A level Biology: Post your doubts here!

[nerdybookworm]

http://www.xtremepapers.com/communi...st-your-doubts-and-please-provide-tips.13121/


plz reply urgeeenttt

somebody please check n replyy

 

[confused123]

ok first the answers are 29 C 32 A 34 C 35 D 37 D

so the question said least likely to be passed directly from parent to child sickle cell anaemia is the most likely as it is genetical

oh , 35th : its D because viruses don't have a cell membrane. viruses don't respire as they live in human cells breed dre. no reason for not having ribosomes in viruses.

37) the pathogen is marked by antigen, macrophage antigen recognises it and gets attached to it. blood plasma has antibodies in it.

 

[hmlahori]

for Q35 Viruses dont have ribosomes they only have a coil of DNA surrounded by a protein coat. they replicate by taking over the host cells organelles
for all explanations thanks.............

 

[Nibz]

Assalamoalaikum wr wb!!
need help with some p4 questions

J’02

Q:3d ​

​

​

"It can be passed along by the frequency of action potentials that are formed."

N’02

Q:1 b

1b(i) When the light source is switched off, the light independant reaction still continues, so RuBP is still converted to GP. GP keeps on producing untill all the RuBP is used up. The level of GP later falls because it's converted to TP in order to make hexose or glucose.

1b(ii) Light dependent reaction stops because there is no light. Since there is no more ATP and reduced NADP production, RuBP is not regenerated. The concentration keeps on decreasing because RuBP is being converted to GP as the time passes, until all of it is used up and it's concentration falls to zero.

7b. Role of NADP:
Being a coenzyme, it serves as an electron accepor in electron transport systemr of photophoshphorylation.
During the photolysis of water, the protons (H+) are also carried by NADP in the form of NADPH. These Hydrogen ions are then released by the NADPH, regenerating NADP, and are used to produce a carbohydrate in the Calvin cycle.

 

[XPFMember]

aoa wr wb!

​

"It can be passed along by the frequency of action potentials that are formed."

jazakAllah

1b(i) When the light source is switched off, the light independant reaction still continues, so RuBP is still converted to GP. GP keeps on producing untill all the RuBP is used up. The level of GP later falls because it's converted to TP in order to make hexose or glucose.

yup...but my doubt is, conversion to TP also requires ATP and red. NADP....so how is it that conversion does occur, but nor the regeneration :s

7b. Role of NADP:
Being a coenzyme, it serves as an electron accepor in electron transport systemr of photophoshphorylation.
During the photolysis of water, the protons (H+) are also carried by NADP in the form of NADPH. These Hydrogen ions are then released by the NADPH, regenerating NADP, and are used to produce a carbohydrate in the Calvin cycle.

jazakAllah!!!!
many duas 4 u..

 

[Scafalon40]

Another question:
Paper:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_31.pdf
Mark Scheme:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_ms_31.pdf
Examiner Report:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_er.pdf
Look at Q1 part (b)(i)
We have to prepare a space to record or results
The marking scheme says "a mean of the dilutions should be calculated"
Mean? How do we calculate the mean of a dilution?
Guys I even posted the marking scheme and examiner report, if you can't answer this then...

Guys why won't you answer?

 

[hassam]

why urea concentration is higher in filtrate compared to urine........k i understand that much of water has been reabsorbbed.....and so amount of water in which urea is now dissolved has decreased markedly....but ms also says ref. to absorption of other substances,.....i cnnt visualise how will this increase urea conc.cn u explain thru example

 

[hassam]

whats the role of this reservoir and the clip below in this experiment......

 

[XPFMember]

whats the role of this reservoir and the clip below in this experiment......

Aoa wr wb!

What I think is, the clip can be opened, so that water from the reservoir could be used to refill the water in the tube..

 

[Nibz]

aoa wr wb!

yup...but my doubt is, conversion to TP also requires ATP and red. NADP....so how is it that conversion does occur, but nor the regeneration :s

Ws!

GP - TP conversion uses the ATP and red. NADP molecules from the light dependent reaction. Apparently, all of ATP and red. NADP are used up, so there are no more available to regenerate RuBP.

 

[hassam]

bt then how does cnversion of gp to tp does occur.....question is flawed

 

[hassam]

http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_w08_qp_5.pdf
q 1 b why readings may nt be anamolous

 

[farhan143]

i donot understand this process !?!?!?!?!?!?

the movement of water molecules in terms of water potential gradient

 

[farhan143]

i donot understand this process !?!?!?!?!?!?

the movement of water molecules in terms of water potential gradient

View attachment 6601

please reply.......

 

[hassam]

http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_s09_qp_5.pdf
q 1 b (i) how i will take the measurements that ll allow me to calculate rate of water uptake

 

[confused123]

Guys why won't you answer?

ms says this: Six from:
All data recorded in table;
Concentration of lead nitrate in first column/top row;
Column headings include concentration with percentage and colour;
At least three dilutions;
At least two readings for each solution;
Estimate of degree of blackness/differences in colour described;
Decrease in reaction with increasing lead nitrate/colour yellow/orange etc. to blue/black;

where does it say to calculate mean of the dilutions. :/

 

[hassam]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s10_qp_42.pdf
in question 7 C
ms mentions prevents H+ FROM lowering pH........IS IT BECAUSE THE Extra H atom on nadh is given to ethanal molecule during redox rxn that takes place......and one more thing....this ms underlines the word ethanal when mentioning ethanal dehydrogenase whereas i have seen places where alcohol dehydrogenase is mentioned

 

[confused123]

i donot understand this process !?!?!?!?!?!?

the movement of water molecules in terms of water potential gradient

View attachment 6601

water is at high potential inside xylem, it will travel via pits to intra cellular spaces in the leaf by apoplast or symplest pathway . and then its travelling down a water potential gradient into guard cells and escaping from stomata. ...

 

[Scafalon40]

ms says this: Six from:
All data recorded in table;
Concentration of lead nitrate in first column/top row;
Column headings include concentration with percentage and colour;
At least three dilutions;
At least two readings for each solution;
Estimate of degree of blackness/differences in colour described;
Decrease in reaction with increasing lead nitrate/colour yellow/orange etc. to blue/black;

where does it say to calculate mean of the dilutions. :/

Read the examiner report too, it says so

 

[confused123]

Read the examiner report too, it says so

sorry no idea. i dnt get it