A level Biology: Post your doubts here!

[Snow Angel]

What is humoral response of the immune system?

Can anyone please state the order in increasing size of cell organelles?

 

[Fahm Deen]

D

p> atrial systole> when both atria contracts
q-s> ventricular systole> when both ventricles contract
t> ventricular diastole> when both ventricles relax to be filled with blood
in the qp he asks flow of current through atria and recovery of ventricular walls
flow of current through atria means waves of excitation send by the pacemaker SAN to both atria for contraction; atrial systole , so it is P
recovery of ventricular walls means ventricular diastole so it is T
answer is P and T which is B

Can u explain 14,15 and 32. May/June 13 /13

 

[Zain Javaid]

This is A.S portion they got in paper 4 ,where u had to remember from immunity chapter the structure of Antibody
1.It have 2 heavy polypeptides and 2 light polypeptides Joined by disulfide bonds in between
2.A variable region in which antigen fits
3.They are protein in nature
4.Hinge region

Can you please draw it and send it as a screen shot please. it wud be helpful. thanks

 

[Karim Nabil]

thnx

you're most welcome!

 

[Karim Nabil]

D

Can u explain 14,15 and 32. May/June 13 /13

• q14> there is competitive inhibitor so increasing the concentration of substrate increase the probability of substrate to form E-S complex because more no. of substrate is competing with the fixed no. of competitive inhibitor, answer is C
• 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
• q32>‘double circulation’ mean The blood passes twice through the heart during one complete circulation. answer is B

 

[BeBeskii108]

Does somebody please explain to me advantages of statistical tests? Chi-squared test, t-test, standard error etc. Their main features... When they are used... advantages and disadvantages. Please

 

[Snow Angel]

you're most welcome!

What is humoral response of the immune system?

Can u plz list the order of the cell organelles sizes from smallest to largest?

 

[Snow Angel]

you're most welcome!

in paper: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_1.pdf question 1

and in paper: papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w13_qp_12.pdf question 1

when C is the correct answer for q 1 from the first link why can't B be the correct answer for question 1 from the second link? please explain. thanks in advance

 

[Karim Nabil]

What is humoral response of the immune system?

Can u plz list the order of the cell organelles sizes from smallest to largest?

humoral response> antigens is in the tissue fluid not inside the cells
nucleus(10um)> chloroplast(5um)> mitochondria(2.5um)> ribosomes> 22nm if any organelle not listed here just tell me about it

 

[Snow Angel]

humoral response> antigens is in the tissue fluid not inside the cells
nucleus(10um)> chloroplast(5um)> mitochondria(2.5um)> ribosomes> 22nm if any organelle not listed here just tell me about it

thnx. please can u anwser the other question?

 

[Karim Nabil]

in paper: papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_1.pdf question 1

and in paper: papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_w13_qp_12.pdf question 1

when C is the correct answer for q 1 from the first link why can't B be the correct answer for question 1 from the second link? please explain. thanks in advance

light microscope can't measure values less than 200nm so in q 1 in first link, first 2 options aren't correct and option D also as ribosomes is measured by nm not um so answer is C
q1 in 2nd link, width of cell walls in nm while diameter of wbc and alveolus is measured in um, answer is C

 

[Snow Angel]

light microscope can't measure values less than 200nm so in q 1 in first link, first 2 options aren't correct and option D also as ribosomes is measured by nm not um so answer is C
q1 in 2nd link, width of cell walls in nm while diameter of wbc and alveolus is measured in um, answer is C

Thank you very much

 

[Karim Nabil]

Thank you very much

my pleasure!

 

[princeali97]

variant 2 q3(d) .graph for both competitive and non-competitive inhibiton both graphs pls ..http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w08_qp_2.pdf

 

[Mohammed salik]

variant 2 q3(d) .graph for both competitive and non-competitive inhibiton both graphs pls ..http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w08_qp_2.pdf

Plz refer to this http://cnx.org/content/m44429/latest/Figure_06_05_04.jpg

 

[princeali97]

Plz refer to this http://cnx.org/content/m44429/latest/Figure_06_05_04.jpg

i dont understand that for non-competitive inhibition why is graph like that? the enzyme is permanently blocked by the inhibitor so the rate of reaction must remain zero.Can any1 explain this?

 

[Snowysangel]

i dont understand that for non-competitive inhibition why is graph like that? the enzyme is permanently blocked by the inhibitor so the rate of reaction must remain zero.Can any1 explain this?

It no longer remains an enzyme catalyze s reaction but that doesn't mean that the reaction doesn't take place at all! Also it's in extremely rare cases that all the enzymes are attacked by the inhibitors. The 'free' enzymes still catalyze the reaction, which just becomes slower

 

[joanna omar]

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 .... ??

 

[Alazne Diamond]

Can you please draw it and send it as a screen shot please. it wud be helpful. thanks

 

[joanna omar]

I need help with June 2013/P1 var 3 Doubts ?

Q15 , Q21 , Q28 ,Q36 and Q39 ?