%>0.7%, which is obviously wrong. 
Yep the cell will swell in a 0.11% solution

hahah I don't really know you so decided to go super polite, but 2am brain=story of my life :p

[larissaaa_]

"DNA always synthesise in the 5' to 3' end. However it is important to realise that the DNA strands are antiparallel and the synthesis direction applies to the strand being replicated, not the parent strand".

What does this mean? So the free nucleotides that are joining to make the new DNA strand is synthesising in the 5' to 3' direction of that strand which is the 3' to 5' direction of the parent strand? Or the other way around? Or did that not make any sense at all?

[HighTide]

"DNA always synthesise in the 5' to 3' end. However it is important to realise that the DNA strands are antiparallel and the synthesis direction applies to the strand being replicated, not the parent strand".

What does this mean? So the free nucleotides that are joining to make the new DNA strand is synthesising in the 5' to 3' direction of that strand which is the 3' to 5' direction of the parent strand? Or the other way around? Or did that not make any sense at all?

The parent strand runs 3' to 5'. The strand being made goes 5' to 3'. Take a quick look at this:
http://highered.mheducation.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html
Note how the 3' to 5' strand is blue. Since the two strands are antiparallel, the other strand is 5' to 3'. So the strand being made by DNA polymerase has to be 5' to 3' as well.

[vox nihili]

"DNA always synthesise in the 5' to 3' end. However it is important to realise that the DNA strands are antiparallel and the synthesis direction applies to the strand being replicated, not the parent strand".

What does this mean? So the free nucleotides that are joining to make the new DNA strand is synthesising in the 5' to 3' direction of that strand which is the 3' to 5' direction of the parent strand? Or the other way around? Or did that not make any sense at all?

Will just add that this means that the parent strand is read in the 3' to 5' direction, so the other strand has to be made in the 5' to 3'

Which kind of makes sense, because we'd read from 3 to 5 rather than in the reverse order yeah?

[Butterflygirl]

Just a question...What happens to the spindle fibres that are not attached to a chromosome during anaphase of either mitosis or meiosis? Do they just break down?

When I draw a cell undergoing meiosis and a question asks to draw one pair of chromosomes, do I show the spindles approaching opposite ends in all the spindle fibres? Even the ones that are not attached to chromosomes?

Thanks in advance! I just thought it would look a bit weird if I draw only one spindle fibre for that one pair.

[kingy123]

I was just wondering is vestigial wings in fruit flies an example of continuous or discontinuous variation???

[solution]

I was just wondering is vestigial wings in fruit flies an example of continuous or discontinuous variation???

Discontinuous variation. There are two discrete categories, wildtype and vestigial wings.

[anotherworld2b]

hahah I don't really know you so decided to go super polite, but 2am brain=story of my life :p

would there be a point where the red blood cells shrivel?

[vox nihili]

would there be a point where the red blood cells shrivel?

Yes

[kingy123]

Hey guys I'm struggling to think of what to discuss in the conclusion of the prac report of our genetic SAC.

We crossed some fruit flies , observing a trait controlled by a single gene loci with 2 alleles and observed the results over several generations.

Could someone help me think of what to talk about? PELISSE MY SACS TOMMOROW

[HasibA]

to what extent should i know 'independent assortment' and 'crossing over' for vce bio? ty (i.e definitions and concepts, or more?) tyy
edit: how much do i need to know about 'polar bodies' and egg cell and sperm cell formation (other than the meiosis theory behind it) ? ty
edit 2 : how much should i need to know about non-disjunctions, aneuploidy and polyploidy etc. ty so much!