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AQA - BIOL4 - 13th JUNE 2014
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Original post by rwilliams5
I always do past papers right at last minute, gets me thinking properly (as in knowing what the examiners want) rather than just looking at notes... Each to their own 
Really? I'm getting bored already. I have just given up writing and my page is full of made-up acronyms and scribbles lol
Original post by rwilliams5
No they cannot that is the competitive exclusion principle.
The competitive exclusion principle states that two species that compete for the exact same resources cannot stably coexist.
One of the two competitors will always have an ever so slight advantage over the other that leads to extinction of the second competitor in the long run (in a hypothetical non-evolving system) or (in the real world) to an evolutionary shift of the inferior competitor towards a different ecological niche.
As a consequence, competing related species often evolve distinguishing characteristics in areas where they both coexist.
This aids in mate recognition, thus maintaining each species' superiority in exploiting slightly different ecological niches.
The competitive exclusion principle states that two species that compete for the exact same resources cannot stably coexist.
One of the two competitors will always have an ever so slight advantage over the other that leads to extinction of the second competitor in the long run (in a hypothetical non-evolving system) or (in the real world) to an evolutionary shift of the inferior competitor towards a different ecological niche.
As a consequence, competing related species often evolve distinguishing characteristics in areas where they both coexist.
This aids in mate recognition, thus maintaining each species' superiority in exploiting slightly different ecological niches.
Thanks! what do u mean my an evolutionary shift of the inferior competitor towards a different ecological niche.
Original post by GD2822
thank you thats fabbbb
thank you thats fabbbb
No problem
Good luck!
Original post by GD2822
Can someone please go over anaerobic respirartion for me please 
- Takes place in cytoplasm
- Only glycolysis takes place
- Pyruvate from glycolysis is reduced to ethanol/lactate and reduced NAD is oxidised to regenerate NAD.
- Which is necessary because NAD is required in glycolysis
- Net 2 ATP produced.
Original post by Rhubarb96
why couldnt you do 400/25 though??
because that wouldn't be rate, that would just be something like how much mass it stored during that day, your mainly looking for the steepest part to find the gradient of it, this lets you know the highest rate as the most change occurred between day 20 and day 25 so you find the change in rate for those days
(edited 9 years ago)
Original post by walkers38
Has anyone got any notes on conservation. I just don't know anything about it?
Hope you can read my writing
Posted from TSR Mobile
Original post by walkers38
Really? I'm getting bored already. I have just given up writing and my page is full of made-up acronyms and scribbles lol
Yeh I got so bored going through my notes so past papers focus me
might do a maths paper to just think about something else soon though. Posted from TSR Mobile
Original post by Jaanu
Thanks! what do u mean my an evolutionary shift of the inferior competitor towards a different ecological niche.
Basically the organism that is "forced out" because it isn't as strong a competitor moves towards a new niche which it can then become better adapted to.
Posted from TSR Mobile
Original post by rwilliams5
Thank you. You're like saviour of this thread haha. just out of random but what did u get in AS, what ums?
Original post by kashagupta
When they say X chromosome they mean sex linked-so only on the 23rd chromosome pair. Since this is proven not to be sex linked, the gene could basically be on any of the other 22, does that make sense? It's a bit of a pain when it comes to explaining inheritance haha-but it'll just click at some point!
Yeah inheritence is one of my weakest topics
so rhesus is not sex linked because it says it in the question ( or did we have to know that)...does that mean therefore X is recessive and Y has the dominant allele for three causing 9 to be negative for rhesus? Is that right or hav i just lost the plot...can u also explain to me the sex linked thing that u mentioned.... thank u!!!!!HELP pleaseee
June 2013 http://filestore.aqa.org.uk/subjects/AQA-BIOL4-QP-JUN13.PDF
Q3 bii)Explain one piece of evidence from the diagram which proves that the allele for
Tay-Sachs disease is not on the X chromosome.
11 is affected, 3 is not; 3/father of 11 does not have a recessive allele on his X chromosome/ Xt
I am confused: 11 if female so she has XX so how come it’s still not on the X chromosome?
June 2011 q 6bii
http://filestore.aqa.org.uk/subjects/AQA-BIOL4-W-QP-JUN11.PDF
Sea otters were close to extinction at the start of the 20th century. Following a ban on hunting sea otters, the sizes of their populations began to increase. Scientists studied the frequencies of two alleles of a gene in one population of sea otters. The dominant allele, T, codes for an enzyme. The other allele, t, is recessive anddoes not produce a functional enzyme.
6Bii)Several years later, scientists repeated their study on this population. They found thatthe frequency of the recessive allele had decreased.What type of natural selection appears to have occurred in this population of seaotters? Explain how this type of selection led to a decrease in the frequency of the recessive allele.
1. Directional;
2. The recessive allele confers disadvantage/ the dominant
allele confers advantage/more likely to survive / reproduce;
My confusion: why is not stabilising selection as stabilising selection is selection of alleles towards the middle of range having reproductive success and occurs when the environment does not change
Whilst directional is response selection for extreme characteristics in response to change in environment
If recessive allele (extreme) is selected against then it may as well mean that the middle range of phenotype could be selected for and the question doesn’t state a change in environment hence implying stabilising selection
So, depending on the mark scheme and question statement that just because recessive alleles are decreasing , we have to assume that the other extreme is favored?
