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A level Biology: Post your doubts here!

thats_me

thats_me

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joanna omar said:
Anyone help me in these doubts !
Nov 2013/p11 ----->>
  • Q6 ...why is it C ,when the first carbon atom of the two B-glucose doesn't contain the OH group up?
  • B may be correct but yet there is no gylcosidic bond formed ? soo ?
Q11....Detailed explanation pls !
Q15 ....I know the water will enter the cell but ....wht is abt the inner and thicker walls ?
Q19...why B ?
Q26 .... ??
Click to expand...

6- Monomers are B glucose & in order for them to form glycosidic bonds successive B glucose molecules have to be flipped to 180 degrees i.e upside down. ( If they are not flipped glycosidic bond cannot be formed so cellulose is not formed)
11-Competitive inhibitor binds the enzyme where the substrate is supposed to bind i.e the active site. If the conc of substrate is increased, the chance of the substrate binding with the active site before the inhibitor is higher. (Non competitive inhibitor binds the allosteric site & increasing the conc of substrate doesn't reduce their effect)
so statement 1 & 2 are correct
statement-3 is Incorrect as enzymes reduce the activation energy not inhibitors.
statement-4 is Incorrect as non competitive inhibitors reduce the max rate of reaction not competitive inhibitors.
15-Not sure about this one but I guess the thick outer walls are lignified so, it won't allow water to enter.
19- Total 19 base pairs,( complementary base pairing A with T & C with G)
strand 1 has 4-T so strand 2 will have 4-A
strand 2 has 5-T so strand 1 will have 5-A
strand 2 has 7-C so strand 1 will have 7-G
base pairs = 4+5+7=16 so 19 - 16=3
26-What exactly do you have problem with here?
 
Karim Nabil

Karim Nabil

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joanna omar said:
I need help with June 2013/P1 var 3 Doubts ?

Q15 , Q21 , Q28 ,Q36 and Q39 ?
Click to expand...
  • q15> 1*60=60sec; 60+33+.54=93.54> 93.54 is not an accurate value so round it to 94 sec, answer is C
  • q21> it asked the combination of gene activity that is most likely to result in breast cancer, so the 3 genes must mutate to produce abnormal or no protein , therefore mutation results in cancer, answer is D
  • q28> root hair cells has the highest water potential, because water is directly diffused to it, while 2nd highest water potential is cortex cell solution, because water is transported from root hair cells to the cortex either by symplast pathway or apoplast, then comes endodermal cell solution, where water transported to it from cortex, so,overall, as distance from water source (soil) increases, water potential decreases abswer is D
  • q36> we should not give antibiotics used for animals to humans, cause, it is not specific, so no specific antibodies to that pathogen are produced,hence
    Pathogenic bacteria may develop resistance to these antibiotics. answer is C
  • q39> greater number of trophic levels in ecosystem X means that a greater percentage of primary producers are likely to be consumed by primary consumers in X than in Y, so option 1 is correct
  1. has less oxygen means that ecosystem X could be a marine aquatic ecosystem, so option 2 is correct
  2. they has less oxygen so less respiration and hence, less energy, so energy losses in ecosystem X is lower than ecosystem Y, so option 3 is correct
  3. lower proportion of decomposers means that there is higher rate of production of organic matter, so option 4 is correct, answer is D
 
joanna omar

joanna omar

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thats_me said:
6- Monomers are B glucose & in order for them to form glycosidic bonds successive B glucose molecules have to be flipped to 180 degrees i.e upside down. ( If they are not flipped glycosidic bond cannot be formed so cellulose is not formed)
11-Competitive inhibitor binds the enzyme where the substrate is supposed to bind i.e the active site. If the conc of substrate is increased, the chance of the substrate binding with the active site before the inhibitor is higher. (Non competitive inhibitor binds the allosteric site & increasing the conc of substrate doesn't reduce their effect)
so statement 1 & 2 are correct
statement-3 is Incorrect as enzymes reduce the activation energy not inhibitors.
statement-4 is Incorrect as non competitive inhibitors reduce the max rate of reaction not competitive inhibitors.
15-Not sure about this one but I guess the thick outer walls are lignified so, it won't allow water to enter.
19- Total 19 base pairs,( complementary base pairing A with T & C with G)
strand 1 has 4-T so strand 2 will have 4-A
strand 2 has 5-T so strand 1 will have 5-A
strand 2 has 7-C so strand 1 will have 7-G
base pairs = 4+5+7=16 so 19 - 16=3
26-What exactly do you have problem with here?
Click to expand...

