A level Biology: Post your doubts here!

[dornam]

What does the rf value say about solubility and the distance travelled?
Is it correct that the greater the rf value the greater the distance travelled?

Yes, it is.

 

[Amaryllis]

guys , how can i find the (degree of freedom) in paper 5 plzz help in http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_5.pdf q3 table 3.1 how to complete it ..and q3 part b i and ii ...can anyone explain them plz.. and thanks

 

[ahmed abdulla]

What could be produced in a terminating step during the bromination of propane

 

[strangerss]

can anybody please explain me the diff b/t plasma cells n memory cells? or are they the same thing?

Plasma cells produce antibodies , where as memory cells are stored during the primary response and on encountering the same antigen again they divide into more memory cells AND plasma cells which secrete antibodies against the antigen.

 

[dornam]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w07_qp_1.pdf

Question 37... answer is D. I put C. Can anyone explain?

Question 38 - answer is C, I put B because I thought that if they belong to different food webs, they can be at different trophic levels.

Question 39 - answer is B. Why does the number of nitrifying bacteria increase?

 

[Noor Ahmad]

Question 1b (ii)
what is meant by estimate the water potential of the plant?
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s11_qp_52.pdf

 

[comrade]

Question 1b (ii)
what is meant by estimate the water potential of the plant?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_52.pdf

It is the amount of water lost or gained by the plant. Or you can say the tendency of the plant to carry the water. You can check the water potential by adding different concentrations of the solution and see if the water is lost or gained. It depends on the concentration of the solution. I hope I'm right.

 

[Noor Ahmad]

It is the amount of water lost or gained by the plant. Or you can say the tendency of the plant to carry the water. You can check the water potential by adding different concentrations of the solution and see if the water is lost or gained. It depends on the concentration of the solution. I hope I'm right.

Yes that's right! Thank you! but if the plant tissue doesn't lose nor gain water how will it get damaged and release the pigment? (in the question,the steps)

 

[comrade]

Yes that's right! Thank you! but if the plant tissue doesn't lose nor gain water how will it get damaged and release the pigment? (in the question,the steps)

If the water doesn't move inside or outside then the potential is same. As for the damaged cell part... Is it necessary that the plant tissue cells will be only damaged by adding extra water till they burst? And do they even burst? They have a cell wall. There could be physical damage as well which may release the pigment. You can cut the tissue and damage the cells. I'm just presenting a theory.

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w07_qp_1.pdf

Question 37... answer is D. I put C. Can anyone explain?

Question 38 - answer is C, I put B because I thought that if they belong to different food webs, they can be at different trophic levels.

Question 39 - answer is B. Why does the number of nitrifying bacteria increase?

37. Macrophages cut up pieces of antigens after phagocytosis and display them on their cell surface membranes for T-cells to detect.
38. Yes, if they belong to different food webs then they can be at different trophic levels, but they can also have different foods to eat, so they won't compete, and therefore they may occupy the same niche permanently. But they can't, because of either predators or food.
39. NH3 increases in the atmosphere. Nitrifying bacteria convert it into NO3-.

 

[Fatima TZ]

can any 1 help me to find http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_s09_qp_5.pdf q3 b(iv) plzzzzzzzzzzzzzzz

 

[Noor Ahmad]

can any 1 help me to find http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_5.pdf q3 b(iv) plzzzzzzzzzzzzzzz

(20x2) - 2 = 38

 

[Noor Ahmad]

HOW DO WE CALCULATE THE RATE OF ABSORPTION OF GLUCOSE? question 2b (i) and (ii)

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Biology%20(9700)/9700_s12_qp_51.pdf

 

[ShootingStar]

Could someone please help me with Q2 a(ii) in the following paper: http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w11_qp_53.pdf

 

[raamish]

hey can somebody tell what is the pattern of doing the question of outline the procedure for 8 marks? and how do i prepare for it?

 

[Student12]

hey can somebody tell what is the pattern of doing the question of outline the procedure for 8 marks? and how do i prepare for it?

A general pattern is..
(1) Independent variable (2) Dependent (3) Variable to be controlled (4) The Procedure (5) Reliability (6) Safety
These points are always mentioned in the ms.
Generally just do all the planning Questions and see the MarkScheme.. you get a idea as to how to go about.
If someone else could give any other explaination.

 

[raamish]

i know the pattern but i write wrong pts in the independent and dependant variables. i i write correctly about standardized and relaiability and safety. can u explain one procedure question that can allow me to understand? plzz ty

 

[Student12]

Even i at times don't get the independent and the dependent variable right.. If anyone could explain ?
Iknow

• Independent Variables are changes that occur in an experiment that are directly caused by the experimenter (you.)
• Dependent Variables are changes that occur due to independent variables.
  
  But when it comes it doing the questions i often get it wrong..
  SOMEONE ?

 

[raamish]

hey how do we write the statement of calculating the mean. sometimes it says take 3 readings and calculate mean. and sometimes it says take mean of whole sample. plzz help

 

[Student12]

hey how do we write the statement of calculating the mean. sometimes it says take 3 readings and calculate mean. and sometimes it says take mean of whole sample. plzz help

i'd Suggest you go to the the Biology Tips thread.. all ur quaries will be answered there