But as I have stated before, it may not necessarily be the extreme being favored as it maybe the middle range because the question (when I look at it) doesn't provide enough information for distinction.
Or is it because there are only 2 choices, dominant and recessive so a decrease in the recessive would automatically lead to an increase in dominant so leading to directional selection
But if so what’s the middle range? Doesn’t there have to be 1? Since T is dominant, ie. Most likely to occur, isn’t it the middle range if so isn’t suppose to be a stabilising selection ?
Does this make sense .....
June 2013 http://filestore.aqa.org.uk/subjects/AQA-BIOL4-QP-JUN13.PDF
Q3 bii)Explain one piece of evidence from the diagram which proves that the allele for
Tay-Sachs disease is not on the X chromosome.
11 is affected, 3 is not; 3/father of 11 does not have a recessive allele on his X chromosome/ Xt
I am confused: 11 if female so she has XX so how come it’s still not on the X chromosome?
June 2011 q 6bii
http://filestore.aqa.org.uk/subjects/AQA-BIOL4-W-QP-JUN11.PDF
Sea otters were close to extinction at the start of the 20th century. Following a ban on hunting sea otters, the sizes of their populations began to increase. Scientists studied the frequencies of two alleles of a gene in one population of sea otters. The dominant allele, T, codes for an enzyme. The other allele, t, is recessive anddoes not produce a functional enzyme.
6Bii)Several years later, scientists repeated their study on this population. They found thatthe frequency of the recessive allele had decreased.What type of natural selection appears to have occurred in this population of seaotters? Explain how this type of selection led to a decrease in the frequency of the recessive allele.
1. Directional;
2. The recessive allele confers disadvantage/ the dominant
allele confers advantage/more likely to survive / reproduce;
My confusion: why is not stabilising selection as stabilising selection is selection of alleles towards the middle of range having reproductive success and occurs when the environment does not change
Whilst directional is response selection for extreme characteristics in response to change in environment
If recessive allele (extreme) is selected against then it may as well mean that the middle range of phenotype could be selected for and the question doesn’t state a change in environment hence implying stabilising selection
So, depending on the mark scheme and question statement that just because recessive alleles are decreasing , we have to assume that the other extreme is favored?
But as I have stated before, it may not necessarily be the extreme being favored as it maybe the middle range because the question (when I look at it) doesn't provide enough information for distinction.
Or is it because there are only 2 choices, dominant and recessive so a decrease in the recessive would automatically lead to an increase in dominant so leading to directional selection
But if so what’s the middle range? Doesn’t there have to be 1? Since T is dominant, ie. Most likely to occur, isn’t it the middle range if so isn’t suppose to be a stabilising selection ?
Does this make sense .....
Original post by walkers38
Thank you. You're like saviour of this thread haha. just out of random but what did u get in AS, what ums?
Haha helping other people helps me to think and I don't have siblings to test me so this works just as well
Not great I didn't think I didn't like AS, I peaked at GCSE...
246/300 whatever that equates to.
What do we need for an A* and A?
Posted from TSR Mobile
Original post by rwilliams5
Basically the organism that is "forced out" because it isn't as strong a competitor moves towards a new niche which it can then become better adapted to.
Posted from TSR Mobile
Posted from TSR Mobile
oh okay that makes sense. Thank u!!!!
Original post by GD2822
Can someone please go over anaerobic respirartion for me please
Yeah sure:
1) It's is an anaerobic, since there is no involvement of Oxygen
2) Glycolysis takes place in the cytoplasm of cells and pyruvate is formed along with Reduced NAD
3) Pyruvate is reduced by NADH, into ethanol + CO2(Yeast) or Lactate(animals). In the process NADH is oxidised back into NAD
4) Regenerated NAD can be used to drive glycolysis.
As you have seen it is much less efficient than aerobic respiration (32 ATP net), since only 2 ATP is produced per cycle. Therefore, anaerobic respiration needs to run 16 times to match the aerobic ATP value. In doing so, a lot of CO2 is released (byproduct of glycolysis), and the potentially toxic ethanol and lactate increase.
Original post by rwilliams5
Haha helping other people helps me to think and I don't have siblings to test me so this works just as well
Not great I didn't think I didn't like AS, I peaked at GCSE...
246/300 whatever that equates to.
What do we need for an A* and A?
Posted from TSR Mobile
Not great I didn't think I didn't like AS, I peaked at GCSE...
246/300 whatever that equates to.
What do we need for an A* and A?
Posted from TSR Mobile
520 for A*, 480 for A. Do you know what u got in ur ISA? You have 6 ums advantage from last year for an A.
Original post by futuredoctorVSB
As you have seen it is much less efficient than aerobic respiration (32 ATP net), since only 2 ATP is produced per cycle.