Thanks A lot ! but I don't understand how 15 is A ??
and ab Q26 I dont get it aslo ...could u explain ?
 
joanna omar

joanna omar

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Karim Nabil said:
  • q15> 1*60=60sec; 60+33+.54=93.54> 93.54 is not an accurate value so round it to 94 sec, answer is C
  • q21> it asked the combination of gene activity that is most likely to result in breast cancer, so the 3 genes must mutate to produce abnormal or no protein , therefore mutation results in cancer, answer is D
  • q28> root hair cells has the highest water potential, because water is directly diffused to it, while 2nd highest water potential is cortex cell solution, because water is transported from root hair cells to the cortex either by symplast pathway or apoplast, then comes endodermal cell solution, where water transported to it from cortex, so,overall, as distance from water source (soil) increases, water potential decreases abswer is D
  • q36> we should not give antibiotics used for animals to humans, cause, it is not specific, so no specific antibodies to that pathogen are produced,hence
    Pathogenic bacteria may develop resistance to these antibiotics. answer is C
  • q39> greater number of trophic levels in ecosystem X means that a greater percentage of primary producers are likely to be consumed by primary consumers in X than in Y, so option 1 is correct
  1. has less oxygen means that ecosystem X could be a marine aquatic ecosystem, so option 2 is correct
  2. they has less oxygen so less respiration and hence, less energy, so energy losses in ecosystem X is lower than ecosystem Y, so option 3 is correct
  3. lower proportion of decomposers means that there is higher rate of production of organic matter, so option 4 is correct, answer is D
Click to expand...

Thanks A BUNCH :D
but why in Q36 ....It can aslo be that they would be allergic to human ?
 
S

Snowysangel

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Karim Nabil said:
  • q15> 1*60=60sec; 60+33+.54=93.54> 93.54 is not an accurate value so round it to 94 sec, answer is C
  • q21> it asked the combination of gene activity that is most likely to result in breast cancer, so the 3 genes must mutate to produce abnormal or no protein , therefore mutation results in cancer, answer is D
  • q28> root hair cells has the highest water potential, because water is directly diffused to it, while 2nd highest water potential is cortex cell solution, because water is transported from root hair cells to the cortex either by symplast pathway or apoplast, then comes endodermal cell solution, where water transported to it from cortex, so,overall, as distance from water source (soil) increases, water potential decreases abswer is D
  • q36> we should not give antibiotics used for animals to humans, cause, it is not specific, so no specific antibodies to that pathogen are produced,hence
    Pathogenic bacteria may develop resistance to these antibiotics. answer is C
  • q39> greater number of trophic levels in ecosystem X means that a greater percentage of primary producers are likely to be consumed by primary consumers in X than in Y, so option 1 is correct
  1. has less oxygen means that ecosystem X could be a marine aquatic ecosystem, so option 2 is correct
  2. they has less oxygen so less respiration and hence, less energy, so energy losses in ecosystem X is lower than ecosystem Y, so option 3 is correct
  3. lower proportion of decomposers means that there is higher rate of production of organic matter, so option 4 is correct, answer is D
Click to expand...
Why isn't 93.54 an accurate value?
 
roxylara

roxylara

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A lymphocyte has a diameter of 1 x 10^-2 millimetres(mm). What is the diameter in nanometers (nm)?

A. 1 x 10^1
B. 1 x 10^2
C. 1 x 10^3
D. 1 x 10^4

Can someone tell me how to do this? :/
 
mehria

mehria

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roxylara said:
A lymphocyte has a diameter of 1 x 10^-2 millimetres(mm). What is the diameter in nanometers (nm)?

A. 1 x 10^1
B. 1 x 10^2
C. 1 x 10^3
D. 1 x 10^4

Can someone tell me how to do this? :/
Click to expand...
the ans is D as=>
1mm=10^6 nm
so (1x10^-2) x (10^6) = 1x10^4 nm
 
S

Snowysangel

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Karim Nabil said:
rounding seconds to the nearest whole no. is more accurate cause in real life it is more difficult to measure 93.54s, instead 94 is more accurate!
Click to expand...
But we're using an accurate measuring instrument which can measure up till 2 decimal places! It's for a similar reason that using a buttered is more accurate than using a measuring cylinder
 
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Snowysangel

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roxylara said:
A lymphocyte has a diameter of 1 x 10^-2 millimetres(mm). What is the diameter in nanometers (nm)?

A. 1 x 10^1
B. 1 x 10^2
C. 1 x 10^3
D. 1 x 10^4

Can someone tell me how to do this? :/
Click to expand...
1 x 10^-2 mm is 1 x 10^-5 m. Since 1 m has 1x10^-9 nm, 1 x 10^-5 m is equal to 1x10^4 nm
 
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