A level Biology: Post your doubts here!

[Nibz]

Aoa!
b (i) Hydrogen ions are pumped out of the companion cells. This creates a gradient across the membranes of companion cells. There are Hydrogen ion channels present in the membranes of companion cells. These channels, being co-transporters, bring sucrose along with Hydrogen ions back to the cells. Due to the presence of numerous plasmodesmata b/w companion cells and sieve tube elements, the sucrose diffuses into C.

b (ii) Sucrose, when diffused into sieve tube elements, decreases the w.p of these 'elements'. Water enters these 'elements' by osmosis. On the other hand, at sinks, sucrose is either used up in respiration or stored as starch. These cells, therefore, have high water potential. Water moves out of these cells by osmosis. As a result of water entering at C and leaving at Sink, a hydrostatic pressure is created which causes a 'Mass Flow' of the sucrose solution along the phloem to the 'Sink'.

 

[rz123]

thanks again! yes this much detail is enuf. this chapter is really annoying.

 

[rz123]

Thanks Nibs. it helped

 

[haniasaleem]

hey will any one help me with this question............how would you demonstrate that leaf of hibiscus rosasinisis contain different types oflight harvesting pigments in there chloroplast??

 

[Majid Mohahammad Qasim]

Salaam hi guys hope r fine. can anybody provide me november 2011 A- level biology papers. plz thnx in advance

 

[XPFMember]

Salaam hi guys hope r fine. can anybody provide me november 2011 A- level biology papers. plz thnx in advance

Waalaikumassalam wr wb!

http://www.mediafire.com/?dgcbc88stxh5f#yf79wogmesmah

 

[Saneeya]

may 09 paper 5 question 1 part b(i)
plz can any one write the answer i am really confused what to write

 

[hassam]

In preparation for in-vitro fertilisation (IVF), women are injected with FSH.
Explain why treatment with FSH is a necessary preparation for IVF?
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w09_qp_41.pdf
markscheme is cnfusing

 

[Paradoxical]

So the best way to prepare for paper 5 is just to do all the past papers? My biology teacher said there's an ATP book for O-Level biology and that's meant to be helpful. Anyone know whether this is true?

 

[Saneeya]

So the best way to prepare for paper 5 is just to do all the past papers? My biology teacher said there's an ATP book for O-Level biology and that's meant to be helpful. Anyone know whether this is true?

i dont think so but most teachers say that

 

[Paradoxical]

i dont think so but most teachers say that

Ah okay. I was asking because I haven't done O-Levels so I thought there might be some stuff I needed to know. Thanks anyway! ^_^

 

[hassam]

why the GP conc . falls in the graph.....ms of this question says that it falls since GP converted to TP but that defies every text book.....since gp cant be
converted to tp in absence of nadph and atp

 

[XPFMember]

assalamoalaikum wr wb!

this is what I wrote:

After the light source is switched off, the RuBP concentration decreases and the GP conc. is seen to increase at first and then decreases. This is because the Calvin Cycle, the light independent reaction, continues. All the available RuBP is converted to GP which accounts for the increase of its conc. at first. The light-dependent reactions will stop, hence no more ATP & reduced NADP is produced. The available ATP & reduced NADP which was formed when the light was on, is used to convert GP to TP, which accounts for the decrease of it’s concentration.​

 

[aliya_zad]

can anyone explain why the ans is D?

 

[Doctor Nemo]

View attachment 3848
can anyone explain why the ans is D?

Unsaturated phospholipids have a lower melting point than saturated phospholipids. This is because the unsaturated phospholipids have a bend in the long molecule so the molecules do not fit so easily in a crystal structure.

Lowering the melting point of the phospholipids in the membrane will keep the bilayer fluid at lower temperatures allowing exocytosis to occur.

 

[aliya_zad]

Thank u!

 

[Majid Mohahammad Qasim]

Waalaikumassalam wr wb!

http://www.mediafire.com/?dgcbc88stxh5f#yf79wogmesmah

thnx

 

[hassam]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_qp_5.pdf
Q2.b(ii)
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_ms_5.pdf
see ms....why he is penalising 3 dp......there's no reason he can do that since in calculations we go by the consistency in significant figures isnt it......and in the b(iv)how i ll know to what s.f i ll give the plus minus confidence interval values

 

[XPFMember]

http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_qp_5.pdf
Q2.b(ii)
http://www.xtremepapers.com/CIE/International A And AS Level/9700 - Biology/9700_w08_ms_5.pdf
see ms....why he is penalising 3 dp......there's no reason he can do that since in calculations we go by the consistency in significant figures isnt it......and in the b(iv)how i ll know to what s.f i ll give the plus minus confidence interval values

Assalamoalaikum wr wb!

in this case, we're going with the decimal place....the whole sf thing is so confusing...i guess it's better when u have dp u go for the same number of dp!
dont know abt the 2nd thing u asked...

 

[Majid Mohahammad Qasim]

salaam hi guys. plz somebody can tell me from where i can find A2 biology notes including plan diagrams