A level Biology: Post your doubts here!

[Igcse stuff]

does anyone have good summarized bio AS and A level notes, really need them

 

[Karim Nabil]

Potometer is not that difficult....just go through the book once, i think you will understand it....and i have seen a potometer related question in p2..so there's a chance

i know but i need summarizing points for it, this will help me alot overcoming my problems in this section
you also have skipped my 2nd question in my quote....

 

[sumeru]

why does concentration of urea increase in distal collecting tubule and collecting duct????

At PCT , urea is some urea is absorbed due to its small size....not all of them.....so at DCT and collecting duct, almost all of the water is absorbed, leaving urea and other waste products....so, its concentration increases....

 

[joanna omar]

Anyone help me out with this
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w09_qp_41.pdf

Explain me Q5 e (i)

sumeru
alevelnerd ??
Zain Javaid

 

[Mohammed salik]

Thank u so muchhh nabil, mehria and salik dat realy helped! So nyc of u

Your Welcome

 

[roxylara]

First find Out What One unit on Graticule represents.
It says the Slide has division of 0.1 mm, which are equivalent to 50 on Graticule. So 1 division on Graticule is 0.1/50 =0.02 mm.
Now look at Diagram One, Take the pollen which grows Straight (parallel to scale), Then place a ruler and see the increase in its size after 4 hours, which turns out to be from 25-35 which is 10 Graticule units. the actual Increase is 10 * 0.02=0.2 mm , But this is in 4 Hours. the question asks for One Hour , then divide this value by 4 which gives 0.05 mm = 5 Micrometer Per Hour.
Hope i Helped !

Here is the calculation,from 1st diagram
50 eyepiece divisions=0.1 stage
1 EP=0.1/50 stage
Convert it to micrometer,
1EP=0.1/50 multiplied by 1000, which is 2 micrometer.
Now from 2nd diagram,
The increment in 4 hours is 10 division
So 1 division of EP=2
10 division of EP=2 into 10
=20
so in 4 hours, there is increment of 20 micrometer
In 1 hour=20/4
=5
So the answer is A.

Thankyou both of you, you're awesome!

 

[Mohammed salik]

Thankyou both of you, you're awesome!

No Problem
My Pleasure

 

[joanna omar]

Help please !

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_23.pdf

Q4 C (i) and Q5 (d)

 

[Mohammed salik]

Help please !

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s13_qp_23.pdf

Q4 C (i) and Q5 (d)

Q4 C (i):- It is a competitive inhibitor which binds to active site reversibly, But as the concentration of Substrate increase we see see more frequent collision between substrate and enzyme rather than inhibitor and enzyme, this reduces the effect Of inhibitor.
So the curve would be lower than normal at start but Vmax reached at higher substrate concentrations.
This might help too.. http://cnx.org/content/m44429/latest/Figure_06_05_04.jpg

I will give a try to Question 5(d) (correct me if i m wrong plz)
I MPF Doesnot break Down, There would be Too many Prophase At the same time, which would cause uncontrolled Mitosis, (but wont form Tumors, because still Anaphase and rest of phase go by Normal Time ) And this would also Disturb the cell Cycle (causing shortened S Phase)

 

[joanna omar]

Q4 C (i):- It is a competitive inhibitor which binds to active site reversibly, But as the concentration of Substrate increase we see see more frequent collision between substrate and enzyme rather than inhibitor and enzyme, this reduces the effect Of inhibitor.
So the curve would be lower than normal at start but Vmax reached at higher substrate concentrations.
This might help too.. http://cnx.org/content/m44429/latest/Figure_06_05_04.jpg

I will give a try to Question 5(d) (correct me if i m wrong plz)
I MPF Doesnot break Down, There would be Too many Prophase At the same time, which would cause uncontrolled Mitosis, (but wont form Tumors, because still Anaphase and rest of phase go by Normal Time ) And this would also Disturb the cell Cycle (causing shortened S Phase)

Thanks a bunch for the Graph

and 5(d) this is correct but they say said that there aslo maybe a risk of tumour ..can u explain me more ?

 

[Mohammed salik]

Thanks a bunch for the Graph

and 5(d) this is correct but they say said that there aslo maybe a risk of tumour ..can u explain me more ?

You r Welcome
Risk of tumor? Where do they say that?
I dont Think there would be Any Tumors???

 

[joanna omar]

You r Welcome
Risk of tumor? Where do they say that?
I dont Think there would be Any Tumors???

