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A level Biology: Post your doubts here!

1357911

1357911

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1357911 said:
measure the size of the nucleas with a scale.Convert into micrometer. magnification is already given. Use the formula Magnification=Size of the image/Size of the specimen
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Im sorry i answered may/june 2008 insted of oct/nov
 
daredevil

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which disease is treated with drugs that have a similar molecular structure to DNA molecule?
A cholera
B HIV AIDS
C malaria
D tuberculosis
 
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strangerss

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daredevil said:
which disease is treated with drugs that have a similar molecular structure to DNA molecule?
A cholera
B HIV AIDS
C malaria
D tuberculosis
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It's B , because in my book it's written there's a drug called zidovudine which is similar to the nucleotide containing the base thymine, zidovudine binds to the viral enzyme reverse transcriptase and blocks it's action , stopping the replication of the viral genetic material and leading to an increase in some of the body's lymphocytes , that's what's in my book . hope you doubt is cleared :)
 
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Is it wrong when talking about HIV virus to say it affects the t lymphocytes without being specific that it's the T helper lymphocytes? I wrote that in p2 , and when CO2 REACTS WITH H2O is it wrong if I right down directly that hydrogen carbonate ions and hydrogen ions are formed , without writing carbonic acid?
 
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white rose said:
can anyone help with q.2, 5, 15, 26, 34 & 35​
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Q2 Mrna leaves the nucleus after being made to reach the ribosomes for DNA translation in protein synthesis and the nucleolus in the nucleus makes ribosomes which leave to stay in the cytoplasm so 2 and 3 are correct and DNA is always in the nucleus.15 it cannot be active transport because it's against a concentration gradient and the graph shows that and increase in glucose increases rate of entry so it's wrong , it cannot be simple diffusion because the graph will not become a straight line but will be a line thats always increasing because the concentration of glucose outside would be increasing so there will always be a concentration gradient so it's definitely only facilitated diffusion which is limited by the number of channel proteins present in the cell membrane so only 1 is correct. q26 B is incorrect because the opposite happens that's very obvious C is wrong because the percentage of oxygen is the same every where it's like a constant like how the percentage composition of CO2 is 0.03% and nitrogen 78% so it doesn't changed and D is absolutely wrong same explanation like C , this leaves us with A WHICH IS COrrect becoz when the partail pressure of O2(NOT percentage) decreases , less oxygen is carried by the red blood cells and hemoglobin is less saturated becoz less 02 is available so it's A. IT's C right? measles is the only disease gievn that is transmitted by direct contact so by a person just touching another person , cholera is through food and water , malaria through mosquito, and sickle cell anemia is through genes so it's C , as when the other ppl that contact the infected person are found the disease will be treated faster.35 is C beacuse during the primary response of the virus , memory cells where made and stored , so during the secondary response they identify the virus and divide to many plasma cells which secrete antibodies in larger amounts than in the primary response and more memory cells in case the virus in encountered another time.
 
white rose

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strangerss said:
Q2 Mrna leaves the nucleus after being made to reach the ribosomes for DNA translation in protein synthesis and the nucleolus in the nucleus makes ribosomes which leave to stay in the cytoplasm so 2 and 3 are correct and DNA is always in the nucleus.15 it cannot be active transport because it's against a concentration gradient and the graph shows that and increase in glucose increases rate of entry so it's wrong , it cannot be simple diffusion because the graph will not become a straight line but will be a line thats always increasing because the concentration of glucose outside would be increasing so there will always be a concentration gradient so it's definitely only facilitated diffusion which is limited by the number of channel proteins present in the cell membrane so only 1 is correct. q26 B is incorrect because the opposite happens that's very obvious C is wrong because the percentage of oxygen is the same every where it's like a constant like how the percentage composition of CO2 is 0.03% and nitrogen 78% so it doesn't changed and D is absolutely wrong same explanation like C , this leaves us with A WHICH IS COrrect becoz when the partail pressure of O2(NOT percentage) decreases , less oxygen is carried by the red blood cells and hemoglobin is less saturated becoz less 02 is available so it's A. IT's C right? measles is the only disease gievn that is transmitted by direct contact so by a person just touching another person , cholera is through food and water , malaria through mosquito, and sickle cell anemia is through genes so it's C , as when the other ppl that contact the infected person are found the disease will be treated faster.35 is C beacuse during the primary response of the virus , memory cells where made and stored , so during the secondary response they identify the virus and divide to many plasma cells which secrete antibodies in larger amounts than in the primary response and more memory cells in case the virus in encountered another time.
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thaaaaank u soo much....i think u forgot to explain q.5
 
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white rose said:
thaaaaank u soo much....i think u forgot to explain q.5
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oh yes I forgot. Okay so we know that in a plan diagram it shows the distribution of TISSUES , so in B a layer of palisade cells is a tissue so it is included , a vascular bundle is also a tissue, again included, now in D xylem vessel elements are actually dead CELLS , and in a plan diagram no individual cells should be included which makes it the right answer , if they would have said only the xylem vessel then it would have to be included in the plan diagram because it's a tissue. Apparently the cuticle is always drawn in a plan diagram , it's a tissue , it's made by the epidermis , but I don't really know why it's present:/
 
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1357911 said:
o/n 2010 varient 11 ques 22 and 38 anyone help.... Plzzzz
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through the trend u can see A & D have almost same %. And B & C have almost same %. So now C cannot b adenine since its niland it is thymine. Now when C is thymine the matching % is B.So the ans is B...
Hope u get it... some one else explained it already :p.. in 38 multiply all the numbers in one row for e.g for P 10000 x0.1 x1.0 , then you would have gotten the total energy for species P , because the energy valu for one individual is o.1 (its mass)x 1.0(amount of enrgy per one unit mass) so for all the species the ans is multiplied by the 10000(number of species) do the same for the others and you will get the answer B
 
white rose

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strangerss said:
oh yes I forgot. Okay so we know that in a plan diagram it shows the distribution of TISSUES , so in B a layer of palisade cells is a tissue so it is included , a vascular bundle is also a tissue, again included, now in D xylem vessel elements are actually dead CELLS , and in a plan diagram no individual cells should be included which makes it the right answer , if they would have said only the xylem vessel then it would have to be included in the plan diagram because it's a tissue. Apparently the cuticle is always drawn in a plan diagram , it's a tissue , it's made by the epidermis , but I don't really know why it's present:/
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thnx
 
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