Needs some explanations in AS Bio P1

[Amy Bloom]

Hi everyone.
Can anybody give me some explanations to the following questions in the attached file please?
Question 10
Question 11
Question 18: Why is it not A?
Question 22
Question 30: Why its not A?

 

[A.Solomon]

Hey Amy,
Question 10:
it depends on the fact that Benedict's test is a qualitative and "semi-quantitative" test, in other words the color change indicates a " relatively high or low concentration of the present reducing sugar" . it takes place as the following:
no sugar = blue
low sugar concentration = green
moderate concentration = yellow
higher concentration = orange
very high concentration = red .... try to answer it now !

Question 11:
it tests your ability to determine first that glycogen is made up of repeated glucose units, thus , you start thinking in answers B & C
second, you have to remember that glucose present in glycogen is in alpha- configuration, with carbon 2 - OH oriented downward !!

Question 18:
actually, A is the correct answer. I didn't understand your question

Question 22:
mmmm, what if i put the question in other words, first, in pulmonary arteries, are there any oxygen remaining ? would you think it will be in a high or low conc. ? depending on this fact, you would expect certain saturation % of hemoglobin , check the corresponding partial pressure from the graph, and it's your answer .

Question 30:
it has been a real tricky question for many students, however to make it easy for you, ask yourself what limits the amount of oxygen delivered to the muscle ? if you figure out that the volume of blood blood flowing to them is the answer, then it is gonna be easy for you to figure the correct answer .
The more popular answer was that the limitation is due to the speed of dissociation of oxyhaemoglobin. However, it is not generally appreciated how quickly dissociation occurs.

hope it helps ...
wish you luck !

 

[Amy Bloom]

Hey Amy,
Question 10:
it depends on the fact that Benedict's test is a qualitative and "semi-quantitative" test, in other words the color change indicates a " relatively high or low concentration of the present reducing sugar" . it takes place as the following:
no sugar = blue
low sugar concentration = green
moderate concentration = yellow
higher concentration = orange
very high concentration = red .... try to answer it now !

Question 11:
it tests your ability to determine first that glycogen is made up of repeated glucose units, thus , you start thinking in answers B & C
second, you have to remember that glucose present in glycogen is in alpha- configuration, with carbon 2 - OH oriented downward !!

Question 18:
actually, A is the correct answer. I didn't understand your question

Question 22:
mmmm, what if i put the question in other words, first, in pulmonary arteries, are there any oxygen remaining ? would you think it will be in a high or low conc. ? depending on this fact, you would expect certain saturation % of hemoglobin , check the corresponding partial pressure from the graph, and it's your answer .

Question 30:
it has been a real tricky question for many students, however to make it easy for you, ask yourself what limits the amount of oxygen delivered to the muscle ? if you figure out that the volume of blood blood flowing to them is the answer, then it is gonna be easy for you to figure the correct answer .
The more popular answer was that the limitation is due to the speed of dissociation of oxyhaemoglobin. However, it is not generally appreciated how quickly dissociation occurs.

hope it helps ...
wish you luck !

Hey thank u soo much, it indeed really helped!

I mistyped for question 18, i got B but its not the correct answer, as the marking scheme says. can u please explain this to me?
For question 11, i think i got confused with glycerol. A is glycerol, isn't it?

One more thing, for question 22, i understand what u told me. I think that in the pulmonary artery, there will be some dissociation of haemoglobin to make cardiac muscles work. but i don't understand by how much?

For question 30, see if i got my facts right: The limiting factor here is the volume of blood flowing through the muscles which implies that if there is more blood flowing, more oxygen is available to the respiring muscle. Hence we are looking at the amount of oxygen delivered to the muscles. But one thing is still doubtful in me is answer A. It has no relevance here? I mean in terms of partial pressures of oxygen?

 

[A.Solomon]

well amy,
Question 18:
you have to keep in mind the following facts:
1. each amino acid is coded "carried" by at least on tRNA molecule
2. tRNAs are "re-usable"; once their cargo is unloaded, they can be used again.
now based on these 2 facts, you can tell that a peptide made up of 10 amino acids of 4 different kinds would require at least 4 tRNAs

Question 11:
yes B is glycerol, but this answer should be eliminated from the beginning; glycerol participate in formation of lipids
do not get confused between glycerol and glycogen

Question 22:
well, now you realized that pulmonary arteries are not devoid of oxygen, which means that the % saturated of hemoglobin is not 0% but it is still a very low value , which eliminates the first answer " it corresponds to % saturation 0%-10%"

Question 30:
i can not say that i understood your wonder completely, would you please try to make it clearer ?

feel free to write back any time....believe me, for AS biology, paper 1 is the one you have to take care of !
wish you luck

 

[Amy Bloom]

well amy,
Question 18:
you have to keep in mind the following facts:
1. each amino acid is coded "carried" by at least on tRNA molecule
2. tRNAs are "re-usable"; once their cargo is unloaded, they can be used again.
now based on these 2 facts, you can tell that a peptide made up of 10 amino acids of 4 different kinds would require at least 4 tRNAs