In M.s only check

 

[Mohammed salik]

In M.s only check

Ohh.. In Ms it says I (ignore) ref to any tumors!!
In M.s
"ignore (risk of), tumour formation / cancerous growth "

 

[joanna omar]

Ohh.. In Ms it says I (ignore) ref to any tumors!!
In M.s
"ignore (risk of), tumour formation / cancerous growth "

Yeah okay then maybe I didn't see that ..thanks

 

[joanna omar]

Paper 1 doubts

June 2012 (v2) ----> Q10 and Q27

Nov 2012 (v2) ----> Q1 - Q17 -Q15 -Q21 -Q24 -Q34 - Q38

Nov 2012 (v3) ---->Q30,Q36 and Q39

Help is appreciated

 

[joanna omar]

Q6 :- (A)The question asks for greatest mass of Non- Reducing sugar, which means the difference between Before and after Hydrolysis must be greatest, which is in A!
Q11:-(A) Triglycrides dont have Hydrogen bonds, So Not D.Cellulose has Hydrogen bonds so Not B either. Collagen is helical in nature (not branched) so not C. Ans is A
Q14:-(C) If the inhibitor binds to E-S complex then active site doesnt change shape. so 1 is wrong. and With inhibitor V(max) never increases, so Ans is C!
Q25:-(B)5 is wrong because they are in Dry conditions, So only ans is B or C. Fewer Stomata would reduce gas exchange so the ans is B.
Q35:-(D) Emphysema has no Link with Atheroma(cant be C). Tar causes more Mucus (if he stopped smoking, so A is wrong).Stopped smoking reduces inflamation to lung tissues so Macrophage decrease. Only other option is D.
Q38:-(A) Vaccine dont only work against viruses, bcz there r vaccines for TB as well,, so only option without 4 is A.
Hope i Helped . if u need detailed explanation do let me Know!

THANKS A LOT
June -2011 (v1)
but I still didn't get Q 14 :/

 

[Mohammed salik]

THANKS A LOT
June -2011 (v1)
but I still didn't get Q 14 :/

Q14:-
1. Option 1 Is wrong because inhibitors of enzyme reactions bind to the enzyme / substrate complex so The Active site doesn't Change Shape.. so answer could only Be C or D.
4.V(max) is never increased with Inhibitor. so Option 4 is wrong.
Only Ans without 1 and 4 is is C..!
Hope i Helped!!

 

[Mohammed salik]

Paper 1 doubts

June 2012 (v2) ----> Q10 and Q27

Nov 2012 (v2) ----> Q1 - Q17 -Q15 -Q21 -Q24 -Q34 - Q38

Nov 2012 (v3) ---->Q30,Q36 and Q39

Help is appreciated

June 2012 (v2)

Q10) It must be Reducing sugar. ANS IS B. Sucrose is Non -reducing.

Q27) Ans is D.. All 4 of them are found In Blood plasma, so They r also present in Tissue fluid and lymph (because these r made from Leaked blood plasma)

Nov 2012 (v2)
Q1)Greastest number of cells mean Least Magnification which is with A (5*10=50)

Q17) The process which move subtances Down the conc. Gradient (i.e From High Conc to Low Conc) result in Equilibrium.
Those are 2 , 3 and 4. So ans is D.

Q15)A, B AND C are related With phoospho lipids. But Option D is Related to Glycolipids which act as receptor (these r not Phospholipids)

Q24) Ans is A.
Option 3 :- Apoplast way never involves cell surface membranes so it is wrong. Only Option without 3 is A .

Q34)(C) First Look at Oxygen Used up .. which is 19-12.5=6.5 cm^3 This is Per 100 cm^3
Wee need to find out in 5 dm^3 = 5000 cm^3
6.5 : 100
X : 5000
X= 325 cm^3.

 

[Mohammed salik]

Paper 1 doubts

June 2012 (v2) ----> Q10 and Q27

Nov 2012 (v2) ----> Q1 - Q17 -Q15 -Q21 -Q24 -Q34 - Q38

Nov 2012 (v3) ---->Q30,Q36 and Q39

Help is appreciated

Nov 2012 (v2)
Q38) (c) iF x decreased so the primary producer Increased causing the Empty Circle to Increase ( bcz they have more food) This inturn Increased B and C.
But B also increased A so No change it overall population of B. C is top Carnivore so they remained Most!

Q21)B it says Two strands... Gene is One strand Only! so its B rest of them are correct!

 

[Mohammed salik]

Paper 1 doubts

June 2012 (v2) ----> Q10 and Q27

Nov 2012 (v2) ----> Q1 - Q17 -Q15 -Q21 -Q24 -Q34 - Q38

Nov 2012 (v3) ---->Q30,Q36 and Q39

Help is appreciated

Q30) It says Mucus is increased which causes More exocytosis in Goblet cell So option 2 is wrong. Only Ans without 2 is B.

Q36) I m Confused Between A and C. I would rather go with C (firstly Mark scheme says So) and Secondly Parasite lives in liver and RBC so vaccine don't Reach there.
A says Many stages but doesnt Explain the change in Antigen In every stage .

Q39) It says energy used For Photosynthesis. so it would be total Energy ( Net + energy lost) Because Energy which was lost was made by photosynthesis.
So (27 000 + 3 000/1*10^6) * 100 = 3.00% ans is D


Hope i Helped