This discussion is now closed.

Check out other Related discussions

OCR Biology AS F211 May 2012

Reply 580

AishaTara

14

Original post by PaulMc94

personally I think translocation may come up as the big mark question

it did last May

Reply 581

PaulMc94

Original post by itsmehello

I'm nervous!

Can someone explain mass flow really quickly?

solutes actively loaded into the phloem
the increase of solutes in the phloem lowers the water potential
water moves from an area of high water potential from the source into the phloem with a low water potential
this generates a high pressure at the source end of the phloem
solutes are actively loaded out of phloem at sink end and generates low pressure in phloem
so the solutes at the source move to the sink down a pressure gradient

Reply 582

Neena

Im super super worried, I hope its an easy paper, could someone please explain Carbon dioxide transpot, Bohr shift & Fetal haemoglobin please, would really help, I don't understand any of it :frown:

Reply 583

Sarabande

15

Define cell signalling (1)

Outline two roles of cholesterol in the plasma membrane (2)

Outline how sucrose is transported from the source to the sink (6)

(edited 11 years ago)

Reply 584

hackashaq

11

Hey can someone tell me 2 arguments against the mass flow theorem in the phloem?

Reply 585

PaulMc94

Original post by hackashaq

Hey can someone tell me 2 arguments against the mass flow theorem in the phloem?

not all of the solute is moved down the phloem to the sink
also sieve plates would create a barrier to the mass flow

Reply 586

supernova99

6

why does the trace for a spirometer slant downwards at rest as well as during exercise?

Reply 587

hackashaq

11

Original post by PaulMc94

not all of the solute is moved down the phloem to the sink
also sieve plates would create a barrier to the mass flow

could you explain what you mean by "not all of the solute is moved down the phloem to the sink" please?

Reply 588

PaulMc94

Original post by Neena

Im super super worried, I hope its an easy paper, could someone please explain Carbon dioxide transpot, Bohr shift & Fetal haemoglobin please, would really help, I don't understand any of it :frown:

fetal haemoglobin

higher affinity for oxygen because it needs to be able to pull the oxygen from the mother
by the time blood reaches placenta from mother the oxygen saturation has decreased
so for the fetus to take oxygen from the mothers blood it must have a higher affinity for the oxygen than the mothers blood

bohr shift

more CO2 then the more carbonic acid formed
more carbonic acid formed the more it dissociates into hydrogen ions
the more hydrogen ions the more haemoglobin it can attach to
more haemoglobin it attaches to the more oxygen is released from the oxyhaemoglobin
good for respiring tissues

CO2 transport

hydrogencarbonate ions diffuse out of red blood cell and transported in the blood plasma
when the blood reaches the lungs the low pressure of carbon dioxide causes the hydrogencarbonate ions and hydrogen ions to recombine into carbon dioxide
the carbon dioxide diffuses into alveoli and is breathed out

Reply 589

PaulMc94

Original post by supernova99

why does the trace for a spirometer slant downwards at rest as well as during exercise?

because the amount of oxygen in the air chamber is decreasing as the person takes in each breath

Reply 590

PaulMc94

Original post by hackashaq

could you explain what you mean by "not all of the solute is moved down the phloem to the sink" please?

sugar travels to many different sinks and not just the one with the highest water potential

Reply 591

niaghez

Good luck to everyone, hope you all do amazing! :smile:

quite scared after I looked at the mark scheme and the SMALL things they penalise. Grr

Reply 592

Neena

Original post by PaulMc94

fetal haemoglobin

higher affinity for oxygen because it needs to be able to pull the oxygen from the mother
by the time blood reaches placenta from mother the oxygen saturation has decreased
so for the fetus to take oxygen from the mothers blood it must have a higher affinity for the oxygen than the mothers blood

bohr shift

more CO2 then the more carbonic acid formed
more carbonic acid formed the more it dissociates into hydrogen ions
the more hydrogen ions the more haemoglobin it can attach to
more haemoglobin it attaches to the more oxygen is released from the oxyhaemoglobin
good for respiring tissues

CO2 transport

hydrogencarbonate ions diffuse out of red blood cell and transported in the blood plasma
when the blood reaches the lungs the low pressure of carbon dioxide causes the hydrogencarbonate ions and hydrogen ions to recombine into carbon dioxide
the carbon dioxide diffuses into alveoli and is breathed out

Oh my goodness! :'D - Thank you so much!!!! :biggrin:

Reply 593

Neena

I hope theres questions about the heart & mitosis in tomorrow's paper! :biggrin:

Reply 594

Sprocket25

This may sound silly, but many of you talk about how you think Hb and the Bohr Shift is likely to come up.
I understand that its to do with the dissociation curve etc, but what exactly does Hb stand for? I've been looking for it in my book the last 15 minutes and can't work it out!

Other than that, good luck everyone tomorrow :biggrin:

Reply 595

AishaTara

14

Original post by rival_

Channel proteins = passive diffusion moving small ions and charged particles e.g. sodium ions and water molecules (Down the conc. gradiet)
Carrier proteins= carries large ions via ACTIVE TRANSPORT which means the ions travel from low to high concerntration AGAINST the conc. gradient.

Anything else?

youve got it wrong. OCR tetbook page 23 says facilitated diffusion requires no ATP in the little table.

Reply 596

mathsclown

7

Prepared for the worst hoping for the best, good luck all!

Reply 597

samiwami

2

omg..i am NOT ready for this exam. I'm so lazy and I didn't revise at all!
I'm just going to have to retake year 12 :'(

Reply 598

tka1

what do we have to learn about the potometer....i just dont get it

some one please help!

Reply 599

Jamie66

Original post by Sarabande

Define cell signalling (1)

Outline two roles of cholesterol in the plasma membrane (2)

Outline how sucrose is transported from the source to the sink (6)

1) The messaging that occurs between cells that triggers an internal response in the targeted cell

2) - Stabilising the membrane
- Retaining the fluidity of the membrane

3) - At the source, hydrogen ions are pumped out of companion cells into surrounding cells by active transport
- This creates an H+ ion concentration gradient back into the companion cells
- These H+ ions diffuse back into the companion cells through cotransport proteins, carrying sucrose molecules with them
- The sucrose molecules then diffuse into the phloem through the plasmodesmata
- This creates a low water potential at the source end of the phloem, so water enters the phloem by osmosis at the source end, creating high hydrostatic pressure
- Meanwhile, at the sink sucrose is either used or stored as starch, so water potential is high and water leaves the sink, creating low hydrostatic pressure
- The sucrose then flows down a hydrostatic pressure gradient from the source to the sink by mass flow

(edited 11 years ago)

OCR Biology AS F211 May 2012

Related discussions

Latest

Trending

Trending

Articles for you