A level Biology: Post your doubts here!

[mehria]

Nov 2010 V1 ---> Q38 and 39

Q 38=> multiply the biomass of 1 individual into the number of individuals to find the total biomass n then u'll get ur ans.
n m nt sure abt Q 39

 

[joanna omar]

PP1 DOUBTs

June 2013 V1 --->Q22,27,34

 

[Karim Nabil]

PP1 DOUBTs

June 2013 V1 --->Q22,27,34

• q22; in q22 questin asks about maximum no. of hydrogen bonds in a DNA molecule of 700 pairs, we know that C pairs with G by 3 hydrogen bonds and A pairs with T by 2 hydrogen bond as he is saying maximum no. of h2 bonds we consider that DNA molecule has only C=G pairs so 3*700=2100 bonds; answer is D
• q27, option A is wrong because humidity decrease transpiration; option B is correct because water must be transported to spongy mesophyll via symplast pathway and then diffuse out of the cells and evaporated to atmosphere via stomata ; option C is wrong because water diffuse out of mesophyll cells then evaporated to atmosphere via guard cells in stomata ; option D is wrong because water is diffused into intercellular air space not evaporated
• q34, it is A because this by-pass surgery is used to reduce atherosclerosis and improve delivery of oxygen and nutrients to cardiac muscle of the heart

 

[Angelina_25]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/
Oct Nov 13 varient 21 question 2)c)How to answer these types of question ?how can we know specifically which kinds of tranport mechanism is occuring ?
Any help would be appreciated!

 

[VelaneDeBeaute]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/
Oct Nov 13 varient 21 question 2)c)How to answer these types of question ?how can we know specifically which kinds of tranport mechanism is occuring ?
Any help would be appreciated!

There are only a handful of mechanisms we are supposed to know at this level. Diffusion (including Facilitated Diffusion), Osmosis and Active Transport. Now do some educated guessing. Osmosis shuts out because ions are involved and not water molecules. Diffusion is not possible because the concentration of ions in the surrounding solution (as depicted by the first column) is lower than that inside the roots (as shown by the second column). Even when the conc. of ions is higher in the root tissue, the ions flush inside. That has to mean that active transport is involved.
Rest, as you would have read in the marking scheme, is stuff related to how carrier proteins maybe involved, how ATP were required for the active transport to happen and blah blah.

Smart tip: Relax, and give a few minutes to the question. Just because there is confusing introduction, numbers in a table and a question worth 5 marks doesn't mean it is impossible to answer.

 

[Angelina_25]

There are only a handful of mechanisms we are supposed to know at this level. Diffusion (including Facilitated Diffusion), Osmosis and Active Transport. Now do some educated guessing. Osmosis shuts out because ions are involved and not water molecules. Diffusion is not possible because the concentration of ions in the surrounding solution (as depicted by the first column) is lower than that inside the roots (as shown by the second column). Even when the conc. of ions is higher in the root tissue, the ions flush inside. That has to mean that active transport is involved.
Rest, as you would have read in the marking scheme, is stuff related to how carrier proteins maybe involved, how ATP were required for the active transport to happen and blah blah.

Smart tip: Relax, and give a few minutes to the question. Just because there is confusing introduction, numbers in a table and a question worth 5 marks doesn't mean it is impossible to answer.

Thanks alot fr the clarification !

 

[emogurl_gl]

Hello everyone!

I have question regarding S12 42 question 3. (b)
In the mark scheme, it says
chance / random ;
only present in low concentration

What does this means?

Thank youu

 

[joanna omar]

How many marks approx do u guys loose in paper 4 ?

 

[joanna omar]

Hello everyone!

I have question regarding S12 42 question 3. (b)
In the mark scheme, it says
chance / random ;
only present in low concentration

What does this means?

Thank youu

I guess this means that there wasn't enough C bases present so that's why there was no enough C bases to pair with G in presence of DNA polymerase

 

[joanna omar]

• q22; in q22 questin asks about maximum no. of hydrogen bonds in a DNA molecule of 700 pairs, we know that C pairs with G by 3 hydrogen bonds and A pairs with T by 2 hydrogen bond as he is saying maximum no. of h2 bonds we consider that DNA molecule has only C=G pairs so 3*700=2100 bonds; answer is D
• q27, option A is wrong because humidity decrease transpiration; option B is correct because water must be transported to spongy mesophyll via symplast pathway and then diffuse out of the cells and evaporated to atmosphere via stomata ; option C is wrong because water diffuse out of mesophyll cells then evaporated to atmosphere via guard cells in stomata ; option D is wrong because water is diffused into intercellular air space not evaporated
• q34, it is A because this by-pass surgery is used to reduce atherosclerosis and improve delivery of oxygen and nutrients to cardiac muscle of the heart

THANKS

In Q 34 ....isn't this surgery even to repay blood in the blocked parts in the coronary artery ?

 

[sumeru]

How many marks approx do u guys loose in paper 4 ?

Depends on the question.....nowadays the difficulty levels are increasing......

 

[sumeru]

THANKS

In Q 34 ....isn't this surgery even to repay blood in the blocked parts in the coronary artery ?

Yes, but it is usually carried when the blood vessels are deposited with high amount of atheroma, which causes resistance to the blood flow in that tissue...

 

[joanna omar]

Depends on the question.....nowadays the difficulty levels are increasing......

This is so true the more I proceed with solving the latest years the more difficult it is and I keep loosing more

 

[Karim Nabil]

THANKS

In Q 34 ....isn't this surgery even to repay blood in the blocked parts in the coronary artery ?

my pleasure!
look,CHD develops if blood supply to the heart muscle is reduced due to thrombus or atherosclerosis , in this case we treat CHD by coronary artery by-pass surgery
this treatment is to improve or increase blood supply to the heart therefore more oxygen and nutrients supplied to heart reducing risk of heart attack or heart failure.

*note:CHD stands for coronary heart disease

 

[emogurl_gl]

I guess this means that there wasn't enough C bases present so that's why there was no enough C bases to pair with G in presence of DNA polymerase

Thank you for your answer, but i still feel confused with it....

This is the question :
suggest why a special nucleotide with a C base was not included by DNA polymerase at the first site requiring a C nucleotide

 

[bubbles1997]

Thank u soo much
I'll pray for ur success ^_^

 

[roxylara]

Guys do you have any idea where I could find old biology papers staring from 1990? :/ basically before 2001

 

[sitooon]

Hi,

What u guys think that about the questions related to which topic can come this
time in A2 Biology Exams . Have u done any survey through pastpapers or anything else.
Lets discuss over own opinions.

Can you help in labelling

 

[Mashal zeb]

Somebody explain ths question plz

 

[kitkat <3 :P]

Somebody explain ths question plz

i think its C not sure :/ do u know the answer??