Can you list where 32 ATP come from in aerobic respiration? I'm so clueless about that
Original post by walkers38
520 for A*, 480 for A. Do you know what u got in ur ISA? You have 6 ums advantage from last year for an A.
Think I got a B in my ISA again... drags me down every time.
What UMS are the papers out of?
ISA is 60 but 4 and 5?
Original post by lalableh
HELP pleaseee
June 2013 http://filestore.aqa.org.uk/subjects/AQA-BIOL4-QP-JUN13.PDF
Q3 bii)Explain one piece of evidence from the diagram which proves that the allele for
Tay-Sachs disease is not on the X chromosome.
11 is affected, 3 is not; 3/father of 11 does not have a recessive allele on his X chromosome/ Xt
I am confused: 11 if female so she has XX so how come it’s still not on the X chromosome?
June 2011 q 6bii
http://filestore.aqa.org.uk/subjects/AQA-BIOL4-W-QP-JUN11.PDF
Sea otters were close to extinction at the start of the 20th century. Following a ban on hunting sea otters, the sizes of their populations began to increase. Scientists studied the frequencies of two alleles of a gene in one population of sea otters. The dominant allele, T, codes for an enzyme. The other allele, t, is recessive anddoes not produce a functional enzyme.
6Bii)Several years later, scientists repeated their study on this population. They found thatthe frequency of the recessive allele had decreased.What type of natural selection appears to have occurred in this population of seaotters? Explain how this type of selection led to a decrease in the frequency of the recessive allele.
1. Directional;
2. The recessive allele confers disadvantage/ the dominant
allele confers advantage/more likely to survive / reproduce;
My confusion: why is not stabilising selection as stabilising selection is selection of alleles towards the middle of range having reproductive success and occurs when the environment does not change
Whilst directional is response selection for extreme characteristics in response to change in environment
If recessive allele (extreme) is selected against then it may as well mean that the middle range of phenotype could be selected for and the question doesn’t state a change in environment hence implying stabilising selection
So, depending on the mark scheme and question statement that just because recessive alleles are decreasing , we have to assume that the other extreme is favored?
But as I have stated before, it may not necessarily be the extreme being favored as it maybe the middle range because the question (when I look at it) doesn't provide enough information for distinction.
Or is it because there are only 2 choices, dominant and recessive so a decrease in the recessive would automatically lead to an increase in dominant so leading to directional selection
But if so what’s the middle range? Doesn’t there have to be 1? Since T is dominant, ie. Most likely to occur, isn’t it the middle range if so isn’t suppose to be a stabilising selection ?
Does this make sense .....
June 2013 http://filestore.aqa.org.uk/subjects/AQA-BIOL4-QP-JUN13.PDF
Q3 bii)Explain one piece of evidence from the diagram which proves that the allele for
Tay-Sachs disease is not on the X chromosome.
11 is affected, 3 is not; 3/father of 11 does not have a recessive allele on his X chromosome/ Xt
I am confused: 11 if female so she has XX so how come it’s still not on the X chromosome?
June 2011 q 6bii
http://filestore.aqa.org.uk/subjects/AQA-BIOL4-W-QP-JUN11.PDF
Sea otters were close to extinction at the start of the 20th century. Following a ban on hunting sea otters, the sizes of their populations began to increase. Scientists studied the frequencies of two alleles of a gene in one population of sea otters. The dominant allele, T, codes for an enzyme. The other allele, t, is recessive anddoes not produce a functional enzyme.
6Bii)Several years later, scientists repeated their study on this population. They found thatthe frequency of the recessive allele had decreased.What type of natural selection appears to have occurred in this population of seaotters? Explain how this type of selection led to a decrease in the frequency of the recessive allele.
1. Directional;
2. The recessive allele confers disadvantage/ the dominant
allele confers advantage/more likely to survive / reproduce;
My confusion: why is not stabilising selection as stabilising selection is selection of alleles towards the middle of range having reproductive success and occurs when the environment does not change
Whilst directional is response selection for extreme characteristics in response to change in environment
If recessive allele (extreme) is selected against then it may as well mean that the middle range of phenotype could be selected for and the question doesn’t state a change in environment hence implying stabilising selection
So, depending on the mark scheme and question statement that just because recessive alleles are decreasing , we have to assume that the other extreme is favored?
But as I have stated before, it may not necessarily be the extreme being favored as it maybe the middle range because the question (when I look at it) doesn't provide enough information for distinction.
Or is it because there are only 2 choices, dominant and recessive so a decrease in the recessive would automatically lead to an increase in dominant so leading to directional selection
But if so what’s the middle range? Doesn’t there have to be 1? Since T is dominant, ie. Most likely to occur, isn’t it the middle range if so isn’t suppose to be a stabilising selection ?
Does this make sense .....
I think it is directional because having the recessive allele is not an extreme. ie. There is shift in the allele frequencies from a certain ratio of Dominant to Recessive, due to some changes in the niches or environment.
The question is implying that the dominant and recssive alleles were in some sort of equilibrium before the shift was observed.
Shift = Directional Selection
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