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A level Biology: Post your doubts here!

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strangerss

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1357911 said:
its okay. Thanks anyways
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.. 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 this a more detailed explanation
 
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strangerss

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1357911 said:
Can i ask u one more question
m/j 2010 varient 11 question 14
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This is a tricky question because we all know that a graph of temperature plotted against rate of reaction will have the same shape as B , but if you see the Y -axis it's not rate of reaction it's time taken for completion of the reaction , which means with an enzyme(which speeds up a reaction) the time takne should decrease with an increase in temperature , so with this min mind we can eliminate B AND C because the time should be decreasing and not increasing as shown in C AND B. the difference between D and A is in the temperature , in the question they say that the enzyme is COMPLETELY DENATURED AT 50 , so there shouldn't be any data AT 50 for the time taken for the reaction this means the graph line shouldn't cross the 50 celsius and that's what's wrong in option D,. you can see in A the line stops exactly at 50 ..hope you got it:)
 
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1357911

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Thanks a lot
strangerss said:
This is a tricky question because we all know that a graph of temperature plotted against rate of reaction will have the same shape as B , but if you see the Y -axis it's not rate of reaction it's time taken for completion of the reaction , which means with an enzyme(which speeds up a reaction) the time takne should decrease with an increase in temperature , so with this min mind we can eliminate B AND C because the time should be decreasing and not increasing as shown in C AND B. the difference between D and A is in the temperature , in the question they say that the enzyme is COMPLETELY DENATURED AT 50 , so there shouldn't be any data AT 50 for the time taken for the reaction this means the graph line shouldn't cross the 50 celsius and that's what's wrong in option D,. you can see in A the line stops exactly at 50 ..hope you got it:)
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..
 
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strangerss

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SalmaXXXX said:
june 2007 Question 3 please !
http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s07_qp_1.pdf
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IDK , about the smooth ER but the rough ER has ribsomes which make proteins these move into the cisternae of the rough ER as they are made , the cisternae then break off , forminf little vesicles, these travel to the golgi apparatus for modification then they are secreted by exocytosis if their function is outside the cell , other wise if the cell needs it stays there
 
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ali sibtain

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Sara syed said:
D is corect Plant cell walls restrict the entry of water, animal cell membranes allow the free entry of
water. This is bcoz plant cell walls are made of cellulose which prevents the cell from bursting when it absorbs alot of water. cellulose can withstand high pressure and become turgid restricting entry of more water
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No the Cell Wall is fully permeable. Or else there wouldnt be a Cell Membrane. Cell Wall only restricts the cell from bursting by exerting a force of its own.
 
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Kyusam

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Lujain M. said:
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w10_qp_11.pdf Q22 HELP PLEASE i dont know how to figure which one is adenine :/
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First thing here is that to know that guanine and cytosine are complementary so will have more or less EQUAL composition which rules out option A and D as they both are complementary and the other thing that nil which means not present, will be either thymine or uracil (as when 1 is present the other one is not) and since C consists of a Nil it is also ruled out leaving you with B :)
 
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strangerss

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ali sibtain said:
Dude, i too find it astonishing. I mean i chose B .....but D, wow. I reckon it must be an error
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They restrict it because when water enter a plant cells it becomes turgid , resulting in a pressure potential building up in it which increases the water potential because the pressure potential is always positive (opposite of solute potential) so water moves out of the cell , thus whenever a plant cell is present in a solution more dilute than it's vacuole and cytoplasm this happens resulting in water always leaving the plant cell , thus it will not burst because of the in elasticity of the cell wall which causes the pressure potential to build up quickly when a small amount of water enters it, AN EQUILIBRIUM will be established between the plant cell and the more dilute environment , as the water leaving the plant cell will be equal to the water entering , how else a plant cell doesn't burst in a dilute solution . the other options are very insensible too. A is not related to why a plant cell has a vacuole , B cannot be true because a cell cannot have a water potential of a fresh water (which is zero , the maximum) because of solutes in it.C IS absolutely incorrect a cell wall is freely permeable to everything so it's definitely D. HOPE YOU GOT IT :)
 
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