Question 11:
yes B is glycerol, but this answer should be eliminated from the beginning; glycerol participate in formation of lipids
do not get confused between glycerol and glycogen

Question 22:
well, now you realized that pulmonary arteries are not devoid of oxygen, which means that the % saturated of hemoglobin is not 0% but it is still a very low value , which eliminates the first answer " it corresponds to % saturation 0%-10%"

Question 30:
i can not say that i understood your wonder completely, would you please try to make it clearer ?

feel free to write back any time....believe me, for AS biology, paper 1 is the one you have to take care of !
wish you luck

Hi.
Question 18:
The "different kinds" are they due to the different types of nitrogenous bases?

Question 22:
Okay i agree with you, but what brings me to B? can u explain?

Question 30:
I want you to confirm if i thought about it well: If more blood flows into the muscles, it means that more molecules of haemoglobin will be present and hence more oxygen molecules available to respiring muscles. Hence we are looking at the amount of oxygen "available" for muscles to do work right?
However, i'm still doubtful about answer A. I thought that since muscles are respiring here, there must be an increase in partial pressure of CO2, so affecting the %saturation of haemoglobin. does this have an impact on the amount of work (respiration)?

Yeah indeed MCQs are really tricky at times!

 

[A.Solomon]

Well amy,
Question 18:
"different kinds" is to describe the present amino acids in the peptide molecule mentioned..... check the structure of amino acids, they all share an amino group, caroxylic acid group and a single hydrogen around a central carbon, however, they differ in what is called " R group" ... the mentioned four different amino acids are different in these groups...
let's say we have 4 amino acids: leucine (leu), Lysine (Lys), Tryptophan (Try) and Histadine (His) , each one of those is carried by at least one tRNA molecule.
now let's build a peptide molecule made up of 10 amino acids, using only these 4 :
Leu---Lys---Try--Try---His---His---Lys---Leu--Lys---His
what is the minimum number of tRNAs needed to build such a molecule?
done?

Question 22:
open your question paper...check the graph
answer A, 0--2 Pka is corresponding to 0--20% saturation, this answer means there would be no oxygen at all in pulmonary arteries.. wrong !
answer B, 2--6 Pka is coressponding to 20--70% saturation, fairly reasonable
answers C and D indicate % saturation when blood is highly oxygenated, which is never to take place in pulmonary arteries !
convinced ?

Question 30:
you thought it right, however, there is no need to think that produced carbon dioxide would affect the oxygen dissociation rate ...
and take care, your mind is taking you away from the real question! it asks about the limiting factor for respiring muscle, the factor that would directly increase the amount of work if increased ! any doubt now that this limiting factor is answer D?

Move forward Amy, there're still too many papers to go through, each with wonders and tricky points .... keep thinking as you do and post any question or thoughts you have concerning biology, even if they are not directly related to the syllabus, and i'm sure you would have plenty of !

take care and hopefully this individual paper " s03" is done !

 

[Amy Bloom]

Well amy,
Question 18:
"different kinds" is to describe the present amino acids in the peptide molecule mentioned..... check the structure of amino acids, they all share an amino group, caroxylic acid group and a single hydrogen around a central carbon, however, they differ in what is called " R group" ... the mentioned four different amino acids are different in these groups...
let's say we have 4 amino acids: leucine (leu), Lysine (Lys), Tryptophan (Try) and Histadine (His) , each one of those is carried by at least one tRNA molecule.
now let's build a peptide molecule made up of 10 amino acids, using only these 4 :
Leu---Lys---Try--Try---His---His---Lys---Leu--Lys---His
what is the minimum number of tRNAs needed to build such a molecule?
done?

Question 22:
open your question paper...check the graph
answer A, 0--2 Pka is corresponding to 0--20% saturation, this answer means there would be no oxygen at all in pulmonary arteries.. wrong !
answer B, 2--6 Pka is coressponding to 20--70% saturation, fairly reasonable
answers C and D indicate % saturation when blood is highly oxygenated, which is never to take place in pulmonary arteries !
convinced ?

Question 30:
you thought it right, however, there is no need to think that produced carbon dioxide would affect the oxygen dissociation rate ...
and take care, your mind is taking you away from the real question! it asks about the limiting factor for respiring muscle, the factor that would directly increase the amount of work if increased ! any doubt now that this limiting factor is answer D?

Move forward Amy, there're still too many papers to go through, each with wonders and tricky points .... keep thinking as you do and post any question or thoughts you have concerning biology, even if they are not directly related to the syllabus, and i'm sure you would have plenty of !

take care and hopefully this individual paper " s03" is done !

Thank you very much for clearing those doubts in me. Okay now i'm convinced about the answers, they are definitely clearer to me now.
Indeed! there's a lot to go, this is my 2nd P1 i'm practising.
Thanks again.